You appear to be saying that you think this could be explained by some natural variation. That seems plausible, but is not supported by scientific evidence.

The term "man-made climate change" is a term for the truth of these three claims:

1. Human activity has increased the concentration of CO2 (and other green-house gases) in the atmosphere.

2. The global temperature has risen over the last 150 years.

3. An increase in the concentration of CO2 in the atmosphere is the cause of the rise in global temperature over the last 150 years.

Point 2 is simple scientific fact by now. Measurements show that this is the case, despite being critically revised and corrected for sampling biases over the years. Point 3 is also scientific fact; the theoretical effect has been shown to be true in simple laboratory expirements (it has been known for over 100 years) and the strong correlation of CO2 concentration and temperature over the last 150 years overwhelmingly implies that this laboratory effect applies for the atmosphere as well.

That could still mean that the source of all of this greenhouse gas is natural. Still seems plausible, but again scientific evidence shows that the large majority of this "new CO2" is sourced by human activity [1]. Various sources of evidence exist; the isotopic signature of CO2 in the atmosphere is atypical for natural sources, the concentration of CO2 in the oceans is rising fastest near the surface, and there are many more pieces of evidence.

It is true that there is still a large degree of ignorance on how global temperature varies "naturally" over long periods of time. However, we can show that this specific warming we're observing today is not just a natural variation. It is caused by humans.

[1] http://www.skepticalscience.com/co2-increase-is-natural-not-...

This is a fair perspective. I propose that the scientific community's collective stance is not that this is a wild deviation from typical variations, but that a significant change will result in unfavorable consequences for humanity as a species. Such change is occurring based on the data we have available to us. If we can mitigate or delay such change, we will be better off for it. This leads to emission controls, etc.

I believe the cause for concern among the proponents of awareness and regulation is that a notable change is happening, and we desperately want the status quo. Whether or not this change falls within normal variations is irrelevant to this argument.

This is a refreshingly honest analysis. Personally I'm not convinced by the need to maintain the status quo, however. We can read all about 'X species going extinct in Y years', 'Average temperatures will go up by .X degrees in Y years', and 'X miles of coastline will be destroyed in Y years', and yet none of this explains /why/ these are undesirable outcomes. The unstated premise is that "change is bad", which is a strange position to take, to say the least.

Living in a country where a large part is located below sea level, I can assure you that a rising water level concerns me. But you're right, in the grander scheme of things global warming isn't necessarily a good or a bad thing, it just is.

I don't understand why that line of thought makes you a skeptic. Apparently you found something the current data can not answer. But why do you think your question is even relevant - more important than, say, average temperature? Just because there are questions a model can't answer, the model isn't proven wrong. It just shows that there are things we don't know yet, not that everything we know is wrong.

(I am not a climate scientist so I don't know what the main data points are that are employed in the arguments. I also don't know if your claim that your question can not be answered is correct or not)

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.

The problem is you're focusing only on one part of the evidence. The other part is the law of conservation of energy, the fact from which follows (after some modeling) that atmosphere will heat up when you add greenhouse gases.

And, quite interestingly, these two independent lines of evidence, match. (There are several others.)

In other words, you doubt the relevance of historical data. But the evidence is not just historical, it's also based on our understanding of the underlying physical mechanism.

What difference does it make if the cause is entirely man made or not. Should we let 80% of worlds population who live on the coast just deal with rising sea levels, because it natural? Do you really need to know it's causing a rise in temperature to want less trucks and cars polluting the air in your city? Or does the fact that we will never have the historic data to know for sure if humans are causing global warming, make it okay to ignore the issue entirely, forever?

>What difference does it make if the cause is entirely man made or not.

If it's not entirely man made, it would mean that efforts to curtail emissions (and consequently economic output) would be pointless and unnecessary.

>Should we let 80% of worlds population who live on the coast just deal with rising sea levels, because it natural?

It's not like the sea will simply rise several meters overnight, if it does actually rise. And again, if it's natural, then wouldn't that mean that we must, in fact, "deal with it"?

>Do you really need to know it's causing a rise in temperature to want less trucks and cars polluting the air in your city?

The air pollution you are concerned about here is sulfur, particulates, and other things unrelated to the CO2 debated over by politicians currently.

>Or does the fact that we will never have the historic data to know for sure if humans are causing global warming, make it okay to ignore the issue entirely, forever?

It certainly moves one's focus of concern to more pressing environmental and social issues.

I agree that I want humans to stop fucking up the earth and I want less pollution. But those feelings do not prove climate change exists. Science doesn't work this way.

Lets say we have my blood alcohol level measured in the last 5 mins. It's 0.2g/dL. Whats my blood alcohol level throughout my lifetime though - i reckon it goes up and down quite a bit? How do i know I'm drunk or that it was caused by this keg I just drank?

Any data gathered from physiological models I will just arbitrarily ignore... just because...[waves hands]

That's a terrible analogy. Blood alcohol level only rises upon consumption of alcohol. Temperature rises and falls due to tons of external (not fully understood) factors.

Not to mention BAC has a known baseline of 0. What is the known baseline for mean global surface temperature? Why is 1951-1980 a good choice for a base period?

well I was trying to be funny.. but blood alcohol does indeed have a physical model that relates consumption to levels in the blood.

And atmospheric temperature has a simple physical model that relates it to C02 levels. And I use the term "simple" deliberately because whilst the short term fluctuations of climate are indeed vey complex - on geological time we have always seen rising temperatures with rising CO2 and have a simple compelling atmospheric model to explain it.

Without arguing over the resolution of the historical scientific data or how fast global warming will happen - it seems inevitable that with the current CO2 levels it will happen.