Reading climate changes in an Ice Age map.

Reading climate changes in an Ice Age map

Long before the age of automobiles, long before the invention of the wheel, natural events caused atmospheric carbon dioxide levels to climb dramtically at the end of the last Ice Age. Uncovering reasons for that increase may help researchers better predict the climatic impact of the present carbon dioxide build-up caused by human activities.

European boranists now report on one piee of the puzzle: how the continents affected atmospheric levels of this gas. After constructing a global map of vegetation at the peal of the glacial age, the researchers found that soils and land plants actually helped damp some of the carbon dioxide increase at the end of the last Ice Age.

Jonathan M. Adams of Cambridge University in England and his colleagues from France and Germany produced their map of the vegetation existing 18,000 years ago by sitting through published reports on ancient pollen and other plant remains in sediments from around the world. They then estimanted how much carbon dioxide was locked within the plants, soil and peat in specific regions.

Continental vegetation and soils contained far less carbon dioxide during the Ice Age that they do today, the researchers report in the Dec. 20 NATURE. Carbon storage on the continents totalled 968.1 billion tons 18,000 years ago, compared with 2,319.4 billion tons now, an increase of 140 percent.

The atmospheric level of carbon dioxide increased at the end of the Ice Age, from 200 parts per million (ppm) during glatical times to 280 ppm in the 1800s. While many researchers believe that oceans supplied this extra carbon dioxide, they wondered what was happening on land. The work by Adams' group suggests that as the climate warmed after the Ice Age, land plants and soils worked against the oceans by absorbing some of the ocean-liberated gas -- a finding that runs counter to earlier studies based on computer models.

The issue of carbon storage on the continents remains a major question for those studying the current rise in carbon dioxide, caused by fossil fuel burning and forest destruction. Only about half the carbon dioxide emitted each year remains in the atmosphere, indicating that "sinks" on land or in the ocean must absorb the rest. While experts have long considered the world's oceans as the major sink, Pieter Tans of the National Oceanic and Atmospheric Administration in Boulder, Colo., and his co-workers suggested last year that land vegetation takes up and stores a major portion of the carbon dioxide that does not stay in the atmosphere (SN: 8/26/89, p.132).

William H. Schlesinger, a biogeochemist from Duke University in Durham, N.C., debates that theory. The new work by Adams' group suggests land vegetation and soils absorb carbon dioxide slowly and can only store a small fraction of the gas emitted into the air each year by human activities, comments Schlesinger in the same issue of NATURE.

Adams, however, cautions against using the new study to judge current events because the changes at the end of the Ice Age occurred over thousands of years. Soils and vegetation could respond quite differently to the more rapid carbon dioxide increase occurring today and may in fact absorb a large fraction of the emitted has, he told SCIENCE NEWS.