In September 2013, the Intergovernmental Panel on Climate Change (1) published its fifth assessment of the physical science. The following is a synopsis (2) of the findings.
It is extremely likely (95-100% probability) that most of the global warming since 1950 has been due to human influences.
Multiple lines of evidence confirm that the extra heat being trapped by greenhouse gases is:
- warming the Earth’s surface to record levels,
- heating the oceans,
- raising sea levels,
- melting ice caps and glaciers, and
- changing weather patterns and extremes.
The global mean average surface temperature rose by 0.89°C from 1901 to 2012. (Global average surface temperature for the decade 2001-2010 was 14.47°C.)
- Each of the last three decades has been warmer than all proceeding decades since 1850,
- The first decade of the 21st century was the warmest of all.
It is virtually certain that the upper ocean has warmed from 1971 to 2010.
- Ocean warming accounts for most of the extra incoming solar energy stored by the Earth, about 93% between 1971 and 2010.
The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia.
- The global mean sea level rose by about 19 cm from 1901 to 2010 due to increased ocean warming and melting glaciers and ice sheets.
- The rate of rise accelerated between 1993 and 2010.
- During the last interglacial period, when the climate was 2°C warmer than pre-industrial levels, maximum global sea levels were 5 to 10 meters higher than they are today.
Seawater has become more acidic (its pH has decreased by 0.1) since the beginning of the industrial era due to humanity’s carbon dioxide emissions.
Ice and snow cover
The annual extent of Arctic sea ice decreased between 1979 and 2012 at a rate that was very likely between 3.5 and 4.1% per decade (about ½ million km2/decade).
There is very high confidence that glaciers have continued to shrink and lose mass world wide, with very few exceptions.
- The extent of Northern Hemisphere snow cover has decreased since the mid-20th century, especially in spring.
Changes in extreme weather events have been observed since about 1950.
- In the North Atlantic, increases in intense tropical cyclone activity are virtually certain.
- In large parts of Europe, Asia and Australia, it is likely that the frequency of heat waves has increased.
- It is very likely that, on the global scale, the number of cold days and nights has decreased and the number of warm days and nights has increased.
(1) established in 1988 by the World Meteorological Organization and the United Nations Environment Programme.
(2) distilled by John Hollins from the IPCC Summary for Policy Makers.