James Hansen and I share a background in astrophysics. Both of us have PhDs from prominent astrophysics groups at Midwestern universities. We even agree on many things. But that does not include atmospheric carbon dioxide. Hansen sees carbon dioxide as diabolical. Many others including me see it as the gas of life, with little climate significance.

How are such disagreements addressed in science? Hansen would probably want to argue the theoretical, while I would argue the practical. Hansen would surely tell you that carbon dioxide is a greenhouse gas that slows the departure of heat from the Earth's surface. Hence, adding more to the atmosphere SHOULD cause warming. It sounds so simple that it should be correct. But it is far from that simple.

First of all, as an experimental physicist, I know that robust empirical data have the last word in science, not theory. If the data we gather disagree with the theory, then the theory is wrong. That is the way science works. It does not matter how many supporters a theory has or who they are. If the data disagree, the theory is dead. In the case of Global Warming, the minute amount of warming observed over the last 150 years and when it occurred relative to increasing CO2 says that carbon dioxide is not the cause.

And if Hansen wants to reach back to the previous interglacial period known as the Eemian, then the ice core data must be discussed. It not only shows the very regular global temperature cycles we call ice ages but also the very close tracking with atmospheric carbon dioxide of the time. Hansen knows, even if Al Gore will not admit it, that atmospheric CO2 followed the global temperature and therefore could not be the cause.

Hansen is also well aware that we were warmer 8,000 years ago during the peak of the present interglacial we call the Holocene Climate Optimum when CO2 levels were lower. He is also aware of the fact that we have been cooling on average since then due to an advancing Milankovitch Cycle, involving changes in the Earth's orbit, primarily caused by the planet Jupiter. The brief warm periods that have occurred in recent millennia go by the names of the civilizations they spawned: Minoan (Greek), Roman, Medieval, and Modern. They have nothing to do with man-made CO2.

Even more fundamentally, we should ask if our burning of fossil fuels and even our breathing is really contributing to the observed slow rise in atmospheric CO2. We release about 10 Gt of carbon into the atmosphere each year (as CO2) that already contains about 800 Gt. Yet the annual increase in carbon is only 5 Gt. That says there is a big leak! And the atomic bomb tests in the 1950s and 1960s revealed that specially marked carbon-14 disappears within about five years.

Where does the CO2 go? It turns out that the Earth has vast sinks for carbon, involving a total amount of about 40,000 Gt. That makes human emissions of a mere 10 Gt per year remarkably insignificant. The Earth's biosphere and oceans are the big players in the carbon cycle, along with the atmosphere.

Hopefully our children will find this subject sufficiently fascinating to learn the real science. It is infinitely more fascinating than the mind-numbing politics. If politics are allowed to supersede science, we will indeed face an apocalypse of major proportions. Our civilization depends on competent science.