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| The Mediterranean, central Brazil and the lower 48 states of the US are among the areas likely to warm by 2 degrees by about 2030. Photo: Leigh Henningham |
The Paris pact to limit global temperature increases to less than 2 degrees will still result in some parts of the planet warming by as much as 6 degrees due to regional variations, researchers in Switzerland and Australia said.
While the world will likely pass two degrees of warming by the 2040s on the current trajectory of greenhouse gas emissions, some parts of the Arctic had already passed the 2-degree mark by 2000 compared with pre-industrial times, the scientists at ETH Zurich and the University of New South Wales found.
The Mediterranean, central Brazil and the lower 48 states of the US are among the areas likely to warm by 2 degrees by about 2030, according to the research published on Thursday in Nature journal.
The paper noted that purported impacts of drought in Syria and the regional unrest may be an indication of what is to come if worsening regional extreme undermine fragile socieities.
"Given current political tensions around the Mediterranean basin, implications of locally more rapid climate change could extend to regional impacts, adding to wider political instability," the paper said.
Globally, most land regions will warm faster than oceans in part because the loss of soil moisture and ice or snow amplifies the heating trend.
Sea circulation can also transport additional heat to ocean depths in a manner not possible on land, said Markus Donat, a research fellow at UNSW's ARC Centre for Excellence for Climate System Science and one of the paper's authors.
Interestingly, Australia generally avoids the biggest changes in land temperatures, roughly rising at the same pace as the global average, according to the modelling based on work done for the Intergovernmental Panel on Climate Change.
"There are two possible reasons [for the Australian result]," Andy Pitman, a co-author and director of the ARC Centre, said. "There is something peculiar about the nature of the feedbacks that link average and extreme warming," which leads to land areas in the southern hemisphere warming at a slower pace than in the north.
"Or, it could be that the models are biased to the areas where the modellers are based" in the northern Hemisphere, he said. "Perhaps there are systematic errors so we don't see the amplification."
At the Paris climate summit late last year, almost 200 nations agreed to keep average global warming to less than 2 degrees. On the pledges made so far, temperatures are on track to rise at least 2.7 degrees from pre-industrial times - assuming countries keep their promises to cut back greenhouse gas emissions towards zero net pollution by the second half of the century.
The global budget to keep within 2 degrees mean warming level is cumulative emissions of about 850 gigatonnes (GT) of carbon, the paper said.
To prevent the Mediterranean region warming by that amount, however, the budget is about 600 GT. Since emissions have totalled about 500 GT, rising at about 10 GT, the world has 10 years or less on current trends to avoid that mark, Professor Pitman said.
"It was an urgent problem 25 years ago," he said. "Now it's way past urgent to look at deep and meaningful emission reductions."
One reason for the urgency is that the pattern of warming is unlikely to be a smooth one, with unexpected "tipping points" accelerating the process.
"We have no way of knowing when our climate may change abruptly from one state to another, meaning we could potentially see even greater regional variation than these findings show," Dr Donat said.
The Arctic, as it warms, will likely see more melting of the permafrost, which will release more methane. Methane is about 25 times more potent in trapping heat than C02 over a century.
"Whilst Paris did put us on a better path, it's not a path that is consistent with the science," Professor Pitman said.
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