A U.N. report on climate change said that while human activity is "extremely likely" to blame for global warming, temperatures aren't expected to rise as quickly as previously thought. Gunnar Myhre, coordinating lead author for the IPCC, explains the details to WSJ's Gautam Naik.
STOCKHOLM—A much-anticipated United Nations report issued Friday reaffirmed growing belief that human activity is the dominant cause behind a rise in global temperatures, but presented a more moderate estimate on rising temperatures.
A summary of the report, the work of more than 800 scientists working for the U.N.'s Intergovernmental Panel on Climate Change over several years, said there is a 95% likelihood that humans are behind global warming, up from the 90% level reported in a similar 2007 report. The IPCC noted that air and oceans are getting warmer, ice and snow is less plentiful, and sea levels are rising.
An iceberg floats through the water on July 20, 2013, in Ilulissat, Greenland.
"Observations of changes in the climate system are based on multiple lines of independent evidence," Qin Dahe, co-chair of the IPCC working group, said in a statement. The IPCC said the past three decades have been successively warmer at the Earth's surface that any preceding decade since 1850.
The trend is "a robust signal of a changing planet," said IPCC co-chair Thomas Stocker at a news conference in Stockholm.
Kali, an orphaned male polar bear cub from Point Lay, Alaska, explores the enclosure outside the infirmary at the Alaska Zoo, in a photo taken on March 22, 2013.
IPCC reports draw the attention of governments, environmentalists and key industries such as the oil, gas and coal sector because they provide the scientific backing for many governments' policies on climate change.
The summary issued on Friday previews a full report that will be issued next week as part of the group's fifth assessment, which will come out in several phases. It is considered a more definitive document than its predecessors because it incorporates more recent scientific findings, a larger set of satellite, oceanic and terrestrial measurements, and more robust computer modeling.
The IPCC's credibility took a hit after some shoddy data made its way into the 2007 report, including a claim that Himalayan glaciers would melt by 2035. More recently, climate change science has come under attack because of a flattening of temperatures over the past 15 years, even though greenhouse gas emissions have continued to rise.
Scientists at the IPCC are playing down the apparent slowdown, arguing that a 15-year period is too short to reflect long-term climate trends. Several factors could be behind the apparent slowdown in warming. They say these include a cooling of the Pacific Ocean, a natural change in the 11-year solar cycle and nearly a dozen volcanic eruptions since 2005, which can spew sunlight-blocking particles into the atmosphere.
"We couldn't attribute exactly what was the contribution from each of these factors," said Corinne Le Quere, a geophysicist at the University of East Anglia in the U.K. and a lead author of a chapter in the U.N. report. "But the overall picture is that the earth is continuing to take up heat even when the surface is warming slowly."
The IPCC has moderated projections of rising temperatures for the end of this century. The latest report outlines four scenarios, with the worst scenario predicting a possible increase of 4.8 degrees Celsius, or 8.6 degrees Fahrenheit, toward the end of the century. The prior report had outlined six scenarios, with the worst scenario peaking above 6 degrees Celsius.
The newest measurements suggest that current carbon-dioxide concentration in the earth's atmosphere is 40% above preindustrial levels. Such levels are "unprecedented in at least the last 800,000 years," the report said. The 2007 report had calculated the same figure but only for the past 650,000 years.
Between 1750 and 2011, human activity released 545 gigatons of carbon dioxide, the main greenhouse gas. If a total of 1,000 tons is emitted, there is a one-in-three chance that the two-degree limit will be breached, said Dr. Le Quere.
"We're eating up our allocation very rapidly. At the current rate, we'll hit the 1,000-ton-level sometime between 2040 and 2050," she added.
Of all the carbon dioxide emitted so far, two-thirds comes from burning fossil fuels and one third from land-use change and deforestation. However, in the last decade, 90% of the carbon dioxide released has come from burning fossil fuels, according to Dr. Le Quere.
Arctic sea ice cover has been on a declining trend for several decades. The IPCC now says it is "very likely" that the ice cover will continue to shrink and thin, and there will be a reduction in glacier volumes and declines in spring snow cover in the northern hemisphere. This past summer, Arctic sea ice levels registered an increase, but that partly reflected the record low levels achieved a year earlier.
The U.N. report also concludes that global mean sea level will "very likely exceed that observed during 1971 through 2010."
Write to Johannes Ledel at johannes.ledel@dowjones.com
Corrections & Amplifications
Thomas Stocker said the global surface temperature change for the end of the 21st century is projected to be likely to exceed 1.5 degrees Celsius, which is about 2.7 Fahrenheit. A previous version of this article gave an incorrect conversion of Celsius to Fahrenheit.
via Science - Google News http://news.google.com/news/url?sa=t&fd=R&usg=AFQjCNG_RRkcIqIj7LSYlHdGhDCRh5HXsg&url=http://online.wsj.com/article/SB10001424052702303342104579100593218822558.html
Put the internet to work for you.
No comments:
Post a Comment