Intergovernmental Panel on Climate Change
External web sites:
The Intergovernmental Panel on Climate Change (IPCC) is an inter-agency programme of the United Nations, established in 1988 under the auspices of the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP). IPCC's mandate is to gather scientific, technical, and socio-economic information pertaining to human-induced climate change and possibilities for its mitigation. Its major products are the assessment reports on climate change science, impacts, and mitigation, prepared in 5 to 7-year intervals; the first in 1990 (FAR), the second in 1995 (SAR), the third in 2001 (TAR), and the fourth assessment report in 2007 (AR4).
These main IPCC assessments are prepared by three separate working groups:
- WG-1 - This working group covers the science of climate change. The full IPCC AR4 WG-1 report was published online May 22, 2007: http://ipcc-wg1.ucar.edu/wg1/wg1-report.html
- WG-2 - Working Group 2 is responsible for analyzing impacts, adaptation, and vulnerability to human-induced climate change. For AR4 the summary for policymakers was published April 6, 2007: http://www.ipcc-wg2.org/ - the full report will be available here later in 2007.
- WG-3 - This working group deals with strategies and costs for mitigation. The summary was published May 4, 2007: http://www.mnp.nl/ipcc/
For each working group, the final report includes a complete list of contributors and reviewers.
As the IPCC assessments have progressed, the science has become more certain on the evidence for warming and human causation. AR4 contains the most strongly worded statements so far, confirming that human emissions of greenhouse gases is causing the temperature of the Earth to rise, which is resulting in increasing changes to the planet's climate. The consequences of this include disruption to agriculture and global food supply, extinction of species, rising sea levels, loss of human habitat, increased erosion and property damage due to more violent storms. AR4 also finds the predicted economic impact of reduced emissions of CO2 through changes in energy use and production to be considerably less than the economic impact of climate change without mitigation.
Combustion of the Carbon in fossil fuels such as coal and oil releases carbon dioxide (CO2). CO2 is the second most important greenhouse gas (after water vapor), and because of its long residence time in the atmosphere, the present increase in atmospheric CO2 levels (from 280 ppm in 1750 to over 380 ppm now) is the primary driving factor in Global Warming
Among the high-confidence (very likely) findings of IPCC AR4:
- present concentrations of CO2 far exceed the levels found in ice cores dating back 650,000 years
- Radiative forcing from all long-lived greenhouse gases, and their rate of increase, is unprecedented in at least 10,000 years
- The increase in atmospheric CO2 is responsible for a radiative forcing of 1.66 - 0.17 W/m^2, significantly larger than all other "forcings".
- The source of this increased CO2 is primarily (2/3) from human combustion of fossil fuels and (1/3) changes in land use (burning of forests). About 45% of this CO2 is still in the atmosphere, about 30% has been taken up by the oceans, and the remainder absorbed by plants. Because of the different cycles of terrestrial and ocean processes, about half of emitted CO2 beyond the normally balanced carbon cycle is removed within 30 years, about 30% removed within a few centuries, and the remainder will stay for thousands of years.
- Taking aerosols, methane and other greenhouse gases, and changes from human activity into account, the net forcing from human activity since 1750 is a positive 1.6 ( 0.6 to 2.4) W/m^2.
- Natural forcings from solar and volcanic activity are found to be 0.12 ( 0.06 to 0.30) W/m^2; about 10 times less than the human-caused change
- 2005 and 1998 were the warmest two years (for global average surface temperature) in the instrumental record that has been kept since 1850
- The 100-year trend of temperature increase (1906-2005) is 0.74 - 0.18 degrees C. Total temperature increase from 1850-1899 to 2001-2005 is 0.76 - 0.19 degrees C.
- The effect of urbanisation and land use change on the average temperature record ("heat island effect") is negligible - less than 0.006 degrees C per decade over land, zero over oceans.
- satellite measurements of lower atmosphere temperature are now in agreement with the surface temperature trends.
- Stratospheric temperatures have been declining at between 0.3 and 0.6 degrees C per decade since 1979.
- Tropospheric water vapor levels are increasing. This leads to increased precipitation, and is a positive feedback on the CO2 contribution to warming.
- Heavy precipitation events have become more common
- The most intense tropical cyclones have become more common even while the total number of cyclones shows no trend.
- Snow cover has decreased
- Glaciers and ice caps have experienced widespread mass loss, contributing to sea level rise
- The upper ocean has warmed
- The upper ocean has become more acidic, with a decrease in surface pH of 0.1 units
- Sea level rise has increased from about 1.8 mm/yr for the 1961 to 2003 period, to 3.1 mm/yr for the 1993-2003 period; part of this is from thermal expansion of the oceans as they warm, and part from melting glaciers, ice caps, and ice sheets.
- Average Northern Hemisphere temperatures from 1950-2000 were very likely warmer than any other 50-year period in the past 500 years, and likely the warmest in the past 1300 years.
- Sea level was likely between 4 and 6 m higher during the last interglacial period 125,000 years ago.
- It is very likely that anthropogenic greenhouse gas increases caused most of the observed warming since the mid 20th century.
- The increase in greenhouse gases so far will lead to a committed warming and future climate change even with no further releases of these gases from human activities, of about 0.1 degrees C per decade for the next 2 decades at least, and 0.6-0.7 degrees C over the next century as the ocean warms and Earth's energy flows re-balance.
- Under the most optimistic carbon-intensity economic scenario, global temperatures will increase 1.8 (1.1 to 2.9) degrees C by 2100, and sea level will increase 18 - 36 cm, not including a possible acceleration in ice-sheet loss
- Under the most pessimistic carbon-intensity economic scenario considered, global average temperature will increase 4.0 (2.4 - 6.4) degrees C by 2100, with sea level increasing 26 to 59 cm, not including ice-sheet acceleration.
- The projected temperature changes are positive everywhere. Nowhere will experience cooling while the rest of the world warms.