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. In
the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1400 years (medium confidence).