Factfile: The evidence for climate change

Saving the planet: Climate change protesters hold up a banner in front of the U.S. embassy in Jakarta, Indonesia. Activists urge the U.S. to live up its commitment to slow global warming. The 13th Conference of Parties to the United Nations Framework Convention on Climate Change (UNFCCC) is being held in Bali over the next two weeks. Credit: AFP

The data comes from a summary to policymakers issued this month by the Intergovernmental Panel on Climate Change (IPCC) ahead of the U.N.’s global-warming conference in Bali, Indonesia, taking place from December 3 to 14.

What we already know

• 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.
• Since 1900, the mean global atmospheric temperature has risen by 0.8 °C and the sea level by 10 to 20 cm. Eleven of the past 12 years rank among the dozen warmest years on record.
• Human-generated greenhouse gases rose by 70 percent between 1970 and 2004 from 28.7 to 49 billion tonnes per year in carbon dioxide (CO₂) or its equivalent. Levels of CO₂, the main greenhouse gas, have risen by around 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.

Forecast for this century

• By 2100, global average surface temperatures could rise by between 1.1 °C and 6.4°C compared to 1980-99 levels. But this average rise will mask big variations, according to region and country.
• Within this range, “best estimates” run from 2.4°C for a scenario based on a major switch to non-fossil fuels and 4.0°C for a fossil-fuel intensive “business-as-usual” scenario.
• Sea levels will rise by at least 18 cm 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.
• Man-made 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 to 30 per cent of plant and animal species are threatened with extinction if average global temperatures increase by 1.5 to 2.5 °C compared to the average temperature between 1980 to 1999.
• “All countries” will be affected, especially poor tropical countries struggling with water stress and few resources.
• In Africa, by 2020, 75 to 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 five to eight percent 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.

Coping with the heat

• To stabilise emissions at 445 to 535 parts per million (ppm) of CO2 equivalent would limit the overall rise in global warming since pre-industrial times to 2.0 to 2.8 °C. (Concentrations in 2006 were 381.2, according to the World Meteorological Organisation, WMO). The cost in 2030 for emissions in that range would be less than 0.12 percentage points of annual world GDP growth, says the IPCC.
• 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.