by David Herring
April 27, 1999

There is clear evidence that Earth's surface temperature has risen by about 0.5°C over the last 100 years. However, there is some uncertainty as to the causes of this temperature increase, as well as what its short- and long-term effects will be on regional and global scales. Predictive computer models indicate that given a steady rise in levels of greenhouse gases, such as carbon dioxide, there will be a corresponding increase in surface temperatures. Yet surprisingly, despite a 30 percent increase in carbon dioxide levels since the beginning of the Industrial Revolution, temperatures haven't risen as much as the models predicted. Why? Because greenhouse gases aren't the only influence on temperature. There are many other variables--such clouds, aerosols, and the ocean--that also affect temperature.

Air and sea embrace

The Earth's ocean and atmosphere are locked in such an intricate embrace--as one changes so changes the other. At the interface between air and sea, there is a constant flow of information, as vast amounts of energy and chemicals (in the form of gases and aerosols) are continually being exchanged. If energy and chemicals are the languages that program the behavior of atmosphere and ocean, then regional and global scale climate variations are the outputs from this complex system. If scientists could learn to better interpret the "dialogue" between ocean and atmosphere, they could do a better job of predicting regional and global climate change.

Since the 1960s, scientists have developed sophisticated computer models to help them understand the ocean's role in moderating climate. Yet many questions remain unanswered. In recent decades, the ocean has partially offset the anticipated global warming due to rising greenhouse gas levels by exerting a cooling effect on climate. But, over the long run, scientists don't know whether the ocean's cooling influence will persist. Some theorize that if the ocean's circulation system changes, then the ocean could contribute to, or even amplify, global warming. At the heart of global-scale oceanography are the following questions: How will global warming affect life in the ocean? How do ocean temperature, chemistry, and biology influence climate? Are human activities contributing to changes in the marine environment and, in turn, how might these changes feed back to affect us?
 

Other Ocean Fact Sheets:
What are phytoplankton?
What are coccolithophores?
El Niño
La Niña

Reliable sea surface temperature measurements from space-based sensors have been a goal of oceanographers since the late 1960s. For the first time ever, NASA's Earth Observing System (EOS) missions will provide oceanographers with the radiometric resolution and precision, the scientific calibration, the surface viewing geometry, and the ability to remove atmospheric effects (such as clouds and aerosols) that will enable measurements of sea surface temperature accurate to within 0.5 Kelvin. These data will enable a better understanding of physical ocean-atmosphere coupling--particularly during El Niño events.

Moreover, by precisely measuring ocean color, scientists can accurately estimate the concentrations of phytoplankton on a global scale. Coupling ocean color measurements with atmospheric aerosol and trace gas measurements will also yield new insights into the chemical links between ocean and atmosphere.

next: The ocean's physical interactions with the atmosphere

The SeaStar spacecraft, developed by OSC, carries the Sea-viewing Wide-Field-of -view Sensor (SeaWiFS). SeaStar was launched on August 1, 1997, into a low Earth orbit. SeaWiFS is specially designed to precisely measure ocean color, allowing scientists to monitor the abundance and distribution of phytoplankton, as well as ocean currents. (Courtesy of the SeaWiFS Project)