The climate of Earth varies over time and place, influencing how plants grow, where people live and what wildlife can be found. Climate research involves collecting and analyzing weather data, studying the Earth’s history through things like ice cores and tree rings, and developing computer models that simulate past and present climate to predict future trends.
One of the most important discoveries in climatology is that carbon dioxide and other greenhouse gases are causing the Earth to warm. The discovery was based on the observations of early climatologists, including Alessandro Volta and Svante Arrhenius. It was confirmed by a series of careful scientific analyses, culminating in James Hansen’s historic 1988 Senate testimony that warned of the dangers of global warming.
The current international consensus is that the observed increase in global average surface air temperature since 1850 is unequivocal and largely due to human-caused anthropogenic greenhouse gas (AGG) emissions. This remarkable conclusion is based on rigorous statistical analysis of observations and proxy records that demonstrate within a reasonable margin of error that the observed change meets three criteria: it is unlikely to be due to natural internal variability; it is consistent with estimated responses to combinations of natural and anthropogenic forcings; and, it is not inconsistent with alternative, physically plausible explanations of recent changes in observational records. This methodology, known as detection and attribution, is critically dependent on the quality of data and sophisticated model simulations. The latest GCM/ESMs routinely simulate the entire Earth system at a high degree of resolution and include multiple levels of complexity, from basic atmospheric processes to dynamic vegetation and carbon-cycle models.