14 - Forest Macroclimates

Summary

The processes by which forests influence large-scale climate are well known, but the specific response to changes in forest cover varies with background climate (e.g., tropical, temperate, boreal), the extent of forest change and type of conversion, and time of year, and differs between day and night. Forests remove carbon dioxide from the atmosphere, thereby lessening planetary warming. Forests also affect climate through exchanges of energy, water, and momentum with the atmosphere, which can warm or cool the climate depending on geographic location, time of year, and time of day. There is a distinct latitudinal pattern from tropical to temperate to boreal forests, with different influences on temperature and different underlying mechanisms. In general, forests cool the daytime surface climate during the growing season through evapotranspiration and other non-radiative processes, and they warm the nighttime climate. Outside of the growing season, forests are generally warmer than open fields, especially in locations where snow is present. Further climate influences occur through chemical emissions that produce aerosols. Much of this understanding comes from models of Earth’s climate.