Stop the press! GrahamY has a graph that shows our CO2 is lower than ever before.

From a random political blog without any referencing as to the scientific source, but we're all gullible idiots here so who's to question it?

Actually, my son drew a line when he was three that, to this day I am convinced shows that CO2 didn't even exist until 1815, so who are we to believe?

Personally, I prefer to refer to information from reliable sources Graham, such as the graphs on this page from NASA:

http://climate.nasa.gov/keyIndicators

But I'm sure your unknown political blogger knows better than NASA when it comes to all things climate science.

rstuart – in the spirit of the article, I was offering an alternative perspective of this issue; trying to zoom out a bit to avoid the wood-for-trees blinkers often seen on both sides of the AGW fence.

Your responses?

(1) Man has seen CO2 levels lower than 200ppm and it is increasing now. I’m not sure whether you are suggesting that 200 – 300 ppm should be the benchmark concentration or you are agreeing with the fact that we have narrowly avoided calamity at these low levels.

(2) That there was a mass extinction at the end of the Permian following the Carboniferous when the atmospheric CO2 was reduced from about 5000ppm to less than 1000ppm (this is the same CO2 we are naughtily re-releasing back into the atmosphere). Again, I’m not sure whether you are agreeing with my hypothesis or not.

Graham Y – thanks for the graph. I like the expression “carbon drought”.

TrashcanMan - oops, you should check your timeframes before you start huffing and puffing mate.

The NASA graph shows 400,000 years (a eye-blink in geological time) while GrahamY's graph shows 500 million years. Even rstuart's wikipedia pages provide a graph showing CO2 levels similar to GrahamY's graph.

Where did you think the carbon came from to make all the coal? Or was this black stuff simply placed there on the sixth day?

Peter Mac/ GrahamY

I should have looked at that. I jumped the gun and admit to being wrong in that respect. But you can understand it's invariably irritating when people post up links to internet bloggers as evidence.

So I did the hard work for you, which wasn't that hard, and found the original paper from which the graph was taken. It is, indeed, quite a legitimate source after all:

http://www.pnas.org/content/99/7/4167.full

The science behind this is credible, so my apologies again.

What's interesting is that the high CO2 levels 200 million years plus ago can be attributed to large levels of magmatism (which is half the basis of the relationship this paper's theory is based on) and less so to climate variations.

According to the paper, CO2 levels started dropping 200million years ago, about the time mammals started getting about on earth, as magmatic activity died down.

We don't have huge amounts of magmatic activity occurring now to be forcing CO2 up, so the periods of high CO2 in the graph lose their relevance to what is happening now.

So the longer term CO2 levels are not as relevant as the shorter term levels which have seen a steady cycle of warming and cooling

@Peter Mac: That there was a mass extinction at the end of the Permian

Indeed. Conditions were so good the planet life went into exponential overshoot, triggering an anoxic event in the oceans. Evidently you add up the explosion of life during overshoot followed by the extinction of 96% of marine species followed again by an explosion as life recovered, and get a positive ledger. I'd say that is a matter of taste, but perhaps the real point is I'm glad our species didn't have to survive the greatest extinction event the planet has seen.

@Peter Mac: I’m not sure whether you are suggesting that 200 – 300 ppm should be the benchmark concentration or you are agreeing with the fact that we have narrowly avoided calamity at these low levels.

I not suggesting either. The plants in the past seem to do equally well under all conditions. Beyond that, who knows? You evidently don't. I don't, and I am not certain anybody else does either as I've read contradictory opinions from biologists. So why bring it up? Seems like a red herring to me.

@Peter Mac: Even rstuart's wikipedia pages provide a graph showing CO2 levels similar to GrahamY's graph.

One would hope so.

@Peter Mac: Where did you think the carbon came from to make all the coal? Or was this black stuff simply placed there on the sixth day?

You seem to think carbon available to life is a zero sum game. It's not. There is a geological carbon cycle. Google it to get a background. It's ultimately more powerful than anything life can do, so if life buries carbon it provides more, it life releases carbon it turns it into rock. It will have no effect on AGW, as it operates over many millennia, not centuries.

@GrahamY: It also provides a cross-reference against world temperature at the time too.

And you point out they aren't directly correlated. I presume you have seen the explanations and reject them, but in case you haven't here is the best I've seen: http://www.youtube.com/watch?v=fpF48b6Lsbo

Trashcanman, the graph was linked to the original source, but thanks for the apology. However, the source of the CO2 shouldn't really concern us as the fact is that it was there.

rstuart, I'm not sure what your argument is about the Permian extinction. How is life supposed to go into "exponential overshoot" and exactly how is that supposed to lead to an anoxic event. As far as I know no-one has a particularly good theory as to what called the extinction.

Also not sure what your theory is as to why there is no correlation between CO2 and global temperature over historical time scales. I don't have time to watch a YouTube video.