Are human-induced changes to the environment causing global warming? Policy makers and the general public want to know now whether increased amounts of "greenhouse gases" such as carbon dioxide are permanently altering our climate. Their sense of urgency is understandable, given what is at stake. A warming of even a few degrees could have serious implications for weather patterns and water resources. But in the rush for fast answers, it's tempting to overlook what the science reveals.

That is what happened recently when a National Research Council panel on which we participated released a report on measuring the Earth's surface and atmospheric temperature changes - one aspect of the global warming debate. When the report hit the streets, several news outlets across the country cited it as one more piece of definitive evidence that greenhouse gases were causing the Earth to warm. Policy makers rushed to announce initiatives to combat the problem. To add to the confusion, some interest groups with entrenched positions tried to discredit findings that did not support their views. Others misused our report to tell only part of the story.

But by trying to turn global warming into a "pro" or "con" issue, a scientific matter suddenly becomes politicized. Instead of learning from the latest scientific findings and getting closer to the truth about global warming, we become mired in an artificial debate that nobody can win. To really understand long-term global climate change, we have to pay attention to what the science tells us. And like it or not, the evidence to date is telling us that while we're making great strides, we still don't have all the answers.

Our panel was asked to settle some of the puzzling inconsistencies that have helped spur the controversy over global warming in the first place. Many in the scientific community were troubled by an apparent incongruity between two different sets of temperature data. Surface-temperature measurements indicate that the Earth has warmed. But data collected by satellites and balloon-borne instruments since 1979 indicate little, if any, warming of the upper atmosphere.

After reviewing the data, we found that despite these differences in temperature data, the Earth has indeed warmed by about 1 degree Fahrenheit in the past century. In fact, surface temperatures in the past two decades have risen at a rate substantially greater than average for the past 100 years. These are important findings, to be sure. But we also need to be aware that although the Earth's surface temperature has increased substantially in the past 20 years, that increase may not necessarily be representative of any long-term climate change caused by greenhouse gas emissions.

The differences between the surface and upper-air data are probably due to a combination of factors. For example, depletion of ozone in the stratosphere may have cooled the atmosphere without affecting the surface temperature. And the debris that entered the atmosphere when Mt. Pinatubo erupted in 1991 also produced cooling, which was probably more pronounced in the satellite measurements than in those recorded at the Earth's surface. When these factors are taken into account in atmospheric models, the simulated trends agree more closely with the temperature observations, although some discrepancies remain.

So we know that despite differences in the two sets of temperature data, the Earth's surface is in fact warming. Our panel did not address whether greenhouse gases have led to the temperature increases of the past two decades. Unfortunately, the important distinction between greenhouse warming and global warming was all but ignored by some policy makers and interest groups who seized on our findings to further their own agendas. Many scientists do believe that increasing greenhouse gases or other human-induced changes are responsible for the warming, but some still have reasonable doubts. As scientists, it's our responsibility - and it's a hallmark of sound science - to point out the many uncertainties that need to be explored.

If we really want to understand global warming, then it's time to forget about choosing sides and let science do its job. It's the only way to ensure that our decisions are based on the best available information.