IPCC Policymaker Summary

Report

Warming of the climate system is unequivocal, and since the 1950s, many of the observed
changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed,
the amounts of snow and ice have diminished, sea level has risen, and the concentrations of
greenhouse gases have increased

Each of the last three decades has been successively warmer at the Earth’s surface than any
preceding decade since 1850 (see Figure SPM.1). In the Northern Hemisphere, 1983–2012 was
likely the warmest 30-year period of the last 1400 years
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