Global warming may be twice what climate models predict

Future global warming may eventually be twice as warm as projected by climate models under business-as-usual scenarios; and even if the world meets the 2°C target, sea levels may rise six metres or more, according to an international team of researchers from 17 countries.

The report by the University of New South Wales said that findings published recently in Nature Geoscience are based on observational evidence from three warm periods over the past 3.5 million years when the world was 0.5°C-2°C warmer than the pre-industrial temperatures of the 19th Century.

The research also revealed how large areas of the polar ice caps could collapse and significant changes to ecosystems could see the Sahara Desert become green and the edges of tropical forests turn into fire dominated savanna.

“Observations of past warming periods suggest that a number of amplifying mechanisms, which are poorly represented in climate models, increase long-term warming beyond climate model projections,” said lead author, Prof Hubertus Fischer of the University of Bern.

“This suggests the carbon budget to avoid 2°C of global warming may be far smaller than estimated, leaving very little margin for error to meet the Paris targets.”

To get their results, the researchers looked at three of the best-documented warm periods, the Holocene thermal maximum (5000-9000 years ago), the last interglacial (129,000-116,000 years ago) and the mid-Pliocene warm period (3.3-3 million years ago).