Effect of Global Warming and the Arctic As reported in the Intergovernmental Panel on Climate Change (IPCC), it is the certain fact that the earth's temperature is increasing. It has been said that the Arctic region is the one of the places which will be greatly affected by this world-known global warming phenomenon, and will affect the global climate. In this edition, we should like to introduce our research activities for global warming in relation to researches in the Arctic. Is the Sea Ice Decreasing Trend Caused by Global Warming? It has been said that there has been rapid decrease of the sea ice in the Arctic Ocean. Dr. Ikeda will explain the research on the relationship between global warming and decrease of sea ice. Motoyoshi Ikeda(Advisor, FRSGC's Program for International Arctic Research Center) T he sea ice cover in the Arctic Ocean has been decreasing greatly in last 40 years, equivalent to three times of Japan territory (Ikeda et al., 2003). Decadal oscillations are also remarkable in particular after 1970. Is it possible to relate the ice variability to the atmospheric variability? Is there any feedback from the ice cover to the atmosphere? Will the ice cover disappear as global warming proceeds? As suggested by Thompson and Wallace(1998), a major variability in the atmosphere is called the Arctic Oscillation (AO), whose positive phase is defined by a stronger cyclonic Polar Vortex. The AO has a clear decadal component. In Fig.1, a difference in the sea level pressure between two latitudinal circles is taken to show interannual variabilities. The ice-covered areas are shown in Fig.2. In summer, when open water appears in the Arctic Ocean, the ice areas clearly exhibit decadal oscillations and also the decreasing trends. We have found significant correlations in the decadal variabilities between the ice cover and the sea level pressure pattern (Fig.1). The decadal signals in the ice cover propagate from the Beaufort-Chukchi seas to the East Siberian-Laptev seas and to the Kara-Barents seas in four years, in which the positive AO matches with the minimum ice cover between the East Siberian-Laptev and the Kara-Barents.
		Fig.1 The time series of the sea level pressure difference in the averages between 85°N and 75°N in four seasons. The time series have been smoothed by Hanning filter. Fig.2 The time series of the ice-covered areas (Wang and Ikeda 2000) over Region 1-the Beaufort and Chukchi seas, Region 2-the East Siberian and Laptev seas and Region 3-the Kara and Barents seas. A 3-year running mean, Hanning filter, is applied. The linear trends are drawn after 1962.
		An idealized version of a coupled ice-ocean model is driven by the atmospheric data. The atmospheric pressure field is given the basic state, along with the Polar Vortex as a variable component at a 12-year period. As shown in Fig.3, the ice cover varies responding to the atmospheric pressure field similar to the observed variability.
		Fig.3 (a) The idealized version of coupled ice-ocean Arctic model, (b) ice thickness, its anomaly and sea level pressure from the top panel at four phases in one Arctic Oscillation period.
		Silicate concentration at 200-m depth in the Canada Basin. The newly distributed hydrochemical data have provided us to reveal an oceanic variability. In the Canada Basin, the silicate distribution represents the Pacific Water along with a secondary modification due to a biological production. The silicate has a maximum around a 100-m depth and a general downward decrease. Its variability at 200-m depth should correspond to a vertical motion of the Arctic Water. As the positive AO reduces Ekman transport toward the center of the Canada Basin, the water column goes up, and the silicate increases (Fig.4). Longwave radiation is a major component in the radiation balance over the Arctic. As shown in Fig.5, the clear sky ratio decreased, and hence, clouds and their downward longwave radiation increased in last 40 years. These effects reach 5 W/m 2 and are comparable with the effects of the albedo reduction associated with the recent ice cover reduction. A positive feedback is expected between an increase in clouds and a reduction of ice cover. The time series of the percentage of clear sky (0 to 2 tenths) in four seasons. The time series have been smoothed by Hanning filter. Although ice reduction is often related to global warming, we should more carefully look at various components in the observed and modeled trends in a global warming experiment. The key component for a successful prediction is a feedback mechanism from the ice-ocean to the atmosphere. More approaches should be directed to summer. A coupled atmosphere-ice-ocean model may be useful to represent an oceanic heat storage, which can carry the effects in summer to the following winter. References Ikeda, M., Wang, J., and A. Makshtas, 2003: Importance of clouds to the decaying trend in the Arctic ice cover. J. Meteorol. Soc. Japan (in press). Polyakov, I. V., and M. A. Johnson, 2000: Arctic decadal and inter-decadal variability, Geophys. Res. Lett., 27, 4097-4100. Thompson, D. W. J. and J. M. Wallace, 1998: The Arctic Oscillation signature in the wintertime geopotential height and temperature fields. Geophys. Res. Lett., 25, 1297-1300. Wang, J., and Ikeda, M., 2000: Arctic oscillation and Arctic sea iceoscillation, Geophys. Res. Lett., 27, 1287-1290.