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One thing that scientists look at is the range of variation of different climate models, or multiple runs of a single model.
This is discussed in the IPCC reports that I referred you to previously. See here, here, and here, for example. Additional explanation can be found here

One thing that scientists look at is the range of variation of different climate models, or multiple runs of a single model.
This is discussed in the IPCC reports that I referred you to previously. See here, here, and here, for example. Additional explanation can be found here

One thing that scientists look at is the range of variation of different climate models, or multiple runs of a single model.
This is discussed in the IPCC reports that I referred you to previously. See here, here, and here, for example. Additional explanation can be found here

One thing that scientists look at is the range of variation of different climate models, or multiple runs of a single model.
This is discussed in the IPCC reports that I referred you to previously. See here, here, and here, for example. Additional explanation can be found here

I take it you're not disputing that 98% of climatologists are convinced that climate change is occurring, and is human-caused.

As for the negative effects of this change, IPCC Working Group II covered that pretty well. There's plenty of similar reports from other bodies too, including individual climatologists.Are you claiming that these do not represent the majority opinion, or just nit-picking about the exact figure?

Fair point; I'm not aware of any formal surveys of climatologists about actual recommendations as to solutions, only on the proposition that greenhouse gas emissions are the cause.

However, the IPCC Working Group III addresses mitigation, and recommends a variety of measures, most of which are designed to reduce emission or increase uptake of CO2, and in some cases methane. I wouldn't describe this as a survey, but given that it was produced in consultation with a large number of scientists and scientific bodies, I'd call it the best representation of consensus available. Certainly I'm unaware of consensus on any other methods.

Keep in mind that these physical models do not model the complex social and economic factors that dictate the time course of atmospheric CO2 increase. As a result, they do not predict the trajectory of global temperature change—they predict the temperature change given a specific trajectory of CO2 increase. For this reason, the term "projection" is commonly used instead of "prediction" to describe the model output. So to evaluate the predictions of a climate model, it is necessary to plug in the actual CO2 values. When this is done, Hansen's 1988 model still looks quite good. Of course, as historically important as Hansen's pioneering work was in demonstrating that rising CO2 implies a problematic rise in global temperatures (a prediction that has been dramatically confirmed since then), there has been considerable scientific progress in quarter century plus since then, and he is no longer the only scientist doing this kind of work. There are multiple competing models from independent research groups, although they agree qualitatively in predicting that rising CO2 will result in climate change sufficient to cause multiple severe problems. For a full discussion of the modern state of the art in climate models, see the IPCC reports.

I doubt there are really too many numbers. For instance you could pick just one weather station and show the annual averages over a 30 year period. That would give you only 30 numbers.

Perfect example. The trend will be much smaller than the random year-to-year variation at a single weather station over 30 years. If you do see a trend, it may be due to global warming, it might be random chance, or it might be because they built a parking lot next door a few years ago. To see a clear signal, you need to take the average of every weather station on Earth, and you need to account for the spatial distribution of stations, changes in the landscape near the stations, and a host of other factors.

The changes are too subtle to see at a single weather station, but that doesn't mean they're not real or important.

Also if the data is "publicly available" then how about a link?

http://iridl.ldeo.columbia.edu/
That ought to satisfy your curiosity for a few centuries.

Admittedly even if I found the temperature data to be convincing. Even if the warming trend seemed conclusive. I would hesitate to jump to the conclusion that combustion was the cause of it. That really is a very difficult thing to demonstrate. Because the 'experiment' lacks a control. If climate scientist can figure out a way around that problem it would certainly help to sell the idea of AGW to rational skeptics.

We have figured out several ways. The important ones are:
* The spatial pattern of warming (in particular, stratospheric cooling) matches predicted greenhouse gas changes, but does not match other natural processes.
* Computer climate models of 20th century climate reproduce what actually happened in the 20th century only if human greenhouse gas emissions are included, and not otherwise.
* 20th century climate change appears to exceed all natural changes in the past 1000 years, implying that a human process is at work. (This data is too uncertain to prove the point on its own, but it does corroborate.)

Combine these arguments that natural changes cannot explain the current warming with a demonstration that what humans have done is *sufficient* to cause the observed changes (confirming that we do emit enough CO2, and it is powerful enough to cause the right amount of warming), and you've got a pretty solid argument.

