A paper was published in the journal Nature Geoscience this week describing an investigation into the influence of the Bering Strait on oceanic circulation between the Pacific, Arctic and Atlantic Oceans. The investigation found that sea-level fluctuations in the last glacial period were due primarily to changes in Northern Hemispheric ice sheet volumes and not solely to variable solar radiation. This study (and others in progress) was made possible by more supercomputing resources at NCAR in Boulder, CO.
The relationships between historical ice sheet volume, sea-level height, solar radiation and climatic effects are important to scientists’ efforts to accurately model and interpret model results from ongoing climate research.
The group ran two pairs of experiments: one pair with the North American ice sheets and one pair without. Within the pairs, all conditions were identical except on had an open Bering Strait and the other a closed Bering Strait. With an open Bering Strait, relatively fresh water is allowed to circulate from the Pacific Ocean into the Arctic Ocean and then into the Atlantic Ocean – the real world’s conditions for the past 70,000 years or so.
With a closed Bering Strait, that fresh water supply to the Atlantic is largely cut off. As a result, the overturning current in the Atlantic strengthens, redistributing heat and fresh water on the global scale in different ways. For instance, northeast North America warms up to 1.5 °C annually, while the North Pacific cools up to 1.5 °C and a smaller warming occurs over parts of Antarctica. Precipitation is reduced over most of North America. As a result, Northern Hemispheric ice sheets melt faster – at a rate of 0.112m per year. Over millenia, the North American and Greenland ice sheets thin by 560m, increasing global sea-levels by 33m. It is important to note that these experimental results match up well with observations.
Eventually, the rising sea-levels re-open the Bering Strait circulation. Pacific waters are then allowed to be transported to the Atlantic, weakening the overturning circulation and shifting heat and fresh water patterns. This process cools the North Atlantic while precipitation increases over North America. Cooler temperatures and more precipitation mean more snow lasts throughout the year to rebuild the ice sheet volumes. Sea levels eventually drop, closing off the Bering Strait and starting the cycle over again. The model results mesh well with observed ice sheet and sea-level trends observed in nature.
The way in which radiation has been observed (and now modeled) to influence sea-levels and ice sheet volumes does not match well with a simpler case of no Bering Strait influence. Thus, a prime result of this study indicates that changes in the radiation budget cannot account for climate shifts by itself. Processes like the Bering Strait’s modulation of climate are indeed very important for climatologists to consider and take into account. Put another way, the simple way in which climate change deniers view the world have been shown to once again not be sufficient to explain the real world.
I will also note that no mention was made in the paper of future climate scenarios with greatly reduced ice sheet volumes as a result of greenhouse gas pollution. Logically, one can speculate that deeper seas means more flow through the Bering Strait, leading to weaker circulations, cooler regions of the North Atlantic and more precipitation over North America. It could eventually act as a modulator on anthropogenic climate change (i.e. cooling a much warmer world), but the time-scales involved (many thousands of years) should be no comfort to policy makers in 2010. Once again, it is clear that the best way to deal with climate change is to reduce our system forcing.
Cross-posted at SquareState.