This one was done by NASA and the Earth Institute of the University of Columbia.
According to the web page related to the article : “(…) research finds that human-made greenhouse gases have brought the Earth’s climate close to critical tipping points, with potentially dangerous consequences for the planet.”
The page also gives worrying facts and estimates :
The researchers also investigate what would be needed to avert large climate change, thus helping define practical implications of the United Nations Framework Convention on Climate Change. That treaty, signed in 1992 by the United States and almost all nations of the world, has the goal to stabilize atmospheric greenhouse gases “at a level that prevents dangerous human-made interference with the climate system.
Based on climate model studies and the history of the Earth the authors conclude that additional global warming of about 1ºC (1.8ºF) or more, above global temperature in 2000, is likely to be dangerous.
In turn, the temperature limit has implications for atmospheric carbon dioxide (CO2), which has already increased from the pre-industrial level of 280 parts per million (ppm) to 383 ppm today and is rising by about 2 ppm per year. According to study co-author Makiko Sato of Columbia’s Earth Institute, “the temperature limit implies that CO2 exceeding 450 ppm is almost surely dangerous, and the ceiling may be even lower.”
This means that carbon dioxide emissions have to stop increasing as soon as possible and that decreasing those emissions in an important way has to be done quickly as well.
The big problem being that this gas lasts a hundred years. So, if we totally stopped emitting CO2 now, climate change will continue for a century.
The authors note that :
Climate changes are so large with ‘business-as-usual’, with additional global warming of 2-3ºC (3.6-5.4ºF) that Hansen concludes “business-as-usual’ would be a guarantee of global and regional disasters.”
However, the study finds much less severe climate change – one-quarter to one-third that of the “business-as-usual” scenario – when greenhouse gas emissions follow the alternative scenario. “Climate effects may still be substantial in the ‘alternative scenario’, but there is a better chance to adapt to the changes and find other ways to further reduce the climate change,” said Sato.
While the researchers say it is still possible to achieve the “alternative scenario,” they note that significant actions will be required to do so. Emissions must begin to slow soon. “With another decade of ‘business-as-usual’ it becomes impractical to achieve the ‘alternative scenario’ because of the energy infrastructure that would be in place” says Hansen.
So, if we decrease by 25 to 35 % our greenhouse gases, Mankind would be safe from most of the harm that would occur if nothing was done to mitigate climate change. But it is time to act and these actions will have to be important in both size and speed.
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Image from the page of NASA, showing Antarctica.