What is the purpose of this page? To highlight that the IPCC scenarios to keep global emissions to a level to prevent crossing a 2 degree (let alone a 1.5 degree) threshold is unachievable, WITHOUT a massive deployment of negative emission technologies that “offer only limited realistic potential to remove carbon from the atmosphere and not at the scale envisaged in some climate scenarios….. If such technologies are seen as a potential fail-safe or backup measure, they could influence priorities on shorter term mitigation strategies, since the promise of future cost-effective removal technologies is politically more appealing than engaging in rapid and deep mitigation policies now.” (EASAC Report)  i.e. Is 2 degrees achievable? YES – in the models NO in the real world. 

Time to get real – Fairyland of 2 degrees

What you will find on the page: 10 myths about net zero targetsAll we have to do is suck out all the excess CO2 – right? WRONG! change the frame for decision makersawful truth about climate change no one wants to admit; understanding how scenarios work (video); UN Emissions Gap Report 2017Don’t know what NETS are? Negative Emission Technology – no silver bullet; the Tinkerbell Effectnegative emission technologies – what role in meeting Paris Agreement targets? devil’s bargain – aerosolsreducing emissions alone won’t stop climate change: new researchFocus on Negative Emissions Scenarios and Technologies; website for assessing climate engineeringBioenergy carbon capture & storage (BECCS); carbon capture and storage (CCS); GEOENGINEERING“OVERSHOOT” another scenario component; Also refer to “Global Action/Inaction” and “Australian Response” pages as the issues are closely related

Latest News

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Fig. 1

a, Maximum greenhouse gas emissions (expressed as CO2 equivalents) compatible with a 2 °C trajectory in 2020, 2025 and 2030, as given by the UNEP Emissions Gap Reports23,24b, Benchmark values in the 2015 edition are about 20% higher than in the 2013 edition. This shift was a result of the introduction of a new scenario category — “limited action until 2020” — in the face of insufficient mitigation and slightly increasing global greenhouse gas emissions, resulting in widening emission gaps. The benchmark for 2020 (52 Gt) has been kept stable in the 2016 edition, whereas the 2017 edition does not contain a benchmark for 2020 anymore. Panel b courtesy of UN Environment Programme. Source: Shifting Benchmarks

All we have to do is suck out all the excess CO2 – right? WRONG!

It is far more complicated than that. A short read of this research paper will give a basic understanding of the complexity humanity has yet to come to grips with. t is why it is so important to reduce our emissions as fast as we can and not really on yet to be developed and proven technology.

ACCESS FULL REPORT HERE: The Effects of Carbon Dioxide Removal on the Carbon Cycle: Increasing atmospheric CO2 is having detrimental effects on the Earth system. Societies have recognized that anthropogenic CO2 release must be rapidly reduced to avoid potentially catastrophic impacts. Achieving this via emissions reductions alone will be very difficult. Carbon dioxide removal (CDR) has been suggested to complement and compensate for insufficient emissions reductions, through increasing natural carbon sinks, engineering new carbon sinks, or combining natural uptake with engineered storage. Here, we review the carbon cycle responses to different CDR approaches and highlight the often-overlooked interaction and feedbacks between carbon reservoirs that ultimately determines CDR efficacy. We also identify future research that will be needed if CDR is to play a role in climate change mitigation, these include coordinated studies to better understand (i) the underlying mechanisms of each method, (ii) how they could be explicitly simulated, (iii) how reversible changes in the climate and carbon cycle are, and (iv) how to evaluate and monitor CDR…

When carbon is deliberately transferred to or removed from a reservoir, the carbon cycle responds by redistributing the carbon in other reservoirs (Figs. 1 and 2), as well as within them, as biological, chemical, and physical processes adjust to the changing quantities of carbon within the reservoir and steeper gradients at the reservoir interfaces. By reducing the greenhouse effect, which leads to cooling, CDR also triggers climate-carbon cycle feedbacks. Together, these responses affect the efficacy of CDR and mean that removing 1 Gt of CO2 from the atmosphere will not ultimately reduce the atmospheric CO2 concentration by 1 Gt. The short-term efficacy of any CDR method depends on the state of the climate system and the carbon cycle…

Although CDR has been simulated in idealized scenarios that remove massive amounts of carbon in a short time, studies that apply more realistic constraints show that most sequestration rates are likely to be low and limited by many factors, such as land area or local environmental conditions (e.g., temperature, hydrology, chemistry) that impact reaction or growth rates [1••, 28293637•, 6871•, 73••]. This does not mean that CDR could not potentially work, just that most methods are relatively slow acting and might take many decades to centuries to reduce atmospheric CO2 to some desired level. The few methods that have the theoretical potential to rapidly remove more CO2 remain technologically immature and would likely take decades to be fully developed and deployed at climatically relevant scales…

For anthropogenic CO2 emissions, it is well established that only a fraction of the emissions effectively remains in the atmosphere because carbon cycle feedbacks adjust the carbon cycle to the anthropogenic perturbation by redistributing carbon among the interacting oceanic, terrestrial, and atmosphere reservoirs. Because of the different response times of terrestrial and oceanic carbon reservoirs, this partitioning changes with time and also depends on the state of the climate system. The same processes apply when CO2 is removed from the atmosphere, yielding an airborne fraction of CO2 removal, i.e., the perturbed airborne fraction [15••]. As a corollary, taking CO2 out of the atmosphere will lead to backfluxes of CO2 from the ocean and the land. The services that the land and ocean have provided in taking up a substantial portion of anthropogenic CO2 emissions can be viewed as a “carbon debt” that will have to be started to be paid back if large-scale CDR is ever deployed.

Source: Keller, D.P., Lenton, A., Littleton, E.W. et al. The Effects of Carbon Dioxide Removal on the Carbon Cycle. Curr Clim Change Rep 4, 250–265 (2018). https://doi.org/10.1007/s40641-018-0104-3. PublishedIssue Date

10 myths about net zero targets and carbon offsetting, busted

11 December 2020, Climate Home News: Comment: Carbon neutrality targets are often not as ambitious as they sound, relying on problematic carbon offsets and unproven technologies. The idea of carbon offsetting, which underpins so-called net zero targets, is founded on a number of myths. In many cases, offsetting relies on capturing carbon in vegetation and soils. Such capacity is however limited and is needed to store carbon dioxide that we have already emitted. Assumptions of future technologies and targets decades ahead delay immediate action. Countries and corporations must shift focus from distant net zero targets to real emissions reductions now.

The impacts of the climate crisis are becoming increasingly severe, everywhere. We are experiencing heat waves, floods, droughts, forest fires and sea level rise as a result of global heating. The average global temperature is rising at an unprecedented rate, rapidly diminishing the prospect of keeping global warming below 1.5C and with increasing risks of crossing irreversible tipping points. In the face of growing demands for action, many countries and companies are making promises and setting targets to reach “net zero” emissions or “carbon neutrality”. These often sound ambitious and may even give the impression that the world is awakening and ready to take on the climate crisis.

In practice, however, net zero targets several decades into the future shift our focus away from the immediate and unprecedented emissions reductions needed. Net zero targets are generally premised on the assumption that fossil fuel emissions can be compensated for by carbon offsetting and unproven future technologies for removing carbon dioxide from the atmosphere. But offsetting does not cancel out our emissions – yet action to do so is immediately needed.

There are a number of myths about net zero targets and carbon offsetting that must be dispelled. By revealing them, we aim to empower people, so that they can pressure governments and companies to create real solutions, here and now: Read more here

The need to change the frame – reality not doom

14 May 2018, Nature Geoscience, Politically informed advice for climate action: …..Researchers are not in a position to change core features of the policymaking process that limit the use of evidence, such as time constraints, path dependencies, limited capacity to digest new information, industries exerting their influence, and competing values. And scientific advisers will not be able to force policymakers to overcome inconsistency between talk, decisions and actions. But they can play their part in hedging inconsistency in climate policy.

