Here's my counterargument to claims that increases in global CO2 do not "cause" global warming. A straw argument claims that scientists say that rises in global atmospheric CO2 precede global warming events. Climate scientists do NOT claim that, as says the section below that I copied from a recent review article in New Scientist.
The article says that increases in CO2 sometimes lagged behind the beginning of warming events as many as 800 years during past episodes. But this is no argument for claims that CO2 is NOT a greenhouse gas nor that current warming is NOT due to anthropogenic causes. Perhaps the problem is semantic: that between "trigger" and "cause." Build-up of CO2 is not the trigger, but it is a driver of atmospheric warming.
The article: Climate myths. Brahic, Catherine, Chandler, David L., Le Page, Michael, McKenna, Phil, Pearce, Fred, New Scientist, 5/19/2007, Vol. 194, Issue 2604.
From the article: "With so much at stake, the last thing we need is for the real issues to be obscured by discredited arguments and wild theories. We must act now to avoid the worst effects. So for those who are not sure what to believe, here's our guide to climate myths and misconceptions. [...] Decide for yourself."
"Myth: Carbon dioxide levels only rose after the start of warm periods, so CO2 does not cause warming. [...] [I]t appears the lags might sometimes have been 800 years or more. [...]These lags show that rising CO2 did not trigger the initial warming at the end of these ice ages--but then, no one claims it did. They do not undermine the idea that more CO2 in the atmosphere warms the planet."
The climate-change scenario is complex and models have not reached full potential. But, claiming that because increases in CO2 levels do not precede warming events and that there have been triggering events such as ones due to Milankovitch cycles (periodic changes in sun radiation) does not fully explain rises in warming, especially the recent one that we are now in.
Here is how the scientists in New Scientist begin: "Our planet's climate is anything but simple. It depends on the interplay of many factors, from massive events in the sun to microscopic creatures in the oceans. Yet a clear picture has emerged, supported by an overwhelming amount of evidence: the world is warming, this warming is due to increasing levels of greenhouse gases caused by human activity, and if emissions continue unabated the warming will too, with ever more serious consequences."
As a physical geographer, who is a climate scientist and my mentor on this subject, said to me last year: "Global warming is real; anthropogenic causes are real; and you should feel it your duty to teach it."
And, I do.