In 2015, the Paris Agreement was adopted with a goal of limiting warming to “well below 2°C.” The United Nations Intergovernmental Panel on Climate Change (IPCC) then embarked on a study of the difference in climate change effects between a 1.5°C warming and a 2°C warming. A 1.5°C warming would result in increases in extreme temperatures, precipitation, heat-related morbidity and mortality, vector-borne diseases, sea level, droughts, forest fires, spread of invasive species, ocean acidification, and crop failure, but a 2°C raise in global temperature would make these effects markedly worse. The IPCC report predicts that the half-degree difference in warming between 1.5°C and 2°C will result in coral reef loss of over 99% as opposed to 70-90%, a decrease in fishery yields of 3 million tons as opposed to 1.5 million tons, an increase in people affected by water stress of 50%, and hundreds of millions of additional people “exposed to climate-related risks and susceptible to poverty.” At a 2°C increase, global changes will occur faster, giving the population less time to adapt.
In the wake of the Paris Agreement, individual countries made commitments to domestic climate change reduction measures. If every country adheres to its commitment, temperatures would rise by 3°C. Another round of commitments is due in 2020. For warming to remain under 1.5°C, the world would have to reduce emissions by 45% from 2010 levels by 2030 and reach zero emissions by 2050.
The State Department accepted the report, but stated that “acceptance of this report by this panel does not imply endorsement by the United States of the specific findings or underlying contents of the report.” The U.S. government remains committed to withdrawing from the Paris Agreement.