Consider the following thought experiment: assume that during the course of the IPCC Sixth Assessment Cycle, the research community adopts standards for assessing the achievability of climate stabilization targets more realistically19, and, for instance, communicates its findings in a slightly different way. Instead of saying “yes, meeting the 1.5 °C target is still feasible, but only if A, B and C happens”, the core message would be “no, meeting the 1.5 °C target is currently not plausible, unless governments implement A, B and C”.

The difference in wording is small, and scientifically, both versions are probably equally valid. But the climate policy perspective changes considerably. In the first case, policymakers can focus on the ‘big prize’, the cherished long-term target that is still in sight, and achievement of the target is already assumed. This is a common way of exploiting the future for today’s political gains12, because governments are quite lenient when it comes to delivering the appropriate action. In the second case, instead of handing over the ‘big prize’ to policymakers early on, climate researchers hold it back, but define clear requirements for bringing it again into play, based on the latest scientific findings.

Such a communication would help to shift everybody’s attention, from talk and decisions to actions, and from the far-away future to the next 5 to 10 years20. Shifting the communication from a “yes, if…” to a “no, unless…” frame would prevent climate research and advice from resetting the clock time and again. Instead it puts the pressure where it belongs — on governments. Read full article here 

Also access: Carbon budgets and the 1.5 °C target. Budgets of carbon emissions that are consistent with limiting warming to no more than 1.5 °C over pre-industrial temperatures have been hotly debated, following the Paris Agreement on climate change targets. Here we present comments and primary research discussing the impacts of the debate on decision making processes, and the issues that the climate science community now needs to grapple with.

Also access: Beyond carbon budgets.The remaining carbon budget consistent with limiting warming to 1.5 °C allows 20 more years of current emissions according to one study, but is already exhausted according to another. Both are defensible. We need to move on from a unique carbon budget, and face the nuances.

The awful truth – barring miracles, humanity is in for some awful shit

15 May 2015, VOX, The awful truth about climate change no one wants to admit. There has always been an odd tenor to discussions among climate scientists, policy wonks, and politicians, a passive-aggressive quality, and I think it can be traced to the fact that everyone involved has to dance around the obvious truth, at risk of losing their status and influence. The obvious truth about global warming is this: barring miracles, humanity is in for some awful shit. Here is a plotting of dozens of climate modeling scenarios out to 2100, from the IPCC:

The black line is carbon emissions to date. The red line is the status quo — a projection of where emissions will go if no new substantial policy is passed to restrain greenhouse gas emissions. We recently passed 400 parts per million of CO2 in the atmosphere; the status quo will take us up to 1,000 ppm, raising global average temperature (from a pre-industrial baseline) between 3.2 and 5.4 degrees Celsius. That will mean, according to a 2012 World Bank report, “extreme heat-waves, declining global food stocks, loss of ecosystems and biodiversity, and life-threatening sea level rise,” the effects of which will be “tilted against many of the world’s poorest regions,” stalling or reversing decades of development work. “A 4°C warmer world can, and must be, avoided,” said the World Bank president. 

But that’s where we’re headed. It will take enormous effort just to avoid that fate. Holding temperature down under 2°C — the widely agreed upon target — would require an utterly unprecedented level of global mobilization and coordination, sustained over decades. There’s no sign of that happening, or reason to think it’s plausible anytime soon. And so, awful shit it is. Nobody wants to say that. Why not? It might seem obvious — no one wants to hear it! — but there’s a bit more to it than that. We’ll return to the question in a minute, but first let’s look at how this unsatisfying debate plays out in public. Read More here (ED: Even though this is written in 2015 it is still true today -2018 – see below)

ALSO ACCESS LATEST LEAKED DRAFT OF IPCC SPECIAL REPORT: No surprises and continued watered down language for the leaked IPCC draft 1.5o / 2o implications.

Another way of looking at it:In plain language, the complete set of 400 IPCC scenarios for a 50% or better chance of 2°C assume either an ability to travel back in time or the successful and large-scale uptake of speculative negative emission technologies. A significant proportion of the scenarios are dependent on both ‘time travel and geo-engineering’. Access the full article here: Duality in climate science – A commentary published in Nature Geoscience (online Oct. 2015)

What if negative emission technologies fail at scale? Implications of the Paris Agreement for big emitting nations: “A cumulative emissions approach is increasingly used to inform mitigation policy. However, there are different interpretations of what ‘2°C’ implies. Here it is argued that cost-optimisation models, commonly used to inform policy, typically underplay the urgency of 2°C mitigation.” Access full paper here

Understanding how scenarios work

Image result for Emissions Gap Report 2017 role of carbon dioxide removal in climate change mitigation

Emissions Gap Report 2017: Figure 7.2 Note: This figure shows emission reductions from conventional mitigation technologies combined with carbon dioxide removal. This exemplary  scenario is consistent with an at least 66 percent chance of keeping warming below 2°C relative to pre-industrial levels. Emission reductions are shown against a business-as-usual scenario without any additional climate policies. Global net emissions levels turn to net negative towards the very end of the century, but carbon dioxide removal is already being deployed much earlier. Some residual greenhouse gas emissions remain at the end of the century, as they are too difficult to mitigate in the scenario. Note that the scenario used is different from the scenarios used in Chapter 3, which leads to small variations in emission levels and timing of negative emissions. Source: Jérôme Hilaire (Mercator Research Institute on Global Commons and Climate).

The Emissions Gap Report 2017 A UN Environment Synthesis Report – November 2017

EXTRACTS: CHAPTER 7: Bridging the Gap – Carbon dioxide removal (pages 58-66) Access full report here

  • Scenarios consistent with the 1.5°C target depend on the large-scale availability of negative emissions technologies. There are no scenarios available that can keep warming below 1.5°C by 2100 without removing carbon from the atmosphere via negative emissions technologies (Fuss, 2017; Minx et al., 2017).
  • In general, the deployment of negative emissions technologies in the second half of the century occurs on a large scale, and with a very rapid scale-up to 8 GtCO2 per year by 2050 (range 5–15). By 2100 the median (2010–2100) removal of carbon dioxide via negative emissions technologies is 810 GtCO2 (range 440–1,020). This corresponds to about 20 years of global emissions at current emission rates.
  • In the 2°C scenarios with immediate climate action, the median (2010–2100) deployment of negative emissions technologies is considerably lower: 670 GtCO2 (range 320–840). In addition, the scale-up towards mid-century is much slower.
  • Delay in adequate near-term climate action swiftly locks 2°C pathways deeply into negative emissions. To limit warming to 2°C, current Nationally Determined Contributions lead to pathways that are fundamentally dependent on the large-scale availability of negative emissions technologies (like 1.5°C pathways today, and with similar deployment rates and technology upscaling requirements).
  • Compared to emissions pathways that are less efficient in energy use, 1.5°C and 2°C emissions pathways that feature aggressive energy savings are less dependent on negative emissions technologies.


7.6 Conclusions and recommendations “…..Carbon dioxide removal remains an important set of undertakings following the Paris Agreement, to supplement immediate and aggressive mitigation action. In order to achieve the goals of the Paris Agreement, to keep the global mean temperature increase well below 2°C (or even below 1.5°C), carbon dioxide removal is likely a necessary step. Although there is much ongoing work worldwide on this topic, the field of carbon removal remains very young (particularly for technology-based solutions), with relatively little scholarship on the direct topic of carbon dioxide removal. In some cases, efforts aimed at strengthening approaches to carbon dioxide removal can build on deep understanding and experience from other industries, for example, agribusinesses or heavy industry. Nonetheless, specific questions concerning current and future costs of carbon dioxide removal options, the longevity of carbon retention, the environmental consequences of scale-level deployment of carbon dioxide removal and other key questions remain largely unexplored…..”

