NASA currently has more than a dozen Earth science spacecraft/instruments in orbit studying all aspects of the Earth system (oceans, land, atmosphere, biosphere, cyrosphere), with several more planned for launch in the next few years.
In 2004, NASA's spending on climate science exceeded all other Federal agencies, combined. NASA spent $1.3 billion on climate science that year, out of a $1.9 billion total. The agency provides data on solar output, sea level rise, atmospheric and ocean temperature, ozone depletion, air pollution, and changes in sea ice and ice sheets. NASA scientists regularly appear in the mainstream press as climate experts. So how did the space agency take on so big a role in climate science?
It has to do with the planetary exploration NASA carried out during the 1960s and early 1970s. The Jet Propulsion Laboratory, NASA's lead agency for planetary science, sent "Mariner" series probes to Venus and Mars. Astronomers considered these to be the "Earth-like" planets in the solar system, most likely to have surface conditions able to support life.
But that's not what they found. Venus had been roasted by a super-charged greenhouse effect. It had about three hundred times as much carbon dioxide in its atmosphere, no significant water vapor, and had a surface temperature hotter than molten lead.
Mars had an atmospheric pressure about one percent of Earth's, a surface that looked like the Moon's, and temperatures far below freezing. Pictures showed no surface water—it would have been frozen anyway—but they also seemed to show that it once had liquid water.
These discoveries left planetary scientists with unanswered questions. How did Earth, Venus, and Mars wind up so radically different from similar origins? How could Mars have once been warm enough to be wet, but be frozen solid now? This was especially strange since astronomers believe the Sun was much cooler when it formed than it is now. These questions revolved around climate, and the intersection of climate, atmospheric chemistry, and (on Earth), life.
Moving back to Earth
But just as planetary scientists began confronting these questions, NASA and Congress lost interest in planetary exploration. NASA's planetary exploration budget sank dramatically starting in 1977, and the Reagan administration threatened to terminate planetary exploration entirely. This was partly due to bad economic conditions in the U.S., and partly due to the agency's focus on the Space Shuttle, which could only reach low Earth orbit. The Shuttle focused agency leaders on Earth remote sensing, not on the other planets.
The same decade had witnessed a revolution in Earth scientists' understanding of the Earth's climate. Prior to the mid 1960s, geoscientists believed that Earth's climate could only change very slowly, on time scales of thousands of years or longer. But evidence from ice and sediment cores showed that belief was wrong. The Earth's climate had changed rapidly in the past—in some cases, within mere decades. Recognition that climate could change on human timescales made climate processes much more interesting research topics. It also spurred political interest.
It had been known since 1960 that humans were increasing the amount of greenhouse gases in the atmosphere. Would this warm climate noticeably? Scientists also knew that human emissions of aerosols could cool the Earth. Which effect would dominate? A 1975 study by the U.S. National Academy of Science said, in effect, "We don't know. Give us money for research." A 1979 study of carbon dioxide's role in climate put it slightly differently. They had found "no reason to doubt that climate changes will result and no reason to believe that these changes will be negligible."
Declining planetary funding and growing scientific interest in the Earth's climate caused planetary scientists to start studying the Earth. It was closer, and much less expensive to do research on. And NASA followed suit, starting to plan for an Earth observing system aimed at questions of "global change." This phrase included climate change as well as changes in land use, ocean productivity, and pollution.
In May 1985, NASA's trend toward Earth science was reinforced by the announcement of the famous "Antarctic Ozone Hole" by scientists at the British Antarctic Survey. NASA had been made the lead U.S. agency for stratospheric ozone research in the middle 1970s, and it had been ‘scooped' by the British. Goddard Space Flight Center's Total Ozone Mapping Spectrometer's science team quickly confirmed the discovery. Joint NASA/National Oceanic and Atmospheric Administration field expeditions in 1986, 1987, and 1989, and the Upper Atmosphere Research Satellite in 1991, demonstrated that common refrigerants called chlorofluorocarbons were responsible for the ozone hole. These chemicals have gradually been banned and replaced by less harmful ones in the decades since.
In 1988, the National Academy of Sciences' concern about climate change started to come true. A NASA climatologist testified before Congress that "the scientific evidence for the greenhouse effect is overwhelming. The greenhouse effect is real, it is coming soon, and it will have major effects on all peoples." The same year, the World Meteorological Organization established the Intergovernmental Panel on Climate Change to assess the state of climate science. Its first report, in 1990, affirmed that the world was getting warmer, but that more research was needed before the warming could be solidly attributed to human activities.
In the United States, the climate research program that was taking form was called the Global Change Research Program. It was a multi-agency effort, and NASA's role was the provision of global data from space. Approved in the fiscal year 1991 budget, the resulting "Earth Observing System" would be the agency's primary contribution to American climate science. In 1993, the United States signed the Framework Convention on Climate Change, further committing itself to "research and systematic observation"in support of climate science.
The Earth Observing System era
By 2007, NASA had 17 missions contributing space-borne data to climate science, and its Earth science budget varied between $1.2 and $1.4 billion per year. It had active programs to obtain and convert data from Defense Department and National Oceanic and Atmospheric Administration satellites as well as from certain European, Japanese, and Russian satellites. It also sponsored field experiments to provide "ground truth" data to check instrument performance and to develop new measurement techniques.
Instruments on the Terra and Aqua satellites have provided the first global measurements of the distribution and properties of atmospheric aerosols. Others aboard Aura study the processes that regulate the abundance of ozone in both the stratosphere and troposphere. Data from the Grace and Icesat missions and from space-borne synthetic aperture radars show unexpectedly rapid changes in the Earth's great ice sheets. The Jason mission is monitoring an increasing rate of sea level rise. The Earth Observing System's weather instruments have enabled the first improvement in weather forecasting skill in more than a decade. Many EOS instruments contribute to studies of clouds. These play the most important role in controlling Earth's climate, by changing the amount of sunlight that reach the Earth's surface.
Nearly thirty years of satellite-based solar irradiance and atmospheric temperature data helped enable the Intergovernmental Panel on Climate Change's 2007 statement that "Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations." But while there's little doubt that humans are making the world warmer, there's still a lot to learn about what the consequences will be. How much warmer will it get? How much faster is sea level likely to increase? What will happen to soil moisture, and therefore agricultural production, in a warmer world? NASA scientists and engineers will help answer these and other questions in the future.
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