Two degrees Celsius warming above pre-industrial levels is an important milestone for climate change. For years, global leaders have agreed that 2 degrees of warming is the point above which “dangerous” climate change will commence. In the Paris Agreement, nearly 200 nations agreed to work together to limit global warming to well below the 2 degree level and pursue efforts to keep it below 1.5 degrees.
At a minimum, breaching 2 degrees requires us to be beyond the pre-industrial baseline and to be beyond it for a while. It sounds easy enough to measure global warming: see how hot it was, compare it to how hot it used to be. But climate scientists have several ways of measuring how hot it used to be. It is also representative of the world’s 20th-century climate and can help us understand how much warmer the world has become while many of us have been alive.
The overall mood in the climate science community is grim. After years of warning that the planet is warming, researchers are becoming increasingly outspoken about the effects already being seen. Average temperatures have risen by about 0.85 degrees Celsius over pre-industrial norms. The Arctic is warming twice as fast as the rest of the globe, and scientists say Arctic sea ice will vanish during summertime by the middle of the century. At the other pole, the West Antarctic Ice Sheet is threatening to collapse, which could have major impacts on sea level rise.
Researchers are also becoming less reluctant to attribute weather events to climate change. Scientists say climate change raises the risk of unusual and extreme weather. The California drought of 2014 was partially due to greenhouse gas warming. 22 separate research teams analyzed data over five droughts and heat waves in 2013 and they found evidence of climate change’s impact on all of them.
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