Calspace - Glossary of Terms -

Calspace Courses

Climate Change · Part One
Climate Change · Part Two
Introduction to Astronomy
Life in the Universe

Glossary: Climate Change
Glossary: Astronomy
Glossary: Life in Universe

Glossary of Terms - G to L

Index: A to F | G to L | M to R | S to Z

Gaia Hypothesis - (n.)

"Gaia" is the name for the goddess of Earth in Greek mythology. The English words geology, geochemistry, geography all contain the same root referring to Earth. "Gaia" and "Gaia Hypothesis" are concepts introduced by the British engineer and science writer James Lovelock (born 1919). They represent the thought that the dynamic life support systems of Earth (including the ocean, air, soil and the flux of elements) act much like an organism and appear to be internally controlled. An analogous concept from the early history of economics was Adam Smith’s "Invisible Hand" that controls market dynamics. "Gaia" is the "Invisible Hand" of biogeochemistry. Lovelock suggests that life processes regulate the radiation balance of Earth to keep it habitable. Since Earth is indeed habitable, and since the carbon cycle has helped to keep it that way throughout Earth history despite any changes in the Sun's brightness, there can be little argument that the "Gaia hypothesis" cannot be falsified. Some critics have made much of the fact that this personified “Life” cannot be expected to do things for future life. Yet, somehow life processes did help to keep the system "in check" - if this were not so, humans would not be here. Nevertheless, just as the "Invisible Hand" does not prevent market crashes, thus also "Gaia" cannot prevent major setbacks to life on Earth, from outside disturbance or even from internal runaway processes. While not strictly a "hypothesis" in the scientific sense since it cannot be falsified, the "Gaia hypothesis" has great merit as an educational tool, regarding the concepts of biogeochemical cycling. Do biogeochemical processes indeed combine forces to favor life on Earth? Critics suggest that the processes of living organisms in the past were not necessarily favorable for the long-term survival of the then existing life. For example, the growth of oxygen in the atmosphere, through expanding photosynthesis, greatly diminished opportunities for anaerobic organisms. However, new life forms evolved that took advantage of the new situation (for example, highly mobile multicellular organisms, including humans). See also “Biogeochemistry” and the people glossary entries, “Vernadsky” and “Hutchinson.”

Gates, William L. -

American climatologist. A pioneer in climate modelling.

Gauss, Karl Friedrich -

(1777-1855): German mathematician and astronomer at the observatory in Göttingen. Sometimes called the "Prince of Mathematics," he is considered along with Newton, Euclid and Archimedes to be one of the great mathematicians of all time. His major work, Disquisitiones Arithmeticae, was published in 1801. He invented mathematical statistics (i.e. Gaussian distribution and Gaussian error calculation) as well as making contributions to the science of geomagnetism and planetary motions. Much of his work remained unpublished during his lifetime and was later rediscovered in the later 19^th century.

General circulation of the atmosphere - (n.)

The science of meteorology may well be said to have begun when George Hadley, in 1735, attempted to explain from physical principles why the trade winds exist. The trades are the easterly winds north and south of the equatorial doldrum belt. The trades got their name from English sailors, for their steadiness (as in "the wind blows trade," i.e. on track). Doldrums refers to the becalmed ships with flapping sails (as in the term "in the doldrums"). Hadley pointed out that equatorial solar heating would make tropical air lighter than air at high latitudes. Tropical air would thus rise, high latitude air would sink, winds at the surface would blow towards the equator, and winds aloft would blow towards the poles. Hadley realized that the rotation of the earth would cause the surface wind blowing toward the equator to veer towards the west, thus producing the system of trades familiar to the mariners of his day. This picture is quite realistic as concerns the trades and the doldrums. It had to be modified considerably, however, to account for the other global wind belts, notably the westerlies. The physicist Carl-Gustaf Rossby did this in the 1930's and 1940's, thus founding modern meteorology. Not one, but several circulation cells are involved, with air rising not only at the tropics, but also at the polar front, and with air descending in the zone separating the westerlies and the trades, the great high pressure belt which contains the centers of the ocean gyres and the deserts on land.

