aerosols. A system of solid particles uniformly distributed in a finely divided state through a gas, usually air.
albedo. Reflective power or reflectivity; specifically the fraction of incident radiation (such as light) reflected by a surface or body (such as the moon or a cloud). Usually measured as a percentage or decimal factor between 0.0 and 1.0.
atmosphere. The envelope of gases surrounding Earth or another planet.
average residence time. Also known as removal time, this is the average amount of time spent in a control volume by the particles of a fluid.
baroclinic. A measure of the stratification in a fluid.
bjerknes feedback. Interaction between the ocean and the atmosphere in the central equatorial Pacific in which the easterly surface wind stress enhances the zonal sea surface temperature gradient, which in turns amplifies the wind stress.
blackbody. An idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. It is simultaneously a perfect emitter of radiation.
causation vs. correlation. If there is a correlation between two measured quantities, we sometimes assume that the dependent variable changes solely because the independent variables change. However, correlations can be spurious and related to changes in an unmeasured quantity, in which case the correlation does not imply direct cause and effect.
chaotic properties. A branch of mathematics focused on the behavior of linear dynamical systems that are highly sensitive to initial conditions. Earth’s climate is an example.
climate sensitivity. The factor relating change in temperature for a given change in radiative forcing.
cloud radiative feedback. Clouds are both reflective to energy received from above and absorbing to energy received from below. Changes in Earth’s temperature will give rise to changes that can enhance or diminish these properties.
coriolis effect. The effect of Earth’s rotation on bodies not attached to Earth but moving N-S or S-N across Earth’s surface.
cryosphere. Those parts of Earth where water is in solid form.
cyclotherm. Alternating fine stratigraphic sequences of marine and nonmarine sediments, sometimes interbedded with coal seams.
doldrums. A colloquial maritime expression referring to those parts of the Atlantic and Pacific oceans affected by a low pressure area around the equator where the prevailing winds are calm.
dynamic models vs. statistical models. In mathematics, a dynamic system is one in which a function describes the time dependence of a point in a geometrical space. Examples include the mathematical models that describe the swinging of a clock pendulum, the flow of water in a pipe, and the number of fish each springtime in a lake. A statistical model is a class of mathematical model that embodies a set of assumptions concerning the generation of some sample data, and similar data from a larger population. A statistical model represents, often in considerably idealized form, the data-generating process.
eccentricity. Deviation of a planet’s axis of rotation from normal to the plane of the ecliptic.
eemian period. The interglacial period that began about 130,000 years ago and ended about 115,000 years ago. It is the most recent period before the present day in which temperature was similar to that of today.
el niño southern oscillation (enso). An oscillating weather phenomenon associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific, including off the Pacific coast of South America. ENSO switches between a warm state, El Niño, and a cold state, La Niña, in periods between four and seven years.
electromagnetic spectrum. The range of wavelengths exhibited by electromagnetic radiation. Classified by wavelength into radio wave, microwave, terahertz (or submillimeter) radiation, infrared, or visible region that is perceived as light, ultraviolet, X-rays, and gamma rays. Wavelength is determined by the temperature of the body emitting the radiation.
ellipticity. Having the characteristics of a regular oval shape, traced by a point moving in a plane so that the sum of its distances from two other points (the foci) is constant, or resulting when a cone is cut by an oblique plane that does not intersect the base. In climate science, it refers to the deviation from circular of Earth’s orbit around the Sun; all the solar planets have this feature.
eustatic. Relating to or characterized by worldwide change of sea level caused by changes in the solid Earth and the melting of glaciers.
evapotranspiration. The sum of evaporation and transpiration from surface water bodies, plants, and soil.
feedback. The modification or control of a process or system by its results or effects.
geoengineering. The deliberate, large-scale manipulation of an environmental process that affects Earth’s climate in an attempt to counteract the effects of global warming.
glacial period. A period in Earth’s history when polar and mountain ice sheets were unusually extensive across Earth’s surface.
global warming potential (gwp). A relative measure of how much heat a greenhouse gas traps in the atmosphere. It compares the amount of heat trapped by a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide.
greenhouse effect. Trapping the Sun’s warmth in a planet’s lower atmosphere due to the greater transparency of the atmosphere to visible radiation from the Sun than to infrared radiation emitted from the planet’s surface.
greenhouse gas (ghg). A gas in the atmosphere that contributes to the greenhouse effect by absorbing and reradiating long-wavelength infrared radiation.
gtc. Giga tonne of carbon or carbon equivalent.
gyre. A spiral or vortex in ocean surface currents.
hertz (hz). The unit of frequency in the International System of Units and is defined as one cycle per second. It is the inverse of wavelength.
higgs boson. An elementary particle in the standard model of particle physics.
horse latitudes. Subtropical latitudes between 30 and 38 degrees both north and south where Earth’s atmosphere is dominated by the subtropical high, an area of high pressure, which suppresses precipitation and cloud formation and has variable winds mixed with calm winds.
ice albedo feedback. A positive feedback climate process in which a change in the area of snow-covered land, ice caps, glaciers, and sea ice alters the albedo, which in turn alters the climate system.
insolation. The amount of solar radiation reaching a given area; a constructed word from “incoming solar radiation.”
interglacial period. A geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods.
isobars. A line on a map connecting points having the same atmospheric pressure at a given time or, on average, over a given period.
jet stream. Region of very strong upper atmospheric winds. Each hemisphere has a polar jet and a subtropical jet. Wind speeds can exceed 200 mph.
