Global warming and fall in temperature

Sir, -- The popular perception of global warming is that it is linked to rising temperature, changes in rainfall, rising sea levels, and powerful storms. It is amazing that, in certain regions, it may even reduce the temperature. Dr Harry Bryden and his colleagues at the National Oceanography Centre in Southampton, UK, published a paper in Nature in the first week of December 2005. The authors have claimed that northwest Europe is getting colder for the past two decades due to global warming. It has been reported earlier that ocean currents play a significant role in conveying heat from the tropics to the polar region. The influence of the ocean currents may overshadow the greenhouse effect and the consequent global warming weakens the hot ocean current in a particular region, it may lead to a fall in temperature.

Dr. Bryden and his team have collected evidence that indicates that northwest Europe is vulnerable to a fall in temperature due to global warming. The warm North Atlantic current keeps the region warmer than its latitude suggests. But for the past two decades, these currents have weakened significantly. These currents originate in the Gulf of Mexico and carries warm water up to the edge of the Arctic Ocean. Indeed, the Gulf Stream splits into two. A part of its waters return past the coast of Africa, known as the Subtropical Recirculation (SR), while the rest flows towards the north and returns as the Deep Southerly Return Flow (DSRF).

Dr. Bryden is convinced that over the past two decades, the flow of water in the North Atlantic Conveyor Belt (NACB) has dropped by nearly 30 per cent, leading to a fall of average temperature of Britain by 1 degree C, enough to be perceptible. If the trend persists, the NACB may stop altogether. Britain will then chill like Greenland or Newfoundland. Dr. Bryden’s paper was published when a meeting was being held in Montreal to take stock of the situation after the Kyoto conference.

“Even if the Kyoto agreements were implemented in full, it would not have saved the slowing down of the North Atlantic Conveyor Belt”, says Dr. Bryden. Yours, etc., R Brahmachari, Professor, Department of Applied Physics, University of Calcutta, 26 January.