The scientific effort to determine if the earth's atmosphere is growing warmer because of all the fossil fuel we burn may be delayed as a result of Mt. St. Helens. The volcano has spewed tons of ash into the air, which could cause a slight, temporary cooling effect. Ash in the upper layers of the atmosphere absorbs sunlight, warming those layers but reducing the amount of energy that reaches the surface. This, fears Dr. Kirby Hanson of the National Oceanic and Atmospheric Admistration, could mask the warming effect that scientists are looking for. Hanson directs a series of stations around the world monitoring minor constituents of the air that may influence climate. He and others are studying the socalled greenhouse effect, which scientists believe results from the large-scale burning of fuels such as coal and oil. Burning these fuels gives off carbon dioxide which, in the air, absorbs heat radiating from the earth's surface, preventing some of it from escaping into space. Hanson's group has detected a 5 percent increase in carbon dioxide in the atmosphere over the past 20 years, and anticipates that in 50 years the concentration could climb to twice what it was before the industrial revolution. That level of increase could result in a net warming of the earth's surface by 4 or 5 degrees Fahrenheit, resulting in widespread alteration of the climate.

Meanwhile, the ash, which is extremely light, could hang in the air for several years, masking the greenhouse effect without curing it. This means that early detection of climatic change might be delayed until 1985 or later, Hanson fears.