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Climate change is a global phenomenon, but its effects are not experienced uniformly. Glaciers retreat, sea levels rise, vegetation changes, ice sheets lose mass and extreme events affect communities in different ways. Understanding these changes requires observations collected over long periods and across enormous geographical areas. This is where Earth observation has become indispensable. Satellites provide one of the few ways of systematically observing the planet at global scale and over decades.
Why satellites matter to climate science
Many climate variables cannot be measured effectively from the ground alone. Consider an ice sheet thousands of kilometres across, a remote glacier, or changes occurring across the entire world’s oceans. Field observations remain essential, but they cannot provide complete spatial coverage. Earth-observing satellites complement ground measurements by repeatedly observing large areas using a range of instruments. ESA’s Climate Change Initiative, for example, transforms satellite observations into long-term datasets covering essential climate variables including sea level, sea ice, glaciers, permafrost and soil moisture. The important point is that satellite imagery is not being used in isolation. It contributes to an observing system alongside weather stations, ocean measurements, field observations and models.
Measuring sea-level rise
Sea level is one of the clearest examples of how Earth observation contributes to climate science. Satellite radar altimetry measures the height of the ocean surface by timing the return of radar pulses from the sea. When combined with precise information about the satellite’s position, these measurements provide sea-surface height. The record is now decades long. ESA reports that global mean sea level has risen by just over 3 mm per year on average since 1993, with the rate increasing in recent years. Importantly, satellites also help researchers investigate why sea level is changing. Ocean warming causes thermal expansion, while additional water enters the ocean from melting glaciers and ice sheets. Satellite observations can contribute measurements of several of these components, allowing scientists to investigate the overall sea-level budget.
Watching glaciers from space
Glaciers provide another powerful example. Many glaciers are located in remote and difficult terrain. Their size and accessibility make systematic field measurement challenging. Satellite observations provide repeated coverage that allows researchers to track changes in glacier extent, elevation and movement. ESA notes that satellite instruments can systematically monitor glaciers over large areas and help quantify changes such as retreat and melting. Optical imagery can reveal changes in glacier boundaries, while radar and other sensors can provide complementary information under conditions where optical observations are limited. Long-term records are particularly valuable because a single image cannot tell us whether a glacier is stable, advancing or retreating. A sequence of observations can.
Ice sheets and the cryosphere
The polar regions present an even greater observational challenge. Satellite missions have provided measurements of ice-sheet elevation, mass change and dynamics over areas that are difficult to observe consistently from the ground. ESA reports that observations from missions including ERS, Envisat, CryoSat and Sentinel-1 have been important in monitoring ice-sheet change and understanding contributions to sea-level rise. This illustrates another important principle of Earth observation: no single sensor provides everything we need. Radar, optical imagery, altimetry and gravimetry each measure different aspects of the Earth system. Combining them provides a much richer picture.
Vegetation and land change
Climate monitoring is not only about ice and oceans. Vegetation responds to changes in temperature, precipitation, soil moisture and disturbance. Earth observation allows these responses to be monitored across large areas. Sentinel-2’s multispectral observations, for example, are designed to support monitoring of vegetation, agriculture and forests. Its spectral bands can be used to derive information related to plant properties including chlorophyll and water content. Long-term Landsat observations add another dimension. The Landsat archive now spans more than 50 years, providing an extraordinary baseline against which land-cover and environmental changes can be compared. Researchers have used this record to study ecosystems, agriculture, water resources, climate impacts and the changing human footprint.
Why continuity matters
One of the less glamorous but most important aspects of Earth observation is consistency. If every satellite measured the Earth in a completely different way, comparing observations across decades would be extremely difficult. Long-term programmes therefore invest heavily in calibration, processing and data consistency. The USGS Landsat Collection 2 archive, for example, was reprocessed to provide more consistent products across the satellite series, including improved geolocation and global surface-reflectance and surface-temperature products. This is critical for climate applications, where researchers are interested in trends rather than isolated observations.
From observation to evidence
Earth observation does not, by itself, explain climate change. Satellites measure physical quantities and their changes. Scientists combine these measurements with models, ground observations and knowledge of physical processes to understand what is happening and why. That distinction is important. A satellite might detect a reduction in ice extent. Establishing the causes of that change requires additional evidence and analysis. This is where the wider remote-sensing and Earth-observation community plays an essential role. Sensor development, calibration, photogrammetry, image processing, geospatial analysis and modelling all contribute to building reliable evidence.
The future of climate observation
As climate change accelerates, the demand for reliable Earth observation is likely to increase. New satellites will provide more frequent, higher-resolution and more diverse measurements. At the same time, decades of existing data will remain invaluable. The future is therefore not simply about launching more satellites. It is about creating long, interoperable records and combining observations intelligently. For climate science, perhaps the greatest value of Earth observation is its ability to provide something that is otherwise extremely difficult to obtain: a consistent view of a changing planet across space and time.