Current climate and recent trends

While the paleoclimatic record is based on indirect measurements—for example, biological and geological indicators—more recent climate history is defined largely by in situ observations over the last 100–150 years. This chapter centers on what these observations and theoretical understanding reveal about the climate of North America. The focus is on: the current climate and the physical and geographical features that regulate it; natural climate variability on time scales of weeks to many decades; and recent trends in key climate variables such as temperature and precipitation, snow cover, and sea ice.