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

A new evidence-based study of past warm periods suggests that global warming could be double what is expected.

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 target, according to an international team of 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 ° warmer C at 2 ° C as the pre-industrial temperatures of the research also revealed how large areas of ice caps could collapse and significant changes in ecosystems could see the Sahara Desert become green and the edges of the rainforests become turn into savannah dominated by fire.

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, "said Professor Hubertus. Fischer, lead author. "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 achieve the Paris targets."

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 Pliocene (3.3-3 million years ago).

The warming of the first two periods was caused by predictable changes in the Earth's orbit, while the Pliocene environment was the result of atmospheric concentrations of carbon dioxide of 350 to 450 ppm, which is significantly the same as today. By combining a wide range of measurements from ice cores, sediment layers, fossils, atomic isotope dating, and a host of other established paleoclimatic methods, the researchers reconstructed the impact of these measurements. climate change

. str A proof of the appearance of a warmer Earth once the climate stabilized. By contrast, today, our planet is warming much faster than any of these times, as human-caused carbon dioxide emissions continue to grow. Even if our emissions stopped today, it would take centuries or millennia to reach equilibrium.

Changes to the Earth in these past conditions were profound – there were substantial retreats of the Antarctic and Greenland icecaps 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 declined, temperate tropical forests were reduced, and in the Mediterranean areas deciduous vegetation dominated.

"Even with only 2 ° C warming – and potentially 1.5 ° C – the impacts on the Earth's system are deep" "We can expect sea level rise to become irresistible for millennia, affecting a large part 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 polar regions

"Climate models seem reliable for small changes, as low emissions over short periods, but as the change becomes larger or more persistent, either because of higher emissions, for example a status quo scenario, or because we are interested in the long answer term of a low-emissions scenario, it seems that they underestimate climate change, "said the co-author of the Prof. Katrin Meissner, Director, Center for Climate Change Research, University of New South Wales

"This research is a powerful call to action, do not urgently tackle our emissions , global warming will bring profound changes to our planet and our way of life, not just for this century but beyond. "

Learn more:
Lessons on a warmer future world using data from the past

More information:
Hubertus Fischer et al. Paleoclimatic constraints on the impact of anthropogenic warming at 2 ° C and beyond, Nature Geoscience (2018). DOI: 10.1038 / s41561-018-0146-0