Volcanic warming during dinosaur days.

Volcanic warming during dinosaur days

While many geoscientists think a meteorite impact caused the mass extinctions at the end of the Cretaceous period some 65 million years ago, some argue that an extraordinary set of volcanic eruptions in India did the dirty deed. According to one theory, the volcanoes belched out enough carbon dioxide to raise the planet's temperature significantly via the greenhouse effect. But two researchers who tested this hypothesis now conclude that the ancient eruptions would have warmed Earth only weakly.

Computer simulations of Earth's carbon cycle suggest the eruptions slowly raised global mean temperatures by a maximum of about 0.8[degrees]C over several hundred thousand years, report Ken Caldeira and Michael R. Rampino of New York University in the August GEOPHYSICAL RESEARCH LETTERS. In contrast, the world now faces the threat of a 3[degrees]C warming by the end of the next century due to fossil-fuel burning and deforestation, according to a recent report by an international panel of scientists (SN:6/23/90, p.391).

Caldeira and Rampino's simulations suggest that over thousands of years, Earth's climate system limited carbon dioxide buildup in the atmosphere. At first, the rising levels of the gas elevated temperatures and rainfall rates, stimulating the growth of land plants. Eventually, these effects forced the oceans to absorb much of the carbon dioxide from the eruptions, keeping temperature down.

The researchers conclude that the species extinctions at the end of the Cretaceous did not stem from a greenhouse warming caused by volcanic eruptions. But that doesn't absolve the eruptions entirely. Other scientists have proposed that sulfur from the volcanoes could have dramatically cooled the planet.