Don’t know what NETS are?

The purpose of Negative Emission Technology s to remove carbon dioxide from the atmosphere at a large-scale. The main NET technologies are: 

  • Afforestation and reforestation.
  • Land management to increase and fix carbon in soils.
  • Bioenergy production with carbon capture and storage (BECCS).
  • Enhanced weathering.
  • Direct capture of CO2 from ambient air with CO2 storage (DACCS).
  • Ocean fertilisation to increase CO2.


Carbon Brief Guest Post: The problem with net-zero emission targets

30 September 2019: Prof Duncan McLaren is a research fellow at Lancaster University’s Lancaster Environment Centre The UK and several other countries now aim to deliver “net-zero” greenhouse gas (GHG) emissions by 2050, broadly in line with advice from the Intergovernmental Panel on Climate Change (IPCC). Both the IPCC and the UK’s Climate Change Committee have also highlighted the likely need for negative emissions, in addition to increased efforts to cut greenhouse gas outputs, if emissions are to fall to ‘net-zero’. However, our newly published research – based on findings from expert interviews and stakeholder deliberations – suggests that combining emissions reductions and negative emissions into a single target of reaching “net-zero” may create problems. These could include delayed emissions cuts, but also insufficient focus on developing negative emissions technologies. Here, Carbon Brief explain how these problems arise and suggest one possible solution. Read more here

There is a grey area when it comes to NET’s and geoengineering

Negative Emission Technology – no silver bullet

1 November 2018, Carbon Brief, Negative emissions: Scientists meet in Australia to discuss removing CO2 from air. An international group of researchers and policymakers met in Australia’s capital this week for the country’s first major conference dedicated to the topic of “negative emissions”. The two-day event, held at the Australian Academy of Science’s Shine Dome in Canberra, played host to a range of ideas for removing CO2 from the atmosphere and storing it on land, underground or in the oceans. The topics discussed ranged from “natural” solutions, such as boosting the carbon stores of soils and giant kelp forests, to the more experimental, including “fertilising” the world’s oceans. Carbon Brief was at the conference, which was organised by researchers from Australian National University and the University of Tasmania, to take in the presentations, talks and discussions. The Australian perspective This year has seen a ramping up of interest in negative emissions technologies (NETs) on both national and international levels. In January, the European Academies Science Advisory Council (EASAC) – an independent group that offers science advice to EU policymakers – published a reportlooking at the feasibility and overall potential of NETs from a European perspective. This was followed by the world’s first international conference on NETs, which was held in Sweden in May. The three-day event, which was covered in depth by Carbon Brief, saw scientists debate a range of issues, with a particular focus given to land-based methods such as afforestation and bioenergy with carbon capture and storage (BECCS). Access more here

1 June 2018, Carbon Brief, Guest post: Seven key things to know about ‘negative emissions’. Despite the ambitious long-term climate goals of the Paris Agreement, there remains a distinct lack of success at ushering in immediate and sustained reductions in global CO2 emissions. This cognitive dissonance has seen the topic of “negative emissions” – also known as “carbon dioxide removal” (CDR) – move into the limelight in climate science and policy discussions. Increasingly, the only way to bridge the growing gap between short and long-term climate policy ambition appears to be developing the ability to remove billions of tonnes of CO2 from the atmosphere and store it on land, underground, or in the oceans. Yet, the current knowledge on negative emissions technologies (NETs) is diffuse and incomplete. This makes it hard for assessment bodies, such as the Intergovernmental Panel on Climate Change (IPCC), to evaluate the state of knowledge. In a three-part literature review, published in Environmental Research Letters, we did some of the leg work and systematically assessed what we know and do not know about NETs. We presented our findings at last week’s international conference on negative emissions. Here are seven central insights from our three papers. Read more here

25 May 2018, Carbon Brief, Negative emissions: Scientists meet in Sweden for first international conference. This week, Gothenburg in Sweden played host to the first international conference on “negative emissions”. The three-day event brought together around 250 researchers at Chalmers University of Technology to discuss the different ways to remove CO2 from the atmosphere and store it on land, underground or in the oceans. The topics presented and debated ranged from “natural” solutions to the technologically advanced, through to the potential limitations and risks. Running parallel to the scientific discussions was a focus on the policy challenges. Eva Svedling, Sweden’s secretary of state for development and climate, marked the occasion by launching a public enquiry into the potential for forests, soil and bioenergy to provide carbon removal for the country. Sweden already has a legally binding targetto reach net-zero carbon emissions by 2045. Carbon Brief was at the conference to watch the 11 keynote speeches, 140 presentations and three panel debates. A range of presenters, such as Dr James Hansen and Dr Sabine Fuss, was asked on camera (see below) what they each think is needed for negative emissions to become a reality at scale. Read more here

22 May 2018: Negative emissions—Part 1: Research landscape and synthesis: Here, we synthesize a comprehensive body of NETs literature, using scientometric tools and performing an in-depth assessment of the quantitative and qualitative evidence therein. We clarify the role of NETs in climate change mitigation scenarios, their ethical implications, as well as the challenges involved in bringing the various NETs to the market and scaling them up in time. Read More here

31 January 2018 Carbon Brief: The potential for using negative emissions technologies to help meet the goals of the Paris Agreement could be more “limited” than previously thought, concludes a new report by European science advisors. Negative emissions technologies (NETs) describe a variety of methods – many of which are yet to be developed – that aim to limit climate change by removing CO2 from the air. Some of these techniques are already included by scientists in modelled “pathways” showing how global warming can be limited to between 1.5C and 2C above pre-industrial levels, which is the goal of the Paris Agreement. However, the new report says there is no “silver bullet technology” that can be used to solve the problem of climate change, scientists said at a press briefing held in London. Instead, “the primary focus must be on mitigation, on reducing emissions of greenhouse gases,” they added. Read More here

Image result for no quick fixes CO2


From about year 2030 to 2100, it would be necessary for the world to somehow miraculously suck out of the air some 1,000 gigatons of CO2 to meet the heat limit criteria. Understand what 1,000 gigatons of CO2 that would need to be magically sucked out of the air and buried forever means in real world terms. Just one gigaton of weight is 1,000,000,000 X 2,204.6 = 2,206,400,000,000, over two trillion pounds.  Converting to elephants, a gigaton is over 100,000,000 African elephants in weight, about one for every three Americans. Now, there are not nearly that many elephants alive, so one must use their imagination. That means in order to meet the reductions so the world does not blast past 2°C, it would be necessary to capture and bury 1,428,571,428 “elephants of CO2” each and every year from 2030 to 2100 – almost one per family of humans (at today’s population level) each and every year for 70 years. Source: The Tinkerbell Effect

EASAC REPORT: February 2018 – the European Academies’ Science Advisory Council: Negative emission technologies: What role in meeting Paris Agreement target

EASAC – the European Academies’ Science Advisory Council – is formed by the national science academies of the EU Member States to enable them to collaborate with each other in giving advice to European policy-makers. It thus provides a means for the collective voice of European science to be heard. EASAC was founded in 2001 at the Royal Swedish Academy of Sciences. Some extracts follow

“Having achieved a global consensus at the Paris meeting of the UN Convention on Climate Change in December 2015, there may be a tendency to think the problem of climate change is finally on the way to being solved. This may be one reason for the lack of recognition in the public and political debate of the severity of the emission reductions required to achieve the target of restricting warming to within 2 °C of pre-industrial levels, let alone the 1.5 °C aspiration enshrined in the Paris Agreement.

