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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Last week proved to be an excellent case study into the uneasy relationship between the Bush administration and the science (and scientists) of global warming.

On Friday, the administration embraced a study from the U.N. Intergovernmental Panel on Climate Change that concluded with "90 percent certainty" that human carbon emissions over the last 250 years have caused the global climate to warm. Before warning of possible "unintended consequences" of mandatory carbon caps, Bush's Energy Secretary Samuel Bodwin went so far as to say:

Human activity is contributing to changes in the Earth's climate. That issue is no longer up for debate.

You might think that acknowledging the human responsibility for climate change while worrying about possible economic consequences of fixing the problem seems a bit disingenuous, but that's just because you've been reading too much Orwell.

While all this was happening, California Rep. Henry Waxman was holding hearings in the House Oversight and Government Reform Committee on a recently released report (PDF) from the Union of Concerned Scientists accusing the Bush administration of systematically manipulating science to meet their policy goals. More than 1600 government climate scientists were asked about their experiences, and findings in the report include:

Nearly half of all respondents (46 percent of all respondents to the question) perceived or personally experienced pressure to eliminate the words "climate change," "global warming," or other similar terms from a variety of communications.

Two in five (43 percent) perceived or personally experienced changes or edits during review that changed the meaning of scientific findings.

More than one-third (37 percent) perceived or personally experienced statements by officials at their agencies that misrepresented scientists' findings.

Nearly two in five (38 percent) perceived or personally experienced the disappearance or unusual delay of websites, reports, or other science-based materials relating to climate.

Nearly half (46 percent) perceived or personally experienced new or unusual administrative requirements that impair climate related work.

The report, and the subsequent Waxman hearings, inspired an exceptional editorial from the Minneapolis Star Tribune:

Good climate scientists have no political agenda. They seek to apply their skills within the long-established norms of scientific inquiry to understanding what is happening to global climates and what that portends. Their findings are critical to ensuring that the U.S. government embraces the wisest possible climate policies. Ensuring the integrity of federally funded climate science should thus be a high priority for the U.S. government, which does most U.S. climate research. Unfortunately, the Bush administration has turned that priority on its head. [...]

The reason for the political interference is clear: The Bush administration has an indefensible pro-business bias that trumps even the health and welfare of the nation's citizens. Because efforts to reduce the greenhouse gas emissions that cause global warming could have severe impacts on deep-pocket companies close to the administration, its perverse logic dictates that the global warming science be suppressed.

Scientists often have good news for us ("We cured polio!"), but sometimes they figure things out that we'd rather not hear ("Sorry, but the earth isn't the center of the universe."). Climate science is no different. It turns out that when a few billion people participate for decades in the uninterrupted practice of releasing heat-trapping gasses into the earth's fragile atmosphere, things start to heat up a bit. Denying, censoring, and distorting science in the past has set us back centuries in the quest for knowledge and truth. Denying, censoring, and distorting climate science may not leave us with too many more centuries.