Last year, several major oil companies got together and produced two commercials that tried to convince Americans that the more CO2 we produce, the merrier. We breathe it out. Plants breathe it in. It's part of the circle of life. Just like that Elton John song! CO2 is our life-supporting friend, they said. We need as much of it as we can get. Thankfully, those ads were laughed off the air.

They did, however, help continute the "debate" on carbon dioxide's connection to rising global temperatures. CO2 may be necessary for life, but too much of it causes global warming. Really, it does! Look:

No, it isn't proof. Scientists don't often speak in the language of proof and absolute truths. With that said, the above variation of a graph developed and published in the journal Nature by J.R. Petit in 1999 shows a striking correlation between the levels of CO2 in the atmosphere and temperature over the last 450,000 years. The graph also shows that the earth does a lot of its own regulating of both CO2 and temperature, a truth that climate change and CO2 connection skeptics are all too eager to point out. Fair enough, but in that entire 450,000 year span, CO2 parts per million levels were never above 300. Today, atmospheric CO2 concentration has surpassed 380 ppm, and is climbing rapidly (think Al Gore riding the lift up to the top of the screen in An Inconvenient Truth).

Will the temperature line in the graph follow the CO2 line's lead? The earth hasn't needed this degree of self-regulation for at least 800,000 years. Worse still, we haven't yet experienced the full consequences of this astonishing carbon dioxide concentration.

It isn't just me and Al who say so. The recent Intergovernmental Panel on Climate Change (IPCC) report confirmed the CO2 connection and the human responsibility for the dramatic increase in its atmospheric levels. They concluded (PDF):

Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.

"Very likely" is defined as a greater than 90% probability. As summarized in the UK's Independent, the IPCC also reported:

The target for stabilising CO2 levels in the atmosphere which some scientists and politicians increasingly hope to aim for - an upper limit of 550 parts per million - would probably involve a rise of 3C, perhaps one as high as 4.5C, and almost certainly no lower than 1.5C, the report says.

But a 3C rise would bring about enormous damage to agriculture, weather patterns and ecosystems across the world with catastrophic effects on human society.

The figure of 550ppm represents a doubling of atmospheric CO2 compared with the level pertaining before the Industrial Revolution. The current CO2 level is about 382ppm, having risen from 315ppm 50 years ago, and is rising by more than 2ppm annually, with the rate increasing.

The IPCC, a collection of more than 2000 of the world's top climate scientists, concluded without reservation that climate change is happening, that humans are responsible, and that emitting billions of tons of carbon dioxide into the atmosphere is one significant culprit. But can their findings really be trusted? The NRDC writes:

• Overall, the IPCC report will include work from more than 2,000 scientists appointed by more than 130 countries…

• The process is rigorous, based on open and transparent peer review.

• The Summary for Policymakers is reviewed line-by-line by scientists and government experts to ensure that it is a completely accurate reflection of the detailed scientific findings and that all comments have been fully considered.

• The IPCC brings fresh eyes to the issue — 75 percent of Fourth Assessment Report writers were not involved in the Third Assessment.

Now that we all agree that carbon dioxide is a major contributor to climate change, I know what your next question will be: "But what about the much discussed 'issue' of 'global warming' on SUV-free Mars?" Well, unless you're planning on buying a timeshare there, it's not much of an issue at all. More importantly, that globe isn't really warming, at least not in terms that have any parallel here on earth.

Some warming has been observed over the past 30 years, but it is largely confined to Mars's South Pole Cap region. To the extent that any truly "global" warming has occurred on Mars in recent years, it is a warming trend with decidedly unearthly roots. Mars's climate, unlike the earth's, is highly sensitive to immense dust storms. When these storms are active, the dust absorbs the sun's heat and warms the thin Martian atmosphere. When the storms aren't active, no such warming happens. Massive dust storms are not a cause of global warming or much of anything else on earth, making the comparison of the two planets' climate mechanisms crude at best and grossly misleading at worst.

Coming back to our little blue world, it is important to remember that carbon dioxide is not the only cause of global climate change. Other greenhouse gasses like nitrous oxide and methane are intense heat trappers as well, and their levels have also increased dramatically in the earth's atmosphere in the Industrial Age.

It's not just gasses, either. A variety of feedback loops also intensify warming trends. For instance, ice at the poles does our planet the great service of bouncing sunlight away from the surface and back out into space. When this ice melts, however, the (no longer white) water molecules absorb the sun's heat instead of radiating it away. The oceans warm. More ice melts. More heat is absorbed… Vicious, isn't it?

That viciousness is why we need to take immediate steps to curb carbon emissions and other climate change triggers. Mandatory carbon caps? Market-based carbon reduction incentives? Individual carbon taxes (while reducing personal income taxes)? I'm for it. All of it.

Now.

Temperature and CO2 image credit: Woods Hole Research Center

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