CLIMATE CHANGE -- September 27, 2013 at 12:12 PM ET
U.N. report declares climate change is here to stay, and it's our fault
Protesters in Stockholm demand political action on climate change as the United Nations panel released its latest assessment on Friday. Photo by Jonathan Nackstrand/AFP/Getty Images.
On Friday, a group of sleep-deprived climate scientists in Stockholm revealed highlights from the latest assessment of the state of global climate change, after several all-night sessions and more than six years of new data. Here are some key points:
Climate change is continuing, and the report concludes that it's "extremely likely," with a probability of more than 95 percent that humans are a dominant cause. That's up from 90 percent, or "very likely" in 2007 and "likely" at 66 percent in 2001.
Each of the last three decades has been successively warmer at the Earth's surface than any decade preceding it since the start of the Industrial Revolution in 1850. In the Northern hemisphere, 1983-2012 is likely to have represented "the warmest 30-year period of the last 1400 years."
Since pre-industrial times, carbon concentrations in the atmosphere have increased by 40 percent, and combined concentrations of carbon dioxide, methane and nitrous oxide "have increased to levels unprecedented in the last 800,000 years." The ocean has absorbed about 30 percent of human-caused carbon dioxide emissions, causing ocean acidification.
The Greenland and Antarctic ice sheets have been steadily losing mass, and Arctic sea ice, spring snow cover in the Northern Hemisphere and glaciers worldwide have been shrinking. Sea level rise is projected to increase the risk of flooding along many coastlines.
Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010.
Scientists responded to questions about a "slowdown" or "hiatus" in the rate of warming over the past 15 years. They presented possible hypotheses that might explain it, including natural fluctuation in the Earth's climate system, increased heat uptake by the oceans and a number of small volcanoes from the late 90s, which spewed enough aerosol into stratosphere to have a discernible cooling effect.
For more coverage of the effects of climate change on society, view the PBS NewsHour's series Coping With Climate Change.