What you will find on this page: main non-CO2 gases; global anthropogenic GHG emissions: global emissions by sector; methane budget (updated Dec ’16): radiative forcing (video); curbing non CO2 gasesGlobal Warming Potential tableactions to lessen non-CO2 gases; also refer to page “the mitigation battle” as the issues are closely related 

Carbon Dioxide is not the only thing we are pumping into the atmosphere

greenhouse-effect-09-2014

Source: Center for Climate and Energy Solutions (USA) 

What are the main greenhouse gases other than carbon dioxide?

Climate Change Connection website: The three main greenhouse gases (not including water vapour) and their 100-year global warming potential (GWP) compared to carbon dioxide are:

  • carbon dioxide (CO2) – 1 x
  • methane (CH4) – 25 x more powerful
  • nitrous oxide (N2O) – 298 x more powerful

Water vapour is not considered to be a cause of man-made global warming because it does not persist in the atmosphere for more than a few days.

There are other greenhouse gases which have far greater global warming potential (GWP)but are much less prevalent. These are sulphur hexafluoride (SF6), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs).

There are a wide variety of uses for SF6, HFCs, and PFCs but they have been most commonly used as refrigerants and for fire suppression. Many of these compounds also have a depleting effect on ozone in the upper atmosphere.

Global Anthropogenic GHG Emissions 

emissions by gas international-gas

Global anthropogenic GHG emissions by sector

Emissions by international-sector

Source of charts: C2ES

Methane Budget


12 December 2016, Climate News Network, Methane’s rapid spurt risks climate curbs plan. A recent rapid rise in methane could damage global attempts to slow climate change through cuts in carbon dioxide emissions.
 One year ago today, with huge relief, scarcely able to believe their achievement, world leaders finally agreed to reduce emissions of carbon dioxide. But a bare 12 months later comes sobering news: atmospheric concentrations of another gas, methane, are growing faster than at any time in the last 20 years, putting further pressure on the historic Paris Agreement to deliver substantial cuts in emissions very soon. Some scientists say the world now needs to change course and do more about methane to have a chance of keeping average global temperatures from rising by more than 2°C. And one seasoned Arctic watcher says the changes there in the last decade are altering a system which has remained intact since the Ice Age. Methane is the second major greenhouse gas, with agriculture accounting for 40% of emissions. Over a century it is 34 times more powerful as a greenhouse gas than carbon dioxide (though far less abundant), but over 20 years methane is 84 times more potent than CO2. In an editorial in the journal Environmental Research Letters, an international team of scientists reports that methane concentrations in the air began to surge around 2007 and grew steeply in 2014 and 2015. In those two years concentrations rose by 10 or more parts per billion annually. In the early 2000s they had been rising by an annual average of 0.5 ppb. Read More here

Also refer to:

 

23 September 2013, Global Carbon Project, excerpt highlights:  After carbon dioxide (CO2), methane (CH4) is the second most important well-mixed greenhouse gas contributing to human-induced climate change. In a time horizon of 100 years, CH4 has a Global Warming Potential (GWP-100) 28 times larger than CO2. The level of CH4 in the atmosphere is above 150% from pre-industrial times (cf. 1750), and it is responsible for 20% of the global warming produced by all well-mixed greenhouse gases. Methane is transformed into water vapour in the stratosphere. Methane also produces ozone in the troposphere, which is a pollutant with negative impacts on human health and ecosystems. The atmospheric life time of methane is 10 ± 2 years.

For the decade of 2000-2009, global emissions of methane are 548 (526-569) Tg CH4 per year as estimated from atmospheric inversions (top-down approach). The global CH4 sink is 540 (514–560) Tg CH4 per year. The source–sink mismatch reflects, and is consistent with, the observed average imbalance in the atmosphere of 6 Tg CH4 per year (the CH4 growth rate). The sum of all sources as estimated from inventories and modeling (bottom-up approaches) is 678 (542-852) Tg CH4, 20% higher than estimated from the top-down approach and reflecting the compounded uncertainties of the multiple CH4 sources.

There are opportunities and challenges ahead. The opportunity lies in the possibility of developing short-term climate change mitigation policies that take advantage of the relatively short atmospheric lifetime of CH4 of about 10 years, and the known technological and agronomical options available for reducing emissions. The challenges include the potential intensive exploitation of natural gas from shale formations around the world that could lead to significant additional CH4 release if leakage rates are left uncapped. In the longer term, the thawing of permafrost and methane hydrates could increase CH4 emissions, and introduce large positive feedbacks to long-term climate change. A better and regular quantification of the global CH4 budget and its attribution to sources and sinks is key to embracing the opportunities and meeting the challenges. Read More here

What is radiative forcing?

