Brief Review Of The Methodologies Applied

Attempts at super-long forecasts of ice extent for some regions of the Arctic Ocean have a long history. They have mainly focused on the sub-Atlantic part of the Arctic, because long series of ice observations are available for that area. Maksimov (1955) made the first forecast, based on space-geophysical factors and, primarily, a century-long cycle of solar activity. According to this forecast, maximum ice extent in the region was expected in 1990. This forecast, however, was not correct (nor were other forecasts based on the "100-year" cycle of solar activity). In updating Maksimov's forecast, Latukhov and Sleptsov-Shevlevich (1995) based their work on the relationship of ice extent and the magnetic perturbation index Kp, which also reflects the 100-year cycle; they predicted that maximum ice extent in 2000-2020 would be comparable to the conditions of the early twentieth century. As we can see now, this prediction was also incorrect. The results of reconstructing ice extent changes in the eighteenth and nineteenth centuries presented by these authors suggests some doubt about the validity of their methodology. According to their results, the second half of the nineteenth century was distinguished by decreased ice extent in the sub-Atlantic region of the Arctic. However, data collected by Norwegian scientists (Vinje, 2000) showed that during this period, increased ice extent was observed there.

Rudyaev et al. (1985) provided a more realistic climate forecast for the first half of the twenty-first century based on 65-year and 33-year cycles in the Earth's rotation speed. This forecast predicts maximum warming between 2005 and 2010, followed by a period of cooling that will last until the middle of the century. It seems likely that the Earth's rotation speed is an important indicator of climate change as large-scale anomalies of air temperature, atmospheric circulation, and ice extent are statistically connected with it. The angular speed increases during periods of climate warming and decreases during periods of cooling. The proposed physical mechanism for this relationship is based on the assumption that large-scale anomalies in atmospheric circulation lead to changes in west-to-east atmospheric circulation in temperate latitudes, with corresponding changes in the integral moment of wind tangential stress at Earth's surface and resulting significant changes in the planet's angular rotation speed after about 10 years. The correlation coefficient between the mean annual values of Earth's angular rotation speed in the twentieth century and the NAO index showing west-to-east air transport about 10 years later is 0.85 (Gudko-vich et al., 2004).

Co-authors of the monograph (Climatic Regime, 1991) detected a 15-year phase shift between fluctuations in ice extent and pole deflection, and predicted ice extent in the Arctic Ocean and the Kara Sea for 1990-2005. Ice extent was expected to reach its maximum by 2005 and not to exceed the anomalies observed in the twentieth century. However, by 2005, no significant increase in average ice extent was observed. The same study also touches upon the possible influence of dissymmetry of the solar system's center of mass on average air temperature, and suggests some increase in temperature by 2005.

Gudkovich and Kovalev (2002b) forecast average anomalies in total ice extent of North Asian shelf seas by 5-year periods through the middle of the twenty-first century. The forecast is based on a physical-statistical model that incorporates the long-period cyclic changes and the linear trend of the twentieth century. It assumes a gradual growth in total ice extent during the first half of the twenty-first century, with a maximum expected in the middle of the second quarter (2025-2050) of the century. These changes in ice extent are within the framework of actual fluctuations observed in the twentieth century.

Forecasts of twenty-first century changes in Arctic Ocean ice extent developed by the supporters of a decisive role for greenhouse gas accumulation in climate change and based on coupled ocean-atmosphere models, are discussed in Section 5.1.

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