Ice In The Greenhouse:
Earth May Be Cooling, Not Warming
By Jens Bischof
Climate change has become a topic of great public interest. Hardly a week goes by without newspaper articles proclaiming global warming, the greenhouse effect, melting polar ice caps and retreating glaciers. No self-respecting weather forecaster can resist the temptation to see a connection between slightly abnormal weather patterns and El Nino, the eternal culprit. And while it is clear that the burning of fossil fuels such as petroleum, coal and wood, and the ensuing rise of carbon dioxide levels in the atmosphere must trigger a reaction of the global climate system, it is completely unknown exactly what kind of reaction will occur.
Indeed, there are signs from some natural systems that global warming is under way. Observations of the pack-ice thickness of the Arctic Ocean from submarines with upward-looking sonar, for example, show a thinning trend since the 1970s. The margin of permafrost is moving north, and the vegetation in the high northern parts of the world is changing toward more temperate forms. But it is by no means clear whether these signs indicate real, worrying proof of manmade, permanent and potentially disastrous climate change, or just regular, naturally occurring variations in the Earths climate system.
If proven a reality, the most troubling aspect of global warming is that it would cause melting of the polar ice caps, which in turn would cause the global sea level to rise and flood some of the most densely populated regions on Earth. Other effects could be changes in rainfall patterns, which could lead to widespread droughts and threaten agricultural production. One need not be a prophet to imagine the ultimate consequences: forced emigration of unprecedented scale into higher elevations, straining the economies and societies of the involuntary host nations, causing political turmoil and, knowing how humans traditionally react to such changes, most likely war.
But are these assumptions correct? In science, as in other sectors of public life, outcomes of investigations are very often guided, if not determined, by an a priori idea, a tenet. One could also call it a belief. In the case of global warming, this belief is that, if enormous amounts of greenhouse gases are released into the atmosphere, a temperature rise must occur. This prior assumption has guided scientific thinking and triggered a true deluge of investigations, all desperately trying to prove just that. What has been totally forgotten is the fact that natural climate changes occur as well as manmade ones, and on time scales on the order of decades, in some cases.
Overdue Cold Snap
I believe the only way to detect these changes is from the geologic record of marine sediments. In the high northern latitudes, those sediments contain ice-rafted debris, or IRD. The IRD is deposited on or within ice sheets, portions of which eventually calve as icebergs and then travel on vast ocean currents. The composition and movement of this drifting ice can provide insights into the future direction of climate change. Contrary to the prevailing beliefs inside and out of the scientific community, my studies indicate that warming may not be the direction in which global climate is headed after all.
The last 10,000 years of geological history are referred to as the Holocene Era. During that time, global climate has been relatively stable, with swings from warmer temperatures to cooler and back again. On average, however, there has not been the kind of extreme climate oscillation that has in the distant past led to periods of glaciation. Nevertheless, Earth is overdue for a cold snap. Close examination of the way ice is presently traveling in ocean water, from frigid to warmer regions of the globe, suggests that the mechanisms for widespread planetary cooling may once again be engaging.
Ice rafting is a simple idea: particles such as stones, pebbles and fine grains become embedded in ice. As that ice drifts, it melts, depositing those particles in oceanic sediments, leaving a drift track indicative of its source. Geologists are then able to reconstruct past ice-drift directions by finding a method by which particles can be connected to a specific point of origin.
The process of ice rafting is intimately connected to temperature changes on global and regional scales. The physical movement of excessive amounts of ice from polar regions to lower latitudes by shifting ocean currents can lead to substantially lower temperatures. If, for example, the air pressure distribution over the Arctic Ocean was such that winds blew from the Bering Strait across the North Pole toward Fram Strait, then massive amounts of pack ice would be moved into the Norwegian Greenland Sea. In the winter, this process would continuously produce additional sea ice in the open leads created by offshore winds in the Bering Strait region, setting in motion a veritable ice machine. The regional extent of ice and snow cover in the Greenland Sea would increase, cooling the region, and boosting the albedo, or amount of solar radiation reflected back into space, further amplifying cooling.
Depending on the strength and duration, this process could lead to an episode of relatively cold climate over the North Atlantic region, perhaps lasting from a few years up to decades. But if it were sufficiently strong and durable, it could set the stage for global climate to return to full glaciation.
Ice As Predictor
If sea ice were to thicken and expand by other means, such as cooling forced by celestial mechanisms, including variation in solar radiation or orbital changes, declining temperatures would occur seasonally, during winter and summer, but also on much longer time scales, such as thousands and tens of thousands of years. Polar fronts would be pushed toward the Equator. Such cooling is self-perpetuating, increasing the extent of snow- and ice-covered regions, thus augmenting the albedo. The albedo increase, in turn, further amplifies the cooling trend, creating a positive feedback loop that leads to additional cooling, which leads to more ice and snow, higher albedo and more cooling.
Global cooling brought on by ice drift, however, does not require an external motor, such as the periodic variation in the Earths orbit that brings it closer to or farther away from the Sun, or a slight change in the tilt of the Earths axis, also periodic. Rather, a mere change of the ice-drift direction in the Arctic could set cooling on its way, possibly even on a global scale. The geologic record is certainly clear: The climate pendulum has repeatedly swung between a relatively warmer worldas we experience today, and glacial climates during which much of Earth was submerged under thick sheets of ice.
In my book Ice Drift, Ocean Circulation And Climate Change, I look not just at older data that otherwise would never have seen the light of day but also new data that I believe is persuasive that ice drifting can be as predictive as it is archival. That is, to understand the future, at least in terms of climate, one must understand the past. Any computer model designed to predict future climate change such as greenhouse gas-induced global warming must also reproduce the reconstructed past changes of ice drift in order to be considered reliable. Ice rafting is not just a passive recorder of past surface-ocean circulation, but also actively influences and changes present ocean circulation as well.
At present we do not yet know if the circulation changes occur over one or more decades relevant to humans. This is simply because the low, and in some cases, very low sedimentation rates of the polar oceans do not permit time resolution at these short scales. But recent progress in the analysis of Arctic Ocean sediments has shown that it is possible to find areas with high resolution. This, and the prospect of new equipment in the form of a polar icebreaker able to be on station 200 days per year, hold the promise that the mystery of the driving forces of climate change may be eventually solved.
In the meantime, we should prepare ourselves for the possibility that our cherished ideas about global warming may be, if not dead wrong, only partially correct. Intriguing recent evidence gathered from ice-rafted debris looks remarkably similar to a much older pattern that preceded an ice age. We may have to entertain the possibility that Earths natural climate development may be on a return to another such period, or at least to colder conditions than we now experience. If so, and ironically, the very greenhouse warming we fear may either mitigate the cooling or cancel it altogether.
Jens Bischof is author of Ice Drift, Ocean Circulation And Climate Change and is a research assistant professor in Old Dominions Department of Ocean, Earth and Atmospheric Sciences.