200 years clearly isn't enough, 100 isn't either, 10,000 also is not, 100'000 is a little better but according to historical evidence that covers only a single cycle, the rate of change occurs about every 100,000 years. Long story short going back 100,000 years gives us a look at how this current cycle has developed, going back 200,000 years gives us a cycle to compare it to, so on and so forth.
Looking at this chart.
http://en.wikipedia.org/wiki/File:Vostok_Petit_data.svg
variations over 400,000 years the peaks and valleys are more or less similar, the one that is most interesting is that over the last 10 several thousand years our temperatures have more or less remained stable. This shows that if anything all we have done is slowed the cooling cycling, however about 300,000 years ago we were 4 degrees of variance, where as we are currently about .8 degrees of variance (from a previous link).
What was the cause of the sudden spike of 2 degrees 300,000 years ago, it certainly wasn't human influence.
What this chart does show is that over the last several thousand years the cooling has slowed somewhat from previous cycles, this can be attributed to green house gases, but we aren't warming, we are stabilizing if anything and slowing the cycle down.
Like I said the evidence is not enough to conclude on way or another. Have we had an impact, sure, it is evident that we have altered the cycle somewhat, but to what degree of significance is anyones guess, we are not as hot as we were 300,000 years ago, but we are not cooling as fast either. So how can you make an argument that it is an attribution of Warming when we have yet to come anywhere close to the variation seen just 300,000 years ago. If anything we have caused stabilization of the temperature which we have not seen before, and don't have a record of. The only way to know for sure is too keep going through natural records to try and determine if we have indeed caused this issue or perhaps there is yet another over arching cycle that we have not mapped out yet.
We have already determined that every 100K years or so the earth sees a massive shift in temperatures, we have also seen that every 20,000 thousand years or so we have some spike in heating or cooling, what if every 400,000 years we see a cycle that has the earth stabilize for a long period of time, before it begins to vary again.
The point is we have no idea how the climate history is made up, most of these findings are only a few decades old, and it is naive to make an assertions based on such limited historical data. Until we have mapped out several hundered cycles we can not definitively say that we are witnessing something that has never happened. Sure it has never happened in our life time, it hasn't happened since the last major ice age.
http://en.wikipedia.org/wiki/File:Five_Myr_Climate_Change.svg
The earth has been warming over the last 5 million years, who is to say we are any more responsible then the natural cycle found in sedimentary deposits. The further and further back you go the "human influence" appears less and less significant and likely.
(granted we likely have much more pollutants now, which is more than enough reason to alter our position on environmental policies.)
Edited, Oct 26th 2011 2:30pm by rdmcandie
Edited, Oct 26th 2011 2:31pm by rdmcandie
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