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NASA Finds Arctic Replenished Very Little Thick Sea Ice since 2005
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Authoritative Report Confirms Human Activity Driving Global Warming
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NASA Finds Arctic Replenished Very Little Thick Sea Ice in 2005

A new NASA study has found that in 2005 the Arctic replaced very little of the thick sea ice it normally loses and replenishes each year. Replenishment of this thick, perennial sea ice each year is essential to the maintenance and stability of the Arctic summer ice cover.

The findings complement a NASA study released in fall 2006 that found a 14-percent drop in this perennial ice between 2004 and 2005. The lack of replenishment suggests that the decline may continue in the near future.



Image right: QuikScat measurements of Arctic perennial sea ice coverage (shown in red) in winter 2006 were 14-percent less than in winter 2005. Image credit: NASA/JPL

Perennial ice coverage fluctuates seasonally for two reasons: summer melting and the transport of ice out of the Arctic. When perennial ice, which is three or more meters (10 or more feet) thick, is lost in these ways, new, thinner, first-year seasonal ice typically replaces it. Some of this seasonal ice melts in the following summer, and some is thick enough to survive and replenish the perennial ice cover.

"Recent studies indicate Arctic perennial ice is declining seven to 10 percent each decade," explained Ron Kwok of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Our study gives the first reliable estimates of how perennial ice replenishment varies each year at the end of summer. The amount of first-year ice that survives the summer directly influences how thick the ice cover will be at the start of the next melt season."

Using satellite data from NASA's QuikScat and other data, Kwok studied six annual cycles of Arctic perennial ice coverage from 2000 to 2006. The scatterometer instrument on QuikScat sends radar pulses to the surface of the ice and measures the echoed radar pulses bounced back to the satellite. These measurements allow scientists to differentiate the seasonal ice from the older, perennial ice.

Kwok found that after the 2005 summer melt, only about four percent of the nearly 2.5 million square kilometers (965,000 square miles) of thin, seasonal ice that formed the previous winter survived the summer and replenished the perennial ice cover. That was the smallest replenishment seen in the study. As a result, perennial ice coverage in January 2006 was about 14 percent smaller than the previous January.

Kwok examined how movement of ice out of the Arctic affected the replenishment of perennial sea ice in 2005. That year, the typically small amount of ice that moves out of the Arctic in summer was unusually high -- about seven percent of the perennial ice coverage area. Kwok said the high amount was due to unusual wind conditions at Fram Strait, an Arctic passage between Antarctic Bay in Greenland and Svalbard, Norway. Troughs of low atmospheric pressure in the Greenland and Barents/Norwegian Seas on both sides of Fram Strait created winds that pushed ice out of the Arctic at an increased rate.



The effects of ice movement out of the Arctic depend on the season. When ice moves out of the Arctic in the summer, it leaves behind an ocean that does not refreeze. This, in turn, increases ocean heating and leads to additional thinning of the ice cover.

These findings suggest that the greater the number of freezing temperature days during the prior season, the thicker the ice cover, and the better its chances of surviving the next summer's melt. "The winters and summers before fall 2005 were unusually warm," Kwok said. "The low replenishment seen in 2005 is potentially a cumulative effect of these trends."

Kwok also examined the 2000-2006 temperature records within the context of longer-term temperature records dating back to 1958. He found a gradual warming trend in the first 30 years, which accelerated after the mid-1980s. "The record doesn't show any hint of recovery from these trends," he stated. "If the correlations between replenishment area and numbers of freezing and melting temperature days hold long-term, its expected the perennial ice coverage will continue to decline."

Kwok points to a possible trigger for the declining perennial ice cover. In the early 1990s, variations in the North Atlantic Oscillation, a large-scale atmospheric seesaw that affects how air circulates over the Atlantic Ocean, were linked to a large increase in Arctic ice export. It appears the ice cover has not yet recovered from these variations.

"We're seeing a decreasing trend in perennial ice coverage," he said. "Our study suggests that, on average, the area of seasonal ice that survives the summer may no longer be large enough to sustain a stable perennial ice cover, especially in the face of accelerating climate warming and Arctic sea ice thinning."

Data from the 2005-06 season have not yet been analyzed.

The study appeared March 2 in Geophysical Research Letters.

For more information about QuikScat, visit: http://winds.jpl.nasa.gov/index.cfm.

JPL is managed for NASA by the California Institute of Technology in Pasadena.

