compared to earlier indirect estimates resulting in improved climate models. Over the years, as radiometers improved, these measurements achieved the precision, spatial resolution, and global coverage necessary to observe directly the perturbations in Earth’s global energy budget associated with short-term events such as major volcanic eruptions or the El Niño-Southern Oscillation (ENSO). In addition, radiometers in orbit nearly continuously since the 1960s directly measure the equator-to-pole heat transport by the climate system, the greenhouse effect of atmosphere trace gases, and the effect of clouds on the energy budget of Earth. These observations advance our understanding of the climate system and improve climate models.

Another important contribution to climate science was made by the long-term record of sea surface temperature (SST) from the Advanced Very High Resolution Radiometer (AVHRR) flown on the Television Infrared Observation Satellite series (TIROS-N) and the National Oceanic and Atmospheric Administration (NOAA) satellite series. As the longest oceanographic data record from remote sensing, it had broad impact. The SST record exposed the role of the ocean in regional and global climate variability and revealed important details about ocean currents. Trend analysis of the SST record provided evidence for global warming as 80 percent of the excess heat is entering the ocean and also helped improve understanding of the important climate-atmosphere feedbacks in the tropics that are also responsible for ENSO events. Understanding the increase in SST and anthropogenic heat input to the surface ocean also has important ramifications for quantifying and predicting sea-level rise in response to global warming.

Very accurate measurements of sea surface heights by the Topographic Experiment (TOPEX)/Poseidon altimeter have revolutionized our understanding of ocean dynamics. These observations allow scientists to characterize the scales and energy of mesoscale² features at a global scale and thus have revolutionized our understanding of basin-scale interannual variability, such as El Niño events. Altimetry observations also improved our understanding of mean ocean circulation. The newly discovered prevalence of ocean eddies revolutionized the way oceanographers think about the mesoscale energy sources for deep-ocean mixing. The new paradigm is that of a very dynamic, turbulent system, with the energy primarily provided by winds and tides that are variable on many timescales.

The most broadly used products from satellites are weather observations that enable forecasts. Since satellite images have become readily available, no tropical cyclone (hurricane or typhoon) has gone undetected, which provides affected coastal areas with advance warning and crucial time to prepare. This exemplifies not only how satellite observations have transformed the Earth sciences but also how the improved predictability of Earth processes can provide direct societal benefits. Weather forecasts more than a few hours into the future are made with the aid of numerical weather prediction models. By assimilating satellite observations, which yield dramatically improved and continually updated knowledge of the state of the atmosphere, meteorologists can devise models that project the weather into the future with much improved accuracy compared to presatellite forecasts. Consequently, 7-day forecasts have improved significantly in accuracy over the past decades, particularly for the relatively data-sparse southern hemisphere.³ Needless to say, these improvements in forecast skills are saving countless human lives and have an enormous economic value (saving the energy sector alone hundreds of millions of dollars).

The ability to detect land-cover changes at all spatial