Blow hot blow cold
THE record highs of summer, this past, year in the us, could be attributed to the phenomenon of global warming. But what about the blizzard of 1996 which lashed throughout northeastern us, depositing more than 50 cm of snow in most areas, dipping mercury levels and paralysing normal life? The blizzard has left scientists wondering if global warming had masterminded this spell of chilling weather or if it was simply an unforeseen natural phenomenon.
Whatever be the reasons behind such occurrences,' "extremes of this kind are becoming more frequent," say researchers from the National Climatic Data Centre, Asheville, North Carolina, us. They have analysed the temperature and precipitation data of the us for the 20th century and found that the period between 1980 and 1994 has experienced the maximum instances of extreme one- day precipitation, over-all precipitation, The mean location and velocities of the westerly jet-stream in -the Northern Hemisphere in January above normal temperatures and droughts. "It is rather interesting that we seem to be getting these 'storms of the century' @very few years," remarks Thomas R Karl, heading the Asheville research team.
Climatologists in their assessment of the situation in the us this winter, are subscribing to a variety of explanations. Some favouring the global warming theory, have presented evidence which suggests that climatic changes associated with global warming could indeed create such heavy snowstorms and on the whore, greater extremes in precipitation. According to them, the warming of the earth will not result in seasons disappearing but will only mean more rain, sleet or snow, as the rate at which water from the oceans evaporates, increases. And in regions where global atmospheric circulation does not permit precipitation, global warming shall produce hotter heat waves and even more severe droughts.
Another theory on the deluge this winter postulates that the, blizzard was not a rare event but simply one with a higher intensity. Research meteorologist Vernon E Kousky of the National Weather Service's Climate Prediction Centre, Maryland, us, points his fingers at the super powerful jet stream (a current in the upper mosphere), moving across the region. According to Kousky, the jet stream was strong and sucked up huge amounts of Arctic air. The resulting creation of a low pressure zone over the northeastern us prompted the inflow of air. Warm moist air from the Gulf of Mexico was pushed up high into the atmosphere, where it met a mass of heavy cold air moving south from the Arctic region and Canada. When the warm moistqre- laden mass met the cold polar air, tur- bulent conditions were created. The snowfall this time was heavier than usual as the temperature of the cold air was extremely low. These climatologists feel that such seasonal movements of air are much more significant than the smallscaJe changes produced by global warming.
The shortcomings of our forecasting skills are further pushed to the fore when such disasters strike. The undet- standing of the earth's turbulent atmos- phere is still imperfect and analytical tools like computer models cannot really be on par With real weathe! condi- tions. An element of uncertainity seems unavoidable. For instance, scientists had predicted that this year's winter would be a mild one but as one knows, th~ situation has been far from being mild.