One factor possibly contributing to a lack of urgency may be the belief that somehow ‘technology’ will come to the rescue. The present report shows that such expectations may be seriously over-optimistic. Intergovernmental Panel on Climate Change (IPCC) future scenarios allow Paris targets to be met by deploying technologies that remove carbon dioxide from the atmosphere. However, putting a hypothetical technology into a computer model of future scenarios is rather different than researching, developing, constructing and operating such a technology at the planetary scale required to compensate for inadequate mitigation.

Whether consciously or subconsciously, thinking that technology will come to the rescue if we fail to sufficiently mitigate may be an attractive vision. If such technologies are seen as a potential fail-safe or backup measure, they could influence priorities on shorter term mitigation strategies, since the promise of future cost-effective removal technologies is politically more appealing than engaging in rapid and deep mitigation policies now. Placing an unrealistic expectation on such technologies could thus have irreversibly damaging consequences on future generations in the event of them failing to deliver. This would be a moral hazard which would be the antithesis of sustainable development. A range of potential approaches exist for removing carbon dioxide (CO2) from the atmosphere, at least in theory, and we thus decided to assess the potential of such technologies.

Having reviewed the scientific evidence on several possible options for CO2 removal (CDR) using negative emission technologies (NETs), we conclude that these technologies offer only limited realistic potential to remove carbon from the atmosphere and not at the scale envisaged in some climate scenarios (as much as several gigatonnes (one billion or 109 tonnes) of carbon each year post-2050). Negative emission technologies may have a useful role to play but, on the basis of current information, not at the levels required to compensate for inadequate mitigation measures. Implementation is also likely to be location-, technology- and circumstance specific. Moreover, attempts to deploy NETs at larger scales would involve significant uncertainties in the extent of the CDR that could be achieved, as well as involving high economic costs and likely major impacts on terrestrial or marine ecosystems.”


  • Given the somewhat unclear technical and economic viability of NETs in the longer-term future, the EU should thus continue to be fully committed to mitigation as laid down in the EU’s nationally determined contributions in the Paris Agreement.


  • In addition, most analyses of the potential of individual NETs have focused on the physical, chemical and geological aspects, and less attention has been paid to impacts on the planet’s ecosystems. Clearly, transforming the uses assigned to substantial proportions of the Earth’s landmass, or interfering on a large scale with the ocean ecosystem, has substantial implications for the Earth’s remaining natural ecosystems and the species they support.


  • The dominant role assigned in IPCC integrated assessment models to NETs (in particular BECCS) face serious challenges in taking fully into account these interactions, as well as allowing for factors that potentially may reduce or even reverse CDR capacity. This adds further uncertainties to the calculation of the cumulative potential in integrated assessment models. Current scenarios and projections of CDR’s future contribution to CDR which allow Paris targets to be met thus appear rather optimistic on the basis of current knowledge, and should not be seen as offering a realistic pathway to meeting Paris Agreement targets. When developing, analysing and comparing scenarios of longer-term energy pathways for the EU, these constraints in the potential of NETs should be given appropriate attention.


  • The focus on forestry as a NET can divert attention from the potential of continued deforestation to release very large quantities of CO2 (1800 GtCO2 remain sequestered in tropical forests As well as considering reforestation or afforestation, therefore, it is essential to slow and reverse current continued high rates of deforestation which have turned tropical forests from carbon sinks to carbon sources. Equally, since efficient and off-the-shelf CCS is a precondition for BECCS (and the carbon storage aspect for DACCS), and CCS is a critical means of increasing mitigation from existing point sources, efforts should continue to develop CCS into a relevant and relatively inexpensive mitigation technology….. Maximising mitigation with such measures will reduce the future need to remove CO2 from the atmosphere.


  • The emphasis we place on mitigation to avoid an overshoot in ‘safe’ levels of CO2 is supported by the reality that removal of a given quantity of a greenhouse gas later would not fully compensate for an earlier overshoot of emissions. The existence of a significant time gap (many decades) between an overshoot and its potential compensation means that climatic and environmental consequences of the overshoot would continue and not be fully cancelled by future CO2 removal. As pointed out by CBD (2016), the consequences of that delay during which warming continues would lead to significant and potentially irreversible consequences for biodiversity and the Earth system.”

Access full report here

Devil’s Bargain – aerosols

Mount Pinatubo’s eruption showed how aerosol dispersal could cool the planet.

8 February 2018, GRIST, We already have planet-cooling technology. The problem is, it’s killing us. A trope of sci-fi movies these days, from Snowpiercer to Geostorm, is that our failure to tackle climate change will eventually force us to deploy an arsenal of unproven technologies to save the planet. Think sun-deflecting space mirrors or chemically altered clouds. And because these are sci-fi movies, it’s assumed that these grand experiments in geoengineering will go horribly wrong. The fiction, new evidence suggests, may be much closer to reality than we thought. When most people hear “climate change,” they think of greenhouse gases overheating the planet. But there’s another product of industry changing the climate that has received scant public attention: aerosols. They’re microscopic particles of pollution that, on balance, reflect sunlight back to space and help cool the planet down, providing a crucial counterweight to greenhouse-powered global warming. An effort to co-opt this natural cooling ability of aerosols has long been considered a potential last-ditch, desperate shot at slowing down global warming. The promise of planet-cooling technology has also been touted by techno-optimists, Silicon Valley types and politicians who aren’t keen on the government doing anything to curb emissions. “Geoengineering holds forth the promise of addressing global warming concerns for just a few billion dollars a year,” wrote Newt Gingrich in an attack on proposed cap-and-trade legislation back in 2008. But there’s a catch. Our surplus of aerosols is a huge problem for those of us who like to breathe air. At high concentrations, these tiny particles are one of the deadliest substances in existence, burrowing deep into our bodies where they can damage hearts and lungs. Read More here  Read also 6 December 2011, GRIST: The brutal logic of climate change. Another one – 10 November 2017, Climate News Network – Geo-engineering can work – if the world wants it

22 January 2018, Nature: Biomass-based negative emissions difficult to reconcile with planetary boundaries

Website for assessing implications of climate engineering

The Forum for Climate Engineering Assessment’s (FCEA) overarching objective is to assess the social, ethical, political, and legal implications of emerging technologies that fall under the broad rubric of climate engineering (sometimes referred to as “geoengineering” or “climate intervention”). We produce policy-relevant research and commentary, and work in a variety of ways ensure that the climate engineering conversation maintains a focus on issues of justice, equity, agency, and inclusion. FCEA is an initiative of the School of International Service at American University in Washington, DC. FCEA was constituted in 2013, out of a recognition that the conversation about climate engineering responses to climate change was growing rapidly in importance, yet was narrowly restricted in terms of the scope of actors and interests.

