Don't blame Mt. St. Helens for this summer's unusual weather

With one of the wettest Wimbledon tennis tournaments on record in Great Britain and with intransigent heat in the US Southwest, it's easy to believe suggestions that dust from Mt. St Helens is affecting the weather.

However, climatologists at the Environmental Data Service (EDS) of the US National Atmospheric and Oceanic Administration (NOAA) remain skeptical. They still cannot find enough dust to convince themselves it will have any significant weather effect.

The suggestions come from a variety of sources. Japanese meteorologists claim to have detected a dust veil 30 kilometers high over their area that they think could cause cooling, according to news reports. Other reports have quoted British climatologist H. H. Lamb as suggesting that a high-altitude dust veil is responsible for making Britain unusually cold and wet.

And in the United States, NOAA meteorologist Kirby Hanson warned recently that Mt. St Helens dust might interfere with research to detect any warming due to accumulation in the air of the heat-absorbing gas carbon dioxide released by burning fossil fuels. Any cooling by the dust, he said, "would likely rule out early detection of carbon dioxide-induced temperature changes." However, he did not say there definitely will be such cooling -- a subtlety news reports of his statement have tended to overlook.

All of this might lead one to suspect that volcanic dust may be to blame for some of this summer's "freak" weather. The heat wave in the US Southwest might then be part of a weather pattern set up at least partially be colling at higher latitudes.

The problem with using the dust as a scapegoat, however, is that US monitoring stations cannot find much of it.

J. Murray Mitchell Jr., senior climatologist at EDS, notes that lidar (laser radar) used by the US has seen no high-level dust. It has picked up sporadic dust clouds, typically at 13 to 16 kilometers. Yet there has not been enough of it even to dim the sun noticably, as Dr. Mitchell's colleague Lester Machta reported at congressional briefings July 11.

Thus, Dr. Mitchell says, it is hard to see how dust from Mt. St Helens could cause enough cooling to soak Wimbledon. It is even harder to see how it might be forcing the Southwestern heat wave in the US.

"We've been sitting around here trying to figure out a connection, but we just can't come up with anything plausible," Dr. Mitchell says.

Neither the British cold nor the Southwest heat is outside the range of present climate. In fact, the heat wave reminds meteorologists of the drought patterns of the mid-1950s. Dr. Mitchell notes, "The atmosphere has many ways to cross its legs and this just happens to be a way of doing it that is comfortable right now."

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