Earth’s Past is Telling Us that Global Warming Might Be Much Worse than We Thought

A new study has found that the temperature increases from global warming may be twice as bad over what previous climate studies have forecast. This study made use of historical data from previous geological periods when Earth’s climate was 0.5°C-2°C warmer than the 19th Century’s pre-industrial average, illustrating that the consequences of runaway global warming could spell the collapse of many ecosystems, ranging from the Sahara Desert becoming green, to tropical regions converting to a fire-prone 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," explains the study’s lead author, Professor Hubertus Fischer, with the University of Bern. The findings Fischer and his international team of colleagues made suggest that previous climate models may be underestimating many of the more profound changes a warming Earth might produce, as they tend to focus on near-term effects, while missing the more drastic effects that long-term changes such as Arctic Amplification might bring about.

The study, published in the journal Nature Geoscience, employed data from three of the best-documented warm periods, including the Holocene thermal maximum that occurred between 5,000 and 9,000 years ago; the last interglacial period, 129,000 to 116,000 years ago; and the mid-Pliocene warm period, from 3.3 million to 3 million years ago. While warming from the Holocene thermal maximum and last interglacial were caused by predictable cycles in Earth’s orbit, the mid-Pliocene warm period was caused by an increase in global carbon dioxide levels, when levels rose to between 350 and 450 parts per million, much like the 410 ppm we’re experiencing now.

However, the onset of global warming is occurring much faster today than it was in Earth’s past, with human-generated CO2 concentrations shooting up by nearly fifty percent over the past century-and-a-half, meaning that the shifts being experienced by regional climates will be that much more abrupt than what Earth has gone through in the past. And the previous shifts were not subtle: the Antarctic and Greenland ice sheets retreated considerably, raising ocean levels by a minimum of 6 meters (20 feet); marine plankton fields shifted, affecting entire marine ecosystems; and as polar regions warmed, permafrost melted and forests advanced poleward into previously-frozen regions, bringing their local fauna with them.

The long-term problem with short-term global warming is that while it may take mere decades to get underway, it may take millennia for individual ecosystems to settle into a new state of equilibrium. For instance, polar ice melt begets more melting ice, as the Earth’s surface shifts from a solar radiation-reflecting layer of ice to darker, sunlight-absorbing open water. "Even with just 2°C of warming — and potentially just 1.5°C — significant impacts on the Earth system are profound," warns Oregon State University’s Prof Alan Mix. "We can expect that sea-level rise could become unstoppable for millennia, impacting much of the world’s population, infrastructure and economic activity."

"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," said co-author Professor Katrin Meissner, Director of the University of New South Wales Climate Change Research Centre. "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.

"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."