This indicator measures the “radiative forcing” or heating effect caused by greenhouse gases in the atmosphere.

Stacked area graph showing the amount of radiative forcing caused by various greenhouse gases for each year from 1979 to 2015.This figure shows the amount of radiative forcing caused by various greenhouse gases, based on the change in concentration of these gases in the Earth’s atmosphere since 1750. Radiative forcing is calculated in watts per square meter, which represents the size of the energy imbalance in the atmosphere. On the right side of the graph, radiative forcing has been converted to the Annual Greenhouse Gas Index, which is set to a value of 1.0 for 1990. Data source: NOAA, 20161 Web update: August 2016

 

Focus needed on other greenhouse gases as well as carbon dioxide

2015, Center for Climate and Energy Solutions (C2ES): There is growing recognition within the scientific and policy communities that efforts to address climate change should focus not only on substantially reducing carbon dioxide (CO2) emissions, but also on near-term actions to reduce those climate pollutants that remain in the atmosphere for much shorter periods of time.

With atmospheric lifetimes on the order of a few days to a few decades, the primary short-lived climate pollutants (SLCPs) are methane, black carbon and certain hydrofluorocarbons. SCLPs are responsible for 30-40 percent of global warming to date. Actions to reduce their emissions could reduce by half the amount of warming that would occur over the next few decades. In the past few years, considerable attention has shifted to these compounds. New policies have advanced both within the United States and by the international community aimed at reducing emissions of these pollutants.

Reductions Required in both CO2 and SLCPs

To effectively slow the rate and magnitude of climate change, a strategy that significantly reduces both carbon dioxide and SLCPs is critical:

  1. Reducing CO2 emissions limits the ultimate amount of warming. Because CO2 represents by far the largest source of climate-warming emissions, and because it stays in the atmosphere for hundreds of years, large reductions in CO2 emissions are required to meet any long-term climate stabilization goal, such as the 2°C goal set by the international community.
  2. Reducing emissions of short-lived climate pollutants would, on the other hand, effectively slow the near-term rate of climate change. Because SLCPs remain in the atmosphere for a relatively short period of time (compared to CO2) reducing their emissions would result in more immediate benefits. In addition to limiting climate change impacts already underway, including important regional impacts such as glacial melting, SLCP reductions would reduce local air pollution and produce other co-benefits. The U.N. Environment Programme recently estimated that aggressive efforts to reduce SLCPs would avoid 2.4 million premature deaths by 2030 and reduce warming between now and 2040 by a half a degree.

 

Key Short-Lived Climate Pollutants (SLCPs)

Methane has an atmospheric lifetime of about 12 years and a global warming potential of 25 times that of carbon dioxide. It makes up approximately 9 percent of GHG emissions in the United States and roughly 14 percent worldwide. Methane emissions result primarily from oil and gas production and distribution, coal mining, solid waste landfills, cultivation of rice and ruminant livestock, and biomass burning. Reductions in methane emissions also improve local air quality by reducing ground-level ozone, which harms agriculture and human health, and is itself a SLCP.

Black carbon (BC) results from incomplete combustion of biomass and fossil fuels. Its major sources are diesel cars and trucks, cook stoves, forest fires, and agricultural open burning. Black carbon has a short atmospheric lifetime, on the order of a few days to weeks. Because of a very brief atmospheric lifetime measured in weeks, black carbon’s climate effects are strongly regional. BC particles give soot its black color and, like any black surface, strongly absorb sunlight. In snow-covered areas, the deposition of black carbon darkens snow and ice, increasing their absorption of sunlight and making them melt more rapidly. BC may be responsible for a significant fraction of recent warming in the rapidly changing Arctic, contributing to the acceleration of sea ice loss. BC also is contributing to the melting of Himalayan glaciers, a major source of fresh water for millions of people in Asia, and may be driving some of the recent reduction in snowpack in the U.S. Pacific Northwest. Black carbon’s short lifetime also means that its contribution to climate warming would dissipate quickly if emissions were reduced. Additionally, since BC contributes to respiratory and cardiovascular illnesses, reductions in BC emissions would have significant co-benefits for human health, particularly in developing countries.

Hydrofluorocarbons (HFCs) are a family of industrially produced chemicals widely used in refrigeration and air conditioning, foam blowing, and other applications. They were developed to replace ozone-depleting substances (primarily chlorofluorcarbons and hydrochlorofluorocarbons – CFCs and HCFCs) a few decades ago. While HFCs now contribute around 1 percent of total global warming emissions, their use is expected to grow dramatically over time. HFC-134a, the most widely used of these compounds, has an atmospheric lifetime of 13 years and a global warming potential of 1300.