A bit of history re BECCS (Bio-Energy with Carbon Capture and Storage)

12 October 2017, WIRED, The Dirty Secret of the World’s Plan to Avert Climate Disaster. IN 2014 HENRIK Karlsson, a Swedish entrepreneur whose startup was failing, was lying in bed with a bankruptcy notice when the BBC called. The reporter had a scoop: On the eve of releasing a major report, the United Nation’s climate change panel appeared to be touting an untried technology as key to keeping planetary temperatures at safe levels. The technology went by the inelegant acronym BECCS (Bio-Energy with Carbon Capture and Storage), and Karlsson was apparently the only BECCS expert the reporter could find. Karlsson was amazed. The bankruptcy notice was for his BECCS startup, which he’d founded seven years earlier after an idea came to him while watching a late-night television show in Gothenburg, Sweden. The show explored the benefits of capturing carbon dioxide before it was emitted from power plants. It’s the technology behind the much-touted notion of “clean coal,” a way to reduce greenhouse gas emissions and slow down climate change…..But here’s where things get weird. The UN report envisions 116 scenarios in which global temperatures are prevented from rising more than 2°C. In 101 of them, that goal is accomplished by sucking massive amounts of carbon dioxide from the atmosphere—a concept called “negative emissions”—chiefly via BECCS. And in these scenarios to prevent planetary disaster, this would need to happen by midcentury, or even as soon as 2020. Like a pharmaceutical warning label, one footnote warned that such “methods may carry side effects and long-term consequences on a global scale.” ……   Still, negative emissions are not mentioned in the Paris Climate Agreement or a part of formal international climate negotiations. As Peters and Geden recently pointed out, no country mentions BECCS in its official plan to cut emissions in line with Paris’s 2°C goal, and only a dozen mention carbon capture and storage. Politicians are decidedly not crafting elaborate BECCS plans, with supply chains spanning continents and carbon accounting spanning decades. So even if negative emissions of any kind turns out to be feasible technically and economically, it’s hard to see how we can achieve it on a global scale in a scant 13 or even three years, as some scenarios require. Read More here

Carbon Capture and Storage

Click on above image to access Climate Institute’s carbon removal animation for an understanding about what is carbon capture and storage.

SOURCE: Carbon Tracker, 7 December 2015

IPCC Special Report Chapter 3 – Capture of CO2 The purpose of CO2 capture is to produce a concentrated stream that can be readily transported to a CO2 storage site. CO2 capture and storage is most applicable to large, centralized sources like power plants and large industries. Capture technologies also open the way for large-scale production of low-carbon or carbon-free electricity and fuels for transportation, as well as for small-scale or distributed applications.There are four basic systems for capturing CO2 from use of fossil fuels and/or biomass:

  • Capture from industrial process streams (described in Section 3.2): CO2 has been captured from industrial process streams for 80 years (Kohl and Nielsen, 1997), although most of the CO2 that is captured is vented to the atmosphere because there is no incentive or requirement to store it. 
  • Post-combustion capture (described in Section 3.3): Capture of CO2 from flue gases produced by combustion of fossil fuels and biomass in air is referred to as post-combustion capture. Instead of being discharged directly to the atmosphere, flue gas is passed through equipment which separates most of the CO2 . The CO2 is fed to a storage reservoir and the remaining flue gas is discharged to the atmosphere
  • Oxy-fuel combustion capture (described in Section 3.4): In oxy-fuel combustion, nearly pure oxygen is used for combustion instead of air, resulting in a flue gas that is mainly CO2 and H2 O. If fuel is burnt in pure oxygen, the flame temperature is excessively high, but CO2 and/or H2 O-rich flue gas can be recycled to the combustor to moderate this.
  • Pre-combustion capture (described in Section 3.5). Pre-combustion capture involves reacting a fuel with oxygen or air and/or steam to give mainly a ‘synthesis gas (syngas)’ or ‘fuel gas’ composed of carbon monoxide and hydrogen. 


Other Ways of Carbon Capture

  • Chemical scrubbers using certain chemical reactions to remove CO2 that’s already in the atmosphere such as this plan for artificial trees.
  • Reducing ocean acidification by adding crushed limestone to the oceans.
  • Fertilizing the oceans with iron or urea to promote plankton growth.
  • Reducing the CO2 from decomposing plant matter by either burring it or turning it into biochar, to be burnt like coal.


Carbon Storage – There are three places geoengineers are looking to put the carbon after capturing it.

  • Geologic storage-pumping condensed CO2 in old oil reservoirs, or in non efficient coal deposits.
  • Ocean storage putting CO2 in the natural sink of the oceans
  •  Storage in deep saline aquifers in the earths crust.


Access a range of articles on the issue from The Conversation here

16 February 2018, The Guardian, It’d be wonderful if the claims made about carbon capture were true. The International Energy Agency warned this week that, under current energy policies, Australia is unlikely to meet its 2030 climate commitments. While the agency had lots to say about the plunging costs of renewables and the need for strong market signals to encourage the retirement of old and inefficient coal generation, Josh Frydenberg, the federal environment and energy minister, seized on the agency’s support for carbon capture and storage (CCS) – despite the technology’s long history of big promises and meagre results. Last April, Frydenberg visited the newly opened Petra Nova CCS project in Texas. In a video posted to social media the minister, decked out in the obligatory hi-vis vest and hard hat, yells above the noise that the $1bn project is “helping to reduce the carbon footprint by some 40%”. It’d be wonderful if it were true. An estimated 6.2% of the Petra Nova power station’s emissions are captured, compressed and then piped 130km to help extract stubborn oil out of a depleted oil field. In the process, an estimated 30% of the carbon dioxide leaks back into the atmosphere, not to mention the emissions that will ultimately be released when the extracted oil is consumed. Last month, the Minerals Council of Australia was spruiking the “21 large-scale CCS facilities in operation or under construction around the world including in Canada and Texas”. Sounds impressive, if you still trust the MCA’s spin. You shouldn’t – 19 of the 21 projects have nothing to do with coal; there are exactly two “large scale” coal CCS projects globally. And, no, they’re not large. The Canadian project, Boundary Dam, has averaged only 0.591 million tonnes of carbon dioxide over each of its first three years. The $1.5bn project would need to be scaled up 31 times to capture the emissions of New South Wales’s Bayswater power station – an inconceivable investment. Read More here

2 July 2015, Climate News Network, Carbon capture goes down the tubes: One of the much-heralded solutions to climate change which its supporters believe could enable the world to continue to burn fossil fuels looks likely to be a failure. Carbon capture and storage (CCS) is backed by governments and the International Energy Agency (IEA) as one of the best methods of reducing carbon dioxide levels in the atmosphere and saving the planet from overheating. The problem is that despite this enthusiasm and the fact that CCS (also called carbon sequestration) is technically possible, it is not happening. It is cheaper and easier to build wind and solar farms to produce electricity than it is to collect and store the carbon from coal-powered plants’ emissions. For years CO2 has been used by injecting it into old oil wells to extract more fuel, but the cost of building new plants just to store the gas is proving prohibitive. Hundreds of plants were expected to be up and running by 2030, but so far none has been built. Despite this, the IEA and governments across the world are relying on CCS to save the planet from climate change. For example, official policy in the UK still envisages up to fifty industrial plants and power stations using CCS being linked to CO2 pipelines which would inject the gas into old oil and gas wells, removing it from the atmosphere for ever. But research by Mads Dahl Gjefsen, a scientist at the TIK Centre of Technology, Innovation and Culture at the University of Oslo, Norway, says pessimism prevails within the industry about the future of carbon capture and storage in both the US and the European Union. Read More here

29 June 2015, Science Daily, Pessimism prevails about the future of carbon capture and storage in both the USA and EU. This is despite the fine promises that it was precisely this technology that would save the oil and gas industry. “There’s a sombre mood among people who work with carbon capture and storage now. Lobbyists in the US and the EU wonder how much longer they can keep going,” says Mads Dahl Gjefsen, a scientist at the TIK Centre of Technology, Innovation and Culture at the University of Oslo. In his PhD thesis: “Vehicle or destination? Discordant perspectives in CCS advocacy”,he has studied how different players work to gain support for CCS. Murkiness in the corridors of Power Norway has invested several billion kroner in the research and development of carbon capture and storage (CCS). The technology was intended to reduce emissions from the oil and gas industry, and in 2007 former Prime Minister Jens Stoltenberg said that CCS would be Norway’s moon landing. But a full-scale treatment plant at Mongstad never came to fruition. The major challenge has been that the technology is energy-intensive and too costly for large-scale use. And this is not just a Norwegian  problem. According to Gjefsen, the enthusiasm for CCS in the corridors of power has gradually dissipated in both the USA and EU. Read More here

Geoengineering: Desperate measures when no one else is doing enough? Or, ‘wildly, howlingly barking mad!’