A general scheme of circulation has the following elements: Moist air rises in a low pressure zone along an equatorial belt. This is the Intertropical Convergence Zone, or ITCZ. In the Northern Hemisphere, the ITCZ tends to move north in summer and south in winter. Also, it is deflected away from the equator by monsoonal winds, especially in the Indian Ocean region, and over Africa. Away from the ITCZ the de-watered air sinks, heating up while doing so, and produces an inversion on top of the trades. The term "inversion" refers to a vertical temperature profile that discourages convection (that is, it describes slower-than-normal cooling upward). North and south of the ITCZ, air is being sucked in close to the sea surface, just as Hadley envisioned. This air, moving toward the equator, picks up moisture (and heat) from the tropical ocean. The air's motion is deflected to the right on the northern hemisphere, and to the left on the southern hemisphere. The reason for the deflection is the rotation of the Earth, which subjects moving objects and fluid particles to the Coriolis Force. The Coriolis Force deflects every moving particle toward the right on the northern hemisphere and toward the left on the southern hemisphere. It is responsible for converting the Hadley convection into zonal winds. In the mid and high latitudes, the actual flow is much more complicated than a zonal scheme would suggest. The belt around the polar front region (roughly at 35 to 50°N), where the zone of excess heat meets that of heat deficiency, is dominated by cyclones. These are the eddies of counter-clockwise winds. The reason for the formation of eddies is that temperature gradients, heat exchange, and Coriolis forces are at a maximum here in mid-latitudes. This makes zonal air flow highly unstable. The distribution of land and sea, in mid-latitudes, greatly influences where high pressure centers and low pressure centers will develop. On the whole, the ocean gives off heat to the atmosphere. Thus, air tends to rise over the sea which establishes low pressure centers especially where warm water penetrates into high latitudes. The prime examples for more or less fixed low pressure centers resulting from this mechanism are the Iceland Low and the Aleutian Low.

General circulation of the ocean - (n.)

When studying the map of temperature distributions in surface waters of the world ocean, it will be noted that the lines of equal temperature (isotherms) do not follow latitudes entirely faithfully, but are deflected especially in coastal regions. This deflection of isotherms results from surface currents, especially from boundary currents at the edges of the ocean. Surface currents tend to follow surface winds. The winds, in turn, are part of the atmospheric convection system set up by the sun's radiation (atmospheric circulation). The most important wind belts are the trade-winds on either side of the equator, and the west winds or westerlies in mid-latitudes. The trades blow from the east, the westerlies from the west. Since the ocean basins are bounded by land, the currents corresponding to the trade winds and westerlies cannot run around the globe, but close to form large central gyres. See figure below.

The central gyres dominate the surface circulation patterns of all oceans, except in the Arctic and Antarctic regions. Since there is no barrier to zonal flow in the Antarctic, water flows around the Earth in the great circumpolar current. This is the greatest current in the ocean, about twice as big as the Gulf Stream. In involves not only surface waters, but reaches several miles down. The Gulf Stream itself is also impressive: it has velocities up to 4 knots (about a person’s jogging speed) and transports some 100 million tons of water per second: more than one hundred times the outflow of all the world's rivers combined.

Surface currents move water in the uppermost layer of the oceans. Over most of the oceans (except at high latitudes), a thin layer of warm surface waters overlies the much colder deep waters. The zone of abrupt temperature decrease, as we pass from surface to deep water, is called the thermocline and typically lies between depths of one hundred to one thousand meters.

The circulation of the cold water sphere is poorly known. The water is cold because it "originated" in high latitudes, where the surface waters these in cold regions were cooled, sank, and filled up the deep ocean basins. This process is constantly happening, and without it the abyssal waters would be warm in a few thousand years from the Earth's heat flow through the ocean floor. If waters sink at high latitudes, they must rise at low latitudes. They do so at an overall rate of about 1 cm/day. Most of the abyssal bottom water of the world ocean "originates" ( i.e. sinks from the surface) around Antarctica. The other important deep water source is the northernmost North Atlantic (the Norwegian Sea and Labrador Sea). This is know from mapping the temperature and oxygen content of near-bottom water. As the water moves away from its surface source (i.e. as it "ages") it gradually warms. Also, it slowly loses oxygen because of the respiration of organisms in the deep sea. Thus, "young" water is cold and oxygen-rich, "old" water is less cold and has less oxygen. Most of the deep water in the Atlantic is young, while that of the North Pacific is old.

