29 October 2015, Yale Connections, Long-Term Drought Impacts on Trees. Scientists find that droughts harm trees for longer than previously understood. ANDEREGG: “We’ve known for decades that drought has harmful effects on trees. That during drought they grow slower and they have a higher chance of death.” That’s William Anderegg, a biologist at the University of Utah. He says until recently, researchers were not clear about what happened to the trees after a drought ended. So his team looked at the growth of trees after severe drought in more than a thousand forests across North America, Europe, and Asia. They found that even four years after a drought, trees continued to grow more slowly than normal. ANDEREGG: “Trees take up about a quarter of human emissions of CO2 each year, and that’s a very big slowing effect on climate change. So if droughts cause forests to take up less carbon, that could very much speed up the pace and the severity of climate change.” Anderegg says it is too early to know what the long-term implications will be. ANDEREGG: “Some of our best models suggest that forests could be relatively resilient and others suggest they could really die off en masse and lose a lot of their carbon to the atmosphere. And we don’t know which of those is more likely.” But Anderegg says that the future of the world’s forests is still in our hands. ANDEREGG: “I always like to emphasize that a lot of that future does depend on human decisions and what we do about climate change.” Read More here
Category Archives: Impacts Observed & Projected
28 October 2015, Climate News Network, Rise in wildfires depletes forests’ carbon store. As the world warms, the increasing hazard of forest fires is dangerously tilting trees’ carbon storage balance from positive to negative in some regions of Alaska. In a warming world, forest fires could be about to put more carbon dioxide into the atmosphere than the trees absorb. New research by US scientists looked at decades of wildfire incidence in Alaska, and they have found that at least one region is now a net exporter of carbon. This is a reversal of the normal arrangements, whereby trees photosynthesise tissue from the carbon dioxide in the atmosphere. As they absorb carbon, they sequester it in roots, timber and leaves, and then in leaf litter in the forest soils. Fire is a natural hazard, and some geographical zones –the Mediterranean, the US southwest, and Australia – are adapted to periodic fire. But as the planet warms, there have been increasing levels of fire even in therainforests of the Amazon and in the boreal forests of the near-Arctic. Read More here
26 October 2015, Washington Post, Scientists confirm that East Antarctica’s biggest glacier is melting from below. Earlier this year, we learned some worrisome climate news. Although Antarctic scientists have been most concerned about loss of ice in the western part of Antarctica, a study in Nature Geoscience suggested a vulnerability in the much larger ice sheet of East Antarctica, as well. East Antarctica’s enormous Totten Glacier, you see, has a key similarity with the glaciers of West Antarctica — namely, it is rooted deep below sea level. This means that it is potentially exposed to warm ocean waters, and the study in March uncovered a deep and 5-kilometer wide subsea valley beneath the glacier’s oceanfront ice shelf that, the authors said, could be a route for warm offshore water to reach its base. This might explain why the glacier has been observed to be thinning and lowering, or losing elevation, over time, they noted. Located along East Antarctica’s Sabrina Coast, Totten glacier is the ice sheet’s largest. It holds back 3.9 meters of potential sea level rise, or over 12 feet, and connects with the very deep and vast Aurora Subglacial Basin, which is also rooted well below sea level. So the results were treated as being of enormous consequence. But they’re not the end of the story, as there is vastly more to learn about Totten glacier. A new study out in Geophysical Research Letters reaffirms some of these core concerns about Totten’s melt — while also appearing to partly alleviate others. Read More here
22 October 2015, Carbon Brief, Five charts that show how Arctic and Antarctic sea ice is faring in 2015. At this time of year, there are big differences in what’s going on with sea ice at either end of the world. September saw the Arctic hit its fourth lowest summer minimum on record, while over in Antarctica, the winter maximum finished just above average, ending a streak of record highs in the last three years. Carbon Brief takes a look at what’s happened this year and how it fits in with long term trends. Summer minimum Scientists have been using satellites to measure sea ice extent at the north and south poles since the late 1970s. They take measurements daily, and record the annual minimum and maximum as an indicator of how the poles are changing. In the Arctic, the end of the summer marks the point when sea ice is at its smallest extent, before it freezes up again as temperatures fall. Scientists keep a close eye around the time the low is normally reached – usually mid september – then look for signs of ice accumulating again in order to pinpoint exactly when the summer minimum is reached. According to the National Snow and Ice Data Center (NSIDC) in the US, the summer low occurred this year on 11 September. But because sea ice can throw in a late dip or surge, the NSIDC waited until 6 October before finally confirming this summer’s minimum of 4.41m square kilometers (sq km) – the fourth lowest on record. So how did the rest of the season shape up before this point? Read More here