The scientific community is certain that the Earth's climate is changing because of the trends that we see in the instrumented climate record and the changes that have been observed in physical and biological systems. The instrumental record of climate change is derived from thousands of temperature and precipitation recording stations around the world. We have very high confidence in these records as a whole. The evidence of a warming trend over the past century is unequivocal.
Many types of instrumental records point to a climate warming trend. Our streamflow records show an earlier peak in spring runoff; borehole temperature records in Alaskan permafrost as well as water temperature records on land and sea show the warming trend. The physical and biological changes that confirm climate warming include the rate of retreat in glaciers around the world, the intensification of rainfall events, changes in the timing of the leafing out of plants and the arrival of spring migrant birds, and shifting of the range of some species.