Georg Wüst -

(1890-1977): German physical oceanographer. He used the distribution of ocean properties to obtain clues about motions within the ocean. Wüst also invented the concept of the "core layer," the layer of water within the ocean that has the most extreme values with respect to one or more properties and therefore is the least mixed and thus shows the path of motion.

Global warming - (n.)

The phrase "global warming" is used in a number of different ways. Observations show that the Earth has warmed overall in the last 150 years by almost 2°F (nearly 1°C), especially in the northern hemisphere (Observations in the southern hemisphere are not good enough to determine this.). The reasons for this warming are not clear, however, such warming is within the range expected for an increased greenhouse effect from human activities, including the emission of carbon dioxide from burning wood, coal and petroleum, and the emission of methane from the stomachs of cattle and from the soils of rice fields. "Global warming" is also used to describe the unusual warming seen for the last two decades, when maximum temperatures and also average temperatures were commonly outside the range experienced for the last 1000 years. Much or most of this warming seems to be a result of human activities resulting in an increase in greenhouse gases in the atmosphere. A third use of the phrase is in the framework of expectations for the future. Continued release of greenhouse gases is expected to lead to "global warming" according to the best available computer models of climate dynamics. Many climate scientists eschew the phrase "global warming" because the warming is not necessarily general. In some areas there may be no change, and in others there may be cooling associated with an average warming. Also, warming by itself may not be the most important effect of the change seen. When taking account of these caveats, the phrase "global change" is used in preference to "global warming."

Greenhouse Effect - (n.)

The "greenhouse effect" denotes the trapping of heat radiation within the atmosphere by certain trace gases contained in air, mainly water vapor, carbon dioxide and methane. Earth must radiate heat into space to balance the energy received from the Sun. The greenhouse effect makes it impossible to achieve the balance by re-radiation from the surface of Earth, thus forcing a warming of the ground and the lower atmosphere. Balance is then achieved through radiation from a level within the atmosphere, on average at 5000 m elevation. The term "greenhouse effect" also is used in connection with the emission of greenhouse gases associated with human activities, including industrial compounds (chlorofluorocarbons or CFC’s). This is more correctly referred to as the "excess greenhouse effect" or "additional greenhouse effect," unless the meaning is clear from the context.

Greenhouse gas - (n.)

These atmospheric gases tend to absorb the infrared radiation from the Sun as it is reflected back towards space, thus trapping the heat in the atmosphere. The major greenhouse gases include both naturally occurring species, like water vapor (H₂O), carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and several anthropogenically designed gases, like chlorofluorocarbons (CFC’s), perfluorocarbons (PFC’s) and sulfur hexafluoride (SF₆). Their relative ability to trap heat can be measured in terms of their Global Warming Potential (GWP), the ratio of global warming – both direct and indirect – from one unit mass of a greenhouse gas to that of one unit mass of carbon dioxide over a period of time. Table 1 summarizes the GWP of some of the major greenhouse gases. Table 2 shows the latest changes in US emissions, in terms of the equivalent amounts of carbon.

Table 1: Global Warming Potentials on a 100 Year Time Horizon (Source:IPCC 1996)

Table 2: U.S. Anthropogenic Greenhouse Gas Emissions, 1990-1999 (Source: US Department of Energy; http://www.eia.doe.gov/oiaf/1605/ggrpt/ )

Greenhouse skeptics - (n.)

"Greenhouse skeptic" is a term commonly applied by the media to both scientists and nonscientists who cast doubt on any or all of the following statements, which have been made by climate scientists: the Earth has been warming during the last 150 years; a substantial portion of that warming results from the addition of greenhouse gases to the atmosphere, especially in the last 50 years; most of the addition of greenhouse gases is from human activities; human activities contribute noticeably (or even substantially) to the observed warming; warming has potentially negative effects on living conditions on the planet, for plants and animals, and people; and policies should be worked out to deal with possible effects of global warming. The most basic approach in greenhouse skepticism is to say that the climate machine is complicated and we don't understand it very well, and therefore many of the above statements remain unproven. A prominent exponent of the "too-complicated-to-say-anything" approach is Prof. Richard Lindzen at the Massachusetts Institute of Technology. The most advanced form of greenhouse skepticism is to say that a warm climate is beneficial to human societies, and that carbon dioxide is good for growing food and other plants (i.e. the more the better). A prominent exponent of the "warming-is-good-for-you" approach is Prof. Mikhail Budyko of the Hydrometeorological Institute in Moscow. Budyko thinks Siberia should become a bread basket.

