Glacier melting and sea levels in the 21st century
Not so long ago climatologists, faced with a man made increase in greenhouse gases of about 100 ppm over the last hundred fifty years or so, had the impression that the increased temperatures experienced on land and in the oceans would nevertheless move very slowly, perhaps over hundreds if not thousands of years, before the warming trend significantly impacted on the huge ice packs of Greenland and the Antarctic. But in recent years, giant ice sheets have been detached from these regions and scientists are now puzzled to explain it and eager to re-evaluate how much more rapidly the destruction of giant glaciers is taking place in these regions and the mechanisms by which this is being achieved. This is the new alarming worry in the field of global climate change: how quickly will ocean levels rise? Models of just a few years ago need to be thrown out and replaced with more accurate models, but we don’t yet grasp all the variable needed to make more accurate projections. The two massive ice deposits of Greenland and the Antarctic could, if completely melted, raise the sea level by seventy meters, or more than 200 ft. Should that happen, Florida will be underwater and the Mississippi Riverwill drain into the Gulf of Mexico at the level of Tennessee. Right now, new energies are being focused onto Greenland and the Antarctic region to determine what level of sea water rise can be expected by the end of the century (2100). It is clear that previous estimates and models used for evaluating this problem have been inadequate, but revision of these numbers and estimates will require a lot more study. One issue hampering more detailed analysis of these regions is the loss of satellites that could be used to gather such data on a regular basis. Many of our satellites have come down and have not been replaced. Fortunately, Obama has re-directed NASA’s effort (Bush wanted to send another man to the moon) to focus more on the science of climate change and bills have been passed to achieve this, but funding has yet to be provided.
The central problem with our glaciers is that the water underneath them seems to be warm enough (40 degrees) to melt the ice above them and make glaciers move faster towards the ocean and dissolve more quickly. Not long ago, these ice sheets were considered to be in equilibrium–whatever they lost during warmer months into the ocean, was recaptured during colder periods from more snow. This equilibrium concept has been shattered in recent years by huge chunks of ice that have broken off by mechanisms that are not yet well understood, but thinning of the ice from warm water below is a major suspect, though still an unproven one. Just how this warm water is reaching regions of Greenland and the Antarctic is unclear, but changes in ocean current patterns, another feature of global climate change, might be forcing warmer water to these regions. We can look for this problem to receive intensive study in the future, as this will be the most obvious affect of global climate change that will require changes in social planning well in advance, especially for cities such as London and New York (to name just a few) that will have to accommodate more inundation from the sea. These cities may require an elaborate dike system, like those of the Netherlands.
Scientists are urged to quickly come up with a figure for the global rise in sea level that will be present in the year 2100. The main alarm is whether the ocean levels will rise faster than global societies can make appropriate adjustments to protect their populations. About the middle of this century the global population will reach nine billion people, with hundreds of millions living in areas highly vulnerable to even small increases in ocean levels. The sea levels may have been stable for thousands of years, during the development of human civilization, which took place between the previous and future ice age. But as a result of human activity during the growth of the industrial revolution, and burning of fossil fuels, the greenhouse gases in the atmosphere have progressively increased the temperature of the land and the oceans. Ice coverings serve to reflect the Sun’s radiation back into the atmosphere, but when glaciers retreat, the exposed land absorbs more heat and further intensifies global warming. This would ordinarily establish a new equilibrium, but with further increases in carbon dioxide, this equilibrium gets pushed towards elimination of these ice packs entirely, resulting in a large increase in ocean levels.
The 2007 report from the InterGovernment Panel Climate Change (IPCC), estimated that sea levels would rise by at least 7 inches by 2100, but could rise by as much as two feet. A mere rise of a few feet could place major cities under threat of partial flooding, with some countries such as Bangladesh facing a threat that could cover large parts of the country. But what alarms scientists is that the 2007 IPCC report may have been too conservative and more recent findings suggesting a more accelerated level of glacier melting, are forcing them to increase their own projections, but do so at a time when the mechanisms of Greenland and Antarctic ice breakup are still poorly understood. Recently, Justin Gillis writing in the
the NYT provided a very good summary of some of the issues and problems of ocean level changes and how difficult it is to study and predict them. Anyone interested in this absorbing topic will be much better informed by reading the article in it’s entirety. Ocean levels will rise during this century. That is a guaranteed result of global climate change and warming of the ocean waters. There is some evidence that we are rapidly approaching a level of carbon dioxide in the atmosphere that existed when the Arctic, Antarctic and Greenland ice masses were first formed. Right now, we are at about 380 ppm carbon dioxide, but projections of 400 ppm and beyond get us into the range were some scientists believe we will reach a tipping point at which all three ice packs will melt–it is only a question of the rate of melting. It is very likely we will enter this zone of vulnerability and witness more directly the impact of this new danger zone. Scientists used to think that melting of the Antarctic and Greenland ice sheets would take centuries or more to complete, but the warm water mechanism recently discovered as a new component to glacier melting represents an accelerating factor for which no time table presently exists. We may have to live with the fact that the Earth will eventually see an elevation of more than 200 ft in ocean levels and a change of that magnitude will require huge changes in social organization and planning. It is unlikely that this alarming level of ocean increase will occur by the year 2100. There’s too much ice still embedded above surface level within the Antarctic and Greenland ice packs and these regions are still very cold. Some scientists however suggest that this conservative estimate may be too conservative. The trouble is that until we have a more reliable model of these changes, which may take many years to develop, we will face an uncertain future about the rate of sea level rise, even over the next few decades. When in doubt, stay tuned.
RFM
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