I appreciate your description of yourself as a "rational skeptic", because rational skeptics are willing to listen. It sounds like you believe what you do because you've mostly seen the press releases, and not the actual arguments the scientists behind them are making. I'd encourage you to read the "Attribution" section of the IPCC Working Group 1's "Summary for Policymakers" and Technical Summary. The Wikipedia article on attribution of climate change is also (currently) very good. Many of the objections you make have been made within the scientific community over the years, and eventually addressed with new data.

I doubt there are really too many numbers. For instance you could pick just one weather station and show the annual averages over a 30 year period. That would give you only 30 numbers.

Perfect example. The trend will be much smaller than the random year-to-year variation at a single weather station over 30 years. If you do see a trend, it may be due to global warming, it might be random chance, or it might be because they built a parking lot next door a few years ago. To see a clear signal, you need to take the average of every weather station on Earth, and you need to account for the spatial distribution of stations, changes in the landscape near the stations, and a host of other factors.

The changes are too subtle to see at a single weather station, but that doesn't mean they're not real or important.

Also if the data is "publicly available" then how about a link?

http://iridl.ldeo.columbia.edu/
That ought to satisfy your curiosity for a few centuries.

Admittedly even if I found the temperature data to be convincing. Even if the warming trend seemed conclusive. I would hesitate to jump to the conclusion that combustion was the cause of it. That really is a very difficult thing to demonstrate. Because the 'experiment' lacks a control. If climate scientist can figure out a way around that problem it would certainly help to sell the idea of AGW to rational skeptics.

We have figured out several ways. The important ones are:
* The spatial pattern of warming (in particular, stratospheric cooling) matches predicted greenhouse gas changes, but does not match other natural processes.
* Computer climate models of 20th century climate reproduce what actually happened in the 20th century only if human greenhouse gas emissions are included, and not otherwise.
* 20th century climate change appears to exceed all natural changes in the past 1000 years, implying that a human process is at work. (This data is too uncertain to prove the point on its own, but it does corroborate.)

Combine these arguments that natural changes cannot explain the current warming with a demonstration that what humans have done is *sufficient* to cause the observed changes (confirming that we do emit enough CO2, and it is powerful enough to cause the right amount of warming), and you've got a pretty solid argument.

I appreciate your description of yourself as a "rational skeptic", because rational skeptics are willing to listen. It sounds like you believe what you do because you've mostly seen the press releases, and not the actual arguments the scientists behind them are making. I'd encourage you to read the "Attribution" section of the IPCC Working Group 1's "Summary for Policymakers" and Technical Summary. The Wikipedia article on attribution of climate change is also (currently) very good. Many of the objections you make have been made within the scientific community over the years, and eventually addressed with new data.

If climate change is stopped, billions of people will die

[Citation needed]. The costs (desertification, acidification, extinctions, sea level rises, population displacements, extreme weather events, famines from crop failures due to changing weather patterns etc etc) are hugely greater than the benefits (which are mostly longer-term).

Consider also that the enormous cost to the global economies adapting to such major changes will far outweigh the short-term costs of subsidising a carbon-neutral energy infrastructure.

If you're genuinely interested in learning more, you could start here, or skip straight to the IPCC WGII report that discusses this.

You seem to believe that just because the climate varied naturally in the past, present variation cannot be distinguished from natural variation.

How do you distinguish two 50 year periods, with indistinguishable *outcomes*, to two very separate *causes* (nature, vs. human CO2)?

What is your falsifiable hypothesis to exclude natural climate change?

There aren't very many places where atmospheric heat can come from, and we can look in those places.

Are you kidding me? You think we've actually got a lock on *every* single natural source and sink of heat?

Have you even read the IPCC statement on clouds?

http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch1s1-5-2.html

"the amplitude and even the sign of cloud feedbacks was noted in the TAR as highly uncertain"

We have observed all those things during the modern global warming period, and all of them fail to explain the warming during that period, regardless of what past variations they can explain.

You can't possibly expect me to believe that you've observed every factor of natural variation both in the modern era, and in the historical era. Try again :)

I note that although you have clearly been looking, you have found no example of a null hypothesis that mentions causality.

You didn't read the cite, did you? :)

""The Null Hypothesis is the hypothesis that there is no relationship between two variables. Establishing that there is a relationship between two variables is the first step in establishing whether there is a causal connection between two variables. ""

Note the word *causal*. Go ahead, I'll wait for you to read it again :)

Yes, climate scientists have considered every physically realistic mechanism that could potentially account for the rise in temperatures, including the ones that were likely responsible for past episodes of (what you call "natural") climate change.

