The research, led by Xu Zhang from the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research in Germany, sought to explain why temperatures in the high latitudes of the Northern Hemisphere fluctuated by up to 15 °C over just a few decades during a period of intense glaciation that ended 20,000 years ago.
The results indicate that instead of forcing temperatures up at a consistent and predictable rate, rising carbon dioxide concentrations can result in a tipping point that generates powerful and disproportionate changes to climate.
Using detailed climate models, Zhang’s team found that a gradual increase in CO2 levels created an El Nino-like warming pattern, with more robust effects on the eastern Pacific than the western Atlantic.
This in turn strengthened the trade winds blowing across Central America, which increased evaporation from the Atlantic, thereby boosting water salinity and density. The result was a sharp rise in atmospheric temperature that took place over decades rather than centuries.
Co-author Stephen Barker from Cardiff University in Wales suggests the results may have implications for forecasting using current climate change predictions.
“These findings add to mounting evidence suggesting that there are sweet spots or ‘windows of opportunity’ within climate space where so-called boundary conditions, such as the level of atmospheric CO2 or the size of continental ice sheets, make abrupt change more likely to occur,” he says.
“Of course, our study looks back in time, and the future will be a very different place in terms of ice sheets and CO2, but it remains to be seen whether or not Earth’s climate becomes more or less stable as we move forward from here.”