Geoengineering or let’s keep fiddling until we REALLY stuff up the planet, or here comes another brilliant idea like introducing cane toads! What is it and is it part of the solution? Opening another Pandora’s Box to the mess we are already in. 

10 November 2017, Climate News Network: Geo-engineering can work – if the world wants it. Geo-engineering can stop the Earth warming, at least in theory, scientists say, but doubts persist over the possible risks. Climate scientists now know that geo-engineering – in principle at least – would halt global warming and keep the world at the temperatures it will reach by 2020. It is simple: inject millions of tons of sulphate aerosols into the stratosphere at carefully chosen locations, and keep on doing so for as long as humans continue to burn fossil fuels and release greenhouse gases into the atmosphere. The desired effect: global temperatures will be contained because the pollutants in the upper atmosphere will dim the sun’s light and counteract the greenhouse effect of all the carbon dioxide pumped from power stations, vehicle exhausts, factory chimneys and burning forests. It won’t be the perfect answer. The oceans will go on becoming more acidic, and the skies will become subtly darker. Rainfall patterns could be affected. Repairs to the ozone layer – an invisible shield against dangerous ultraviolet radiation – would be slowed.The volumes of sulphate aerosols that would need to be flown to stratospheric heights and released each year would continue to grow as humans went on burning ever more fossil fuels. The technical and energy demands of such an operation would be colossal. There could be serious geopolitical problems about the impacts and responsibility for such decisions. But, at least in principle, researchers now believe geo-engineering could be made to work. “For decision makers to accurately weigh the pros and cons of geo-engineering against those of human-caused climate change, they need more information,” said Ben Kravitz, of the Pacific Northwest National Laboratory, and one of a consortium which has published a succession of five studies in the Journal of Geophysical Research – Atmospheres. “Our goal is to better understand what geo-engineering can do – and what it cannot.”  Read More here

9 November 2017, DeSmog, Climate Denier Lamar Smith Holds Rare Congressional Hearing on Geoengineering. Geoengineering, hailed in some circles as a potential technofix to the climate change crisis, has taken a step closer to going mainstream.  The U.S. House Committee on Science, Space, and Technology held a rare joint subcommittee hearing on November 8, only the second ever congressional hearing of its kind on the topic (the first was held in 2009). The committee invited expert witnesses to discuss the status of geoengineering research and development. Geoengineering is a broad term encompassing sophisticated scientific techniques meant to reverse the impacts of climate change or pull greenhouse gases out of the atmosphere. Ironically, the Committee on Science, Space, and Technology is chaired by U.S. Rep. Lamar Smith — a climate science denier who has received tens of thousands of dollars in campaign contributions from ExxonMobil throughout his political career. In fact, Smith actually mentioned “climate change” in his opening remarks for the hearing, in discussing his interest in geoengineering. “As the climate continues to change, geoengineering could become a tool to curb resulting impacts,” said Smith, who recently announced he will not run for relection in 2018. “Instead of forcing unworkable and costly government mandates on the American people, we should look to technology and innovation to lead the way to address climate change. Geoengineering should be considered when discussing technological advances to protect the environment.” In the past, Smith has denied climate change in stark terms, referring to those who believe in climate science as “alarmists” in a 2015 op-ed published by The Wall Street Journal. “Climate alarmists have failed to explain the lack of global warming over the past 15 years,” Smith said at the time. “They simply keep adjusting their malfunctioning climate models to push the supposedly looming disaster further into the future.”  Smith has since pivoted to less skepticism about the science, saying at a March 2017 congressional hearing that “climate is changing and humans play a role” and that it’s now just a question of the “extent” to which human activity is the culprit (it is). So perhaps geoengineering, labeled by its critics for years now as a false solution to the climate crisis, will be a “pivot” of sorts for converted deniers and their bankrollers? Read More here   

14 October 2017, The Guardian, Geoengineering is not a quick fix for climate change, experts warn Trump. Leading climate scientists have warned that geoengineering research could be hijacked by climate change deniers as an excuse not to reduce CO2 emissions, citing the US administration under Donald Trump as a major threat to their work. David Keith, a solar geoengineering (GE) expert at Harvard University has said there is a real danger that his work could be exploited by those who oppose action on emissions, at the same time as he defended himself and colleagues from the claims GE strengthens the argument for abandoning the targets set by the Paris climate agreement. Leading climate scientists have warned that geoengineering research could be hijacked by climate change deniers as an excuse not to reduce CO2 emissions, citing the US administration under Donald Trump as a major threat to their work. David Keith, a solar geoengineering (GE) expert at Harvard University has said there is a real danger that his work could be exploited by those who oppose action on emissions, at the same time as he defended himself and colleagues from the claims GE strengthens the argument for abandoning the targets set by the Paris climate agreement. “One of the main concerns I and everyone involved in this have, is that Trump might tweet ‘geoengineering solves everything – we don’t have to bother about emissions.’ Read More here  

11 October 2017, Carbon Briefing, Geoengineering: Scientists in Berlin debate radical ways to reverse global warming. Research scientists, policymakers and ethicists gathered in Berlin this week to discuss the emerging field of “climate engineering” and what it could mean for the planet. Climate engineering, also known as geoengineering, is a term used to describe an array of technologies – many of which remain hypothetical – for altering the global climate in order to lessen the effects of climate change. The four-day conference has been organised by the Institute for Advanced Sustainability Studies (IASS) in Potsdam, Germany, and includes speakers and participants from across the world, including Japan, Jamaica, the US and India. Tuesday Tuesday’s proceedings kicked off with talks aimed at bringing the audience up to speed with the latest research into the two main categories of geoengineering technologies: carbon dioxide removal (CDR) and solar radiation management (SRM). First up was Dr Naomi Vaughan, a researcher from the Tyndall Centre for Climate Change Research at the University of East Anglia. Her talk touched on recent research into a variety of CDR technologies, including biomass energy carbon capture and storage (BECCS), soil carbon sequestration and reforestation projects, and how important these techniques could be to meeting the goals of the Paris Agreement. She told the conference: Read More here

1 August 2017, Building a Climate Engineering ClearinghouseClimate engineering (CE) is an umbrella term for a set of mostly prospective technologies that might be developed and used to counteract some of the effects of climate change. The technologies under consideration could do much good. They also, though, present myriad risks. Because of these risks, CE experts and observers have long emphasized the need for transparency in research, experimentation, and deployment.

27 March 2017, The Guardian, Trump presidency ‘opens door’ to planet-hacking geoengineer experiments. Harvard engineers who launched the world’s biggest solar geoengineering research program may get a dangerous boost from Donald Trump, environmental organizations are warning. Under the Trump administration, enthusiasm appears to be growing for the controversial technology of solar geo-engineering, which aims to spray sulphate particles into the atmosphere to reflect the sun’s radiation back to space and decrease the temperature of Earth. Sometime in 2018, Harvard engineers David Keith and Frank Keutsch hope to test spraying from a high-altitude balloon over Arizona, in order to assess the risks and benefits of deployment on a larger scale. Keith cancelled a similar planned experiment in New Mexico in 2012, but announced he was ready for field testing at a geoengineering forum in Washington on Friday. “The context for discussing solar geoengineering research has changed substantially since we planned and funded this forum nearly one year ago,” a forum briefing paper noted. Read More here

The Forum for Climate Engineering Assessment is an initiative of the School of International Service at American University in Washington DC. Our overarching objective is to assess the social, ethical, political, and legal implications of emerging technologies that fall under the broad rubric of climate engineering (sometimes referred to as “climate geoengineering”). We produce high-quality and policy-relevant research and commentary, and work in a variety of ways to ensure that the climate engineering conversation maintains a focus on issues of justice, equity, agency, and inclusion.