Bullshit detectors redlining to 12 now. From the IPCC: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch1s1-5-2.html

"In spite of this undeniable progress, the amplitude and even the sign of cloud feedbacks was noted in the TAR as highly uncertain"

What kind of magical mystical process have your unnamed climate scientists used to determine the paleo cloud cover? Hint: we call it "curve fitting".

It predicts that increases in CO2 can either lead or follow warming,

Bullshit detectors up to 13, needle is bending. A hypothesis that predicts *everything* predicts *nothing*. Astrology predicts that Cancers are trustworthy, but sometimes dishonest.

There is no relationship whatsoever between the physical mechanisms responsible for climate change and the economic and psychological mechanisms that determine movements of the stock market.

On the contrary, if we can take a simple model of supply and demand, just as we take a simple model of greenhouse gases, we should be able to gloss over all the gory details of psychology (and cloud cover), and come to conclusions that are "settled", right? :)

You really don't understand the limitations of computer models, do you?

I actually worked in consulting and have helped fixing the Y2K bugs in a multinational's ERP system.

You don't know what you're talking about. There was good money to be earned in those days because companies couldn't postpone fixing their systems anymore.

Your "planes dropping from the sky" is likely just a straw-man, though. We're more talking about database errors, failures in logistics systems, that kind of thing.

"Those who are yelling global meltdown"; who's that then?

I happen to also have learned a bit about infrared spectroscopy in my chemistry study, and have *seen* the C=O double bond stretch vibration's broad peak. Arrhenius was right in 1906 that CO2 acts like a blanket and causes the greenhouse effect. It's real. You can try it out at home with 2 jamjars on a sunny day, if you like. Breathe in one of them not the other, cover with a glass plate, measure the temperature after a sunny day.

I also believe the IPCC AR4 consensus report (you can call me gullible if it makes you feel better).

Most of the people concerned about Global Warming believe that it's better to adapt our society to use as much fossil energy as in 1990 (or even less) rather than to wait for the CO2 to reach levels that will have full climate impact 250--500 years from now and will make the Earth a lot less hospitable to mankind *then*. Yes, we will be dead in 250 years. For some people, being dead eventually is no excuse to not try to improve the legacy we leave our children and children's children.

It is arrogant of you that, just because you've not personally experienced something, that therefore you call the people who say they do know what they're talking about, liars and fear mongers. If you'd never seen a hand grenade before and I'd warn you to not play with that thing, you'd probably call me a fear monger as well!

Try to learn as much as you can about the world from different sources, try to experiment yourself (maybe not with hand grenades), and maybe one day you'll learn to see past what the TV is spoon-feeding you.

How much does solar irradiance vary at wavelengths below 400nm

Quite a bit! The UV component of the sun varies far more than the average luminosity with solar activity.

and what are the physical and chemical effects of this variance on the atmosphere and global climate?

That is a subject of research; a lot of people would like to know! For the most part, the UV doesn't make it to the troposphere, so it doesn't have a direct effect, but it's still an unresolved question as to what indirect effects it may have.

The best study I know of looking at the correlation of solar activity with global temperature shows only a plus or minus 0.1 degree variation from solar max to solar min, though, so it doesn't seem to be a major player in temperature (the reference is Camp and Tung, http://depts.washington.edu/amath/research/articles/Tung/journals/GRL-solar-07.pdf ) The Working-Group 1 report links to more references on the subject; you might look at some of them: http://www.ipcc.ch/publications_and_data/publications_and_data_reports.shtm

Do the variance in solar magnetic index and the interaction of the solar and terrestrial magnetic fields have any direct or indirect effects on global climate?

I don't know of any confirmed effects there, other than aurorae.

Shouldn't all science be questioned?

Yes, but the problems with the deniers is that they don't listen to the answers.

Terms like "denier" or "believer" have no place in this debate. Both imply an unwillingness to consider what is known and what isn't.

Let me propose some terminology. The people opposing the anthropogenic theory of global warming can be divided into three distinct categories:
  *skeptics
  *policy critics
  *deniers

Skeptics are asking legitimate questions about the science. Policy critics deny the proposed responses to global warming, for economic or political reasons (I have no problem with this-- there should be more debate on policy.) Deniers deny anthropogenic global warming, period, end of discussion.

