This myth arises from the claim that since carbon dioxide always rises during periods of warming it is merely a symptom of that warming and not a cause. The argument is based on the fact that, indeed, in the past rising global temperatures after ice ages retreat have led to increased CO2 production. While it may seem to conclusive to those without any background in the science of climate change, the truth is it does not prove that CO2 and other greenhouse gases are not contributing to our current increases in average global temperatures, as the authors of The 7 biggest myths about climate change explain:

The ice cores show that there is a remarkable correlation between CO2 levels and temperature over the past half-million years. It takes about 5000 years for an ice age to end and, after the initial lag, temperature and CO2 concentrations in the atmosphere rise together for at least 4000-odd years.

What seems to have happened at the end of ice ages is that an initial warming due to orbital shifts led to more CO2 being released into the atmosphere, resulting in further warming that caused still more CO2 to be released and so on. As the area of ice shrank, temperatures rose still higher.

Where did the extra CO2 come from? The evidence suggests it was from the oceans. The gas is less soluble in warmer water, so warmer seas release it into the air, but this can explain only a little of the increase. Another factor may have been biological: phytoplankton in the seas soak up CO2 as they grow and fall to the ocean floor, but as the world warmed changes in winds, currents and salinity would have cut the phytoplankton's growth. [...]

While CO2 was only a secondary player in the ice ages, further back in time there are examples of warming triggered by rises in CO2 (see below). What the ice ages tell us is that temperature can influence CO2 levels as well as vice versa, which is a cause for concern. [...]

... The warmest period was probably the Palaeocene-Eocene Thermal Maximum (PETM) about 55 million years ago. During this event, which coincided with mass extinctions, global temperatures may have warmed by 5 to 8 °C within a few thousand years. The Arctic Ocean reached 23 °C.

Isotope levels in fossil plankton show the warming was caused by the release of massive amounts of methane or CO2. The latest theory is that this was due to lava from a massive volcanic eruption heating coal deposits. In other words, this may be an example of catastrophic global warming caused by the sudden release of massive quantities of fossil carbon into the atmosphere. The warm period lasted 200,000 years.

So, CO2 increases can and have caused global warming in the past, to levels that caused the mass extinctions of species of life on earth, just like the mass extinctions which are occurring today. The fact that CO2 increases have slowly lagged during periods of interglacial warming after ice ages does nothing discredit the deleterious effect of sudden increases of CO2 and other greenhouse gases into the atmosphere, during past or present episodes of global warming unrelated to the retreat of glacial ice.

Myth No 2: Current warming is no big deal because the earth has experienced greater warming in the past

This is a common fallacy. Just because warming has occurred in the past over millions of years doesn't mean that the current levels of increased warming is good or even acceptable for human beings and other life forms today.

Do these past periods of natural warming mean we can dismiss the rapid warming over the past few years as more of the same? The answer is no. Natural factors such as changes in the amount of solar energy reaching the Earth can explain only a small part of the recent warming.

Nor does the fact that it has been warmer in the past mean that future warming is nothing to worry about. The sea level has been tens of metres higher during past warm periods - enough to submerge many major cities.

Hardly something to ignore just because it happened in the past now is it?

Myth #3: Because Human CO2 production is small in comparison to natural sources, human activity can't be the reason the earth is warming

YES, it's true that CO2 emissions due to human activity are small compared with most natural sources. Yet ice cores show that levels in the atmosphere have remained fairly steady at between 180 and 300 parts per million for the past half-million years, only to shoot up to more than 380 ppm since the industrial age began.

How is this possible? The answer is that natural sources are balanced by natural sinks (see above). The breakdown of organic matter, for instance, releases huge quantities of CO2, but growing plants soak up just as much. CO2 levels have risen because slightly more of the gas has been entering the atmosphere each year than can be soaked up by natural sinks.

How can we be sure that we are responsible for the extra CO2? There are several lines of evidence. For instance, fossil fuels contain virtually no carbon-14, because this unstable isotope, formed when cosmic rays hit the atmosphere, has a half-life of around 6000 years. Nearly all the carbon-14 in a fossil fuel will have long decayed by the time we burn the fuel, so the resulting CO2 will contain almost no carbon-14 too. Studies of tree rings have shown that the proportion of carbon-14 in the air dropped by about 2 per cent between 1850 and 1954 (after 1954, nuclear tests released large amounts of carbon-14).

Finally, claims that volcanoes emit more CO2 than human activities are simply not true. CO2 levels around the world do not rise after major eruptions. [...]

So, by adding more CO2 than the natural processes (oceans, plants, etc.) that absorb natural sources of CO2, it is human activity which is the culprit. Like the levees that failed in New Orleans, we've added just enough carbon dioxide to overcome Mother Nature's ability to balance natural CO2 production with natural CO2 absorption, thus creating conditions for a rapid and unprecedented rise on global temperatures.

