Forgotten in all this is that U.S. temperatures are only a small part of the global mean average temperatures, which remain unchanged even with NASA's re-calculation. Nine of the 10 hottest years globally have occurred in the last decade, although that is not the case in the United States, where there were several very warm years in the 1930s.
Now the warning: The complete collapse of the massive Greenland Ice Sheet -- which has a mean height of about two kilometres -- now appears inevitable, and could raise sea levels seven metres.
"It's a sobering message, I think," says Tim Lenton, of the School of Environmental Sciences at Britain's University of East Anglia.
Lenton's research group surveyed climate and glacial experts around the world and the consensus is that the recent evidence shows that rising temperatures will soon reach the Greenland Ice Sheet's "tipping point," where it will break up within 300 years, raising sea levels by seven metres and flooding millions out their homes long before the year 2300.
Recent calculations show the Greenland collapse could be triggered by temperature rise of just 1 degree Celsius warmer than today. This is an example of what scientists call a "non-linear response," in which a small change can make a big difference, more commonly described as "tipping points."
And this point is coming much sooner than it looks. Due to a time lag in the atmospheric warming response, even if there were no more greenhouse gas emissions from this day forward, temperatures would still rise another 0.6 degrees Celsius.
"I don't want to say the Greenland meltdown is inevitable, but it will be very difficult to avoid," Lenton told IPS.
James Hansen, head of NASA's Goddard Institute for Space Studies, believes that without drastic international efforts, a sea level rise of up to five metres is possible before the end of this century.
"In my opinion, if the world warms by 2 to 3 degrees Celsius, such massive sea level rise is inevitable, and a substantial fraction of the rise would occur within a century," Hansen wrote in the Jul. 25 issue of New Scientist magazine.
He notes that the last time the Earth was that much warmer was around three million years ago: "It was a dramatically different planet then, with no Arctic sea ice in the warm seasons and sea level about 25 metres higher, give or take 10 metres."
This Northern Hemisphere summer, the amount of sea ice in the Arctic is 30 percent lower than normal, and is expected to be the lowest ever recorded, the U.S. National Snow and Ice Data Center (NSIDC) reported last week. It may be that the Arctic sea ice has already passed its tipping point, in which warming temperatures and a "positive ice-albedo feedback" (ice reflectivity) will inevitably result in less and less ice until the Arctic is ice-free in the summer, says Lenton.
While sea ice does not result in sea level rise, it adds more fresh, cold water to the North Atlantic which, along with massive amounts of Greenland Ice Sheet meltwater, has the potential to slow or reverse the Atlantic Ocean thermohaline circulation (THC).
The THC, sometimes called the ocean conveyor belt, drives the deep currents in the oceans around the world. In the Atlantic Ocean, warm waters from the Gulf of Mexico are transported north-east to help moderate temperatures in the British Isles, Ireland and Northern Europe.
The THC is another potential climate tipping point where a rapid shift could occur. If the Atlantic THC reversed, not only would Northern Europe cool, the southern oceans around Antarctica would warm, according to Lenton's analysis soon to be published.
"It's a case of 'domino dynamics.' These are interrelated systems where a change in one affects the others," he said.
A warmer Southern Ocean will rapidly accelerate the current slow rate of melting of the vast West Antarctic ice sheet. A complete collapse of that ice sheet would raise sea levels an additional four to six metres, but that point is unlikely to be reached for another 300 years.
Global temperature rise between 3 to 6 C degrees will not only melt a lot of ice, it will greatly strengthen the El Nino Southern Oscillation, research shows. Among its impacts will be severe droughts in Southeast Asia, the Amazon and elsewhere. El Nino is a cyclical climate phenomenon arising from a warm Pacific Ocean surface current travelling from west to east.
The Intergovernmental Panel on Climate Change estimates a temperature rise this century of at least 1.4 C to as much as 6.4 C degrees in its 2007 assessment report.
"The Indian summer monsoon system could also be in for a rocky ride this century," says Lenton. The Indian monsoon system appears to be sensitive to changes in conditions, switching on and off unpredictably with climate change and affecting millions of people.
Of all these potential events, the melting of Greenland Ice Sheet is both the first and most likely tipping point we will reach. Preparations for coping and adapting to the resulting sea level rise would have to begin now. In addition, strict mitigation efforts are also needed to reduce both the speed and extent of sea level rise and to avoid crossing other potential tipping points, he said.
The public and policy-makers need to be aware of this non-linearity -- that climate change impacts will not be gradual. "Change can come quickly and with a huge escalation in damages and costs," Lenton warns.
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Albion Monitor August
18, 2007 (http://www.albionmonitor.com)
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