In 2004, Dr Hansen returned to the subject. This time, he explained (pdf) that most of Arctic warming and melting is due to dirty snow from soot, not CO2.
"Soot snow/ice albedo climate forcing is not included in Intergovernmental Panel on Climate Change evaluations. This forcing is unusually effective, causing twice as much global warming as a CO2 forcing of the same magnitude," he wrote.
Once the snow dirties, it absorbs sunlight, warms, and quickly melts. Then the land and air above warms, causing higher temperature readings. This affects the Arctic more than the Antarctic simply because there aren't many people living near the Antarctic. The Arctic is polluted by European cities and oil fields in Siberia - where gas flaring generates huge amounts of soot.
In fact, scientists at the University of California have estimated that up to 94 per cent of Arctic melt is due to dirty snow.
In other words, then, Antarctic temperatures and ice are going the opposite direction of what Dr. Hansen predicted, and most of the Arctic warming is due to soot, not CO2. His own research directly contradicts his recent high-profile statements about the Arctic and CO2.
Dr Hansen also talks frequently about the unprecedented temperature rise in the Arctic, yet his own temperature records show that much of the Arctic (including Greenland) was warmer from 1920-1940 than now. The NASA graph below from Nuuk, Greenland is typical of long term records of the region.
Nuuk, Greenland is a key location because it is located in the southwest portion of the island and is not far from the mouth of the Jakobshavn Glacier - the most rapidly moving glacier in the world and a poster child for global warming campaigners. It is also the largest city and capital of Greenland, located just south of the Arctic Circle. NASA literature from the last few years focuses heavily on anomalous melt in southwest Greenland as a concern for sea level rise.
Temperature anamoly at Nuuk
During the ice age scare in the 1970s the Arctic cooled dramatically, and is only now returning to temperatures comparable to sixty years ago. Most of the other Arctic locations with long-term records show similar trends. Long-term NASA temperature records in the Arctic are very sparse, but most show a pattern similar to Nuuk. Most of the other Arctic locations with long-term records show similar trends.
Another pollution problem reported by NASA is known as the Arctic Haze. This is a human-generated brown cloud which hovers over the Arctic and traps heat. Additionally, we know that the summer of 2007 had unusually low cloud cover in the Arctic, which contributed to the unusual melt. But probably the most important factor in the anomalous "melt" was a spate of strong winds which blew all summer up the Bering Strait, across the pole and out into the warm waters of the North Atlantic. This compressed the sea ice towards Greenland and revealed a large area of open water north of Siberia and Alaska.