Myth No. 4: Global Warming is a good thing, at least for people in colder regions

Things will become increasingly dire as temperatures climb to 3 °C above present levels, which could happen long before the end of the century in the worst-case scenario. More than a third of species will face extinction. Agricultural yields will fall in most parts of the world. Millions will be at risk from coastal flooding. Heatwaves, droughts, floods and wildfires will take an ever heavier toll.

There are two factors to bear in mind when thinking about the outcomes of warming. Firstly, even countries that escape the worst direct effects will feel the economic and political fallout from what happens elsewhere. Secondly, there is a time lag between a rise in greenhouse gases and their full effect on climate. Even if CO2 levels were stabilized tomorrow, the world would continue to warm for decades.

There is an even longer lag between any warming and its full effect on sea level. The IPCC is predicting a rise of 0.6 metres at most by 2100, but this will be just the start. Three million years ago, when the temperature was 2 to 3 °C higher, sea level was 25 metres higher - more than enough to inundate New York, London, Tokyo and Shanghai. A similar temperature increase will eventually lead to a similar rise in sea level. The IPCC assumes this will take many centuries, but some think it could happen much sooner due to the catastrophic collapse of ice sheets.

Add in a likely greater increase in violent weather (storms, tornadoes, hurricanes, blizzards, droughts) and increases in infectious diseases (some of which we are already experiencing) and I think it's safe to say that everyone will be effected by global warming in some manner. What happens if Florida and California can no longer produce all the fruits and veggie we've been accustomed to? Or the Great Plains suffer droughts equal to or greater than the Dust Bowl era of the 1930's? Warmer weather in Maine or Upstate Michigan won't make up for massive reductions in our agricultural production, my friends.

Myth No. 5: It's all caused by the Sun

Actually, it's not:

NO ONE denies the crucial influence of the sun on Earth's climate. The total amount of energy reaching Earth varies, but recent variations cannot explain the recent warming.

You want more evidence? Just check out these articles at Real Climate, the premier climate science blog on the web. They expose the canard that solar activity is the driving factor behind global warming better than anything I could say.

Myth No. 6: Antarctica is getting cooler which proves that global warming isn't real

To rebut this, all I need do is link to this recent report about ice melting in the interior of Antartica where no one expected to find melting:

Warm temperatures caused extensive areas of snow to melt in west Antarctica in January 2005, according to a new study.

It was the first widespread Antarctic melting ever detected, said the study conducted by a team of scientists at the National Aeronautics and Space Administration (NASA) and the University of Colorado.

Combined, the affected regions encompassed an area as big as California, according to the study. [...]

The observed melting occurred in multiple distinct regions, including far inland, at high latitudes and at high elevations, where melt had been considered unlikely.

And this story from last year:

The Antarctic ice sheet is losing as much as 36 cubic miles of ice a year in a trend that scientists link to global warming, according to a new paper that provides the first evidence that the sheet's total mass is shrinking significantly. [...]

The new Antarctic measurements, using data from two NASA satellites called the Gravity Recovery and Climate Experiment (GRACE), found that the amount of water pouring annually from the ice sheet into the ocean -- equivalent to the amount of water the United States uses in three months -- is causing global sea level to rise by 0.4 millimeters a year. The continent holds 90 percent of the world's ice, and the disappearance of even its smaller West Antarctic ice sheet could raise worldwide sea levels by an estimated 20 feet.

And this one from 2004:

Glaciers once held up by a floating ice shelf off Antarctica are now sliding off into the sea -- and they are going fast, scientists said on Tuesday.

Two separate studies from climate researchers and the space agency NASA show the glaciers are flowing into Antarctica's Weddell Sea, freed by the 2002 breakup of the Larsen B ice shelf.

Well, you get the idea.

Myth No. 7: It was warmer during the Middle Ages than it is now

Historical anecdotes about climate have to be treated with caution. ... In fact, the slowing of the river by the old London Bridge, demolished in 1831, was a crucial factor in its freezing - which is why the Thames did not freeze in London in the winter of 1963, even though it was the third-coldest in England since 1659. ... There are now a dozen or so temperature reconstructions for the northern hemisphere that go back beyond 1600. These studies show periods of unusual warmth from around AD 900 to 1300, but the details vary.

In the southern hemisphere, there is evidence of both warm and cool periods around this time. This suggests the Medieval Warm Period was partly a regional phenomenon, caused by a redistribution of heat around the planet as well as a small rise in the average global temperature.

The reconstructions and other evidence show that the planet is warmer now than at any time during the medieval period ... What really matters, though, is not how warm it is now, but how warm it's going to get in the future. Even the reconstructions that show the greatest variations suggest that average temperatures remained within a narrow band right up to the 1980s. Now we are out of that band and climbing fast.

So, the next time some uninformed global warming denialist you know starts spouting one of these myths feel free to pass along this information to him or her. Who knows, you might even change someone's mind. After all, with Bush's approval ratings sinking to Dick Nixon territory lately anything is possible.

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