Record breaking temperatures seen as evidence of faster rate of global warming

WASHINGTON -- Researchers at NOAA's National Climate Data Center (NCDC) have found evidence that the rate of global warming is accelerating and that in the past 25 years it achieved the rate of two degrees Celsius (four degrees Fahrenheit) per century. This rate had previously been predicted for the 21st Century.

Writing in the March 1 issue of Geophysical Research Letters, Dr. Thomas R. Karl, Director of NCDC, and colleagues analyze recent temperature data. They focus particularly on the years 1997 and 1998, during which a string of 16 consecutive months saw record high global mean average temperatures. This, Karl notes, was unprecedented since instruments began systematically recording temperature in the 19th Century. During much of 1998, records set just the previous year were broken.

Karl and his colleagues conclude that there is only a one-in-20 chance that the string of record high temperatures in 1997-1998 was simply an unusual event, rather than a change point, the start of a new and faster ongoing trend. Since completing the research, the data for 1999 have been compiled. They found that 1999 was the fifth warmest year on record, although as a La Nina year it would normally be cooler. Outside the band between 20 degrees north latitude and 20 degrees south latitude, 1999 was the second warmest year of the 20th Century, just behind 1998, an El Nino year.

The researchers at NCDC, part of the National Oceanic and Atmospheric Administration (NOAA), based in Asheville, North Carolina, analyzed data from land based and satellite instruments for their study. They conclude that the rate of warming since 1976 is clearly greater than the average rate over the late 19th and 20th Centuries. To account for the string of record setting temperatures, the average rate of global temperature increase since 1976 would have to be three degrees Celsius (five degrees Fahrenheit) per century.

In its Second Assessment Report in 1995, the Intergovernmental Panel on Climate Change (IPCC) projected the rate of warming for the 21st Century to be between one and 3.5 degrees Celsius (two and six degrees Fahrenheit). Karl and his colleagues have already observed over the past 25 years a rate that is between two and three degrees Celsius (four and five degrees Fahrenheit) per century. The IPCC study used a "business as usual" scenario with regard to manmade influences on climate, such as carbon dioxide and other atmospheric constituents.

Karl and his colleagues are not ready to say with certainty that the rate of global warming has suddenly increased, because they recognize that unusual events sometimes happen. There is strong evidence, they say, that the faster rate of climate change since 1976 is human-induced. Given the steady increase in atmospheric greenhouse gases and the length of time, ranging from decades to centuries, that they remain in the atmosphere, they urge that studies be conducted to enable society to minimize the risks of climate change and prepare for more, and perhaps even more rapid, changes to come.

Harvey Leifert
American Geophysical Union

Source: http://eob.gsfc.nasa.gov/Newsroom/MediaAlerts



Greenhouse gases are air pollutants under the Clean Air Act: U.S. policy on global warming today

The Supreme Court ordered the federal government today to take a fresh look at regulating carbon dioxide emissions from cars. In a 5-4 decision, the court said the Clean Air Act gives the Environmental Protection Agency the authority to regulate the emissions of carbon dioxide and other greenhouse gases from cars. Greenhouse gases are air pollutants under the landmark environmental law, Justice John Paul Stevens said in his majority opinion. The case is Massachusetts v. EPA, 05-1120.

Greenhouse gases, flowing into the atmosphere and oceans at an unprecedented rate, are leading to larger extreme climatic events, rising sea levels and other marked ecological changes.

The politics of global warming have changed dramatically since the court agreed last year to hear its first global warming case. Business leaders are saying they are increasingly open to congressional action to reduce greenhouse gases emissions, of which carbon dioxide is the largest. Carbon dioxide is produced when fossil fuels such as oil and natural gas are burned.

The court had three questions before it.

  1. Do states have the right to sue the EPA to challenge its decision?
  2. Does the Clean Air Act give EPA the authority to regulate tailpipe emissions of greenhouse gases?
  3. Does EPA have the discretion not to regulate those emissions?

The court said yes to the first two questions. On the third, it ordered EPA to re-evaluate its contention it has the discretion not to regulate tailpipe emissions. The court said the agency has so far provided a "laundry list" of reasons that include foreign policy considerations. The majority said the agency must tie its rationale more closely to the Clean Air Act.

The decision also is expected to boost California's prospects for gaining EPA approval of its own program to limit tailpipe emissions of greenhouse gases. Federal law considers the state a laboratory on environmental issues and gives California the right to seek approval of standards that are stricter than national norms.

(Source: GWIC)