Global Warming is the long term increase in the average temperature of Earth's near surface environment, particularly the global mean surface temperature, resulting from an imbalance in the planet's energy budget. In contemporary scientific usage, the term generally refers to the warming driven predominantly by human increases in greenhouse gas concentrations since the industrial era.
Global Warming is narrower than Climate Change because warming is one major component of broader climatic transformation that also includes changes in precipitation, sea level, ice, circulation, ecosystems and extremes. The global mean temperature is a statistical measure constructed from observations distributed across land and ocean surfaces, and it does not imply that every location warms at the same rate. Some regions warm faster than the global average, while others may experience different short term trends because of ocean circulation, aerosols, land surface changes and natural variability. The term therefore describes a global average tendency rather than uniform local temperature behaviour.
The physical basis of Global Warming lies in changes to Earth's energy balance. Earth receives energy primarily from the Sun and emits thermal radiation to space. The temperature of the planet adjusts until incoming and outgoing energy are balanced over sufficiently long periods. Greenhouse gases absorb and emit thermal infrared radiation, altering the altitude and conditions from which energy escapes to space.
Increasing concentrations change the radiative properties of the atmosphere and create a positive energy imbalance until the climate system warms enough to restore approximate balance. Because oceans absorb much of the excess energy, atmospheric temperature does not respond instantaneously to changes in forcing. Land, ice and ecosystems also respond at different rates. The resulting warming is therefore a coupled response involving atmospheric, oceanic and surface processes. The basic mechanism is established by radiative physics, spectroscopy, observations and modelling and does not depend on a single dataset or one particular climate model.
Global Warming is measured using multiple independent temperature records derived from land stations, ocean measurements, satellites and other observations. Each record requires adjustments for factors such as station moves, instrument changes, urbanisation and changes in observing practices where appropriate. Ocean temperatures are measured using ships, buoys and other platforms, while satellite instruments provide information about atmospheric temperature at different levels rather than directly measuring the same quantity as surface temperature records.
Global mean surface temperature is an estimate with uncertainty rather than a single perfect measurement. Different datasets use somewhat different methods but show broadly consistent long term warming. Short term variations can be influenced by volcanic eruptions, ocean circulation, solar variability and internal climate variability. These variations can temporarily accelerate or slow the rate of surface warming without eliminating the underlying long term energy imbalance. Consequently, trends are assessed over sufficiently long periods and using multiple datasets rather than relying on isolated annual changes.
Human caused Global Warming results primarily from increased concentrations of greenhouse gases produced by activities such as fossil fuel combustion, industrial processes, land use change and agriculture. Carbon dioxide is the largest contributor to the long term anthropogenic radiative forcing among the major long lived greenhouse gases, while methane, nitrous oxide and halogenated gases also contribute. Carbon dioxide accumulates through an interaction between emissions and natural sinks rather than remaining permanently in the atmosphere as an isolated substance.
Oceans and terrestrial ecosystems absorb substantial quantities, while some carbon remains in the atmosphere and contributes to long term forcing. Atmospheric aerosols can offset part of greenhouse gas warming in some regions by reflecting sunlight or modifying clouds, although their effects are spatially variable and generally shorter lived. The net warming therefore results from multiple simultaneous influences. Attribution studies use observations and models to demonstrate that the observed pattern of warming is consistent with human forcing and difficult to explain through known natural influences alone.
Global Warming produces changes beyond temperature itself because warming alters the physical state of other components of the climate system. Warmer air can hold more water vapour, which affects atmospheric moisture and precipitation potential. Ocean warming contributes to thermal expansion and therefore sea level rise, while warming can reduce snow and ice in many regions. Permafrost thaw can affect carbon storage, while ecosystems can respond through shifts in species ranges, phenology and productivity.
Extreme temperature distributions can change because the entire background climate distribution shifts, although the response of particular extremes depends on atmospheric dynamics and local conditions. Warming can also influence wildfire conditions, drought through changes in evaporative demand and heat stress in humans and animals. These effects are not identical everywhere. Regional circulation, ocean currents, elevation, land cover and local feedbacks influence how global mean warming translates into specific local changes.
Global Warming is influenced by climate feedbacks that determine how much the Earth system responds to an initial forcing. Water vapour feedback generally amplifies warming because warmer air can contain more water vapour, which itself absorbs thermal radiation. Ice and snow reflect incoming solar energy, so reductions in their extent can increase solar absorption. Changes in clouds have complex effects because clouds can reflect incoming sunlight while also reducing outgoing thermal radiation.
The carbon cycle can also provide feedbacks through changes in vegetation, soils and oceans. Ocean warming can alter carbon uptake, while ecosystem changes can either release or absorb carbon depending on circumstances. Feedbacks operate over different timescales, meaning that the eventual climate response to a given forcing can continue after atmospheric concentrations stop increasing. Climate sensitivity is used to characterise aspects of the temperature response to radiative forcing, but its precise value and interpretation depend on the timescale and definition used.
A common misconception is that Global Warming means that every place becomes warmer continuously. Global average warming can coexist with regional cooling episodes, seasonal changes and year to year fluctuations. Another misconception is that cold weather disproves global warming. Short term weather is controlled by atmospheric variability and can produce temperatures far below a long term regional trend even in a warming climate. Another distinction is between warming of the atmosphere and warming of the entire climate system.
The oceans store enormous quantities of heat, so surface air temperature represents only one component of total climate energy accumulation. Global Warming should also not be confused with the natural greenhouse effect, which is a fundamental feature of Earth's climate. The scientific issue concerns changes in the strength of radiative forcing and the resulting energy imbalance, not the existence of greenhouse gases themselves. Precise definitions are therefore important when interpreting observations and scientific claims.
The historical development of Global Warming science includes early theoretical work on the thermal effects of atmospheric gases, nineteenth and twentieth century measurements of atmospheric composition and temperature, development of climate models and extensive modern observational programmes. The scientific understanding has progressed from simple energy balance calculations to coupled Earth system models that represent atmosphere, ocean, ice, land and biogeochemical processes.
Global Warming has important implications for sea level, ecosystems, agriculture, water resources, infrastructure and human health because temperature is a fundamental environmental control. Its rate and magnitude depend on future emissions and on climate feedbacks. Mitigation can influence the eventual magnitude of warming by changing future radiative forcing, while adaptation addresses consequences that occur under a given climate trajectory. The term remains scientifically useful because it identifies the central global temperature trend, but complete understanding requires placing that warming within the broader framework of Climate Change and the coupled climate system.
