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UN IPCC Fifth Assessment Report (WGI): Morceaux Choisis

Working Group I of the United Nations International Panel for Climate Change (IPCC) made public its contribution to the fifth Assessment Report (AR5) on 27 September 2013. WGI focuses on the physical science knowledge as to climate change. Hereafter follow some quotes directly from the report. Those underline the level of seriousness of climate change and the direct link to human activities.

Observed changes in the climate system:

Atmosphere
- "Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia."
- "In the Northern Hemisphere, 1983-2012 was likely the warmest 30-year period of the last 1400 years (medium confidence)."
- "Continental-scale surface temperature reconstructions show, with high confidence, multi-decadal periods during the Medieval Climate Anomaly (year 950-1250) that were in some regions as warm as in the late 20th century. These regional warm periods did not occur as coherently across regions as the warming in the 20th century (high confidence)."

Ocean
- "It is virtually certain that the upper ocean (0-700 m) warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971."

Cryosphere
- "Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent (high confidence)."
- "There is very high confidence that the extent of Northern Hemisphere snow cover has decreased since the mid-20th century."
- "There is high confidence that permafrost temperatures have increased in most regions since the early 1980s. Observed warming was up to 3C in parts of the Russian European North (1971-2010). In the latter region, a considerable reduction in permafrost thickness and areal extent has been observed over the period 1975-2005 (medium confidence)."

Sea level
- "The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia (high confidence)."

Carbon and Other Biogeochemical Cycles
- "The atmospheric concentrations of the greenhouse gases carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) have all increased since 1750 due to human activity."
- "CO2 concentrations have increased by 40% since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions."
- "The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification."

Recent Changes of Climate Change, Detection and Attribution
- "Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations in the atmosphere, positive radiative forcing, observed warming, and understanding of the climate system."
- "Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes. This evidence for human influence gas grown since AR4. It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century."

Future Global and Regional Climate Change
- "Continued emissions of greenhouse gases will cause warming and changes in all components of the climate system."
- "The global ocean will continue to warm during the 21st century. Heat will penetrate from the surface to the deep ocean and affect ocean circulation."
- "Most aspects of climate change will persist for many centuries even if emissions of CO2 are stopped."

Here is the timeline towards the completion of AR5 in its entirety:
  • Working Group II - Impacts, Adaptation and Vulnerability : Yokohama, Japan, 25-29 March 2014
  • Working Group III - Mitigation of Climate Change : Berlin, Germany, 7-11 April 2014
  • Synthesis Report (SYR) : Copenhagen, Denmark, 27-31 October 2014

References:
Website of the UN IPCC: http://www.ipcc.ch/
Website of Working Group I: http://www.climatechange2013.org/
WGI Contribution to AR5 - Climate Change 2013: The physical Science Basis




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