latent heat. The quantity of heat absorbed or released by a substance undergoing a change of state, such as ice changing to water or water to steam, at constant temperature and pressure. Also called “heat of transformation.”
monsoon. A seasonal reversing wind accompanied by corresponding changes in precipitation, or seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea that bring heavy rains.
nino3.4. The average sea surface temperature anomaly in the region bounded by 5° N to 5° S, from 170° W to 120° W.
north atlantic oscillation (nao). A weather phenomenon in the North Atlantic Ocean caused by fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high that modulates the strength and direction of westerly winds and the location of storm tracks across the North Atlantic.
obliquity. The deviation from parallelism or perpendicularity; also the amount of such deviation. In climate science it refers to the deviation of the spin axis of Earth from being normal to the plane of the ecliptic.
orographic effect. Applied to the rain or cloud caused by the effects of mountains on air streams that cross them.
parametrization. The introduction of variables required for model calculations that cannot be based on observations but must be estimated from theory.
planck function. Formula that describes the spectral density of electromagnetic radiation emitted by a blackbody in thermal equilibrium at a given temperature.
plasmodium falciparum. A protozoan parasite, one of the species of Plasmodium that cause malaria in humans. It is transmitted by the female Anopheles mosquito.
power dissipation index (pdi). The sum of the maximum one-minute sustained wind speed cubed, at six hourly intervals, for all periods when the cyclone is at least at tropical storm strength.
ppb. Parts per billion is the number of units of mass of a contaminant per 1,000 million units of total mass. The unit used to measure the concentration of helium in the atmosphere and some other trace gases.
ppm. Parts per million. Usually describes the concentration of something in water or soil. One ppm is equivalent to 1 milligram of something per liter of water (mg/l) or 1 milligram of something per kilogram of soil (mg/kg). It is a common unit for concentration of carbon dioxide in the atmosphere.
precession. The slow movement of the axis of a spinning body around another axis due to a torque (such as gravitational influence) acting to change the direction of the first axis. It is seen in the circle slowly traced out by the pole of a spinning gyroscope. Earth experiences this motion, which is commonly referred to as the precession of the equinoxes.
radiative balance. The relationship between the amount of energy reaching an object (or a portion of it) and the amount leaving the same object. In climate science, it refers to the energy balance at the top of the atmosphere, the troposphere.
radiative forcing. The difference between radiation absorbed by Earth and energy radiated back to space.
rain shadow. The area on the leeward side of a mountain range that typically experiences dry conditions because rain has fallen on the windward side of the range due to orogenic uplift.
residence time. The average length of time during which a substance, a portion of material, or an object is in a given location or condition, such as adsorption or suspension. In climate science, it refers to the amount of time a molecule of any gas remains in the atmosphere.
saffir-simpson scale. Classifies hurricanes (western hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms) into five categories distinguished by the intensities of their sustained winds.
sea level pressure (slp). Pressure of the atmosphere measured at sea level, or reduced to sea level if measured at a different elevation.
solar radiation management (srm). A type of climate geoengineering that seeks to reflect sunlight and thus reduce global warming. Proposed methods include increasing the planetary albedo, for example, by using stratospheric sulfate aerosols or the enhancement of cloud albedo.
spherical spreading. The decrease in energy level when a wave propagates away from a point source uniformly in all directions. Also known as “geometric spreading.”
sst anomaly. Sea surface temperature anomalies, such as those associated with El Niño (La Niña), are a measure of the departure of temperature in the ocean’s surface waters from normal conditions. One method is to use five consecutive three-month running means of sea surface temperature.
steppe. An eco-region in the montane grasslands and shrublands and temperate grasslands, savannas, and shrubland biomes, characterized by grassland plains without trees other than those near rivers and lakes.
steric. The amount of sea level change caused by expansion/contraction of the oceans due only to changes in temperature.
stratosphere. The second major layer of Earth’s atmosphere, just above the troposphere, and below the mesosphere.
teleconnections. Climate anomalies being related to each other at large distances (typically thousands of kilometers). Most commonly used to describe a weather pattern altered by ENSO.
thermocline. A steep, decreasing temperature gradient separating a uniformly warm region immediately below the surface that is heated by the Sun from a deep region of near uniform cold water beneath.
thermohaline. The effects of salinity and temperature, especially with regard to large-scale ocean circulation.
tropopause. The boundary in Earth’s atmosphere between the troposphere and the stratosphere.
troposphere. The lowest layer of Earth’s atmosphere, where nearly all weather conditions take place. It contains approximately 75 percent of the atmosphere’s mass and 99 percent of the total mass of water vapor and aerosols.
tundra. A type of biome where tree growth is hindered by low temperatures and short growing seasons. The term tundra comes from the Russian тундра from the Kildin Sami word tūndâr (uplands or treeless mountain tract).
vector. A quantity having direction as well as magnitude, especially for determining the position of one point in space relative to another.
vegetation. Plants considered collectively, especially those found in a particular area or habitat.
walker circulation. In the tropics, the pattern of atmospheric circulation that includes near-surface winds blowing from east to west, and upper-level winds blowing from west to east. Circulation is broken into two cells during a strong El Niño.
weather front. A boundary separating two masses of air of different densities; it is the principal cause of meteorological phenomena outside the tropics. In surface weather analyses, fronts are depicted using various colored triangles and half-circles, depending on the type of front.
whittaker biome diagram. A graphic in which the dependence of vegetation types globally depends on temperature and rainfall.
wind shear. Variation in wind velocity occurring along a direction at right angles to the wind’s direction and tending to exert a turning force.