COMPARISON OF RADIATIVE AND PHYSIOLOGICAL-EFFECTS OF DOUBLED ATMOSPHERIC CO2 ON CLIMATE

The physiological response of terrestrial vegetation when directly exp osed to an increase in atmospheric carbon dioxide (CO2) concentration could result in warming over the continents in addition to that due to the conventional CO2 ''greenhouse effect.'' Results from a coupled bi osphere-atmosphere model (SiB2-GCM) indicate that, for doubled CO2 con ditions, evapotranspiration will drop and air temperature will increas e over the tropical continents, amplifying the changes resulting from atmospheric radiative effects. The range of responses in surface air t emperature and terrestrial carbon uptake due to increased CO2 are proj ected to be inversely related in the tropics year-round and inversely related during the growing season elsewhere.