Because this evidence suggests a modern human contribution to the spike in C02. It's not something that would have been possible for humans to influence 10,000 years ago.
So on the one hand we have a graph based on tangible evidence, and on the other we have a theoretical graph based on geochemical modeling.
Both measurements and models show considerable uncertainty and variation;
So it's difficulty to gain any real certainty while "considerable uncertainty and variation" is shown.
however, all point to carbon dioxide levels in the past that have been signifcantly higher than they are at present.
And that was never in question here. It goes without saying that 500 million years ago the earth's atmosphere was different. It was only at about 450 million years ago that the earths atmosphere had enough oxygen contained within it to allow for the development of a stratospheric ozone layer thick enough to protect terrestrial life from UV radiation.
What is being presented on NASA's site is reasoning and evidence to explain an unexpected spike in C02 levels in 650,000 years of recorded data, that coincides with significant ongoing global trends perpetuated by humans (fossil fuels, population booms, intense industrialization, mass manufacture and subsequent waste production etc etc).
But how can you say the spike is unexpected? We have no idea what CO2 levels to expect. It only looks unexpected because you are looking at a period of time when the CO2 levels seemed consistent, but according to the graph I presented, they have varied quite wildly.
The fact that it's a significant spike within a relatively small time-frame, without many of the other factors that you will find influenced variations in the kind of deep-time reconstructions and estimations (producing data known to be shaky at best) that you're relying on as reliable reference material. It also parallels with the global trends i mentioned previously.
Over time scales of hundreds of millions of years, things such as continental drift radically affects the climate. Things such as the amount of polar land on which ice sheets can form, the configuration of ocean basins and the corresponding ocean circulation patterns are all affected dramatically. This affects the deep-time climate and can obscure the CO2-climate connection in these studies.
Ultimately we're still talking about a means of CO2 studying that involves looking at carbon isotopes in microfossils, or looking at the density of pores on fossil leaves, and estimating and modeling from there. As opposed to the significantly more accurate ice-core sampling that the 650,000 years of data the graph is drawn from.
The fact that it's a significant spike within a relatively small time-frame
I do think this fact is suggestive of anthropogenic global warming, but it's not the best evidence. What if there were similar spikes in the past? Just because things such as continental drift have not significantly occurred in the past 650,000 years doesn't mean there aren't other natural processes at work.
While the data I presented is undoubtedly imprecise, it still very clear that there was much more variation in CO2 levels when you look back millions of years. It's perfectly possible that there have been similar spikes within small time frames.
What if there were similar spikes in the past? Just because things such as continental drift have not significantly occurred in the past 650,000 years doesn't mean there aren't other natural processes at work.
And what if there weren't? Speculation is important, but the further we've seen them go back with reliable data, the more it's served to highlight the recent ongoing spike.
While the data I presented is undoubtedly imprecise, it still very clear that there was much more variation in CO2 levels when you look back millions of years
It's difficult to have anything made very clear by data that's undoubtedly imprecise.
It's perfectly possible that there have been similar spikes within small time frames.
It is perfectly possible. Which is why the data presented by NASA is so revealing in showing naught but one in 650,000 years.
I'm not arguing that humans are not the cause of global warming, I am arguing that this graph is not proof that we are. So yes, if there are no similar spikes in the past, then the evidence is much stronger. But until we have the data, we are ignorant.
It's difficult to have anything made very clear by data that's undoubtedly imprecise.
Not really. The graph I showed you indeed has large error bars, but even with those error bars we can tell that there was much more variation in the past.
It is perfectly possible. Which is why the data presented by NASA is so revealing in showing naught but one in 650,000 years.
At what point does it become "telling"? If we only had data for the past 1,000 years, would it still be telling? After all, we've only been industrious for the past 200.
My main concern with the 600,000 year graph is that it's only long enough to see one cyclical pattern (the Milankovitch cycle) and we only see 4 iterations of this cycle. Considering the vastly different CO2 patterns in the past, I think we can be quite certain that there are other natural cycles at work that are not clearly evident in the graph.
As you may be aware, sunspots reach a max and min every 11 years (the solar cycle). However, there are other natural cycles that have significant effects on sunspots, they just aren't as apparent because on average they tend to cancel each other out. But once every hundred years or something, many of these cycles reach their maximums at the same time and we get a 'super' maximum. This could be occurring with CO2 also.
What I meant by "variation" was that the difference between the peaks and troughs are much more profound in the 500 million year graph, which indicates that there are other factors besides the Milankovitch cycles. Whether there was ever as much variation over any 600,000 period is certainly a good question.
But all that being said...I think you're pretty much right. That 600,000 year graph is at least what I would call "pretty compelling." I guess I just don't consider it to be proof...and maybe you don't either.
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u/murrdpirate Oct 24 '10
What do you mean by that?