BOSTON — It's easy to blame the sun for global warming. Sunspot activity has doubled in the last 100 years. Now British researchers have shown that the general solar magnetic field has more than doubled, too. Taken together, these trends reveal an invigorated sun. It apparently glows brighter by about 0.1 percent than it did a century ago.
Skeptics have cited this discovery to discount concern about human-made global warming. Changes in solar brightness do correlate with changes in Earth's global temperature. But for climate researchers this only rubs in their ignorance of climate change.
Commenting on the new magnetic findings in Nature last June, University of Chicago astrophysicist E.N. Parker pointed out that increased solar heating, while important, is only one factor in climate change.
Accumulating greenhouse gases, such as carbon dioxide and methane, the cooling effect of dust and aerosols, and changes due to the climate's internal variability also are involved. Mr. Parker explained climate modelers cannot yet include all the influences together in a single simulation.
So, he said, "there is no immediate answer to our questions" of how to share the blame for global warming.
Climate modeler James Hanson from NASA's Goddard Institute for Space Studies in New York made a similar point during a recent NASA-organized climate briefing. He noted, "There is a possibility" that aerosols and dust, generated partly by human activity, have "substantially counteracted" expected greenhouse warming. He said, "In that event, it is possible that an increasing solar irradiance contributed significantly to the [1 degree F] global warming of the past century." He added that scientists can't know how to sort things out until "we have good quantitative data on how all substantial climate forcings are changing."
M. Lockwood, R. Stamper, and M.M. Wild with the World Data Center at Rutherford Appleton Laboratory in Chilton, England, have reminded climatologists to take the sun's magnetic field into account. This is the sun's relatively weak general magnetic field, not the stronger fields associated with sunspots. The wind of electrically conducting gas that flows from the sun carries that field with it. It reaches Earth and interacts with our planet's own magnetic field. The British team worked backward from a century's worth of English and Australian records of geomagnetic activity to sort out the solar influence. They conclude that the sun's general magnetic field has increased by a factor of 2.3 since 1901.
This general field varies in time with the sun's 11-year sunspot cycle and so is in tune with changes in the sun's brightness. Also, the impact of that field on Earth seems related to cloudiness. Its influence can change the amount of cosmic rays that penetrate into our atmosphere. That, in turn, may affect formation of charged particles around which cloud droplets condense.
Scientists can only speculate about such an influence. Climatologists pin their hopes for better understanding on NASA plans to orbit a fleet of Earth-observing satellites. They will keep tabs on such critical quantities as temperatures, winds, clouds, aerosols, soil moisture, sea-surface temperatures, and solar activity.
Those hopes now are hostage to the Washington budget battle. Some of the planned Earth-observing missions probably would be canceled or seriously delayed if NASA cannot get Congress to restore proposed budget cuts.
(c) Copyright 1999. The Christian Science Publishing Society