NOAA Satellites Observe Warming Oceans Profile: Q&A with Sydney Levitus

Syd Levitus

Syd Levitus

Sydney Levitus, an award-winning oceanographer and researcher at NOAA, has tracked historical changes in the world's oceans for the past 25 years. As director of the Word Data Center for Oceanography and chief of the Ocean Climate Laboratory at NOAA's National Oceanographic Data Center, Levitus is recognized as one of the top experts in ocean sciences, and was just elected as a 2010 Fellow by the American Association for the Advancement of Science (AAAS). Recently, he offered insight on the impact of climate change on the oceans and the crucial role satellites have in ocean research.

Q: How is the ocean's absorption of heat impacting weather and sea-level rise? A: The ocean's heat absorption is affecting sea level in a measurable way. One of the reasons for the observed increase in sea level during the past 50 years is that the ocean has warmed and expanded in many places. It's actually the ocean that heats the atmosphere because, nearly everywhere, sea surface temperature is warmer than the temperature of the overlying atmosphere. Any change in how much heat the ocean is storing may affect our weather. We are now seeing the melting of permafrost, mountain glaciers, and many other phenomenon that are the results of a warmer climate. The ocean plays a key role in all of this because of its tremendous capacity to store heat and move this heat around.

Warming Oceans Global Visualization

This image, developed by NOAA Environmental Visualization Laboratory was generated from NODC's World Ocean Atlas. It shows the long-term average sea surface temperature for February.

Q: 2010 was tied with 2005 as the warmest year on record for combined global land and ocean surface temperatures. What would you say is the impact of climate change on the upper ocean versus the mid-to-lower ocean levels? A: The ocean has absorbed about 90 percent of the heat that has been generated by the increasing amount of greenhouse gases in earth's atmosphere during the last 50 years. In fact, by some estimates of the amount of greenhouse gases, aerosols, etc. in earth's atmosphere, we would have expected to see an even larger increase, especially for the past several years when ocean heat content has remained approximately the same in the upper 700 m of the world ocean. It may be that heat is being stored in deeper levels. This heat will warm the atmosphere for many years to come, even if we stopped increasing the amount of greenhouse gases in earth's atmosphere today.

Q: If that's the case, would that mean the warmer waters would eventually make their way closer to the surface at some point? A: Yes that certainly can occur and is one of the reasons that the effect of increased greenhouse gases may be very long-lived. This is also why we need to keep improving our ocean-atmosphere general circulation models. We need to be able to make improved projections of climate change. What happens in the future may critically depend on the heat being stored in the deep ocean.

Q: Is the ocean heat content also a factor in the amount of tropical storms or cloudy days, bacteria and fish kills? A: An ocean region, with more (or less) heat being stored in it than usual, can certainly be a factor in the amount, or intensity, of tropical storms. The existence of the Loop Current in the Gulf of Mexico is an example of this. It is a relatively deep pool of warm water that affects the intensity of storms passing over it. Variations in the intensity or position of the Loop Current will affect storm tracks.

Q: How have satellites made ocean observations easier? A : Using satellites has brought about a revolution in how we're able to observe the oceans and the type of data we're able to acquire. It's simply too expensive to put research ships everywhere to obtain ocean data, and merchant ships sail on the same geographically limited sea-lanes.

Q: Which satellite instruments, or sensors, bring oceanographers the most valuable data? A: There are several satellite instruments making a huge difference in terms of the high-quality data we have: the radiometer, altimeter, gravimeter and scatterometer. The radiometer gives us near-global sea surface temperature observations, which have helped improve weather forecasting. The altimeters provide information about changing sea level and ocean currents. Gravimeter measurements also help determine ocean currents and show us how earth's ice caps and mountain glaciers are changing. Studies of water storage in river drainage basins are now possible on a near-global basis because of satellite gravity measurements. The scatterometer measures the wind stress at the sea surface on a near-global basis. Radiometer instruments on satellites also provide information about ocean color and storm water plumes in the coastal ocean that were generated on land along with bacteria that may accompany these plumes.

Q: Why do we collect these data? How do NODC's data and products benefit the public on a daily basis? Have your scientific findings and research been used for predicting sea level or coastal rise? A: We collect and archive these data because the ocean plays a major role in determining earth's climate and our fisheries. We need to understand how earth's entire climate system works - which includes the atmosphere, ocean and cryosphere (ice) if we are going to improve forecasts of weather, fisheries, sea level, and Harmful Algal Blooms to name just a few quantities of importance to the public. We need to collect and save these data for a record of how earth's climate system is changing -- whatever the cause -- although the great majority of scientists believe that humankind is now having an effect on earth's climate. These data are also needed for testing our prediction models so NOAA can improve its atmospheric and ocean forecasts. Our scientific findings and research have been central to the improvement of understanding the reasons for present day sea level rise and will be of importance in predicting future sea level rise. This is still very much a research topic. Possible melting of parts of the Greenland and Antarctic ice caps will be important for sea level rise depending on how much melting occurs.

Q: With upcoming advanced satellite systems from NOAA- the Joint Polar Satellite System and GOES-R - how much more data about the oceans can scientists expect? A: Both of these systems will fly more advanced instruments and sensors than what are used on today's satellites. But the polar-orbiting satellite missions, like JPSS, which fly in a lower orbit compared with the geostationary satellites, will be absolutely important to furthering our understanding of what's happening in the oceans.

Q: What type of ocean analyses are the WDC and the Ocean Climate Laboratory working on now? A: We are developing climatologies with much greater resolution in the vertical. We are improving our estimates of ocean heat content by adding historical data. We acquire these historical data under the auspices of the Global Oceanographic Data Archaeology and Rescue project of the Intergovernmental Oceanographic Commission. It is partly for leadership of this project that I was elected as a Fellow of the AAAS.

Q: What was it like when you first started your career in oceanography? How has gathering observations changed? A: Even as an undergraduate, I wanted to work with ocean data and make maps of ocean properties and do computations similar to what meteorologists did in their studies of the general circulation of the atmosphere. Oceanographers were then making hand-drawn maps of ocean properties (and some still do today). Within two years of earning my M.S. degree, I was working at NOAA's Geophysical Fluid Dynamics Laboratory in the "Observational Studies Group." That is when I began the work that I do today with the Ocean Climate Laboratory which I have been able to build here at NOAA's National Oceanographic Data Center. We use computers for our data analyses and mapping and the Internet for acquiring much of the data we receive. These tools were almost unimaginable when I started my career. However, visionary oceanographers like Henry Stommel, Doug Webb, Bill Pierson, and John Apel were among those who brought us into the modern era of oceanography. Oceanographers now have a global network of profiling floats, which provide us vertical profiles of temperature and salinity about the subsurface ocean and we have satellites making measurements of the ocean. No longer do oceanographers have to depend on data gathered almost at random for their climate system studies.

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