Skeptics and deniers are actually complete opposites. The key feature of deniers is that they are not skeptical, in fact, they are completely credulous of any argument, no matter how ridiculous, that opposes global warming.

I have a quick heuristic to distinguish deniers from skeptics: ask if they've actually read the IPCC report from Working-Group 1, "The Physical Science Basis of Climate Change" http://www.ipcc.ch/publications_and_data/publications_and_data_reports.shtml
Not "well, no, but I read a critique of it on website-X and I know what's wrong with it, the problem is -xxx--." Actually read it. Not the summary, not the analysis on some page, the actual report.

If you haven't read it, but still want to tell me your opinion on why the science is wrong-- well, your opinion is based on ignorance. You're a denier.

If you have read it-- well, congratulations. You're the one percent. It's a pity that the relentless and highly-amplified shouting of the 99% who don't actually know anything about the science is completely drowning out what you have to say.

What we don't have is another spare Earth running with accelerated time to test whether injecting the quantities of CO2 that have been released (along with aerosols, particulates, and other assorted crap) will have a long term net warming effect, cooling effect, or something else, and the magnitude of that effect.

Luckily we have physics. We know the magnitude of the effect of CO2 is dF=5.35*ln(C/C0)W/m^2 (where C0 is the initial concentration of CO2 in ppm and C is the current).

Aerosols are harder to quantify, but we can determine the outer bounds of their impact: http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter2.pdf

With the information we have we can determine the direction and magnitude within certain bounds. Certain interests would prefer that we wait 100 years and see what happens.

You skipped right over the part where consensus was reached that global warming was caused by man.

Here you go: http://www.ipcc.ch/publications_and_data/publications_and_data_reports.shtml

Unless you are talking about Al Gores and his group of globalist cronie climate change experts that set up companies to make profit from it.

I see you don't care about facts. Don't bother reading the reports then. Talk radio tells you all you need to know.

I read the rebuttal letter, it was printed in Science magazine.[...] I am a little confused as to why the letter was such a poor rebuttal (I believe in climate change, personally).

It wasn't a rebuttal, it was an independent letter published ~18 months ago. The probably reason why there is little science in the letter is because actual science, as opposed to pseudo-science, is complicated. It's a favorite tactic of anti-science debaters to throw out large numbers of wrong claims that take some time to properly refute. So when time or patience run out, the audience is left with the impression of doubt and open questions. And since you are always playing to different crowds, there is no need to take out refuted arguments - just re-run the whole show. Even a very much compacted version of the science, on the other hand, requires not a short editorial, but a 104 page report.

http://science.howstuffworks.com/environmental/earth/geophysics/question473.htm

The main ice covered landmass is Antarctica at the South Pole, with about 90 percent of the world's ice (and 70 percent of its fresh water). Antarctica is covered with ice an average of 2,133 meters (7,000 feet) thick. If all of the Antarctic ice melted, sea levels around the world would rise about 61 meters (200 feet). But the average temperature in Antarctica is -37ÂC, so the ice there is in no danger of melting. In fact in most parts of the continent it never gets above freezing.

At the other end of the world, the North Pole, the ice is not nearly as thick as at the South Pole. The ice floats on the Arctic Ocean. If it melted sea levels would not be affecteÂd.

There is a significant amount of ice covering Greenland, which would add another 7 meters (20 feet) to the oceans if it melted. Because Greenland is closer to the equator than Antarctica, the temperatures there are higher, so the ice is more likely to melt.

The numbers here are likely to be more accurate:
http://www.ipcc.ch/publications_and_data/ar4/wg2/en/spmsspm-c-15-magnitudes-of.html

The complete melting of the Greenland ice sheet and the West Antarctic ice sheet would lead to a contribution to sea-level rise of up to 7 m and about 5 m, respectively [Working Group I Fourth Assessment 6.4, 10.7; Working Group II Fourth Assessment 19.3].

Yet another source: http://nsidc.org/cryosphere/sotc/sea_level.html

Antarctica and Greenland, the world's largest ice sheets, make up the vast majority of the Earth's ice. If these ice sheets melted entirely, sea level would rise by more than 70 meters.

Your move. Let's see what asshole you pulled this "not more than a foot" number from.

