http://www.marshall.org/article.php?id=13
Arctic temperature records – According to the computer forecasts, climate over polar latitudes is very sensitive to global warming.
The forecasts say that the polar regions should have warmed by roughly 2 C in the last 50 years, enough to begin melting polar ice. Melting the polar ice produces a positive feedback that amplifies any warming. The reason is that ice reflects much of the sunlight and helps keep the polar regions cold. But as the temperature rises and the ice melts, the bare ground or sea underneath absorbs more of the Sun’s energy and magnifies the warming. One long-term view of the lower Arctic (Figure 4) comes from proxy records like tree-ring growth.[9]
There is a rapid warming in the record, but it began in the mid-19th century, and must be natural because it predates most of the rise in the air’s carbon dioxide concentration. This record suggests that the Arctic has cooled since 1950. Instrumental measurements (Figure 5) also contradict the intense warming trend projected by the computer scenarios. On the average over the last 40 years, the temperature does not show the large, increasing warming trends projected by the computer simulations.[10] That observed lack of warming may seem contradictory to recent newspaper reports of a thinning or diminishing extent of Arctic sea-ice.[11] However, sea ice will change in response to several factors, including not also temperature, but also ocean currents and salinity, wind, terrain, etc.
The recent observed sea-ice changes cannot have been caused by human-made global warming because Arctic temperatures are not showing the expected increasing warming trend. No increasing warming trend of the kind expected from human-made global warming has occurred in recent decades, when most of the increase in the air’s carbon dioxide concentration took place. In the test of the Arctic temperature record, the computer scenarios exaggerate the observed warming by more than ten-fold.