Avoiding the worst impacts of climate change requires a portfolio of options. The primary focus should be on implementing technologies to reduce greenhouse gas emissions, particularly CO2, complemented by efforts to remove and reliably sequester carbon from the atmosphere and to curb emissions of other greenhouse gases.
It is now more certain than ever, based on many lines of evidence, that humans are changing Earth’s climate. Climate Change: Evidence and Causes (updated 2020), a booklet produced by the National Academies and The Royal Society, lays out the evidence that human activities, especially the burning of fossil fuels, are responsible for much of the warming and related changes observed around the world. The booklet includes a section on Basics of Climate Change for those who want to learn more.
Since 1900, Earth’s average surface air temperature has increased by about 1 °C (1.8 °F), with over half of the increase occurring since the mid-1970s. A wide range of other observations such as reductions in Arctic sea ice, reduced snowpack, and ocean warming, along with indications from the natural world, such as poleward migrations of some species, provide incontrovertible evidence of planetary-scale warming.
Figure 1a: Annual Global Temperature 1850-2019
Figure 1b: Evidence that Earth's Climate is Changing
The average concentration of atmospheric CO2 measured at the Mauna Loa Observatory in Hawaii has risen from 316 parts per million (ppm) in 1959 (the first full year of data available) to more than 411 ppm in 2019.
Rigorous analysis of all data and lines of evidence shows that most of the observed global warming over the past 50 years or so cannot be explained by natural causes and instead requires a significant role for the influence of human activities.
If emissions continue on their present trajectory, without either technological or regulatory abatement, then warming of 2.6 to 4.8 °C (4.7 to 8.6 °F) in addition to that which has already occurred would be expected during the 21st century.
Climate Crisis Demands ‘Urgent and Ambitious’ Response
The presidents of the National Academies said in an October 29, 2021 statement that COP26 presents a historic global opportunity to agree on emissions reduction targets to avoid the most intolerable impacts of climate change.
The National Academies conducts a wide range of ongoing activities related to climate change, including studies, events, roundtables, and initiatives. To learn more, visit our Climate Resources website and subscribe to the National Academies climate email list to stay apprised of news and opportunities to participate.
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