Washington DC (Map, News) - With the possible exception of immigration, no current issue ignites more passion than global warming. The unfortunate consequence of this is that it is difficult to find a discussion of global climate change that isn't slanted in some way.

Yet, there is both far more agreement and far less certainty than the headlines lead us to believe.

Here's what we know: The earth has warmed by one-half to three-quarters of a degree Celsius since 1880. We also know that the warming has coincided with widespread industrialization and a 36 percent increase in atmospheric carbon dioxide. But we don't know if these phenomena merely overlap or there's a cause and effect.

Climate science is extremely complex. Instrumental records cover just a short time period in the broad sweep of geologic history. Moreover, as Prof. Richard Lindzen of MIT told us last fall, climate damage is not a simple consequence of carbon dioxide (CO2) emissions and warming.

Long chains of linkages are required. Scientists may have an excellent understanding of everything in that chain – such as economic output, carbon concentrations, and ice sheets melting – but no one fully understands the myriad factors connecting them.

Despite this complexity, there are vast areas where scientists agree. They agree, for example, that:

• At 382 parts per million (ppm), atmospheric CO2 concentrations are at the highest level in the 150,000-year geological record and that it has taken less than a century to increase from 280 ppm, providing evidence that human activity has contributed at least partly to the increase.
• As a greenhouse gas, CO2 likely contributes to warming. But it's not clear how much.
• Sea levels have risen by approximately eight inches in a century and the oceans have become more acidic.
• Hurricanes are not caused by global warming.

Are humans causing the planet to warm? The evidence is inconclusive. There are also many possible natural explanations, including solar variability; aerosol variation; changes in cloud cover; greenhouse gases; changes in land use; natural variability from factors such as El Niño; the oceans' thermohaline circulation, and more. Changes in any or all of these may account for all of the warming recorded since 1880.

There is also evidence that CO2 is far from the most important contributor to global warming. Previous interglacial periods were much warmer, but had far lower concentrations of CO2 in the atmosphere. We might some day come to conclude that CO2 concentrations lag temperature increases and that there are many, not just one, causes for climate change.

Modern climate science relies on large, complicated computer models that describe and predict the climate system. But the models are inherently unreliable and unstable. For instance, climate models have predicted three to six times more warming than has actually occurred to date. Thus, even a broad climate consensus may prove wrong.

As Gordon Michaels of the Oak Ridge National Laboratory told us at the same conference at which we spoke with Professor Lindzen, the task of reducing CO2 is formidable. But current wind, biomass, solar and other "green" technologies are not capable of "scaling up" to meet global energy needs. Nor is their environmental impact well understood.

The best alternative technology is nuclear power. Not only is nuclear technology carbon-free, aside from the uranium enrichment process, it's just 20 percent to 30 percent more costly than coal. And the supply of uranium-238 needed for fast-breeder reactors could meet projected needs for more than a billion years.

While nuclear energy currently is used mostly to produce electric power, it could be used to generate electricity for electrolysis, the process that extracts hydrogen from water, the most likely energy source of the future.

We all need to be open minded. If it turns out that there is only a weak link between CO2 and climate warming, dedicating trillions of dollars toward reducing emissions would be a foolish investment. As Ken Green of the American Enterprise Institute put it, our wisest policy choice today is whatever we'll least regret if we're wrong.

Michael Rizzo is a senior economist at the American Institute for Economic Research in Great Barrington, Massachusetts.