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RISS 인기검색어
- 검색키워드
- 저자 : Steig, Eric J. (검색결과 3 건)
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Tropical forcing of the recent rapid Arctic warming in northeastern Canada and Greenland
Ding, Qinghua,Wallace, John M.,Battisti, David S.,Steig, Eric J.,Gallant, Ailie J. E.,Kim, Hyung-Jin,Geng, Lei Nature Publishing Group, a division of Macmillan P 2014 Nature Vol.509 No.7499
Rapid Arctic warming and sea-ice reduction in the Arctic Ocean are widely attributed to anthropogenic climate change. The Arctic warming exceeds the global average warming because of feedbacks that include sea-ice reduction and other dynamical and radiative feedbacks. We find that the most prominent annual mean surface and tropospheric warming in the Arctic since 1979 has occurred in northeastern Canada and Greenland. In this region, much of the year-to-year temperature variability is associated with the leading mode of large-scale circulation variability in the North Atlantic, namely, the North Atlantic Oscillation. Here we show that the recent warming in this region is strongly associated with a negative trend in the North Atlantic Oscillation, which is a response to anomalous Rossby wave-train activity originating in the tropical Pacific. Atmospheric model experiments forced by prescribed tropical sea surface temperatures simulate the observed circulation changes and associated tropospheric and surface warming over northeastern Canada and Greenland. Experiments from the Coupled Model Intercomparison Project Phase 5 (ref. 16) models with prescribed anthropogenic forcing show no similar circulation changes related to the North Atlantic Oscillation or associated tropospheric warming. This suggests that a substantial portion of recent warming in the northeastern Canada and Greenland sector of the Arctic arises from unforced natural variability.
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Centennial-scale changes in the global carbon cycle during the last deglaciation
Marcott, Shaun A.,Bauska, Thomas K.,Buizert, Christo,Steig, Eric J.,Rosen, Julia L.,Cuffey, Kurt M.,Fudge, T. J.,Severinghaus, Jeffery P.,Ahn, Jinho,Kalk, Michael L.,McConnell, Joseph R.,Sowers, Todd Nature Publishing Group, a division of Macmillan P 2014 Nature Vol.514 No.7524
Global climate and the concentration of atmospheric carbon dioxide (CO<SUB>2</SUB>) are correlated over recent glacial cycles. The combination of processes responsible for a rise in atmospheric CO<SUB>2</SUB> at the last glacial termination (23,000 to 9,000 years ago), however, remains uncertain. Establishing the timing and rate of CO<SUB>2</SUB> changes in the past provides critical insight into the mechanisms that influence the carbon cycle and helps put present and future anthropogenic emissions in context. Here we present CO<SUB>2</SUB> and methane (CH<SUB>4</SUB>) records of the last deglaciation from a new high-accumulation West Antarctic ice core with unprecedented temporal resolution and precise chronology. We show that although low-frequency CO<SUB>2</SUB> variations parallel changes in Antarctic temperature, abrupt CO<SUB>2</SUB> changes occur that have a clear relationship with abrupt climate changes in the Northern Hemisphere. A significant proportion of the direct radiative forcing associated with the rise in atmospheric CO<SUB>2</SUB> occurred in three sudden steps, each of 10 to 15 parts per million. Every step took place in less than two centuries and was followed by no notable change in atmospheric CO<SUB>2</SUB> for about 1,000 to 1,500 years. Slow, millennial-scale ventilation of Southern Ocean CO<SUB>2</SUB>-rich, deep-ocean water masses is thought to have been fundamental to the rise in atmospheric CO<SUB>2</SUB> associated with the glacial termination, given the strong covariance of CO<SUB>2</SUB> levels and Antarctic temperatures. Our data establish a contribution from an abrupt, centennial-scale mode of CO<SUB>2</SUB> variability that is not directly related to Antarctic temperature. We suggest that processes operating on centennial timescales, probably involving the Atlantic meridional overturning circulation, seem to be influencing global carbon-cycle dynamics and are at present not widely considered in Earth system models.
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Strong Sensitivity of Pine Island Ice-Shelf Melting to Climatic Variability
Dutrieux, Pierre,De Rydt, Jan,Jenkins, Adrian,Holland, Paul R.,Ha, Ho Kyung,Lee, Sang Hoon,Steig, Eric J.,Ding, Qinghua,Abrahamsen, E. Povl,Schrö,der, Michael American Association for the Advancement of Scienc 2014 Science Vol.343 No.6167
<P><B>Cold Glacier Growth</B></P><P>Pine Island Glacier in Antarctica has thinned significantly during the last two decades and has provided a measurable contribution to sea-level rise as a result. Both glacier dynamics and climate are thought to be responsible for thinning, but exactly how they influence the glacier are incompletely known. <B>Dutrieux <I>et al.</I></B> (p. 174, published online 2 January) provide another layer of detail to our understanding of the process through observations of ocean temperatures in the surrounding waters. The thermocline adjacent in the sea adjacent to the glacier calving front (where ice is discharged) lowered by 250 meters in the austral summer of 2012. This change exposed the bottom of the ice shelf to colder surface waters rather than to the warmer, deeper layer, thereby reducing heat transfer from the ocean to the overlying ice and decreasing basal melting of the ice by more than 50% compared to 2010. Those 2012 ocean conditions were partly caused by a strong La Niña event, thus illustrating how important atmospheric variability is for regulating how the Antarctic Ice Sheet responds to climate change.</P>
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