Wavetop fleets of these little disks may be the key to finding out how much heat -- or energy -- is transfered from the ocean to the atmosphere. First, scientists need to figure out how to keep seabirds from pecking them to death.
Photo by Jeff Miller, © Office of News and Public Affairs, University of Wisconsin-Madison.
Taking our planet's temperature |
Signs of a global warming fever, or just noise?
Life would be easy if scientists could simply take the Earth's temperature and note any changes to monitor the climatological health of our planet. But life, we know, isn't all that simple, and neither is keeping track of Earth's vital signs.
Climate, we should note, is always changing. Long before humans walked the Earth and began doing things that might alter climate, long-term weather regimes shifted with the continents, responded mightily to changes in the Earth's orbit and tilt of its axis, and were modified by drastic changes in the chemistry of the atmosphere.
And there are no long-term historical records of weather. It has only been in the last 100 years or so that scientists have been keeping a detailed account of such things as temperature, sea level and rainfall.
So how do scientists take measure of the Earth's climate and weather? How reliable are those methods? What can they tell us about climatological changes that might be taking place? How can we tell if humans are altering climate? The answers to all of those questions are subject to considerable scientific and political debate, and many of the most important climatological mysteries may not be answered for years to come. But scientists, we can be sure, are hard at work figuring out new ways to tap into climate. Here is a sampler of some of the more exotic schemes for measuring climate:
Now that you've had a peek inside the workshop, let's look at one of the really big tools of the modern climatologist.
- Noise. Late last year, oceanographers added a new sound to the ocean deep in an effort to gauge the temperature of the Pacific Ocean. A team of scientists led by researchers from the Scripps Institute of Oceanography began sending a low-frequency rumble through the Pacific from a set of submerged loudspeakers 88 kilometers from San Francisco Bay. Listening posts around the Pacific are tuning in to the scheduled broadcasts, timing the arrival of the faint transmissions. Because warmer water transmits sound more rapidly, this team hopes to discover large-scale changes in ocean temperature.
- Eye in the Sky. In theory, changes in sea level would be a sign that the Earth's atmosphere is heating up or cooling down. Because water expands as it heats, a rise in sea level might indicate a warmer atmosphere. Using the Topex/Poseidon satellite, a joint venture of the United States and France, scientists have noted rising sea levels, an eighth of an inch per year for 1993 and 1994. The satellite uses radar to measure the distance between itself and the ocean surface. On Earth, scientists carefully plot the satellite's orbit to determine its precise distance from the center of our planet. By subtracting the former from the latter, they can calculate sea level as measured from the center of the Earth. While the satellite has detected a rise in sea level for two straight years, that does not a trend make. More data is needed, the scientists conducting the experiment caution, to separate global warming from the usual up and down patterns of the world's ocean levels.
- Frisbees? A big unknown in any global climate scenario is the exchange of energy between the ocean and the atmosphere. Known as "heat flux," this exchange between two critical components of the global climate system is difficult to obtain because scientists do not have the luxury of cruising the oceans to take measurements. But knowing how much heat is transferred from the ocean to the atmosphere is important because, among other things, it gives birth to hurricanes and the big winter storms that frequently lash the eastern seaboard of the United States. The problem could be solved, however, with fleets of cheap wavetop sensors that can drift with the current and transmit data to satellites. Prototypes the size and shape of Frisbees have been deployed in the Atlantic and Pacific Oceans. The devices, developed by scientists at the University of Wisconsin-Madison's Space Science and Engineering Center with support from the National Science Foundation and Sea Grant, are still in the testbed stage, but early results are promising.
- Microspy. Scientists at the National Center for Atmospheric Research in Boulder, Colo., have developed a microsatellite that uses the Global Positioning System (GPS) deployed by the U.S. Air Force for navigation to sense the physical properties of the atmosphere. By detecting the bending that takes place in the GPS signals as they course through the atmosphere, scientists can infer properties of temperature, density, refractivity and moisture. Once refined, the information gleaned from this new method will help sharpen the accuracy and resolution of the computer models of Earth's climate.