My point is that you cannot even begin to ask what humans are doing to the global temperature if you do not even have an idea what it would look like without humans.

But why do you say "we have no idea"? Lots of things are known, like temperature averages and trends.

As I said, I am not a climatologist myself. I am a bit surprised that tree rings are supposedly not accurate enough to say things about a 150 year interval. I was under the impression tree rings develop on a yearly basis? I suppose there are other factors besides temperature that affect their growth. Then again, for standard derivation as you desire, those factors might be easy to cancel out?

For tree rings to tell you what you want, trees would need to have a linear growth-response pattern with respect to temperature, and they don't. It's more of an inverse U-shaped pattern. Trees in temperature-limited areas do tend to grow better if it gets a little warmer, but if it gets a LOT warmer they'd grow worse again. The rings get smaller if it gets too cold, but they also get smaller if it gets too warm.

For this reason, it's essentially impossible to tell based on tree rings if it was warmer than today in times past.

Another thing to keep in mind is "the divergence problem" - several tree ring series right now suggest it's been getting "colder" for the last 50 years. This might be due to that U-shaped response kicking in, or it might be for various other reasons - some hypothesize it's due to changes in air pollution. It's a known issue, but not a solved issue.

Here's a good paper on the subject:

http://icecap.us/images/uploads/Loehle_Divergence_CC.pdf

So would you say the claims are unfounded? I don't think it all hinges on tree rings, they are just one indicator of many.

I'm not sure which claims you mean.

The specific claim that it's significantly warmer now than it was about a thousand years ago during the MWP does mainly hinge on (a) tree rings, (b) ignoring the difference between high frequency and low-frequency information sources, (c) ignoring the error bars. We can't say with any certainty that current temperatures are "unprecedented" compared to the last big peak and it seems likely to me that they are not. (The MWP is making a comeback, scientifically speaking). A couple of relevant reconstructions are plotted here:

http://wattsupwiththat.com/2010/09/28/loehle-vindication/

I don't know if it is true that it all hinges on tree rings. So your claim is that everything global warming scientists have been saying is wrong because they ignored vital evidence?

I must admit to me it sounds a bit like the typical creationist argument: "but you can't explain how bone X came into existence". So never mind that evolution theory doesn't even claim to be able to provide a causal evolutionary path for every animal, and that it has been validated in countless examples (more than any other theory afaik), they find a single example that is not even relevant and use it as an excuse to dismiss the whole theory.

I don't call you a creationist, I just want to warn that you might be victim to the same kind of fallacy.

> So your claim is that everything global warming scientists have been saying is wrong because they ignored vital evidence?

Nope, my claim was only that a few things that some global warming scientists have been saying is wrong because they ignored vital evidence or followed bad evidence. Other things that even those very people say are fine. But there's a lot of confirmation bias going on, and there's a fair bit of propaganda.

A big PART of the propaganda is to mischaracterize what skeptics are saying and why they are saying it. It is simply not true that people who doubt one element of the warmist litany doubt all elements of it. Hence the need for terms like "lukewarmer". The propaganda effort says that "denialists" are disagreeing with "97% of scientists", but in fact if you look at what questions were asked to get that "97% agreement" number you'll notice that essentially all the people accused of being "denialists" are IN the 97%. The stuff skeptics disagree with is mostly stuff that is still quite legitimately up for debate. For another example (besides the "unprecedented" thing), nobody knows what the actual climate sensitivity to CO2 (including all feedback effects operative at any given time) is; the IPCC can't give an exact number on that. They can give a range of guesses, but these are still guesses. Thinking they're guessing on the high side doesn't make one a creationist or even a 3-percent-er.

Does that make sense?

It seems normal that there is debate about details of a theory. However, the relevant aspect seems to be is there significant global warming because of human influence and should action be taken against it.

I think people who deny one or both of those two points are usually called global warming deniers (or skeptics, which might give them too much credit). I don't think arguing about some detail of the theory is in the same camp.

But at the same time we can look at other planets with atmospheres w/ much higher compositions of green house gases and the environment is OBVIOUSLY unsuitable for life. So why do we think we are immune to this? We pump a lot of CO2 into the atmosphere, at non natural rates, what do you expect to happen?

But then, these other planets don't have life to regulate/change/modify/absorb the CO2 from the atmosphere. Clearly they can be used as a normal negative control, but at the same time, the data we have from these planets is minimal to say the least.