Global warming could be twice as large as predicted by climate models

Future global warming could be twice as warm as predicted by climate models and sea level could reach six meters or more even if the world reaches the 2 ° C goal, according to an international team researchers from 17 countries. ] The results published last week in Nature Geoscience are based on observational evidence of three warm periods over the past 3.5 million years when the world was 0.5 ° C to 2 ° C warmer than pre-industrial temperatures of 19 century

Research also revealed how large areas of polar ice caps could collapse and significant changes in ecosystems could see the Sahara Desert become Green and tropical forest edges turn into savannah dominated by fire.

"Observations of past warm-up periods suggest that a number of amplifying mechanisms, which are poorly represented in climate models, increase long-term warming beyond the projections of the climate model," he said. the main author. , Professor Hubertus Fischer of the University of Bern

"This suggests that the carbon budget to avoid 2 ° C of global warming could be much smaller than expected, leaving very little room for error to reach the Paris objectives. "

To obtain their results, the researchers examined three of the best-documented warm periods, the Holocene thermal maximum (5000-9000 years), the last interglacial (129,000-116,000 years) and the warm period of the middle of the Pliocene (3.3-

The warming of the first two periods was caused by predictable changes in the Earth's orbit, while the Pliocene mid-air event was the result of atmospheric concentrations of 350 to 450 ppm, roughly equivalent to

Combining a wide range of measurements of ice cores, sediment layers, fossils, atomic isotope dating and a host of others established methods of paleoclimate, researchers have reconstructed the impact of these climate changes.These periods clearly indicate how a warmer Earth would appear once the climate stabilized. On the other hand, today, our planet is heating up much faster than any of these times, as human-caused carbon dioxide emissions continue to grow. Even if our emissions ceased today, it would take centuries or millennia to reach equilibrium.

The changes of the Earth in these conditions were profound – the ice sheets of Antarctica and Greenland were substantially receding and consequently increased by at least six meters; marine plankton ranges have been reorganized to reorganize entire marine ecosystems; the Sahara became greener and forest species moved 200 km to the poles, as did the tundra; High altitude species have declined, temperate tropical forests have been reduced and in Mediterranean areas the vegetation maintained by fire has dominated.

"Even with only 2 ° C warming – and potentially 1.5 ° C – the impacts on the Earth's system are profound. "We can expect sea level rise to become irresistible for millennia, affecting much of the world's population, infrastructure and economic activity."

changes are generally underestimated in climate model projections that focus on the short term. Compared with these past observations, climate models seem to underestimate long-term warming and heat amplification in the polar regions. "Climate models seem reliable for small changes, such as for low-emission scenarios over short periods of time, but as change becomes more important or more persistent, either because of higher emissions, such as status quo scenario, either because we are interested in the long-term response of a low-emissions scenario, it seems that they underestimate climate change, "said the co-author of the Prof . Katrin Meissner, Director of the Center for Climate Change Research at the University of New South Wales.

"This research is a powerful call to action and it tells us that if today's leaders do not urgently address our emissions, global warming will bring profound changes. to our planet and our way of life – not just for this century but beyond. "

Paper: Fischer, H., Meissner, KJ, Mix, AC, et al .: Paleoclimatic constraints on the impact of anthropogenic warming at 2 ° C and beyond. Geosciences of Nature June 25, 2018 (in press).