Hadley, George -

(1685-1768): English meteorologist. He related the direction of trade winds to the rotation of the Earth in his famous paper "Concerning the Cause of the General Trade Winds," published in 1735. His name is attached to “Hadley cells,” the air circulation that attributes the trade winds as part of a cell driven by rising air in the tropics (a concept first postulated by Edmond Halley in 1686).

Halley, Edmond -

(1656-1742): English astronomer and geophysicist but also diplomat and commander in the Royal Navy. He catalogued the stars of the southern skies and mapped magnetic variation, winds, tides, and related elevation to atmospheric pressure. Other topics he studied included evaporation and salinity of lakes, optics of the rainbow, mortality tables, size of the atom, acceleration of the moon, proper motion of stars, astronomy of comets. He predicted the return of a major comet ("Halley's Comet") for the year 1758.

Hansen, James -

American climatologist and a world expert on climate modelling and climate change. He was one of the first scientific experts to publicly state that global warming has begun.

Hasselmann, Klaus -

(born 1931): German climatologist who developed three-dimensional modeling of ocean-atmosphere interaction.

Index: A to F | G to L | M to R | S to Z

Hays, James -

(born 1933): American micropaleontologist and researcher at the Lamont Doherty Earth Observatory of Columbia University. He was the lead author of the scientific paper that first supported the Milankovitch Theory by investigating the stratigraphy in deep-sea sediment cores from the southern Indian Ocean. In the cores were clear imprints of Milankovitch’s proposed cycles. In his paper he wrote, "We are certain now that changes in the earth’s orbital geometry caused the ice ages. The evidence is so strong that other explanations must now be discarded or modified."

Heat radiation - (n.)

See “Infrared radiation.”

Hegel, Georg Friedrich Wilhelm -

(1770-1831) German philosopher. Studied the patterns of (European) history with a view to the (metaphysical) meaning of history and its underlying rationality. He believed that history reflected goals beyond human understanding (rather than being the chance product of interacting communitites). He also believed that Great Men make history (including himself) rather than, say, availibility of resources, weapons, development, epidemics or climate change. Freedom, Hegel believed, is to internalize the necessary laws so that they are no longer felt as external coersion. He assumed that the laws of the Russian kingdom were good- a kind of pinnacle of human history. For a Prussian citizen this was a convenient conclusion. It is a type of conclusion that is often found with other thinkers in other countries as well.

Herschel, John -

(1792-1871): British astronomer who attributed ocean currents to the action of wind and investigated the nature of the Milky Way Galaxy.

Heyerdahl, Thor -

(born 1914): Norwegian explorer and amateur archeologist. He proposed that ancient seafarers from the Mediterranean brought cotton, beans, and the idea to build pyramids to central America. Heyerdahl supported his contention by building two ships made from papyrus reed, the Ra I and the Ra II, resembling those depicted in ancient Egypt and sailing them from the ancient Phoenician port of Safi, Morocco across the Atlantic, roughly along the path of the voyage of Columbus. In 1970, the Ra II made landfall in Barbados after a 3,300 mile voyage that took 57 days. By comparison, Columbus's first voyage from Las Palmas, Spain to the Bahamas took 36 days.

Houghton, J. T. -

Climatologist and lead author on the Intergovernmental Panel on Climate Change reports, designed to provide an authoritative international statement of scientific opinion on climate change.

Humboldt, Alexander von -

(1769-1859): German naturalist and explorer who described the current off Peru that is named after him as well as making contributions to biogeography, geology and geography.

Hutchinson, G. Evelyn -

(1903-1991): American limnologist and geochemist and a pioneer of the field of biogeochemistry. His work included studies of the geochemical regulation of biotic productivity.

Hutton, James -

(1726-1797): Scottish medical doctor, farmer, businessman and geologist. He is probably best known as the inventor of the uniformitarian theory that states that present processes on earth can explain the geologic record. He is also discoverer of the rock cycle and first scientist to insist on an extremely old age of the Earth. His major work, Theory of the Earth, was written in 1795.

