Weatherwatch

One of the effects of the recession is that Britain will produce less carbon dioxide to pollute the atmosphere. Another significant but less easy to measure consequence, will be a rise in temperatures. Ever since Mount Pinatubo erupted in the Philippines in 1991 scientists have known that dust and pollution in the atmosphere cools global temperatures by preventing some sunlight reaching the Earth's surface. It took nearly two years for the dust and sulfur dioxide fired into the stratosphere from the volcano to fall back to Earth, reducing average global temperatures by 0.3C until 1993. Since then scientists have been able to factor the cooling effect of man-made pollution from coal-fired power stations, industry, aircraft and traffic into computer models to balance against the heating effect of greenhouse gases. Pollution crossing national boundaries has held down world temperatures. Cities, countries, and in the case of Europe and Asia, continents, are considerably cooler than they would otherwise be. Unlike Pinatubo, however, these constant emissions are at low level and in most cases fall back to earth in as little as three days. Turn the sources off by closing power stations, factories and flying less, and more sunlight reaches the Earth. The temperature is bound to rise, but by how much and how soon depends on the depth of the recession. However, it is already certain that 2009 will be a hotter year than it would otherwise have been without the downturn.