First, the IPCC is actually a very conservative document. The sea level predictions ignore the possibility of large-scale ice shedding from Greenland or Antarctica. The temperature predictions ignore a lot of uncertain-but-very-scary feedback mechanisms, like the potential for mass methane releases from the Antarctic. In short, it ignores a lot of potential trouble spots where the science isn't settled.

The IPCC does not predict "a couple of degrees," in the sense that 2.0C is the upper boundary. That's about a midline case. The upper predictions (which may themselves be inadequate to describe the situation) range from 4C to 6C, depending on the scenario. 2C is probably the very upper reaches of what the ecosystem can handle without large-scale extinctions, so yeah, "we're fucked" is a pretty apt turn of phrase.

>> "Humans are only responsible for a small fraction of the CO2 going into the atmosphere."

That's true. But we're responsible for basically all of the change in CO2 concentrations over the last hundred years. Before we started burning fossil fuels in earnest, the Carbon Cycle was essentially in equilibrium. Once we started pushing CO2 into the atmosphere, the equilibrium changed, and CO2 concentrations went higher. We now see the higher concentrations in the warming atmosphere and in the oceans, where it increases acidity and ruins fragile underwater ecosystems.

>> "America is only responsible for a fraction of that (on track for 1-10% by 2050)"

But currently closer to 25%. And where the hell do you get 1% from? I can't see 1% happening unless Dennis Kucinich wins the next ten presidential elections.

Never mind. No country can make a huge difference alone. But just about every other country in the world seems to be taking better responsibility for their emissions than we are. We keep using China as an excuse for ignoring our own responsibilities, even though they only emit about a quarter what we do on a per-capita basis.

>> "We also know that with current technology, alternative energy sources are something like 2-3x as expensive as what we're using and doubling energy costs would completely cripple our economy which is heavily dependent on mechanisation."

Talk about providing me with a target-rich environment.

First, we only spend about 8% of GDP purchasing energy. So if we did indeed double our energy costs, we would lose about 8% GDP. Leaving us essentially as well off as we were in 2005. You call that "crippling the economy?"

Second, your projections assume that alternative energy technology will remain at its current cost. That simply will not happen. The cost of photovoltaics has been dropping by 50% every six years pretty much since the things were invented. It's a veritable Moore's Law of solar power, and it hasn't shown any sign of slowing. So within ten years, it's very likely that the cheapest way to add new energy to the grid will be with solar power. Within twenty years? It's a certainty.*

Third and most important, we could be spending a lot less on energy without significantly impacting our quality of life. Right now, the cheapest form of energy isn't coal or natural gas: it's energy efficiency. There are so many ways to reduce our CO2 footprint at a profit that it is absurd to be talking about CO2 reductions "crippling the economy" until all that money we're flushing down the proverbial toilet is reclaimed. For example, the $20M they sunk into an energy retrofit of the Empire State Building is yielding up $4M/year in dividends.

* Barring fusion/vacuum energy/other energy source that doesn't exist yet.

Here are some good places to start.

Mart

What is *your* falsifiable hypothesis statement of Catastrophic Anthropogenic Global Warming?

Do you believe that the only way science gets done is via experiment?

What would you suggest as a control for Earth?

What is *your* falsifiable hypothesis statement of Catastrophic Anthropogenic Global Warming?

You're asking the wrong guy. Trying to make points by asking a non-scientist a scientific question. I don't do original research. I make decisions based on the work of those who do. Maybe you should ask These guys.

Or these guys.

Or these.

If they can't help you, get back to me, and I'll see if I can't put you in touch with some other climate scientists. Of course, I suppose your certainty that all those guys just "aren't doing science" would probably make you disregard their answer, so maybe I can't help you after all.

I don't "know" in the sense that certain faith based folks "know" that they'll be the ones saved.

I do, however, know in the sense that I've read a lot about it, including impact models ranging from US government predictions (military, civilian), international studies, many of which predict widespread starvation and chaos.

As long as people like you refuse to even discuss rationally in the first place, we're never going to get anywhere.

It is ironic that you, whose responses are full of statements like "I believe in the tooth fairy, too" accuse others of refusing to have rational discussions. As I was saying, trying to shoot down my points does nothing to strengthen yours, so you might as well stop that. You need to make a compelling case that climate change is dangerous because you want political and economic change. The rest of us is happy to go on as before.

and our current civilization and its infrastructure is no more than a couple thousand years old; the vast majority of it being built in the last two hundred or so. What do you think 1-2m of sea level rise over the course of the next couple of centuries would do to said infrastructure?

