Climatology

The complex, interactive system consisting of five major components: the atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere. Energy exchanges and feedbacks among these components determine Earth's climate at local, regional, and global scales.

The difference between the incoming solar radiation absorbed by Earth and the outgoing longwave radiation emitted back to space. Positive radiative forcing warms the surface, while negative forcing cools it. It is measured in watts per square meter (W/m2).

The process by which greenhouse gases in the atmosphere (such as CO2, methane, and water vapor) absorb and re-emit infrared radiation, trapping heat near Earth's surface. Without the natural greenhouse effect, Earth's average temperature would be roughly -18 degrees Celsius instead of the current +15 degrees Celsius.

Periodic variations in Earth's orbital geometry, including eccentricity (shape of orbit), obliquity (axial tilt), and precession (wobble of axis), that occur over tens of thousands of years. These cycles alter the distribution and intensity of solar radiation reaching Earth and are a primary driver of glacial-interglacial cycles.

Processes that amplify (positive feedback) or dampen (negative feedback) an initial climate perturbation. Feedbacks determine the overall sensitivity of the climate system to changes in radiative forcing and are critical for understanding how much warming results from a given increase in greenhouse gases.

Complex computer simulations that represent the physical processes in the atmosphere, ocean, cryosphere, and land surface using mathematical equations. GCMs divide the Earth into a three-dimensional grid and solve equations for energy, momentum, and mass conservation at each grid cell over time.

The global ocean circulation pattern driven by differences in water density created by variations in temperature (thermo) and salinity (haline). This large-scale overturning circulation redistributes heat from the tropics to the poles and plays a fundamental role in regulating regional and global climate.

The study of past climates using natural archives known as proxy records, including ice cores, tree rings, ocean sediment cores, cave speleothems, and coral records. Paleoclimatology provides context for understanding current climate change by revealing how climate has varied naturally over thousands to millions of years.

Frameworks for categorizing Earth's diverse climates into distinct types based on temperature, precipitation, and vegetation patterns. The most widely used system is the Koppen-Geiger classification, which divides climates into five main groups: tropical, arid, temperate, continental, and polar.

The equilibrium change in global mean surface temperature resulting from a doubling of atmospheric CO2 concentration relative to pre-industrial levels. It is a key parameter for projecting future warming and is estimated to lie between 2.5 and 4.0 degrees Celsius based on multiple lines of evidence.