tagged w/ forcings
The National Research Council is pleased to present this video that explains how scientists have arrived at the state of knowledge about current climate change and its causes.
More at the link
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is."
Winston ChurchillThe National Research Council is pleased to present this video that explains how... more
"Accelerating melting on the world’s ice sheets and other new observations have scientists concluding that even a two-degree Celsius rise in temperatures – a benchmark long seen as safe in global climate talks and other emissions reductions scenarios – could lead to an 80-foot rise in sea levels.
“The dangerous level of global warming is less than what we thought a few years ago,” said James Hansen, director of NASA Goddard Institute for Space Studies. “It was natural to think that a few degrees wasn’t so bad…. (But) a target of two degrees is actually a prescription for long-term disaster.”
Antarctica and Greenland are losing ice at a surprising clip, Hansen said, and methane hydrates – a potent source of greenhouse gas frozen beneath the seas – are starting to bubble up.
The key question for climatologists: How sensitive is the climate to increasing amounts of fossil fuel emissions. Last year humanity pumped almost 10 billion tons of carbon dioxide into the atmosphere, a half-billion tons more than 2009 and the largest jump in any year since the Industrial Revolution, according to the Global Carbon Project.
See also Biggest Jump Ever in Global Warming Pollution in 2010, Chinese CO2 Emissions Now Exceed U.S.’s By 50%.
The problem, those researchers said, is the “hang time” for carbon dioxide in the atmosphere. Even if greenhouse gas emissions stopped tomorrow, “climatically important” amounts of carbon dioxide and other compounds emitted today would continue to influence the atmosphere for thousands of years, Caldeira said.
See also Fossil CO2 impacts will outlast Stonehenge and nuclear waste
That kind of pressure, or “forcing,” on the atmosphere could be devastating, he cautioned.
About 55 million years ago a tremendous amount of methane was released into the atmosphere over a period of about 1 million years, and the planet heated by five degrees to eight degrees Celsius, or 10 degrees to 14 degrees Fahrenheit. The result was an ice-free planet with sea levels 230 feet higher than they are today.
In the eons since, carbon dioxide levels dropped and the ice reformed. But humanity’s emissions have the potential to send the globe back to those conditions, Caldeira and Hansen said.
“If you doubled CO2, which practically all governments assume we’re going to do, that would eventually get us to the ice-free state,” Hansen said.
Scientists don’t expect that ice to melt quickly. Assuming the current accelerated melting continues on the world’s ice sheets and glaciers, various climate models predict the ocean would rise between 1.5 feet and 2.3 feet by century’s end, said Tad Pfeffer, a glaciologist with the University of Colorado.
But the ice melted with atmospheric carbon dioxide levels at about 1,000 parts per million, Caldeira said. And he suspects that even 750 ppm, or about double today’s levels, could send the globe spiraling toward an ice-free state. Current emissions trends suggest the globe could reach that by the end of the century.
“We can’t double CO2,” Hansen added. “We would be sending our climate back to a state we haven’t adjusted to as a species.”
The time to act was a while ago, but now is much, much better than later."
•A detailed look at climate sensitivity
•Climate Experts Warn Thawing Permafrost Could Cause 2.5 Times the Warming of Deforestation
More at the link
Around 28:00 minutes into the video is information on CO2."Accelerating melting on the world’s ice sheets and other new observations... more
The area covered by Arctic sea ice reached its lowest point this week since the start of satellite observations in 1972, German researchers announced on Saturday.
"On September 8, the extent of the Arctic sea ice was 4.240 million square kilometres (1.637 million square miles). This is a new historic minimum," said Georg Heygster, head of the Physical Analysis of Remote Sensing Images unit at the University of Bremen's Institute of Environmental Physics.
The new mark is about half-a-percent under his team's measurements of the previous record, which occurred on September 16, 2007, he said.
According to the US National Snow and Ice Data Center (NSIDC), the record set on that date was 4.1 million sq km (1.6 sq mi). The discrepancy, Heygster explained by phone, was due to slightly different data sets and algorithms.
"But the results are internally consistent in both cases," he said, adding that he expected the NSIDC to come to the same conclusion in the coming days.
Arctic ice cover plays a critical role in regulating Earth's climate by reflecting sunlight and keeping the polar region cool.
Retreating summer sea ice -- 50 percent smaller in area than four decades ago -- is described by scientists as both a measure and a driver of global warming, with negative impacts on a local and planetary scale.
It is also further evidence of a strong human imprint on climate patterns in recent decades, the researchers said.
"The sea ice retreat can no more be explained with the natural variability from one year to the next, caused by weather influence," Heygster said in an statement released by the university.
"Climate models show, rather, that the reduction is related to the man-made global warming which, due to the albedo effect, is particularly pronounced in the Arctic."
Albedo increases when an area once covered by reflective snow or ice -- which bounces 80 percent of the Sun's radiative force back into space -- is replaced by deep blue sea, which absorbs the heat instead.The area covered by Arctic sea ice reached its lowest point this week since the start... more