On TV, Moore has painted himself as a conspiracy theorist and termed the scientific consensus a "religious cult." The conspiracy is necessary to his argument because he lacks the extensive research needed to prove his scientific claims. In fact, claims like his have been considered and discarded over and over again in the hundred years that scientists have been studying this topic. When your outlet isn't a peer-reviewed scientific journal but "Hannity" on Fox News, conspiracy theories work better than facts.
Moore's youthful activism has put him in harm's way more than once as he worked to try to convince governments to change their policies on nuclear testing and whale hunting. I have a deep respect for that. But these days, he is bringing that same passion in defense of some backward-looking claims.
How CO2 Warms the Earth
In his testimony, Moore makes the claim, that "no actual proof, as it is understood in science, exists" for the role of carbon dioxide in global warming. But even without the computer models, there is proof. It may not satisfy him and other denialists, but it does exist and it satisfies the majority of climate scientists.
The mechanism by which CO2 serves as a greenhouse gas is fairly simple. Energy from the sun hits the Earth's atmosphere at various wavelengths. Some of that energy bounces off into space, while some passes through the atmosphere and is either absorbed or reflected by the Earth's surface.
As the Earth's surface warms, it radiates heat back to the atmosphere. Some of that radiated heat is lost to the upper atmosphere and to space, while some of it is absorbed by gas in the lower atmosphere and radiated again, back down to the planet.
This effect is important for temperature stability and for life on the planet to exist. Planetary objects like the Moon, which has no atmosphere, or Mars, which has a very thin atmosphere, can fluctuate hundreds of degrees in temperature as the surface passes from light to shadow. Our atmosphere protects us from those extremes, modulating the heat and keeping us within a more livable range of temperatures.
Carbon dioxide is the most important of the atmosphere's so-called greenhouse gases, absorbing more of the Earth's radiated heat and hanging around longer, taking as long as thousands of years to work its way out of the atmosphere.
Its molecular structure makes carbon dioxide more effective as a greenhouse gas. The bonds between its atoms happen to vibrate in resonance with the infrared frequencies given off by the radiation of heat from the Earth's surface. That sympathetic vibration absorbs the energy and radiates it out again, some of it going back down to the surface, like an echo.
As carbon dioxide levels build, the echo gets louder. The lower atmosphere becomes a heavier and heavier blanket and warming of the surface increases.
Scientists can tell the increase of CO2 in the atmosphere is largely man-made by looking in part at the ratio between certain carbon isotopes, or variants of the molecule. That isotope profile points to a growing presence of CO2 from fossil fuels.
Ignoring Science to Prove Science
Comparing the Earth's temperatures and CO2 levels throughout history, using ice core samples, for example, shows the direct correlation between CO2 and surface temperature. Over the last 50 years, CO2 levels have increased dramatically and temperatures have similarly increased.
Moore said that correlation is faulty because of "pauses" in global warming, most notably in the period from 2000 to 2010. In order to make that statement he has to ignore the recent science that has found ocean temperatures increasing as they absorb heat and transfer it to lower levels. The models predicted that scientists would find heat trapped in the oceans -- canceling out the data that indicated a pause in rising temperatures at the surface -- and they did. That gives the science more credibility, not less. His theory correlating changes in surface temperature with solar activity is as old as the topic itself; they have been considered and discounted.