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Carbon dioxide & 800-year lag behind temperature
How alarmists think
As we have explained in 2006, Vostok ice core records show that the carbon dioxide concentration averaged over a few centuries has been correlated with temperature at least for half a million of years. However, we know for sure that the temperature was the cause and the CO2 concentration was its consequence, not the other way around. It follows that the greenhouse effect hasn't been important in the last half a million of years.
There are many ways to see it. The 800-year lag is the most popular one, it has been featured in the Global Warming Swindle (especially in this two-minute-long segment), and we will discuss it below. However, there are other ways to see that the influence of temperature on the concentration of gases has been more important than any influence in the opposite direction. For example, the ice core records show that the concentration of methane was correlated with temperature, too. If the CO2 concentration were the primary cause, we would have no explanation why the CH4 concentration was also correlated. In fact, CO2 and CH4 play the very same role in the ice core records. If some combination of them determined the temperature, we would still have no explanation why these two concentrations were correlated with one another.
Moreover, easy reasoning can be used to show that the ability of oceans to store gases decreases with increasing temperature and this effect is clearly much stronger than the greenhouse effect.
The 800-year lag
However, the most popular - and the most straightforward - explanation of the direction of the causal relationship is the fact that in all cases, the CO2 concentration only changed its trend roughly 800 years after temperature had done the same thing. There have been many papers that showed this fact and incidentally, no one seems to disagree with it. For example, a recent paper by Lowell Stott et al. in Science (2007) showed that 19,000 ago, when the last ice age started to go away, CO2 lagged by about 1,000 years, too.
Every sane person knows that this detailed insight implies that the greenhouse effect couldn't have been among the most important effects. Not only the ice core data fails to provide us with evidence supporting the greenhouse theory of the climate; it provides us with strong evidence against it.
The greenhouse effect has been much less important than outgassing. Although we add more CO2 than what Earth has seen for millions of years, the small characteristic importance of the greenhouse effect probably wins.
For whatever reason, some people are not willing to accept this obvious conclusion. That's why they invent various bizarre verbal constructs to circumvent the otherwise inevitable conclusion. The whole "group" at RealClimate.ORG has agreed that there was a lag. But they say that in the first 800 years when the influence of temperature on CO2 is manifest, it was indeed temperature that drove the gases. But in the remaining 4200 years of the trend, it was surely the other way around: CO2 escalated the warming, they say.
Everyone who has basic understanding of feedback theory knows that what they talk about is a textbook example of a positive-feedback system, and if the climate were such a system, the mutually supportive interactions would lead to exponentially escalating temperatures in one of the possible directions. That's clearly not observed in the data and the positive-feedback hypothesis is thus falsified.