Because ozone-depleting substances (CFCs and HCFCs) are also potent greenhouse gases, their phase-out under the Montreal Protocol has contributed significantly to climate mitigation efforts to date. The treaty’s net contribution to climate mitigation (taking into account the growth of HFCs as replacements) is estimated to be five to six times larger than the Kyoto Protocol’s first commitment period targets. Read More here

Nitrous Oxide makes up an extremely small amount of the atmosphere – it is less than one-thousandth as abundant as carbon dioxide. However, it is 200 to 300 times more effective in trapping heat than carbon dioxide. Nitrogen is removed from the atmosphere by plants and converted into forms such as ammonia, which can then be used by the plants. This is called nitrogen fixation. At the same time, micro-organisms remove nitrogen from the soil and put it back into the atmosphere – denitrification – and this process produces nitrous oxide. Nitrous oxide also enters the atmosphere from the ocean. Nitrous oxide has one of the longest atmosphere lifetimes of the greenhouse gases, lasting for up to 150 years. Burning fossil fuels and wood is one source of the increase in atmospheric nitrous oxide, however the main contributor is believed to be the widespread use of nitrogen-base fertilisers. Sewage treatment plants may also be a major source of this gas. Since the Industrial Revolution, the level of nitrous oxide in the atmosphere has increased by 16%. Due to the long time it spends in the atmosphere, the nitrous oxide that we release today will still be trapping heat well into the next century. Source: BBC Weather Centre

Global Warming Potential (GWP) Table

The following table (from Climate Change Connections) shows the 100-year global warming potential for greenhouse gases reported by the United Nations Framework Convention on Climate Change (UNFCCC). Click here to download an expanded PDF table: GHG Lifetimes and GWPs (144 kB)

How to read this table: The column on the right shows how much that chemical would warm the earth over a 100 year period as compared to carbon dioxide. For example, sulphur hexafluoride is used to fill tennis balls. The table shows that a release on1 kg of this gas is equivalent to 22,800 kg or 22.8 tonnes of CO2. Therefore, releasing ONE KILOGRAM of sulphur hexafluoride is about equivalent to driving 5 cars for a year! (2)

Greenhouse Gas Formula 100-year GWP (AR4)
Carbon dioxide CO2 1
Methane CH4 25
Nitrous oxide N2O 298
Sulphur hexafluoride SF6 22,800
Hydrofluorocarbon-23 CHF3 14,800
Hydrofluorocarbon-32 CH2F2 675
Perfluoromethane CF4 7,390
Perfluoroethane C2F6 12,200
Perfluoropropane C3F8 8,830
Perfluorobutane C4F10 8,860
Perfluorocyclobutane c-C4F8 10,300
Perfluoropentane C5F12 13,300
Perfluorohexane C6F14 9,300

The table above show the lifetimes and direct (except for CH4) 100-year global warming potentials (GWP) relative to CO2 for ozone-depleting substances and their replacements. This table is from the Intergovernmental Panel on Climate Change (IPCC), Fourth Assessment Report (AR4), Working Group 1, Chapter 2, Changes in Atmospheric Constituents and in Radiative Forcing, Table 2.14, page 212. 

A complete summary is available from Climate Change Connections which provides details of GHG Lifetimes and GWPs for ozone-depleting substances and their replacements.

Actions to lessen non-CO2 gases

At a “Technical Expert Meeting” during the October UN Climate Change Conference in Bonn (20 – 25 October 2014) governments, international agencies and companies agreed that there are many ways to effectively curb so-called “non-C02 gases”, even if overall emissions from these gases are expected to grow in the near future.

These are the gases methane, nitrous oxide and hydrofluorocarbons (HFCs), which have a higher global warming potential than carbon dioxide, and result from activities such as agriculture, industry, waste and household appliances.

Essential to Reduce Harmful Industrial Gases

Curbing the impact of these gases is one of the key areas with high potential to enable the international community to reach its goal of staying below a maximum global average two degrees Celsius temperature rise.

The experts agreed that reducing harmful non-CO2 gases has many benefits going beyond greenhouse gas reductions, above all for human health. They also agreed that whilst carbon pricing can play a role in reducing such gases, a priority should be put on reducing particularly harmful industrial gases with the help of the Paris 2015 global climate agreement. Governments are currently looking at how to raise ambition to tackle climate change before 2020, when this new universal climate change agreement is to take effect. To access the potential actions and highlights of the meeting go here