Global warming may be twice what climate models predict

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

The findings published last week 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).

The warming of the first two periods was caused by predictable changes in the Earth’s orbit, while the mid-Pliocene event was the result of atmospheric carbon dioxide concentrations that were 350-450ppm – much the same as today.

Combining a wide range of measurements from ice cores, sediment layers, fossil records, dating using atomic isotopes and a host of other established paleoclimate methods, the researchers pieced together the impact of these climatic changes.

In combination, these periods give strong evidence of how a warmer Earth would appear once the climate had stabilized. By contrast, today our planet is warming much faster than any of these periods as human caused carbon dioxide emissions continue to grow. Even if our emissions stopped today, it would take centuries to millennia to reach equilibrium.

The changes to the Earth under these past conditions were profound – there were substantial retreats of the Antarctic and Greenland ice sheets and as a consequence sea-levels rose by at least six metres; marine plankton ranges shifted reorganising entire marine ecosystems; the Sahara became greener and forest species shifted 200 km towards the poles, as did tundra; high altitude species declined, temperate tropical forests were reduced and in Mediterranean areas fire-maintained vegetation dominated.

“Even with just 2°C of warming – and potentially just 1.5°C – significant impacts on the Earth system are profound,” said co-author Prof Alan Mix of Oregon State University.

“We can expect that sea-level rise could become unstoppable for millennia, impacting much of the world’s population, infrastructure and economic activity.”

Yet these significant observed changes are generally underestimated in climate model projections that focus on the near term. Compared to these past observations, climate models appear to underestimate long term warming and the amplification of warmth in Polar Regions.

“Climate models appear to be trustworthy for small changes, such as for low emission scenarios over short periods, say over the next few decades out to 2100. But as the change gets larger or more persistent, either because of higher emissions, for example a business-as-usual-scenario, or because we are interested in the long term response of a low emission scenario, it appears they underestimate climate change,” said co-author Prof Katrin Meissner, Director of the University of New South Wales Climate Change Research Centre.

“This research is a powerful call to act. It tells us that if today’s leaders don’t urgently address our emissions, global warming will bring profound changes to our planet and way of life – not just for this century but well beyond.”

Paper: Fischer, H., Meissner, K.J., Mix, A.C., et al.: Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond. Nature Geoscience, 25 June 2018 (in press).

2 COMMENTS

  1. Pure bunk………propaganda and scare tactics at it’s finest. All of the global warming projections as to horrible outcomes 20 years ago never came to pass (no snow, the Arctic and Antarctic will melt away, the seas will rise many feet, etc etc.). CO2 has no effect on the ambient temperature and the average temperature around the world has not significantly changed in 18+ years despite a miniscule increase in atmospheric CO2 levels from 0.03 to 0.044%. If anything, the earth is entering a cooling period as was suggested by “climate scientists” in the 1970s. The hottest decade in the last 100+ years was the 1930’s in the USA……..long before CO2 levels changed. As long as people keep writing nonsensical junk science articles like this one, the “global warming aka climate change” movement will never be believed. Take away government funding and make it independent of political agenda’s and we might see the truth come out….namely that man’s activities have little to do with the earth’s climate and weather patterns.

  2. I am wondering if what was behind the rise to carbon dioxide emissions of the mid-Pliocene warm period from 3.3 to 3 million years ago from 350-450 parts per million, was volcanic activity.

LEAVE A REPLY

Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.