What a climate record is
A climate record is a long, consistent series of measurements of the same quantity, such as global temperature, sea level or the amount of ice. Climate is usually defined by averages over decades, so understanding it means looking at observations over a long span. Thermometers, ships and weather stations supply records stretching back well before the space age, and satellites have added a global perspective since the second half of the twentieth century.
Systematic satellite observation of the whole planet began in earnest in the 1960s with weather satellites, and the list of measured quantities has expanded since then. Many of the key records are therefore several decades long, with the length depending on what is being measured. Some, such as continuous satellite measurement of sea level height, begin in the early 1990s.
Why satellites add something new
Ground observations are accurate where they exist, but coverage is uneven, with fewer stations over oceans, polar regions, deserts and forests. Satellites view nearly the entire globe with the same type of instrument. That helps researchers see patterns that cover entire hemispheres and check findings against independent measurements.
Different methods complement each other. Satellite sea level measurements, for instance, are checked against tide gauges. Surface temperature records from thermometers are compared with satellite estimates of atmospheric temperature. When separate methods tell a consistent story, confidence in the result increases. When they differ, researchers investigate why.
The hard part: making one record from many instruments
No satellite lasts forever. Climate records are therefore built by chaining together instruments launched at different times. This creates several technical problems:
- Calibration. An instrument must be calibrated to a reference, and its sensitivity may drift in orbit.
- Overlap. If a new instrument flies alongside an old one for a period, scientists can compare them and adjust the data to be consistent.
- Orbit changes. Some satellites slowly drift in their orbit, changing the time of day they observe. That can create apparent trends unless corrected.
- Algorithm changes. The methods used to convert raw signals to quantities improve, and old data may be reprocessed.
Because of these challenges, independent groups sometimes produce slightly different versions of the same record. Comparing them is part of how the uncertainty is estimated, and it is one reason scientists describe results with ranges.
What the record has helped show
Satellite and other observations have been used to study measurable changes such as the extent of sea ice, shifts in vegetation, ocean heat and color, the height of the sea surface, changes in the mass of ice sheets, and increases in atmospheric greenhouse gases. Individual findings vary in how well they are established, and researchers continue to refine them. Together with ground-based data, they underpin the broader understanding of climate change drivers described elsewhere.
What the record cannot do alone
A measurement describes what is happening, not necessarily why. Attributing a change to a cause requires physical understanding, models and comparisons with natural variations. Satellite records are also finite: a few decades is short compared with natural cycles that can last longer, so scientists supplement them with other evidence, such as ice cores and tree rings, for the more distant past.
Why continuity matters
A gap in a record cannot be filled afterward. Maintaining continuity requires long-term planning and funding, with replacement satellites ready before old ones fail. Calibration and open data policies also help, since many researchers can then test the same observations. The value of the record grows with each added year.