Governments can keep climate change in check at manageable costs but will have to cut greenhouse gas emissions to zero by 2100 to limit risks of irreversible damage, according to a new UN report, as reported by Reuters.
The 40-page synthesis is a summation of 5,000 pages of work by 800 scientists already published since September 2013, and says global warming is now causing more heat extremes, downpours, acidifying the oceans and pushing up sea levels.
“Science has spoken. There is no ambiguity in the message. Leaders must act, time is not on our side,” U.N. Secretary-General Ban Ki-moon said in presenting the report in Copenhagen.
With fast action, climate change could be kept in check at manageable costs, he said, referring to a UN goal of limiting average temperature rises to 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial times. Temperatures are already up 0.85 C (1.4F).
The study by the Intergovernmental Panel on Climate Change (IPCC), approved by more than 120 governments, will be the main guide for negotiators of a UN deal to fight global warming due at a summit in Paris in December 2015.
Deep cuts in emissions would reduce global growth in consumption of goods and services, the economic yardstick used by the IPCC, by just 0.06 percentage point a year below annual projected growth of 1.6 to 3.0 percent.
To achieve good odds of staying below 2C, the report’s scenarios show that world emissions would have to fall by between 40 and 70 percent by 2050 from current levels and to “near zero or below in 2100″, according to Reuters.
Below zero would require extracting carbon dioxide from the atmosphere – for example, by planting forests that soak up carbon as they grow or by burying emissions from power plants that burn wood or other biomass.
To cut emissions, the report points to options including energy efficiency, renewable energies from wind to solar power, nuclear energy or coal-fired power plants where carbon dioxide is stripped from the exhaust fumes and buried underground.
Without extra efforts to cut emissions, “warming by the end of the 21st century will bring high risks of severe, widespread, and irreversible impacts globally,” the IPCC concluded.