7 August 2013, The Promises and Perils of Geoengineering. Worldwatch Institute examines the potential consequences of using geoengineering as a climate quick fix – BY SIMON NICHOLSON Geoengineering, by definition, is any deliberate large-scale manipulation of the planetary environment to counteract human-caused climate change. As the planet continues to warm, the potential solutions offered by geoengineering are tempting, and several serious projects are actively being pursued. In the latest edition of State of the World 2013: Is Sustainability Still Possible? I examine the pros and cons of such an approach to responding to climate change. The technological prospects for geoengineering are vast, and fall into two main camps:

Image result for solar radiation management carbon dioxide removalSolar Radiation Management (SRM), a tactic that aims to reflect solar radiation back into space so that it is not absorbed by the atmosphere. The intent is to counteract heat-trapping gases by scattering or deflecting some percentage of incoming solar radiation by, for instance, streaming sulfate particles into the stratosphere or launching sunshades into space. 

Related imageCarbon Dioxide Removal (CDR), an approach that involves drawing large amounts of carbon out of the atmosphere, and storing it where it won’t cause future harm. Land-based ideas have included carbon dioxide scrubbers that would pull large quantities of carbon dioxide straight from the air, or growing forms of biomass and then reducing it to charcoal, which can be buried. Ocean-based ideas mostly involve the cultivation of plankton, which take in carbon from the atmosphere and bring it to the bottom of the ocean with them when they die.

SRM strategies are receiving the bulk of the attention. It is hard to see a CDR scheme coming online quickly enough or being deployed at a large enough scale to make a real dent in the atmospheric carbon load. Yet solar radiation management is not any kind of real answer to climate change. At best, SRM can reduce the planet’s fever for a period. Talk of geoengineering is gaining traction because it has the appearance of an easy, sacrifice-free approach to tackling climate change. It is critically important to recognize that there are sacrifices, some obvious and some harder to spot, associated with the bulk of geoengineering schemes.

In my chapter, “The Promises and Perils of Geoengineering,” I outline some of the consequences that may arise if geoengineering is pursued:

Climate Catastrophes: The most obvious concern is the potential for causing catastrophic and irreparable damage. Even with computer models and endless calculations, there are still potential unforeseen problems that may occur with any such large-scale plan, due to our still limited understanding of the world’s climate system.

Political Dilemmas: Large-scale climate engineering may curtail the will to develop other forms of climate-protecting actions. If changes in the climate affect various parts of the world, the question of who ought to control the thermostat also raises issues. Less influential countries may be left to suffer as world powers dictate climate behavior to their advantage. Militaries may be able to start using the weather as their greatest weapon of mass destruction.

Rogue ActorsIn October 2012, an American took a ship off the shore of Canada and dumped about 100 tons of iron sulfates into the Pacific Ocean, in hopes of creating a carbon sink. As threats about rising temperatures increase, it is possible that more individuals and organizations will risk taking the climate’s condition into their own hands.

With outlined principles and public decision making, however, geoengineering does have the potential to become one method to battle climate change. Some scientists have suggested a “soft-geoengineering” approach, in which changes we make are still widespread, but are reversible and predictable. Examples include painting roofs white to reflect sunlight, or building up carbon in soil and vegetation. The need is for a middle ground, not geoengineering as a techno-fix but rather geoengineering as one small part of an effort to steer the world to a state of rightness and fitness in ecological and social terms. Worldwatch’s State of the World 2013, released in April 2013, addresses how sustainability should be  measured, how we can attain it, and how we can prepare if we fall short. For more information, visit www.sustainabilitypossible.org.

11 February, Carbon Brief, Geoengineering is no substitute for cutting carbon emissions, conclude US researchers: The US National Research Council has published two new reports on ‘climate interventions’, or what is more commonly known as ‘geoengineering’…. The new reports are the result of an 18-month study into the potential impacts, benefits and costs of geoengineering. The study produces a set of recommendations, which call for more research and development, but also caution that sunlight-reflecting technologies “should not be deployed at this time”. Read More here

2 March 2015, Ensia, Why geoengineering can be only part of the climate solution: The failure of the Kyoto Protocol and the underlying process of the United Nations Framework Convention on Climate Change (UNFCCC) has led to substantial interest in geoengineering technologies, under the usual (and not entirely irrational) view that if policy can’t work, perhaps technology might. And indeed, Wally Broecker in his article in Elementa about CO2 air capture technologies did his usual excellent job of summarizing both the concerns raised by global climate change, and the possibility that technologies, such as air capture of CO2, might be able to respond, at least if events reach a crisis point. From a technologist’s perspective, however, the overall geoengineering discussion is unsatisfactory for several reasons, some of them quite fundamental to rational and ethical responses to the challenges of the Anthropocene. Climate change is not a technological problem, so a technological fix is not enough. Read More here

A quick fix? Think again:This article is from the Australian Academy of Science is sponsored by the Australian Government Department of Climate Change and Energy Efficiency. Geoengineering might cool the Earth, but at what cost? Read More here

Other resources and articles: Geoengineering Monitor

Overshoot – another little understood component of IPCC scenarios

What happens if emissions are NOT reduced enough? What does “overshoot” mean?

OVERSHOOT: The overshoot scenario is an emissions scenario in which atmospheric CO2 concentrations temporarily exceed predefined “dangerous” thresholds before reducing again and stabilizing to the “safe” level that would itself allow global warming to be stabilized at 2°C above pre-industrial levels. 

IPCC Working Group III Report Chapter 6 excerpts

Atmospheric concentrations in baseline scenarios collected for this assessment (scenarios without additional efforts to constrain emissions beyond those of today) all exceed 450 parts per million (ppm) carbon dioxide-equivalent (CO2eq) by 2030 and lie above the RCP  6.0 representative concentration pathway in 2100 (770ppm CO2eq in 2100); the majority lie below the RCP  8.5 concentration pathway in 2100 (1330ppm CO2eq in 2100) (high confidence). The scenario literature does not systematically explore the full range of uncertainty surrounding development pathways and the possible evolution of key drivers such as population, technology, and resources. However, the baseline scenarios do nonetheless strongly suggest that absent explicit efforts at mitigation, cumulative CO2 emissions since 2010 will exceed 700 GtCO2 by 2030, exceed 1500 GtCO2 by 2050, and potentially be well over 4000 GtCO2 by 2100. [Section 6.3.1] Scenarios can be distinguished by the long-term concentration level they reach by 2100; however, the degree to which concentrations exceed (overshoot) this level before 2100 is also important (high confidence). The large majority of scenarios produced in the literature that reach about 450 ppm CO2eq by 2100 are characterized by concentration overshoot facilitated by the deployment of carbon dioxide removal (CDR) technologies at a large scale. Many scenarios have been constructed to reach about 550 ppm CO2eq by 2100 without overshoot. This assessment found that the likelihood of exceeding temperature goals this century increases with peak concentration levels, which are higher in overshoot scenarios. [6.3.2]

Garnaut Review Chapter 9 (excerpts):

Determining limits over time on global emissions involves striking a balance between the benefits associated with smaller and slower climate change and the costs associated with greater and faster mitigation. The appropriate extent of mitigation is defined by the point at which the additional gains from mitigation are similar to the additional costs. In the end, judgment is required on the level of climate change that corresponds to this balancing point. Targeted limits on climate change can be defined at three levels:

  • At the highest level they can be defined in terms of impact or global temperature increase.
  • At the next level they can be defined in terms of the profile for concentration of greenhouse gases in the atmosphere, which drives temperature increases.
  • And at the third level, they can be defined in terms of emissions of greenhouse gases, which drive atmospheric concentrations.

