The Reuters article below uses the following words: "perhaps;" "continued warming could threaten;" "probably." Plus there is the obligatory "if" and "then you can reach a point of no return." Alister Doyle of Reuters must be following a standard script for these articles, if, then, possibly, maybe, could, might and of course cherry picking the years.
Surprisingly the article does note the warming around 1940. (Note: Before 80% of man-made CO2 was in the atmosphere): "Hanna said that there was also a warm period around 1940 in Greenland -- but that warming was triggered by natural variations in the Arctic climate, perhaps shifts in ocean currents. This time, the Greenland warming fits a far broader trend across the planet." How do they know that the c.1940 warm up was "natural variations" but today's recent warming "fits a far broader trend across the planet." It's just an assertion
Climate change has caused the greatest thaw of Greenland's ice in half a century, perhaps heralding a wider meltdown that would quicken a rise in world sea levels, scientists said on Tuesday. "We attribute significantly increased Greenland summer warmth and ice melt since 1990 to global warming," a group of researchers wrote in the Journal of Climate, adding to recent evidence of faster Antarctic and Arctic thaws. "The Greenland ice sheet is likely to be highly susceptible to ongoing global warming," they said. Greenland contains enough ice to raise world sea levels by 7 metres, a process that would take centuries if it were to start.
Melt water from Greenland -- excluding ice losses from glaciers slipping into the sea -- totalled 453 cubic kms in 1998, the most ahead of 2003, 2006, 1995 and 2002 in detailed records stretching back to the 1950s. Preliminary data showed that 2007 would rank second or third highest and confirm the last decade as the biggest melt, said Edward Hanna of England's University of Sheffield who led the study with colleagues in Belgium, the United States and Denmark. So far, the water runoff has been largely offset by rising snowfalls in Greenland that may also be a side-effect of climate change. Even freezing air can hold more moisture, and so deliver more snow, if it gets slightly less chilly.
But continued warming could threaten an irreversible meltdown. The report noted that typical climate models pointed to a warming for Greenland of 4-5 degrees Celsius (7.2 to 9 Fahrenheit) by 2100. "The ice probably wouldn't grow back under current conditions," Hanna said. "If you have an extra 3-5 degrees Celsius warming ... then you can reach a point of no return ... bringing the eventual demise of the ice sheet. That could take probably 1,000 or 2,000 years," he said.
On Monday, a climate researcher said that Antarctica lost billions of tonnes of ice over the last decade, contributing more to rising sea levels around the world. The U.N. Climate Panel, which blames global warming mainly on human emissions of greenhouse gases from burning fossil fuels, projects a rise in sea levels of between 18 cms and 59 cms (7 and 23 inches) by 2100. The panel assumes that the little-understood rate of ice flow from Greenland and Antarctica will not change from 1993-2003, when their mass losses accounted for less than half of annual sea level gains of 3.1 millimetres (0.12 inch).
Hanna said that there was also a warm period around 1940 in Greenland -- but that warming was triggered by natural variations in the Arctic climate, perhaps shifts in ocean currents. This time, the Greenland warming fits a far broader trend across the planet.
RECENT PAPER ON THE HISTORY OF GREENLAND ICE MASS
Showing that, although the Greenland melt has increased during the 1992-2006 period, the melt was even higher in 1900s, 1930s, 1940s, 1950s and 1960s. So there is no indication that the current melt is above natural climate variability. Of course people who look just on the 1990 to 2007 period "see" great melting acceleration and influence of carbon dioxide and anthropogenic climate change.
Remote sensing of Greenland ice sheet using multispectral near-infrared and visible radiances
By Petr Chylek et al.
We present the physical basis of and validate a new remote-sensing algorithm that utilizes reflected visible and near-infrared radiation to discriminate between dry and wet snow. When applied to the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data, our discrimination algorithm has the potential to retrieve melting regions of the ice sheet at a spatial resolution of 0.25 km2, over three orders of magnitude higher than the resolution of current microwave methods. The method should be useful for long-term monitoring of the melt area of the Greenland ice sheet, especially regions close to ice sheet margins and of the outflow glaciers. Our analysis of MODIS retrievals of the western portion of the Greenland ice sheet over the period 2000 to 2006 indicates significant interannual variability with a maximum melt extent in 2005. Collocated in situ meteorological data reveal a high correlation (0.80) between the MODIS melt-day area and the average summer temperature. Our analysis suggests that it is the magnitude of the summer temperature that dominates the melting (not the variability of the length of the melting season). Furthermore, we find that the melt-day area increases by about 3.8% for each 0.1 K increase in the average surface air summer temperature. We combine this empirical relationship with historic temperature data to infer that the melt-day area of the western part of the ice sheet doubled between the mid-1990s and mid-2000s and that the largest ice sheet surface melting probably occurred between 1920s and 1930s, concurrent with the warming in that period.
Citation: Chylek, P., M. McCabe, M. K. Dubey, and J. Dozier (2007), Remote sensing of Greenland ice sheet using multispectral near-infrared and visible radiances, J. Geophys. Res., 112, D24S20, December 2007
Posted by John Ray