Why we Observe the Ocean

The Sustained Ocean Observing System for Climate

Observation is the foundation for all climate information. NOAA deploys a global ocean observing system to fulfill diverse functions, including both its climate and weather forecast missions. Ocean observations also support coastal ocean applications, marine hazard warning systems (e.g., tsunami warnings), transportation, marine environment and ecosystem monitoring, as well as naval and other applications.

The ocean, which covers 71 percent of the Earth’s surface, exerts profound influence on the Earth’s climate system by moderating and modulating climate variability and altering the rate of long-term climate change. The ocean’s enormous heat capacity and volume provide the potential to store 1,000 times more heat than the atmosphere. The ocean also serves as a large reservoir for carbon dioxide, currently storing 50 times more carbon than the atmosphere. Eighty-five percent of the rain and snow that water the Earth comes directly from the ocean; conversely prolonged drought is influenced by global patterns of ocean temperatures. Coupled ocean-atmosphere interactions such as the El Niño-Southern Oscillation (ENSO) influence weather and storm patterns around the globe. Sea level rise and coastal inundation are among the most significant impacts of climate change, and abrupt climate change may occur as a consequence of altered ocean circulation.

Due to high thermal inertia, the “memory” of the ocean is a hundred years or more for certain weather and climate-relevant phenomena, whereas the memory of the global atmosphere is about a week or less. Consequently, the forecast of weather conditions beyond a week or two requires ocean information, and, particularly under storm conditions, even short-term weather forecasts are improved by including ocean-atmosphere interaction. The longer the time-scale, the more important the ocean becomes. Predictions of climate conditions in the seasons and decades ahead, therefore, depend critically on ocean data.

A key feature of the ocean is its constant motion, which redistributes heat and the freshwater the ocean receives from precipitation, snow and ice-melt. The ocean and atmosphere influence global climate in different but complementary ways as they exchange heat and freshwater. For example, evaporation, which adds water vapor that is less dense than air to the atmosphere, induces upward mixing and subsequent release of energy into the upper atmosphere with widespread influence on weather and climate; conversely, precipitation, which adds freshwater to the ocean, makes its surface layer less salty and less dense, reducing downward mixing in the ocean. Cooling the lower atmosphere makes the air more stable, reducing upward mixing, whereas cooling the upper ocean makes surface water denser, increasing downward mixing. Because the relative influences of such phenomena vary regionally, it is important to observe the ocean in many locations. In the tropics, surface ocean warming associated with El Niño increases evaporation and convection, altering distant rainfall patterns; in high latitude regions, atmosphere-induced ocean cooling is a major contributor to global phenomena such as the meridional overturning circulation.