Imbrie, John -

American paleontologist and oceanographer. He is a leading figure in the reconstruction of the ice ages from deep-sea sediments and developed methods to tell past surface temperatures from the composition of fossil assemblages on the seafloor.

Infrared radiation - (n.)

Infrared radiation is in all respects similar to visible light, except that the wave length of the electromagnetic radiation is longer than that of light. Infrared radiation is also called "heat radiation." Our eyes cannot detect infrared radiation, although at high intensity they can get damaged by it. It is however readily sensed when holding your hand or face some distance from a hot object. Your hand or face feels warm even if the air between the skin and the hot object is quite cold. By employing special instruments, infrared radiation can be used for "seeing" in the dark. Many snakes use infrared sensors for hunting small mammals. (An interesting aside: pound for pound, mammals radiate much more energy in the infrared than the Sun does in visible light!)

Index: A to F | G to L | M to R | S to Z

Input - (n.)

Amount of matter entering an Earth biogeochemical reservoir per unit time. In geochemical models, the input is usually taken as equal to the output, which is the necessary condition for keeping a reservoir constant in size.

Intertropical Convergence Zone (ITCZ) - (n.)

A zone close to the equator (usually somewhat north to it, on the "heat equator") where the trade-winds converge and air rises high into the upper reaches of the "troposphere." In the Hadley Cell, the ITCZ is the portion that supplies the upward motion in the cell. The strong updraft in the ITCZ raises the tropopause, the upper boundary of the troposphere, to about 15 km height. In the ITCZ, cumulus convective systems can grow to enormous size. Their central cores are protected from dilution by the large diameter of the systems: the heat released by condensation is trapped within. These giant cumulus systems or hot towers are commonly 35,000 feet tall, and some may be as high as 50,000 feet. At any moment there are several thousand of them active. Each one releases an amount of latent heat energy into the atmosphere equivalent to a hydrogen bomb explosion during a life-time of an hour or so and they make the ITCZ a zone of persistent rainfall and cloudiness readily identifiable on satellite photographs, as below. Note the “line” of clouds located near the equator, indicated the ITCZ.

It is this process of latent heat release that warms the air of the ITCZ rather than direct heating by the sun as Hadley had supposed. Because of the rising air, rain is common and cloudiness (never complete, but broken up by blue sky) is the hallmark of this convection. Within the upper troposphere, winds have a component toward the pole, compensating the flow of the trade-winds. The ITCZ is not usually precisely centered on the equator, but moves north and south, but most of the time it resides north of the equator because the northern hemisphere is warmer than the southern hemisphere (a result of the large ice sheet on Antarctica and the circumpolar air and ocean currents). See also “General Circulation of the Atmosphere.”

Isotopes - (n.)

"Isotopes" are atoms of the same element that have different atomic masses. Radioactive isotopes emit radiation and change to other atoms while stable isotopes do not change through time. The simplest of the elements, hydrogen, has three isotopes: normal hydrogen, deuterium, and tritium. Normal hydrogen consists of one proton and one electron. Deuterium ("heavy hydrogen", which makes "heavy water" with oxygen) has a neutron in addition to one proton and one electron, for an atomic mass of 2. It is stable. Tritium has yet another neutron, for an atomic mass of 3, and is radioactive with a half life of 12.3 years. It decays into helium-3 by emitting beta radiation (which changes a neutron to a proton). The word "isotope" means "same place," referring to the fact that isotopes of a given element have the same atomic number and hence occupy the same place in the Periodic Table. Thus, they are very similar in their chemical behavior. This similarity - and the subtle differences in behavior that arise from the differences in atomic mass - make isotopes useful as tracers of climate-related processes in atmosphere, ocean and biosphere, as well as in the reconstruction of climate history. Such history is contained in tree-rings, corals, mountain glaciers, polar ice, sedimentary deposits in lakes and on the seafloor, and a host of other geological repositories (e.g. soils, loess sequences, cave deposits, pack rat middens, evaporite and reef accumulations).

Keeling, Charles David -

American geochemist. Originator of the famous "Keeling Curve" which depicts the inexorable rise of carbon dioxide in the atmosphere since 1957, with its annual variations superimposed on the accelerating trend of increase. After receiving his Ph.D. at Northwestern University, Keeling came to Scripps Institution of Oceanography at UC San Diego in 1956 to begin the carbon dioxide monitoring program that he has led to this day.

