Leading international climate scientists have warned that the world is at the point of crossing a series of climate “tipping points" and the this risk creates a “state of planetary emergency” and “existential threat to civilization”.
In an article in Nature, the authors (Timothy M. Lenton, Johan Rockström, Owen Gaffney, Stefan Rahmstorf, Katherine Richardson, Will Steffen, Hans Joachim Schellnhuber) describe Arctic sea-ice loss as amplifying regional warming, and that Arctic warming and Greenland melting are driving an influx of fresh water into the North Atlantic. This could have contributed to a 15 percent slowdown since the mid-twentieth century of the Atlantic Meridional Overturning Circulation (AMOC) , a key part of global heat and salt transport by the ocean. Rapid melting of the Greenland ice sheet and further slowdown of the AMOC could destabilize the West African monsoon, triggering drought in Africa’s Sahel region. A slowdown in the AMOC could also dry the Amazon, disrupt the East Asian monsoon and cause heat to build up in the Southern Ocean, which could accelerate Antarctic ice loss.
The climatologists describe a "tipping point" as being reached when the impact of global heating has become irreversible, creating massive loss of ice caps and forests. They argue that the “tipping point” is now estimated to be an increase of 1 degree Celsius instead of the previously thought 5 degree Celsius increase. There is also evidence of a vicious cycle of deterioration...warming temperatures cause permafrost to thaw, thereby releasing methane into the atmosphere, causing even further warning. This generalized warming can cause glaciers to melt and increase sea levels; ash from burning forests create “dark spots” on glaciers, increasing glacier melt.
The scientists state that this growing threat of massive and perhaps irreversible climate change should compel political and economic action on emissions.
They have summarized “evidence on the threat of exceeding tipping points, identify knowledge gaps and suggest how these should be plugged.” The report attempts to “explore the effects of such large-scale changes, how quickly they might unfold and whether we still have any control over them.”