IPCC Summary of Fourth Report

A few tidbits -- just to give a flavor -- from the Summary for Policymakers, which is available here. (Good luck downloading this file! You may want to wait until everyone is asleep...)

1. Observed changes in climate and their effects

Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level

...

There is observational evidence of an increase in intense tropical cyclone activity in the North Atlantic since about
1970, with limited evidence of increases elsewhere. There is no clear trend in the annual numbers of tropical
cyclones. It is difficult to ascertain longer term trends in cyclone activity, particularly prior to 1970.

Changes in Temperature, Sea Level and Northern Hemisphere Snow Cover:

Table SPM.2. Examples of some projected regional impacts (partial table)

Africa

• By 2020, between 75 and 250 million of people are projected to be exposed to increased water stress due to climate change;
• By 2020, in some countries, yields from rain-fed agriculture could be reduced by up to 50%. Agricultural production, including access to food, in many African countries is projected to be severely compromised. This would further adversely affect food security and exacerbate malnutrition;
• Towards the end of the 21st century, projected sea-level rise will affect low-lying coastal areas with large populations. The cost of adaptation could amount to at least 5-10% of Gross Domestic Product (GDP);
• By 2080, an increase of 5-8% of arid and semi-arid land in Africa is projected under a range of climate scenario (TS).

Asia

• By the 2050s, freshwater availability in Central, South, East and South-EastAsia, particularly in large river basins, is projected to decrease;
• Coastal areas, especially heavily-populated megadelta regions in South, East and South-East Asia, will be at greatest risk due to increased flooding from the sea and, in some megadeltas, flooding from the rivers;
• Climate change is projected to compound the pressures on natural resources and the environment, associated with rapid urbanization, industrialization and economic development;
• Endemic morbidity and mortality due to diarrhoeal disease primarily associated with floods and droughts are expected to rise in East, South and South-East Asia due to projected changes in the hydrological cycle.

North America

• Warming in western mountains is projected to cause decreased snowpack, more winter flooding, and reduced
  summer flows, exacerbating competition for over-allocated water resources;
• In the early decades of the century, moderate climate change is projected to increase aggregate yields of rain-fed agriculture by 5-20%, but with important variability among regions. Major challenges are projected for crops that are near the warm end of their suitable range or which depend on highly utilized water resources;
• During the course of this century, cities that currently experience heatwaves are expected to be further challenged by an increased number, intensity and duration of heatwaves during the course of the century, with potential for adverse health impacts;
• Coastal communities and habitats will be increasingly stressed by climate change impacts interacting with development and pollution.