Well, you just answered your own question: we have been able to build that infrastructure over the time span of a couple of centuries, so even in the worst case, rebuilding from scratch it over the next couple of centuries should not be a problem. But even that is overestimating the cost and effort. Most infrastructure depreciates within a few decades, reflecting the fact that it is essentially constantly being rebuilt anyway. There is no permanent, valuable physical infrastructure that needs protection.

What about biodiversity?

Environmental change tends to spur evolutionary change.

Tell that to the Somalis and the Kenyans. I'm sure they'll heartily agree with your assessment of their wonderful situation at present.

Refugee and population problems in Africa existed long before climate change. Africa needs economic and social development, and these people need to overcome their ancient divisions and enmities. If they do that, they can deal as well as Europe and the US with even the worst case climate change scenarios. And if they don't do that, addressing climate change won't make any difference because they'll just kill each other for one of dozens of other reasons.

No, we're having this "discussion" because there's a big problem and some people are too clueless to understand its impact and implications for the future. Fortunately, I don't need to convince you and your ilk. You'll be just another nameless, faceless Joe Blow in the crowd wondering why the world went to shit and having to live with your regret; well, assuming you live long enough TO regret it, anyway.

Even the IPCC report doesn't talk about "the world going to shit", it merely talks about tradeoffs between a few percent of global GDP between mitigation costs and warming costs.

http://www.ipcc.ch/publications_and_data/ar4/syr/en/mains5-6.html

It's people like you who spin such arcane and minor economic tradeoffs into horror scenarios.

The only regret I would have is if people like you manage to reverse the progress the world has made on liberalization and economic development.

(Lastly, I think technologically, the whole issue will become moot when China, India, and the US switch to Thorium, U238 and fusion reactors over the course of this century. Of course, then you will be up in arms about that too, right?)

There is no statistically significant evidence that the modern warming is part of any kind of cycle, nor is there any natural mechanism that could produce a 100 year cycle. There is also no statistically significant evidence that warming stopped in 2000. Moreover, statistical analysis of climate models tells us that the expected warming trend is too small to be reliably detected on anything less than a multidecade climate scale, so such a claim makes no sense.

So now it's some unnamed pundit who predicted a 2C warming by now, which amounts to much the same thing as some guy in a bar--these days, a pundit is a guy who is not an expert but plays one on TV. It certainly was not Al Gore who made such a prediction, despite your ritual invocation of his name. He's more accurate than most so-called pundits in reporting the science, but he's no scientist. If you want to criticize the science, don't you owe it to yourself to look into what the actual scienctists are saying? I refer you again to the IPCC reports.

And yes, scientists qualify their knowledge in terms of probability rather than engaging in the false certainty common in other fields. An engineer will not tell you that a bridge will "probably" stand up. The engineers were quite confident in the soundness of the Tacoma Narrows bridge and the unsinkability of the Titanic. Scientists recognize that any prediction of the future caries some degree of uncertainty. You will find quantification of the degree of certainty in the IPCC reports

Oh, "you remember hearing" that predictions would rise 2C by the end of the century? Where, pray tell? Some guy in a bar, maybe? Slashdot does permit posting of links to citations. All of the IPCC reports are freely available online. So why not spend a couple of minutes to support your claim with actual evidence--if it exists. And while you are at it, why don't you link to the scientific evidence for a "100 year cycle?"

Most of the observed increase in global average tempera- tures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations.8 This is an advance since the TAR's conclusion that "most of the observed warming over the last 50 years is likely to have been due to the increase in GHG concentrations" (Fig- ure 2.5). {WGI 9.4, SPM}

(emphasis mine). The bolded text "very likely" in this context means: after the scientists had their say, in 2007 the governments of China, USA, Saudi Arabia, Kazachstan etc. adopted a consensus phrase that was politically acceptable to most powerful countries, which contains the words "very likely" which if you look at p. 5 of the PDF (it says p.27) par. 5 means "between 90% and 95% sure".
THAT's NOT BINARY THINKING, it's called an "error bar". And you may call 90-95% certainty a "long leap" but I think that's irresponsibly naïve.

