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Tipping points – no safe limit

18 possible tipping points well before +2°C is reached

New research reported by Climate News Network has identified at least 37 “tipping points” that would serve as evidence that climate change has happened – and happened abruptly in one particular region.

Eighteen of them could happen even before the world warms by an average of 2°C, the proposed “safe limit” for global warming.

Researchers report in the Proceedings of the National Academy of Sciences that they “screened” the massive ensemble of climate models that inform the most recent reports from the Intergovernmental Panel on Climate Change, and found evidence of abrupt regional changes in the oceans, sea ice, snow cover, permafrost and in the terrestrial biosphere that could happen as average global temperatures reached a certain level.

The models did not all simulate the same outcomes, but most of them did predict one or more abrupt regional shifts.

But the future is not an exact science according to the researchers. “Our results show that the different state-of-the-art models agree that abrupt changes are likely, but that predicting when and where they will occur remains very difficult. Also, our results show that no safe limit exists and that many abrupt shifts already occur for global warming levels much lower than 2 °C.”

The researchers explore some of the telltale indicators of such abrupt change. One of these would be the wholesale collapse of the Arctic Ocean winter ice: the Arctic is expected to be largely ice-free most summers in the next few decades. Winter ice would then become increasingly thin. Once sufficiently thin, warming and wave power would do the rest, and tend to leave clear blue water even in the coldest seasons.

Another indicator would involve massive unexpected plankton blooms in the Indian Ocean as a consequence of an upwelling of nutrient-rich waters from the ocean bottom, in response to changes in the Asian monsoon regime.

A third would involve massive snow melt on the Tibetan plateau: in 20 years, the annual average snow cover could fall from 400 kilograms per square metre to a trifling 50 kg.

A fourth signal would be massive dieback in the Amazon rainforest over a few decades, mainly because of reduced rainfall.

Yet another telltale aspect of climate change would be the sudden, paradoxical dramatic drop in temperatures in the North Atlantic, as a response to global warming and a collapse of the ocean current that carries warm surface water north, while denser, colder and increasingly more saline water in the Arctic sinks to the bottom and flows back southward.

The researchers conclude: “An additional concern is that the present generation of climate models still does not account for several mechanisms that could potentially give rise to abrupt change. This includes ice sheet collapse, permafrost carbon decomposition, and methane hydrates release.”

Reinhold Pape
Source: Climate News Network

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