Heat Waves To Quadruple By 2040, Regardless Of Emissions Cuts
16 August, 2013
By 2040, 3% of land will have heat waves of a strength rarely seen today (pic: flickr / Licancabur)
Extreme heat waves will increase over the next 30 years, regardless of the amount of carbon emitted between now and then. The second half of 21st Century is likely to be seriously affected by rising levels of greenhouse gases.
Citing a study Sophie Yeo reported  in Responding to Climate Change:
Even if there is no increase in the amount of CO2, existing levels of climate change means that the planet is already locked into a future where extreme heat waves, such as those experienced by the US in 2012, will cover double the amount of global land by 2020. By 2040, they will double.
The study was carried out by researchers from the Potsdam Institute for Climate Impact Research and the Universidad Complutense de Madrid (UCM). The study report has been published on August 15, 2013 in Environmental Research Letters.
“There're already so much greenhouse gases in the atmosphere today that the near term increase of heat extremes seems to be almost inevitable,” said Dim Coumou, the lead author on the study.
The scientists focused on heat waves that exceed the natural variability of summer month temperatures by a large margin in a given region – so called “3-sigma events”. These periods, lasting several weeks, often result in harvest losses, forest fires and additional deaths in heat-struck cities.
Today, this kind of extreme is witnessed on 5% of land area. By 2040, this will increase to 40%.
The heat waves classed as “more severe”, or “5-sigma events” – today virtually absent – will cover around 3% of the global land surface by 2040.
2040 and beyond
It is in the second half of the century that heat waves will start to be affected by today's rising emissions.
Models show that under a low carbon scenario, the number of extremes will stabilize by 2040, whereas under a high emissions scenario, the land area affected by extremes will increase by 1% a year after 2040.
This means that by 2100, under a high emissions scenario, 3-sigma heat waves will cover 85% of the global land area, and 5-sigma heat waves will cover about 60% of global land.
“In general, society and ecosystems have adapted to extremes experienced in the past and much less so to extremes outside the historic range,” said Alexander Robinson of UCM, co-author of the study. “So in the tropics, even relatively small changes can yield a big impact – and our data indicates that these changes, predicted by earlier research, in fact are already happening.”
The inevitability of extreme heat waves means that it becomes important for regions to focus on adaptation as well as mitigation.
Coumou said: “An increase in frequency is likely to pose serious challenges to society.
“Some regions will have to adapt to more frequent and more severe heat waves already in the near-term.”
Citing the study another report  quoted Coumou:
"We find that up until 2040, the frequency of monthly heat extremes will increase several fold, independent of the emission scenario we choose to take. Mitigation can, however, strongly reduce the number of extremes in the second half of the 21st century."
"A good example of a recent three-sigma event is the 2010 heat wave in Russia , which expanded over a large area stretching from the Baltic to the Caspian Sea . In the Moscow region the average temperature for the whole of July was around 7°C warmer than normal -- it was around 25°C. In some parts, temperatures above 40°C were measured," continued Coumou.
In their study, Dim Coumou, from the Potsdam Institute for Climate Impact Research, and Alexander Robinson, from Universidad Complutense de Madrid, used state-of-the-art climate models to project changes in the trend of heat extremes under two future warming scenarios -- RCP2.6 and RCP8.5 -- throughout the 21st century. The historic period was also analyzed, and the results showed that the models can accurately reproduce the observed rise in monthly heat extremes over the past 50 years.
The report also quoted Alexander Robinson:
"Our three- and five-sigma thresholds are defined by the variability a region has experienced in the past, so the absolute temperatures associated with these types of event will differ in different parts of the world. Nonetheless these events represent a significant departure from the normal range of temperatures experienced in a given region."
The study found:
Tropical regions will see the strongest increase in heat extremes, exceeding the threshold that is defined by the historic variability in the specific region. The results show that these changes can already be seen when analyzing observations between 2000 and 2012.
 Story Source:
The story is based on materials provided by Institute of Physics .
Dim Coumou, Alexander Robinson. Historic and future increase in the global land area affected by monthly heat extremes. Environmental Research Letters, 2013; 8 (3): 034018 DOI: 10.1088/1748-9326/8/3/034018
Institute of Physics (2013, August 15). Heat waves to become much more frequent and severe. ScienceDaily. Retrieved August 16, 2013 , from http://www.sciencedaily.com /releases/2013/08/130815084845.htm
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