Climatologists are becoming increasingly concerned about methane, the gas that sometimes burns in a marsh. It pours into the atmosphere from jungles, swamps, and rice paddies. It escapes by the millions of tons from the digestive systems of termites and cattle. Like carbon dioxide, it traps some of the heat Earth radiates toward space, thus warming the air near the ground.
The methane effect has not been at the top of the climatologists' worry list. It has seemed minor compared with possible warming by carbon dioxide produced by burning fossil fuels. But as W.L. Chameides of the Georgia Institute of Technology pointed out recently in Nature, methane appears to have raised average global temperature about 0.23 degrees C. over the past three centuries. That's roughly 38 percent of the warming attributed to the rise in atmospheric carbon dioxide.
This is hardly a negligible effect. What is equally startling, if confirmed, is the finding by some researchers that the methane level has risen at a yearly rate of 1.7 percent since at least 1965.
Furthermore, Harmon Craig and his colleague, Chun-Chao Chou, at the Scripps Institution of Oceanography find that the atmospheric methane level remained stable from 27,000 BC to around AD 1580. Then it began to rise. ''Fossil'' air trapped in glacial ice indicates the level doubled from 0.7 ppm (parts per million by volume) to the present level of 1.65 ppm.
Chameides notes that natural processes which remove methane from the atmosphere may have become less effective, but considers this unlikely. He explains that various kinds of human activity are a more likely cause.
The prime source of the methane is fermentation due to bacteria in such wet environments as swamps or rice paddies. The bacteria aid the digestion of termites and cattle. Indeed, P.R. Zimmerman and J.P. Greenberg of the US National Center for Atmospheric Research, S.O. Wandiga of the University of Nairobi, and P.J. Crutzen of West Germany's Max Planck Institute for Atmospheric Chemistry have shown that termites may account for a substantial part of the 200 million tons of methane cycled through the atmosphere each year.
Chameides notes that the spread of rice paddies and of cattle raising would be expected to raise methane levels. Even the termite contribution may reflect human activity, for termite colonies multiply where forests have been cleared in the tropics.
Methane is active chemically in the air. It changes concentrations of other chemicals such as ozone or carbon monoxide, which also are heat-trappers. Thus a rise in methane level has complex implications.
As Chameides notes, if human activity is behind the rise, methane levels are likely to go on increasing. Thus meteorologists have a new problem - how to take account of the activities of cows, termites, and rice growers in trying to find out where the climate is headed. Return of an endangered species
At the turn of the century hunters had brought the northern elephant seal to the brink of extinction. Charles F. Cooper and Brent S. Stewart of San Diego State University note that in 1911 there were only six known births throughout the seal's Mexican and US range. Last year, they report, almost 25,000 seal pups were born.
As the two biologists point out in Science, a population disaster was turned into population boom once hunting pressure was removed and the seals protected.
Looking at California alone, they find that the elephant seal population has been doubling every five years for more than two decades. Some 11,900 pups were born along California shores last year. This is causing something of a population crush. Cooper and Stewart suggest that natural control mechanisms will come into play to limit further growth. These mechanisms could include such factors as an increase in the proportion of nonbreeding females or greater pup mortality under conditions of crowding.
The challenge to scientists now is to define the optimal seal population. Meanwhile, the recovery of the elephant seal is a monument to the effectiveness of the protection afforded shore-breeding marine mammals in Mexico and the United States over the past half century. Primordial life style
Certain bacteria prefer temperatures above water's boiling point and feed on sulfur, hydrogen, and carbon monoxide. They may be carrying on our planet's primeval life style, according to a West German research team.
Bacteria that love heat, shun air, and thrive on what others might find poisonous are well known. However, F. Fischer and K.O. Stetter of the University of Regensburg and G. Schreiber and W. Zillig of the Max Planck Institute for Biochemistry explain in Nature that the bacteria they are studying carry such tastes to an extreme.
These are part of a group called archaebacteria, which are considered to represent one of Earth's original life forms. The scientists note that the environments they like ''are hot, rich in sulfur, and usually strongly gassed by superheated steam known to contain (carbon dioxide, hydrogen) and possibly carbon monoxide.'' They add, ''Such conditions may well have existed early in Earth's history.'' Hyperactive sun
The current sunspot cycle should be well into its decline. But the sun is refusing to quiet down.
John Katsufrakis, who heads a Stanford University Antarctic project, says 1982 was an unexpectedly active year. The project studies Earth's far outer atmosphere by sending radio signals between Antarctica and a station in Quebec. Solar activity disrupts the transmissions and is a nuisance for Katsufrakis.
The sunspot cycle follows a roughly 11-year pattern between active and quiet periods. The last peak was in 1979 so that, by now, the sun should be quieting down. Instead, Katsufrakis notes, the usual pattern is not being followed. The sun was unusually quiet in 1980 and extraordinarily active last year, ''averaging one event a week,'' he says.
This should provide solar scientists with a unique research opportunity. But it also frustrates the work of others, such as Katsufrakis, who need solar quiet for their studies.