It is “extremely likely” that human activity is the cause of climate change, leading scientists said in a UN report Friday, while warning that global temperatures could rise by as much as 4.8 degrees Celsius by the end of the century.
The existence of climate change is “unequivocal” and it is “extremely likely” that human activity is the cause, a report by leading scientists said Friday.
In its starkest warning yet, the Intergovernmental Panel on Climate Change (IPCC) said that the planet was set to experience more heatwaves, floods, droughts and rising sea levels that could swamp coasts and low-lying islands as greenhouse gases build up in the Earth’s atmosphere.
The current hiatus in warming, when temperatures have risen more slowly despite growing emissions, was a natural variation that would not last, said the report, which was presented at a UN summit in the Swedish capital Stockholm.
UN Secretary-General Ban Ki-moon said the study was a call for governments, many of which have been focused on spurring weak growth rather than fighting climate change, to work to agree a planned UN accord in 2015 to combat global warming.
"The heat is on. Now we must act," he said.
The IPCC said the report, meant to guide governments in shifting towards greener energies, was compiled from the work of hundreds of scientists and using the latest computer models to interpret the data.
According to the study, it is now "extremely likely", a probability of at least 95 percent, that human activities were the dominant cause of warming since the mid-20th century.
That was an increase from "very likely", or 90 percent, in the last report in 2007 and "likely", 66 percent, in 2001.
Rising sea levels threaten coastal cities
The report said temperatures were likely to rise by between 0.3 and 4.8 degrees Celsius (0.5 to 8.6 Fahrenheit) by the late 21st century, with the low end of the range only achievable if governments sharply cut greenhouse gas emissions.
This would mean that world sea levels could rise by between 26 and 82 cm (10 to 32 inches) by the late 21st century, the report warned. The melting ice and the expansion of water as it warms would threaten coastal cities from Shanghai to San Francisco.
That range is above the 18-59 cm estimated in 2007, which did not take full account of Antarctica and Greenland.
“As the ocean warms, and glaciers and ice sheets reduce, global mean sea levels will continue to rise, but at a faster rate than we have experienced over the past 40 years,” said IPCC co-chair Qin Dahe.
Rising temperatures would also have an impact on weather systems around the world, said fellow co-chair Thomas Stocker.
“Heatwaves are very likely to occur more frequently and last longer. As the Earth warms, we expect to see currently wet regions receiving more rainfall, and dry regions receiving less, although there will be exceptions,” he said.
‘Playing with fire’
US Secretary of State John Kerry described the report as "yet another wakeup call" and warned that those who ignore the study’s findings “are playing with fire”.
"This isn't a run-of-the-mill report to be dumped in a filing cabinet. This isn't a political document produced by politicians. It's science," said Kerry.
"The costs of inaction grow beyond anything that anyone with conscience or common sense should be willing to even contemplate."
However, this year’s report faces extra scrutiny after its 2007 predecessor included an error that exaggerated the rate of melting of Himalayan glaciers. An external review later found that the mistake did not affect its main conclusions.
The report said the trend of the past 15 years was skewed by the fact that 1998, at the start of the period, was an extremely warm year with an El Nino event in the Pacific that can disrupt weather worldwide.
It said warming had slowed "in roughly equal measure" because of random variations in the climate and the impact of factors such as volcanic eruptions, when ash dims sunshine, and a cyclical decline in the sun's output.
Slowdown in warming unlikely to last
But the report predicted that this reduction in warming would not last, saying temperatures from 2016-35 were likely to be 0.3-0.7 degree Celsius (0.5 to 1.3 Fahrenheit) warmer than in 1986-2005.
The IPCC said that while the climate was slightly less sensitive than previously estimated to the warming effect of carbon dioxide, a warming trend is "unequivocal".
“Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850,” it said.
Furthermore, some of the effects of climate change are set to last far beyond the lifetimes of people now alive, such as heat penetrating ever deeper into the oceans, regardless of efforts to cut carbon emissions.
"As a result of our past, present and expected future emissions of carbon dioxide, we are committed to climate change and effects will persist for many centuries even if emissions of carbon dioxide stop," said Stocker.
(FRANCE 24 with wires)
Date created : 2013-09-27