Climate Change Evidence & Causes Page: 4 of 36
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GREENHOUSE GASES such as carbon dioxide (CO2) absorb heat (infrared radiation)
emitted from Earth's surface. Increases in the atmospheric concentrations of these
gases cause Earth to warm by trapping more of this heat. Human activities-especially
the burning of fossil fuels since the start of the Industrial Revolution-have increased
atmospheric CO2 concentrations by about 40%, with more than half the increase
occurring since 1970. Since 1900, the global average surface temperature has increased by
about o.8 0C (1.4 F). This has been accompanied by warming of the ocean, a rise in sea
level, a strong decline in Arctic sea ice, and many other associated climate effects. Much
of this warming has occurred in the last four decades. Detailed analyses have shown
that the warming during this period is mainly a result of the increased concentrations of
CO2 and other greenhouse gases. Continued emissions of these gases will cause further
climate change, including substantial increases in global average surface temperature and
important changes in regional climate. The magnitude and timing of these changes will
depend on many factors, and slowdowns and accelerations in warming lasting a decade
or more will continue to occur. However, long-term climate change over many decades
will depend mainly on the total amount of CO2 and other greenhouse gases emitted as a
result of human activities.
2 CLIMATE CHANGE
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National Academy of Sciences (U.S.). Climate Change Evidence & Causes, report, Date Unknown; (digital.library.unt.edu/ark:/67531/metadc949508/m1/4/: accessed September 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.