The reason why I got worked up enough to try to respond to your post, though, is your comment:

But I AM NOT going to allow anyone to wreck the global economy to achieve this.

Can you give us any clues why you think that making industrial processes and house insulation a bit more efficient, and investing in energy sources that don't require limited fuel, is the same as "wrecking the global economy", because I really don't know what you're talking about here. I mean I don't see where you're coming from; what makes you think that. Please remember:

• You exist
• I exist
• Our planet (resources and climate) exists
• "The global economy" however is a meme, a construct in your mind. There is no global economy. There is only people trying to make their livelihood. When they find out that a certain way to do this is no longer attractive to them, they try to adapt and switch to try and eke out an existance in a new, and different way. Just like when Silvio Berlusconi quit his job as a "love-boat" crooner or Foday Sankoh quit his job as a wedding photographer. But I digress..

Anyway, making sure that you're well-informed on the global issues ensures that you're better prepared for transitions both outside and inside your society, surely we'll agree on that?

I think that the reason that denialist propaganda works is that people are not good at long-term thinking and long-term planning. "We're having it so hard already, we can't spare the money to invest in our future so we'll just wait here until events catch up with us." That way people are easily convinced that any change which involves short-term hardship is unacceptable and must be avoided. Another vote for the status quo.
A story by the aptly named prof. Tom Murphy that almost made me physically sick was put on the OilDrum recently about the politics of it all: The Energy Trap (read it and weep).
Yet I believe that we have to move on and keep working because screaming that we're all doomed isn't going to help anyone :-( and calling you uninformed isn't going to help anyone either :-(

If realclimate is not scientific, then the scientific method is not scientific. You'd also have to claim that all current climate science is fraudulent and wrong (which, let's face it, you probably believe).

Not at all. I merely have to realize that realclimate.org chooses which points to present as truth, and which points to present as false. It's goal is to give you an answer to every possible challenge to your faith in climate change. As soon as a challenge comes up, they will have an answer for it. If you use it as a primary source for your information, that explains a lot.

Seriously. You and Dunning-Kruger. Have you ever stopped to think that you might not know as much as you think?

Every single day, I think that. I try to remember the words of a truly great scientist, Thomas Huxley, "Science seems to me to teach in the highest and strongest manner the great truth which is embodied in the Christian conception of entire sur- render to the will of God. Sit down before the fact as a little child, be prepared to give up every preconceived notion, follow humbly wherever and to whatever abysses nature leads, or you shall learn nothing." And in fact, when I get time I am going to go back and review the feedbacks in more depth. It'll be good to understand the exact math behind them. And maybe in the course of things, my opinion will change, but that would apparently contradict the evidence I've investigated to this point.

judging by your capitulation on every point in our discussion so far, I think you at least realise this much.

You only think that because of your own preconceived notions. You're still the idiot who thinks the earth will get hot because Venus is hot. Read on p90 of this document (sorry, it's a PDF), "a 'runaway greenhouse effect'—analogous to Venus-- appears to have virtually no chance of being induced by anthropogenic activities."

This is the kind of unscientific sensationalism we need to get away from.

Ahh. You're one of those people that thinks all the climate change research done so far is bunkum, and we don't need to worry. We're already observing changes. Have you even read the IPCC reports? Actually, don't bother answering. Looking at your other postings in this thread alone, you're clearly entirely closed to the idea that there is a problem, or that it will get worse. The rest of this is for the benefit of people who are prepared to look at the actual evidence.

For example - fresh water;

Current vulnerabilities to climate are strongly correlated with climate variability, in particular precipitation variability. These vulnerabilities are largest in semi-arid and arid low-income countries, where precipitation and streamflow are concentrated over a few months, and where year-to-year variations are high (Lenton, 2004). In such regions a lack of deep groundwater wells or reservoirs (i.e., storage) leads to a high level of vulnerability to climate variability, and to the climate changes that are likely to further increase climate variability in future. In addition, river basins that are stressed due to non-climatic drivers are likely to be vulnerable to climate change. However, vulnerability to climate change exists everywhere, as water infrastructure (e.g., dikes and pipelines) has been designed for stationary climatic conditions, and water resources management has only just started to take into account the uncertainties related to climate change.

Floods;

A warmer climate, with its increased climate variability, will increase the risk of both floods and droughts (Wetherald and Manabe, 2002; Table SPM2 in IPCC, 2007).

