The Intergovernmental Panel on Climate Change (IPCC) is the peak body on the science of climate change. The IPCC recently released the fourth part of its fourth report, which are completed every four years. This fourth document is publicly available (here is the Summary for Policymakers) and integrates the findings of the previous three sections published earlier this year. Here are some of the key findings (adapted from an SMH article I now can't find, though I also note it is here):
• Evidence for global warming is now “unequivocal”, and there is a more than 90 per cent probability of human responsibility for the problem. The main culprit is carbon gas emitted by burning of fossil fuels, which lingers in the atmosphere and traps solar heat.What are the likely implications?
• Since 1900, the mean global atmospheric temperature has risen by 0.8 degrees Celsius and the sea level by 10-20 centimetres. Eleven of the past 12 years rank among the dozen warmest years on record.
• Human-generated greenhouse gases rose by 70 per cent between 1970 and 2004 from 28.7 to 49 billion tonnes per year in carbon dioxide or its equivalent. Levels of carbon dioxide, the main greenhouse gas, have risen by about a third since pre-industrial times and are now at their highest in 650,000 years.
• Climate change is already happening, visible in the loss of alpine glaciers and snow cover, shrinking Arctic summer sea ice and thawing permafrost.
• By 2100, global average surface temperatures could rise by between 1.1 and 6.4 degrees compared to 1980-99 levels. But this average rise will mask big variations, according to region and country.What can be done?
• Within this range, "best estimates" run from 2.4 degrees for a scenario based on a major switch to non-fossil fuels and 4 degrees for a fossil-fuel intensive "business-as-usual" scenario.
• Sea levels will rise by at least 18 centimetres by century's end. There is no estimate for the upper limit, given the unknowns about the impact of warming on ice sheets in Greenland and the Antarctic.
• Greenhouse-gas warming “could lead to some impacts that are abrupt or irreversible”. The risks are related to the rate and magnitude of the climate change.
• 20-30 per cent of plant and animal species are threatened with extinction if average global temperatures increase by 1.5 to 2.5 degrees, compared with the average temperature 1980-99. With a 3.5 degree rise, this rises to 40-70% of all plant and animal species.
• “All countries” will be affected, especially poor tropical countries struggling with water stress and few resources.
• In Africa, by 2020, 75-250 million people will be exposed to increased water stress. Yields from rain-fed agriculture in some African countries could be reduced by up to 50 per cent. Desert-like areas could expand by 5 to 8 per cent by 2080.
• In Asia, available fresh water will decrease by mid-century. Coastal mega-deltas will be at risk from flooding due to rising seas. Mortality due to diseases associated with floods and droughts will increase.
• To stabilise emissions at levels likely to limit the overall rise to 2.0 to 2.8 degrees would cost less than 0.12 percentage points of annual world GDP growth to 2030.Series: I; II; III; IV; V; VI; VII; VIII; IX; IX(b); X; XI; XII; XIII; XIV; XV.
• A "wide variety of policies and instruments" exist to reduce emissions, including carbon taxes, tougher emission standards, caps on emissions, incentives for clean energy production.
• In addition to emissions mitigation, a huge effort is also needed in adaptation, to channel funds, technology and knowledge to poor countries that will suffer disproportionately from climate change.