Targets for global mean temperature compress the multiplicity of possible impacts (ranging from glacial melting to increased weather-related calamities) into a single variable. The European Union, for example, has argued that global mean warming should not be allowed to exceed 2°C from pre-industrial levels (Council of the European Union 2007) (NOTE: This has now been accepted as the international target through UNFCCC 2014). Endorsement of a temperature threshold (and therefore of any target derived from it, for example, greenhouse gas concentration) cannot imply indifference to other factors. There may be tipping points associated with particular temperature thresholds, but the thresholds are not known with certainty.

Figure 9.1 Different concentration goals: stabilisation, overshooting and peaking

Garnaut overshoot

Global warming increases temperature with a long lag. It might take more than a century after stabilisation of greenhouse gas concentrations for a new equilibrium temperature to be reached (see below). Any goals in terms of temperature need to be translated into goals for the atmospheric concentration of greenhouse gases….

Most attention has focused on stabilisation scenarios, and the UNFCCC goal of the ‘stabilization of greenhouse gas concentrations in the atmosphere’ (Article 2). However, special challenges are introduced by the need to reduce greenhouse gas concentrations to low levels. There is great difficulty in moving directly to that outcome from where the world is now. Whether the ultimate aim is stabilisation or prolonged decline after an initial rise (peaking), there is a good chance that the optimal response to climate change will need to involve a period (of uncertain duration) during which concentrations fall. This assumes that emissions can be brought below the natural level of sequestration. Reducing emissions below this level would probably require the development and deployment of technologies for carbon capture, such as new approaches to biosequestration….The 550 scenario is a stabilisation scenario at which the concentration of greenhouse gases in the atmosphere approaches 550 ppm carbon dioxide equivalent (CO2-e) and stabilises at around that level thereafter. The 450 scenario is an overshoot scenario under which concentrations peak at around 500 ppm CO2-e and then stabilise at around 450 ppm CO2-e. Any lower stabilisation objective, for example at 400 ppm CO2-e, would need to involve a longer period of overshooting. Any concentration profile has an associated emissions trajectory. (An emissions trajectory defines the flow of greenhouse gases that converts, through various physical and chemical processes, into a stock of greenhouse gases in the atmosphere. There are different ways in which goals for emissions can be expressed:

  • End-period emissionsThis is the most common way of announcing targets (for example, that emissions will be reduced by 50 per cent by 2050). The advantage of this approach is simplicity. The disadvantage is that a target at one point of time says nothing about the rate at which emissions should approach that target level, and so does not constrain cumulative emissions or the concentration profile at that point of time.
  • Annual emissionsSince a concentration profile implies annual values for emissions, annual targets for emissions can be articulated. The disadvantages of this approach are complexity and inflexibility. There may be little difference in the environmental impact of two trajectories that end with similar concentrations but that have different annual emissions levels. However, the two paths could have quite different costs.
  • Cumulative emissionsThis is the budget approach, by which the total emissions determined by a target concentration profile over a number of years are summed up into a single target budget. In this approach, year-to-year variation from the target profile is allowed; what matters is to the total emissions over a number of years. The benefit of the budget approach is its flexibility: it allows intertemporal trade-offs and smoothing. Variations in timing would have to be large to have material environmental impacts. 


There is increasing recognition in both science and policy communities that stabilising at low levels of CO2-e (around or below 450 ppm) requires ‘overshooting’ the concentration target (den Elzen et al. 2007; Meinshausen 2006; IPCC 2007a: 827). The climate change impacts of the higher levels of greenhouse gas concentrations reached in an overshoot profile are dependent on the length of time the concentrations stay above the desired target, and how far carbon dioxide overshoots…..Some scientists have also expressed the view that stabilisation at 450 ppm is too high (Hansen et al. 2008). For any such scenarios to be feasible, there would need to be a considerable period of overshooting.

Figure 2.9 shows the different temperature outcomes for a range of cases of overshooting. All three cases show stabilisation at the same level in a similar time frame, but with varying amounts of overshooting. The temperature output demonstrates that while the ‘small overshooting’ case remains under the target temperature, the other cases do not. Hence, due to inertia in the climate system, a large and lengthy overshooting will influence the transient temperature response, while a small, short one will not (den Elzen & van Vuuren 2007).

Figure 2.9 Temperature outcomes of varying levels of overshooting

Figure 2.12

Source: Concentration and temperature pathways developed using SIMCAP (Meinshausen et al. 2006).

An overshooting profile requires a period in which emissions are below the natural level of sequestration before they are stabilised. Another mitigation option is to follow a ‘peaking profile’. Under a peaking profile, the goal is to cap concentrations at a particular level (the peak) and then to start reducing them indefinitely, without aiming for any explicit stabilisation level. Stabilisation is therefore not conceived as a policy objective for the foreseeable future.

The key benefit of a peaking profile is that it allows concentrations to increase to or above the level associated with a given long-term temperature outcome, but reduces the likelihood of reaching or exceeding that temperature outcome. The higher level of peak concentrations means that current trends in emissions growth do not need to be reversed as quickly to achieve any given temperature goal. This decreases the costs of meeting a given temperature target (den Elzen & van Vuuren 2007).

Following a peaking profile could be a disadvantage if the climate is found to be more sensitive to increases in greenhouse gases than anticipated. Due to the higher concentrations reached under a peaking profile, there is less flexibility to adjust to a lower concentration target at a later point in time, so there is greater risk that a threshold may be crossed.

Designing a mitigation pathway—whether an overshooting or a peaking profile—that requires a decrease in the concentration of greenhouse gases assumes that emissions can be brought below the natural level of sequestration. Figure 2.10 shows the emissions pathways required to achieve a low concentration target following an overshoot. A lower concentration target following an initial overshoot will require negative emissions net of natural sequestration for a longer period.

Figure 2.10 Emissions pathways required to achieve a low concentration target following an overshoot

Figure 2.13

Source: Based on CASPI (2008).

The costs of reducing emissions below natural sequestration levels would be lower if controls on gross emissions were supported by cost-effective means of removing carbon dioxide from the atmosphere. Bringing emissions below the natural rate of sequestration would require rigorous reduction of emissions from all sources, but might also require extraction of carbon dioxide from the air. Possible methods include:

  • increasing absorption and storage in terrestrial ecosystems by reforestation and conservation and carbon-sensitive soil management
  • the harvest and burial of terrestrial biomass in locations such as deep ocean sediments where carbon cycling is slow (Metzger et al. 2002)
  • capture and storage of carbon dioxide from the air or from biomass used for fuel
  • the production of biochar from agricultural and forestry residues and waste (Hansen et al. 2008).


The simplest way to remove carbon dioxide from the air is to use the natural process of photosynthesis in plants and algae. Over the last few centuries, clearing of vegetation by humans is estimated to have led to an increase in carbon dioxide concentration in the atmosphere of 60 ± 30 ppm, with around 20 ppm still remaining in the atmosphere (Hansen et al. 2008). This suggests that there is considerable capacity to increase the level of absorption of carbon dioxide through afforestation activities. The natural sequestration capacities of algae were crucial to the decarbonisation of the atmosphere that created the conditions for human life on earth, and offer promising avenues for research and development. Technologies for capture and storage of carbon from the combustion of fossils fuels currently exist, and the same process could be applied to the burning of biomass.

As yet, there are no large-scale commercial technologies that capture carbon from the air. Some argue, however, that it will be possible to develop air capture technologies at costs and on timescales relevant to climate policy (Keith et al. 2006). Research and development in Australia on the use of algae is of global importance. Captured carbon dioxide could be stored underground or used as an input in biofuel production.