Glossary of key terms
Abrupt climate change: a significant climate change that occurs over a few decades or less, lasts for at least a few decades, and disrupts human or natural systems in major ways.
Anthropogenic: caused by human activities
Climate archive: a preserved natural specimen that contains paleoclimate information. For example, tree rings, ice cores, marine/lake sediments, etc., all serve as archives of past climate.
Climate change: Climate is defined as the long-term (usually 30-year) average of weather over a large area. Thus, climate change is a departure from long-term weather averages that persists for a significant period of time (usually decades or longer).
Climate sensitivity: the change in global mean surface temperature resulting from a doubling of atmospheric CO2.
Cryosphere: all features of the Earth that are composed of frozen water, including ice sheets, glaciers, permafrost, and lake/river ice.
Dansgaard-Oeschger (DO) event: abrupt climate events recognized in Greenland the North Atlantic region that are characterized by a cold phase, followed by a rapid transition to a warm phase, followed by a slower transition back to a cold phase.
External forcing: a forcing agent outside of the climate system that results in a change in climate—for example, changes in solar radiation, volcanic activity, and changes in atmospheric composition are all external forcings.
Climate feedback: a phenomenon in which a change in one climate parameter results in a change in a second climate parameter, and that second change eventually causes additional change in the first parameter. If the additional change in the first parameter has the same sign of the original change (as in a positive change in temperature causes melting of permafrost, which then releases stored greenhouses gases to the atmosphere, which then causes further positive change in temperature), it is known as a positive feedback. Conversely, if the additional change in the first parameter has the opposite sign of the original change (as in a positive change in temperature causes accelerated weathering of silicate minerals, which then causes additional burial of carbonate sediment in the deep ocean, which then causes a drawdown of CO2 and a negative change in temperature), it is known as a negative feedback.
Greenhouse gases (GHGs): atmospheric gases that have a net effect of absorbing infrared radiation emitted by the Earth’s surface (rather than allowing it to be emitted to space), effectively trapping extra heat in the Earth’s atmosphere. The primary GHGs are water vapor (H20), carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), and ozone (O3). GHGs refer to both anthropogenic and natural gases.
Insolation: The amount of solar radiation reaching the Earth's surface in a particular place in a particular season. Measured in watts per square meter.
Irreversibility: a change in the climate system is considered irreversible if the amount of time it takes for the change to first occur is significantly longer than the amount of time it takes for the climate system to recover back to baseline.
Orbital forcing: changes in incoming solar radiation due to variations in the Earth’s orbital parameters (the shape of the Earth’s path around the sun) and axial tilt (the angle of the Earth’s axis). These variations are collectively known as Milankovitch Cycles (LINK to Wikipedia?) and are the primary cause of glacial-interglacial cycles.
Proxy: an indirect record of past climate variability through a physical, chemical, or biological process that is sensitive to one or more climate parameters. For example, tree rings and ice cores have characteristics like ring/layer thickness that provide quantitative climate reconstructions.
Radiative forcing: a change in the net radiative flux (the amount of solar energy hitting a given area on the Earth’s surface; measured in Watts per square meter) caused by a driver of climate change, such as a change in atmospheric CO2.