Climate change science
The Earth's surface temperature is measured in many ways. Thermometers have recorded air temperature at weather stations or surface seawater temperature from ships for many decades, with almost global coverage extending back to 1861. Instruments on satellites have monitored infrared radiation for many years, which is then converted to temperature to provide global records back to 1979. In addition, proxy records—data relating to climate, such as tree rings and ice cores— extend the global surface temperature record back hundreds and even thousands of years.
Urbanisation, with its heat-absorbing structures and materials such as concrete, can change the local climate by raising local temperatures. Researchers take into account such changes when looking for long-term trends in regional and global temperatures. Satellites and weather balloons record average temperature in the lower atmosphere and at the Earth's surface. Measurements from the satellites and weather balloons show warming rates that are similar to those directly recorded at the surface.
Computer-based climate models use mathematical formulae to represent the important physical and chemical processes that drive the world's climate. They are the best tools available for making climate change projections. While the models still have shortcomings, there has been enormous progress over past years in our understanding of important climate processes and their representation in climate models.
Confidence in the reliability of these models for climate projections has also improved, based on tests of the ability to simulate:
Models do a better job of simulating average temperature and pressure than rainfall. Simulation of climatic variability due to monsoons, the El Niño Southern Oscillation and the North Atlantic Oscillation has improved. Small-scale extreme events are harder to simulate, but models can simulate features of tropical cyclones.
Simulations that include estimates of natural and human influences can reproduce the observed large-scale changes in surface temperature over the 20th century, including the global warming that has occurred during the past 50 years.
Climate models are good at simulating most climatic variables that are needed for studying global and continental climate change. Climate models are also useful tools for exploring likely regional changes to climate.
