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Greenhouse and icehouse Earth
Greenhouse and icehouse Earth are Earth's two recurring climate states, defined by polar ice, alternating for over 2.5 billion years; Earth is now in an icehouse state.
Greenhouse effect
The greenhouse effect, also called greenhouse warming, warms a planet's surface as gases like water vapor and carbon dioxide absorb infrared radiation, adding about 33 °C on Earth.
Greenhouse gas
A greenhouse gas (GHG) is a gas, such as carbon dioxide, methane, or nitrous oxide, that absorbs infrared radiation and warms Earth's lower atmosphere and surface.
Greenhouse gas emissions
Greenhouse gas emissions, also known as carbon or GHG emissions, are releases of gases like carbon dioxide and methane that warm the atmosphere, reaching 59 GtCO2-eq in 2019.
Greenhouse Gas Pollution Pricing Act
The Greenhouse Gas Pollution Pricing Act is a 2018 Canadian federal statute establishing the federal carbon pricing backstop, upheld by the Supreme Court of Canada in 2021.
Greenland Ice Core Project
The Greenland Ice Core Project (GRIP) was a European project that drilled a 3,029-meter ice core to bedrock at Summit, Greenland, between 1989 and 1992, covering 250,000 years of climate.
Greensburg tornado
The Greensburg tornado was a violent EF5 tornado that struck Greensburg, Kansas, on May 4, 2007, destroying about 95 percent of the town and killing 11 people.
Greta Thunberg
Greta Thunberg, born in Sweden in 2003, is a climate activist who began a school strike outside the Swedish Parliament in 2018 that grew into Fridays for Future.
GRIB
GRIB, or General Regularly-distributed Information in Binary form, is a binary format defined by the World Meteorological Organization for exchanging gridded weather and climate data.
Gridpoint Statistical Interpolation
The Gridpoint Statistical Interpolation (GSI) is a NOAA data assimilation system, developed at NCEP and operational since 2007, that generates initial conditions for weather forecast models.
GRUAN
GRUAN, the GCOS Reference Upper-Air Network, is an international network of sites measuring climate variables from the surface into the stratosphere, envisaged by the WMO in 2007 to calibrate satellites and radiosonde data.
Gust factor
The gust factor is the ratio of a peak wind speed over a short duration, such as 3 seconds, to the mean wind speed over a longer period.
Gust front
A gust front is the leading edge of gusty surface winds produced by a thunderstorm's downdrafts, often marked by a shelf cloud, that produces wind shear hazardous to aircraft.
Haboob
A haboob (Arabic habūb) is a wall of dust or sand pushed by thunderstorm outflow winds that can cut visibility to zero; the term began in Sudan and now covers similar storms worldwide, especially in Arizona.
HadCRUT
HadCRUT is a series of global historical temperature datasets produced jointly by the Met Office Hadley Centre and the University of East Anglia's Climatic Research Unit since 1850.
Hadley cell
The Hadley cell, or Hadley circulation, is an atmospheric circulation in which air rises near the equator and descends near latitude 30° in each hemisphere.
Hadley Centre for Climate Prediction and Research
The Hadley Centre for Climate Prediction and Research, founded in 1990 within the UK Met Office, is the United Kingdom's primary source of climate change information and climate models.
Hail
Hail is precipitation in the form of ice pellets more than 5 mm across that falls from thunderstorms, causing about $10 billion a year in US damage.
Hailstorm
A hailstorm is a thunderstorm that produces hail, ice pellets that damage roofs, vehicles, and crops, causing about $10 billion a year in the United States.
Hanukkah Eve windstorm of 2006
The Hanukkah Eve windstorm of 2006 was a powerful windstorm that struck western Oregon, Washington, and British Columbia in December 2006, leaving 1.5 million customers without power.
Harmattan
The Harmattan, also called the doctor, is a dry, dust-bearing northeasterly wind over West Africa from late November to mid-March, carrying Saharan dust toward the Gulf of Guinea.
HARMONIE-AROME
HARMONIE-AROME is a kilometer-scale, non-hydrostatic numerical weather prediction model for limited-area regional forecasting in which convection is treated explicitly, built on the shared ALADIN-HIRLAM code framework.
Hawk Fire
The Hawk Fire was a wind-driven wildfire that burned on Peavine Peak northwest of Reno, Nevada, in August 2026, destroying 47 homes and prompting evacuations of roughly 90,000 people.
Haze
Haze is a suspension of extremely small dry particles, such as dust, smoke, or pollution, that reduces visibility and gives the air an opalescent appearance.
Health effects of climate change
The health effects of climate change include heat deaths, shifting infectious disease, degraded air, and food insecurity, with the WHO projecting 250,000 extra deaths yearly by the 2030s.
Heat dome
A heat dome is an exceptionally warm air mass trapped beneath a high-pressure system aloft, suppressing clouds and precipitation; the term became widespread during the June 2021 Pacific Northwest heatwave.
Heat index
The heat index, also called the humiture or temperature-humidity index, combines air temperature and relative humidity to estimate how hot conditions feel to a resting person in the shade.
Heat lightning
Heat lightning, also called summer lightning, is the light from a distant thunderstorm too far away for thunder to be heard, often seen as silent flickers on hot summer nights.
Heat wave
A heat wave is a period of unusually hot weather lasting several days, defined by local thresholds, and human-caused warming has made heat waves more frequent and intense.
Heinrich events
Heinrich events are episodes of massive iceberg discharge into the North Atlantic during the last glacial period, named for Hartmut Heinrich, who documented their sediment layers in 1988.