Few environmental issues have gotten as much attention from both scientists and the public as global warming. Debate over the extent and the causes of planet-wide climate change has pitted citizens against industry in what could only be described as a battle between David and Goliath.

At issue is whether Earth's temperature is truly rising and, if so, what is causing this increase. To find out, researchers need to record temperatures at many different places around the world -- a gargantuan task given the size of Earth and the near-inaccessibility of some of its locations.

What's more, temperatures change radically all the time. A drop in temperature of forty degrees or more is commonplace in some locations, as they transition from day to night or from one season to the next. To account for daily and seasonal fluctuations, and to balance out climatic anomalies, researchers collect data from as many sources as possible over a long period of time. Global temperature data from as far back as one hundred thousand years ago are particularly important because they allow scientists to compare recent observations to warming and cooling trends of the distant past. Such comparisons provide a basis from which to argue that an observed warming trend in the last century is in or out of synch with the natural rhythms of climatic change.

Indeed, climate studies focused on the last hundred years show that Earth's temperature has risen about one degree Fahrenheit since the early 1900s. Other studies reaching back much further in time suggest that global climates have seldom been stable for long. Ice samples collected as part of the North Greenland Ice Core Project, which provide a snapshot of temperatures from the last hundred thousand years, tell a dramatic story. It seems Earth has been subject to recurring ten-thousand-year warm periods followed by ninety-thousand-year cold spells -- with most of the transitions between warm and cold periods being extremely abrupt.

The most difficult question and, not surprisingly, the one that is the most politically charged is whether this century's global temperature changes are in or out of synch with natural climatic flux. The answer to this question would indicate, indirectly at least, whether humans are responsible for global warming. Many scientists are convinced that the changes we're seeing now are related to an increase in the industrial emissions of heat-trapping gases like carbon dioxide. Even so, most of those scientists would admit that the extent to which human actions are affecting the global climate, and where this will all lead are questions yet to be answered.