With respect to greenhouse gases, current carbon dioxide atmospheric concentrations of carbon dioxide and methane far exceed those of any time in the last 650,000 years. The report examines a wide range of less significant greenhouse gases. Increases in concentrations are primarily due to fossil-fuel combustion, agriculture and land-use change.
On global warming,
the observed change is now unequivocally evident in air and ocean temperatures, melting of snow and ice, rising sea-levels (through thermal expansion) and is a result of human activities. This effect is at least five times greater than that due to natural solar emission variations.
With respect to changes in the climate system, changes include shifts in wind patterns and precipitation, ocean salinity and acidity, sea ice, ice sheets and aspects of extreme precipitation. Paleoclimate comparisons confirm the unusual nature of recent warming.
It is very likely (more than 90 per cent) that greenhouse gas increases caused most of the warming since the mid-20th century. It is extremely unlikely (less than 5 per cent) that the warming was caused by natural variability.
Looking ahead, it is anticipated through this century that mean temperatures will rise by 0.6-0.7 degrees Celsius by 2025, 1.3-1.7 degrees by 2055 and 1.7-4.0 degrees by 2095. There will also be more frequent, intense, longer-lived heat waves, minimum temperatures will warm faster than maximum temperatures, there will be a decrease in frost days (in mid to high latitudes) and an increased growing season (in mid to high latitudes).
There will be an increase in mean rainfall in the tropics (monsoons) and high latitudes, a decrease in the subtropics and mid latitudes. The intensity of extreme rainfall events will increase and there will be longer periods between events in the subtropics and mid latitudes.
Tropical cyclones will deliver increased peak winds and precipitation and possibly become less frequent with geographic shifts of occurrence.
Mid-latitude storms will become fewer with a pole-ward shift by several degrees but will have lower central pressure leading to increased wind speed and wave heights.
The extent of snow cover and sea-ice will decrease, glacier and ice sheets will lose mass, and the summer Arctic sea ice could be lost as early as the middle of this century. There will also be an increase in the depth of the thaw.
There is agreement that the Earth will lose its current carbon dioxide absorption efficiency, greater atmospheric accumulation of carbon dioxide although there are significant model differences and uncertainties still exist.
By the end of this century there will be a further 0.19-0.58 metre rise in sea level, although there will be regional differences and there remain outstanding uncertainties with respect to additional contribution of ice flows to the sea-level rise.
Atlantic ocean overturning is expected to decrease by 0-25 per cent but it is unlikely to be the precipitation of a collapse in the overturning.
There is still uncertainty surrounding El Nino. The phenomenon is likely to continue as a cause of year-to-year climate variability but trends in its frequency and magnitude are confused. There is also some uncertainty about monsoons, with likely increased precipitation but some confusion due to the impact of aerosols (dust).
Australia
Mean temperatures south of 30 degrees south will rise 2.6 degrees Celsius (2.4-2.9 range) by 2100, and north of 30 degrees south mean temperatures will rise 3.0 degrees (2.8-3.5 range) by 2100. Rises in mean temperatures will be less in coastal regions, but more inland.
Extreme temperatures - days over 35 degrees - will become more frequent. Melbourne can expect an increase from eight now to 9-12 by 2020 and 10-20 by 2070. Perth can expect an increase from 15 now to 16-22 by 2020 and 18-39 by 2070.
Mean precipitation south of 30 degrees south, from June to August will experience a 26 to 7 per cent decrease by 2100. On the east coast rainfall will increase in summer and decrease in winter although that is a less robust projection.
In New South Wales and Queensland summer rainfall will increase in magnitude by 30 per cent, with one in 40-year events becoming one in 15-year events. Return periods of extreme rainfall events will halve through this century and there will be a marked increased in the frequency of rainfall deficits, doubling in some cases by 2050.
Snow cover will be reduced. 30-day snow cover will be reduced to 14-54 per cent by 2020 and 30-93 per cent by 2050.
Almost all indications are for a moisture balance deficit, and thus a drier Australian environment.
There will be a modest strengthening of winds over the inland and the north and a slight weakening on the southern coasts.
Some of the factors contributing to existing uncertainties are include El Nino which significantly influences Australian climate yet there is as yet no clear view of how this will change in a warmer world; monsoon projections vary across models; detailed assessments of the performance of models representing existing Australian climate is still lacking; representation of topography in the models is limited; and more downscaling (connecting the resolution of the models to the resolution at which details for decisions are required) is still needed for our region.
The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by two United Nations organizations, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), to evaluate the risk of climate change caused by human activity.
The IPCC shared the 2007 Nobel Peace Prize with former Vice President of the United States Al Gore
sorry if this makes you uneasy or disagrees with your religion.
