Insects take a bigger bite out of plants in a warmer, higher carbon dioxide world.

Abstract

Carbon dioxide is a potent “greenhouse” gas. The dramatic increase in its concentration in the atmosphere as a result of human activities, beginning with accelerated fossil fuels combustion in the late 18th century, and perhaps even earlier, with modern agricultural expansion 8,000 years ago (1, 2), is driving a striking rise in global temperature (3). For the past 650,000 years, until relatively recently, the concentration of CO2 in the atmosphere was 280 ppm or less; however, the current concentration exceeds 380 ppm and, on its present trajectory, will surpass 550 ppm by 2050 (3). The accumulation of CO2 and other greenhouse gases in the atmosphere is forcing an elevation of global mean temperature; during the lifetime of child born today, the average temperature of the earth will increase by as much as ≈6°C (3). Working in concert, elevated temperature and CO2 are redistributing plant and animal communities on the surface of the earth (4). Because of the direct effect of CO2 and temperature on global food supplies, the influence of these changes on plant physiology and ecology is being actively studied (4–7). How these elements of global change may alter the interactions between plants and the insects that feed on them is relatively unknown. By bringing to light secrets contained in the fossil record, Currano et al. (8), published in this issue of PNAS, found that the amount and diversity of insect damage to plants increased in association with an abrupt rise in atmospheric CO2 and global temperature that occurred >55 million years ago. If the past is indeed a window to the future, their findings suggest that increased insect herbivory will be one more unpleasant surprise arising from anthropogenic climate change.