Koeppen, Wladimir Peter -

(1846-1940): Russian-German pioneer of climatology. Between 1900 and 1936 he developed a climate classification system based on temperature, rainfall and vegetation, the basic philosophy of which is still widely used today. This system distinguished five general climate types: tropical rainy, dry, warm temperate, cold forested, and polar. Modifications to these basic types were derived from seasonal information (i.e. climate with no dry periods, with a dry winter period, and with a dry summer period) and from general geography (i.e. steppe, desert, tundra, and perpetual frost).

Kukla, George J. -

American paleoclimatologist, born in Czechoslovakia who was the first to apply records of loess, deposits of silt laid down by wind, to reconstruct the ice age climate.

Kutzbach, J. E. -

American climatologist and a pioneer in applying climate models to climate history.

Ladurie, Emmanuel Le Roy -

French historian. He is leader in the reconstruction of climate from historical records. His major work is Times of Feast, Times of Famine: A History of Climate Since the Year 1000.

Lamb, Hubert Horace -

(1913-1997): British climatologist. He was one of the first to reconstruct climate from historical records. He invented the "dust-veil index" for volcanic eruptions, showing that such eruptions cool the climate (e.g. the Krakatoa explosion in 1883). His major work, published in 1972 and again in 1977, was Climate: Present, Past and Future.

Lamont-Doherty Earth Observatory - (n.)

One of the leading oceanographic institutes in the USA, it is engaged in a wide variety of studies concerning the solid Earth, the ocean and the atmosphere. It was prominent in the history of discoveries leading to the understanding of plate tectonics. It was founded in 1949 by Maurice Ewing (1906-1974) and named the "Lamont Geological Observatory" after the estate of Thomas W. Lamont upon which it was built.

Laplace, Pierre Simon -

(1749-1827): Marquis de Laplace was a French mathematician and astronomer. He worked on celestial mechanics and perturbations in the motions and rotations of planet and determined that the obliquity of Earth's axis is not constant, but varies cyclically.

Index: A to F | G to L | M to R | S to Z

Latent heat - (n.)

The energy contained in water and in water vapor, relative to ice or water, respectively. When water vapor condenses, the latent heat is released, warming the surrounding air. This heat powers storms, including the great hurricanes. When water freezes, latent heat is also released, warming the air in contact with the forming ice. Latent heat plays an important role in the redistribution of heat on the surface of Earth, especially through evaporation in the tropics and subtropics and the subsequent precipitation in higher latitudes.

Libby, Willard Frank -

(1908-1980): American chemist who developed the radiocarbon dating method at the University of Chicago from 1948 to1950, for which he received a Nobel Prize. The application of the radiocarbon dating method revolutionized research in climate history and archeology.

Lorenz, Edward N. -

American climatologist. He investigates climate models and the predictability of weather. He discovered the “Butterfly Effect” in which slight differences in a few variables in a computer model result in highly unpredictable results. Applying this concept to climate and weather in his famous 1963 paper, Lorenz argued that a butterfly flapping its wings in Beijing could, in theory, affect the weather thousands of miles away some days later.

Lorius, Claude -

French physicist and climatologist and major figure in the reconstruction of the climate record from Antarctic ice cores. In 1979, he helped discover a large change in the concentration of carbon dioxide between glacial and postglacial conditions.

Lovelock, James -

(born 1919): British engineer, science writer and originator of the "Gaia Hypothesis." He was the first to measure ozone-depleting CFC’s (chlorofluorocarbons) in the air at very low concentrations.

Lyell, Charles -

(1797-1875): Scottish naturalist, geologist and geographer. He suggested that similarity of fossil assemblages in the stratigraphic sequence suggested a relationship of rocks of similar age over a distance. He also promoted James Hutton’s theory uniformitarianism, which states that processes observable at present can explain what happened in the past, and he openly opposed Cuvier’s theory of catastrophism. He believed in "glacial drift," the distribution of glacial-age deposits by debris-carrying ice floes. From 1830 to 1833 he wrote the first textbook in geology, Principles of Geology.

Index: A to F | G to L | M to R | S to Z