Caldeira Lab Research:Energy, Global Carbon Cycle, and Climate/Land Plants, Carbon, and Climate

Land Use Changes and Northern Hemisphere Cooling

G. Bala, P.B. Duffy, & K. Caldeira

Before current global warming, the Northern Hemisphere experienced a long term cooling trend from 1000 - 1900 AD. Several possible explanations have been posed, including large scale changes in land use. This is an investigation of land use change as a cause of cooling.

G. Bala, P.B. Duffy, and K. Caldeira, Land use changes and Northern Hemisphere cooling, Geophysical Research Letters 28, 291-294, 2001.

Human land use change and a decrease in temperature: Two models were run over a period of 900 years. One used predicted "natural" vegetation that would have developed without human interference (1000AD), while the other used recorded data (1900AD) about the actual vegetation development, including land changes made my humans.


Recent reconstructions of Northern Hemisphere mean temperatures over the past millennium show a long-term cooling of about 0.25K between 1000 and 1900 AD, prior to the 20th century's warming. In this paper, we present the results of equilibrium climate model simulations that indicate that the land-use change occurring over this period may largely explain this observed cooling, although other factors also could have played a significant role. The simulated annual mean cooling due to land-use change is 0.25K globally and 0.37K for the Northern Hemisphere, suggesting that the cooling of the prior centuries could have been largely the result of anthropogenic interference in the climate system.