Biological consequences of global warming

The prospect that increases in atmospheric concentrations of greenhouse gases will have measurable effects on the earth’s climate over the next few decades has attracted a vast research effort. Climatologists have faced two main challenges. The first has been to distinguish the signal of human-induced climate change from the noise of interannual and decadal natural variability. The second has been to predict probable climate scenarios for the future. Climate monitoring over the past century and longterm reconstructions of climate over the past millennium indicate that the earth is indeed warming up (Fig. 1)1. Moreover, the recent patterns of warming and of changes in precipitation are generally consistent with the patterns predicted by global circulation models (Box 1)1–7. Physical features of the earth’s surface, such as sea ice and glaciers, also appear to be responding in a predictable way to the warming trends (Box 2)2,8–11. For ecologists, physiologists and land managers, the challenge is to predict the effects of human-induced climate and atmospheric change on species and on communities. These predictions can be broadly summarized into four categories (Fig. 2): (1) Effects on physiology: changes in atmospheric CO2 concentration, temperature or precipitation will directly affect metabolic and developmental rates in many animals, and processes such as photosynthesis, respiration, growth and tissue composition in plants. (2) Effects on distributions: a 38C change in mean annual temperature corresponds to a shift in isotherms of approximately 300–400 km in latitude (in the temperate zone) or 500 m in elevation. Therefore, species are expected to move upwards in elevation or towards the poles in latitude in response to shifting climate zones. (3) Effects on phenology: life cycle events triggered by environmental cues such as degree days might be altered, leading to decoupling of phenological relationships between species. (4) Adaptation: species with short generation times and rapid population growth rates might undergo microevolutionary change in situ. Biological consequences of global warming: is the signal already