German and Dutch scientists say that they’ve reason to believe that abrupt climate change tipping points are unavoidably connected with positive feedback mechanisms that lead to self-propelling change which can be massively destructive. If the scientists are right, our climate could be on course to a tipping point to worse conditions than those anticipated by the International Panel on Climate Change.
Until now it’s been difficult to determine whether nature’s feedback mechanisms were strong enough to cause tipping points. But the European researchers say that historic records they've studied imply this is the case. The scientists, who are attached to the German Potsdam Institute for Climate Impact Research and Wageningen University (the Netherlands) researched eight historic periods including four glaciation periods.
They found that periods of relatively stable climate have often been interrupted by sharp transitions to a contrasting state. The main reason for this is that self-propelled change triggered tipping points. One example is the ice-albedo feedback. If ice caps melt, more sunlight is absorbed by the darker surface that is exposed. This causes further warming.
Self propelled change has massive effects. For instance, glaciation periods typically ended suddenly. And about 34 million years ago the Earth’s long lasting tropical state, in which most recent life forms evolved, shifted abruptly and irreversibly to a cooler state with ice caps. This shift is known as the "Greenhouse-Icehouse-Transition".
The scientists reported their findings in the Proceedings of the National Academy of Sciences, saying that sharp climatic shifts in the past are systematically preceded by subtle alterations in fluctuation patterns.
These alterations are proven to be characteristic of systems approaching tipping points. This finding supports the theory that the sharp climatic shifts in the past have happened as the Earth system went over critical thresholds where self-catalyzing change pushed it further towards a contrasting state,” they say.
The demonstration of tipping points also has implications for the thinking about current climate change, the authors state.
The well known projections by the Intergovernmental Panel on Climate Change are based on the assumption of rather linear change. Although some feedbacks in the Earth system may dampen change, the new results imply that we should also consider the possibility that the climate will cross a tipping point after which changes will be amplified,” the scientists point out.
Whether climate as a whole is now approaching a tipping point is difficult to judge with new techniques because human influence is simply too fast to generate data records long enough for the detection method, according to the European scientists. However, for certain parts of the climate system the method may be readily applicable to predict future abrupt change, they say.
The researchers analyzed the geological records of eight ancient events of abrupt climate change; the end of the greenhouse Earth, the end of the Younger Dryas, the Bølling-Alleröd-Transition, the desertification of North Africa and the ends of four glaciation periods.