Global warming 'set to speed up to rates not seen for 1,000 years'

 Extract from The Guardian

By 2020 the average temperature rise per decade will be 0.25C in the northern hemisphere, more than double the 900 years preceding the 20th century

A coal mine in Wyoming in the US. Global warming caused by burning fossil fuel burning is due to speed up, according to a new study published in Nature Climate Change. Photograph: Mae Ryan for the Guardian

Press Association

Tuesday 10 March 2015 04.08 AEDT

People need to brace themselves for accelerating climate change that could alter the way we live even over short time scales, scientists have warned.
New evidence suggests the rate at which temperatures are rising in the northern hemisphere could be 0.25C per decade by 2020 - a level not seen for at least 1,000 years.
The analysis, based on a combination of data from more than two dozen climate simulation models from around the world, looked at the rate of change in 40-year long time spans.
Lead scientist Dr Steve Smith, from the US Department of Energy’s Pacific Northwest National Laboratory, said: “We focused on changes over 40-year periods, which is similar to the lifetime of houses and human-built infrastructure such as buildings and roads.
“In the near term, we’re going to have to adapt to these changes.”
Overall, the world is getting warmer due to increasing greenhouse gas emissions that trap the Sun’s heat.
But, given natural climate variability over short times scales, the likely effect of global warming over humanly relevant periods such as the length of a person’s life is not so well understood.
The new study started off by calculating how fast temperatures changed between 1850 and 1930, a period when the amount of fossil fuel gases collecting in the atmosphere was low.
This was compared with temperature data for the past 2,000 years obtained by studying tree rings, corals and ice cores and predicted 40-year rates of change between 1971 and 2020.
Over the 900 years preceding the 20th century, 40-year warming trends rarely showed an average rate much higher than 0.1C per decade, the study found.
But by 2020 the rate was expected to have risen to an average of 0.25C per decade, give or take 0.05C.

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Average C temperature rise per decade, assuming carbon emissions peak in 2040 and decline afterwards. Photograph: Smith et al/Nature Climate Change

Different scenarios of future emissions showed that even at the lower end of greenhouse gas generation, climate change picked up speed in the next 40 years.
The findings are published in the journal Nature Climate Change.
Dr Smith added: “In these climate model simulations, the world is just now starting to enter into a new place, where rates of temperature change are consistently larger than historical values over 40-year time spans. We need to better understand what the effects of this will be and how to prepare for them.”