Ecology Terms Starting With G
Ecology Glossary: G
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Glaciation
/ glay-see-AY-shun / · Latin glacies, ice; -ation, process
Glaciation is a period when large ice sheets and glaciers grow and spread across continental areas, reshaping terrain by carving valleys, depositing debris, and lowering sea levels worldwide.
During a glaciation, average global temperatures drop enough for snow to accumulate year after year in polar regions and on mountains until it compresses into ice sheets hundreds or thousands of meters thick. As glaciers flow slowly downhill under their own weight, they scrape out U-shaped valleys, smooth rock surfaces, and deposit mixed rock material called till wherever the ice melts. The last major glaciation peaked about 20,000 years ago, when ice covered much of North America, Europe, and Asia and sea levels stood roughly 120 meters lower than today.
Retreating ice sheets left behind features still visible across the Northern Hemisphere, including the Great Lakes of North America, which occupy basins scoured by glacial erosion and later filled with meltwater.
The Laurentide Ice Sheet, which covered most of Canada during the last glacial maximum, was in places over 3 kilometers thick, depressing the underlying crust so much that parts of Canada are still rebounding upward today at rates of up to 1 centimeter per year, a process called isostatic rebound.
Glaciers are static blocks of ice. Glaciers slowly flow under their own weight and can grind the land beneath them.
During the last glacial maximum, ice sheets covered much of Canada and northern Europe, and many species survived in ice-free refugia before recolonizing deglaciated areas. Genetic studies of European brown bears (Ursus arctos) show that modern populations descend from lineages that persisted in southern refugia such as the Iberian Peninsula and the Carpathians, with recolonization routes traceable through mitochondrial DNA.
Grassland
/ GRAS-land / · Old English graes (grass) + land
Grassland is a biome where grasses and herbaceous plants dominate the vegetation, trees are scattered or absent, and annual precipitation typically ranges from 250 to 900 millimeters.
Grasslands form where rainfall is too low for closed-canopy forest but sufficient for continuous grass cover, and they occupy roughly 40 percent of Earth’s ice-free land surface. Grass species with deep fibrous root systems extending 2 to 4 meters survive seasonal droughts and recover rapidly after fire or grazing. Periodic fires suppress woody plant establishment, maintain nutrient cycling through ash deposition, and promote grass regeneration from belowground rhizomes.
Large herbivores such as bison (Bison bison) and wildebeest (Connochaetes taurinus) evolved to thrive in these systems, moving in herds that distributed grazing pressure and allowed vegetation recovery. Grassland soils accumulate rich organic matter from dense root systems, and conversion to cropland has eliminated over 95 percent of native tallgrass prairie in North America.
The Eurasian steppe once supported the largest continuous grassland on Earth, stretching over 8,000 kilometers from Hungary to China. This system sustained enormous herds of saiga antelope (Saiga tatarica), whose populations have declined by more than 95 percent since the mid-twentieth century due to hunting and habitat loss.
Grasslands are empty spaces waiting to become forests. Many are stable biomes maintained by fire, grazing, and seasonal drought, with specialized plants and animals that cannot persist under forest canopy.
The North American tallgrass prairie supports big bluestem grass (Andropogon gerardii) with roots reaching 3 meters deep, allowing plants to survive both drought and fire. Before European settlement, an estimated 30 to 60 million bison grazed these prairies, and their wallowing created shallow depressions that collected water and supported distinct plant communities.
Greenhouse Effect
/ GREEN-hows ih-FEKT / · Dutch groenhuis + Latin effectus
Greenhouse effect is the warming of Earth's surface that occurs when atmospheric gases absorb outgoing infrared radiation and re-emit it back toward the surface rather than allowing it to escape to space.
Solar radiation passes through atmospheric gases and warms Earth’s surface, which then emits infrared radiation that certain gases absorb and re-emit back toward the surface. Water vapor, carbon dioxide, methane, and nitrous oxide trap heat through vibrational absorption of infrared wavelengths between 8 and 13 micrometers. The natural greenhouse effect maintains Earth’s average surface temperature at approximately 15 degrees Celsius; without it, the planet would average minus 18 degrees Celsius and lack liquid water.
Human combustion of fossil fuels has increased atmospheric carbon dioxide from 280 parts per million in 1850 to over 420 parts per million today, intensifying heat trapping by approximately 50 percent. This enhanced warming causes the lower atmosphere to increase in temperature at a rate of approximately 0.18 degrees Celsius per decade, disrupting climate patterns and driving more frequent weather extremes.
Venus provides a stark example of an extreme greenhouse effect: its atmosphere is 96 percent carbon dioxide, producing surface temperatures of about 465 degrees Celsius, hot enough to melt lead, even though Venus receives only about twice the solar energy that Earth does.
Types of Greenhouse Gases →The greenhouse effect is always harmful. The natural greenhouse effect is necessary for liquid water and life on Earth; the problem arises when human emissions strengthen it beyond the range in which current ecosystems and climates developed.
Carbon dioxide and water vapor absorb outgoing infrared radiation from Earth's surface, and the energy they re-emit warms the lower atmosphere. Measurements from satellites and surface stations show that the amount of infrared radiation escaping to space at wavelengths absorbed by carbon dioxide has decreased since the 1970s, directly confirming that more heat is being retained.
Greenhouse Gas
/ GREEN-hows GAS / · Dutch groenhuis + Latin gas (coined by Jan Baptist van Helmont)
Greenhouse gas is an atmospheric gas that absorbs outgoing infrared radiation from Earth's surface and re-emits it in all directions, including back toward the surface, raising surface temperatures above what they would be without that gas present.
Carbon dioxide, methane, nitrous oxide, and water vapor are the most abundant greenhouse gases, but they differ substantially in their heat-trapping potency and atmospheric lifetimes. Methane absorbs infrared radiation roughly 80 times more effectively than carbon dioxide over a 20-year period, though it persists in the atmosphere for only about 12 years compared to centuries for carbon dioxide. Nitrous oxide, released from agricultural soils and livestock waste, has a global warming potential approximately 273 times that of carbon dioxide over a 100-year period.
Water vapor is the most abundant greenhouse gas by volume, but its concentration in the atmosphere responds to temperature rather than driving it directly, making it an amplifying feedback rather than a primary forcing agent. Human activities have raised atmospheric methane concentrations from roughly 722 parts per billion before industrialization to over 1,900 parts per billion today.
Sulfur hexafluoride, used as an electrical insulator in power equipment, is the most potent measured greenhouse gas: it traps heat approximately 23,500 times as powerfully as carbon dioxide over a 100-year period and persists in the atmosphere for roughly 3,200 years.
Greenhouse Gases →Only carbon dioxide is a greenhouse gas. Methane and nitrous oxide are far less abundant than carbon dioxide but trap heat far more strongly per molecule, making their emissions significant contributors to warming even at lower concentrations.
Methane is released by wetlands when microbes break down organic matter without oxygen, a process called methanogenesis. Northern peatlands store an estimated 500 billion metric tons of carbon, and warming temperatures are accelerating microbial activity in these systems, increasing methane emissions and creating a feedback that further raises atmospheric greenhouse gas concentrations.