Food:
Water balance and weather extremes are key to many agricultural and forestry impacts. Decreases in precipitation are predicted by more than 90% of climate model simulations by the end of the 21st century for the northern and southern sub-tropics (IPCC, 2007a).

There's plenty more of that sort of thing in the IPCC reports. But if you live in a wealthy country away from the seaboard and can afford the increases in prices for fresh water, food and military spending to keep the oil flowing from areas less lucky than you; then yes, the impact won't be so bad in your lifetime. Lucky you. Shame about the rest of the planet, and our descendants though.

This is the kind of unscientific sensationalism we need to get away from.

Ahh. You're one of those people that thinks all the climate change research done so far is bunkum, and we don't need to worry. We're already observing changes. Have you even read the IPCC reports? Actually, don't bother answering. Looking at your other postings in this thread alone, you're clearly entirely closed to the idea that there is a problem, or that it will get worse. The rest of this is for the benefit of people who are prepared to look at the actual evidence.

For example - fresh water;

Current vulnerabilities to climate are strongly correlated with climate variability, in particular precipitation variability. These vulnerabilities are largest in semi-arid and arid low-income countries, where precipitation and streamflow are concentrated over a few months, and where year-to-year variations are high (Lenton, 2004). In such regions a lack of deep groundwater wells or reservoirs (i.e., storage) leads to a high level of vulnerability to climate variability, and to the climate changes that are likely to further increase climate variability in future. In addition, river basins that are stressed due to non-climatic drivers are likely to be vulnerable to climate change. However, vulnerability to climate change exists everywhere, as water infrastructure (e.g., dikes and pipelines) has been designed for stationary climatic conditions, and water resources management has only just started to take into account the uncertainties related to climate change.

Floods;

A warmer climate, with its increased climate variability, will increase the risk of both floods and droughts (Wetherald and Manabe, 2002; Table SPM2 in IPCC, 2007).

Food:
Water balance and weather extremes are key to many agricultural and forestry impacts. Decreases in precipitation are predicted by more than 90% of climate model simulations by the end of the 21st century for the northern and southern sub-tropics (IPCC, 2007a).

There's plenty more of that sort of thing in the IPCC reports. But if you live in a wealthy country away from the seaboard and can afford the increases in prices for fresh water, food and military spending to keep the oil flowing from areas less lucky than you; then yes, the impact won't be so bad in your lifetime. Lucky you. Shame about the rest of the planet, and our descendants though.

This is the kind of unscientific sensationalism we need to get away from.

Ahh. You're one of those people that thinks all the climate change research done so far is bunkum, and we don't need to worry. We're already observing changes. Have you even read the IPCC reports? Actually, don't bother answering. Looking at your other postings in this thread alone, you're clearly entirely closed to the idea that there is a problem, or that it will get worse. The rest of this is for the benefit of people who are prepared to look at the actual evidence.

For example - fresh water;

Current vulnerabilities to climate are strongly correlated with climate variability, in particular precipitation variability. These vulnerabilities are largest in semi-arid and arid low-income countries, where precipitation and streamflow are concentrated over a few months, and where year-to-year variations are high (Lenton, 2004). In such regions a lack of deep groundwater wells or reservoirs (i.e., storage) leads to a high level of vulnerability to climate variability, and to the climate changes that are likely to further increase climate variability in future. In addition, river basins that are stressed due to non-climatic drivers are likely to be vulnerable to climate change. However, vulnerability to climate change exists everywhere, as water infrastructure (e.g., dikes and pipelines) has been designed for stationary climatic conditions, and water resources management has only just started to take into account the uncertainties related to climate change.

Floods;

A warmer climate, with its increased climate variability, will increase the risk of both floods and droughts (Wetherald and Manabe, 2002; Table SPM2 in IPCC, 2007).

Food:
Water balance and weather extremes are key to many agricultural and forestry impacts. Decreases in precipitation are predicted by more than 90% of climate model simulations by the end of the 21st century for the northern and southern sub-tropics (IPCC, 2007a).

There's plenty more of that sort of thing in the IPCC reports. But if you live in a wealthy country away from the seaboard and can afford the increases in prices for fresh water, food and military spending to keep the oil flowing from areas less lucky than you; then yes, the impact won't be so bad in your lifetime. Lucky you. Shame about the rest of the planet, and our descendants though.

This is really sad, as there isn't even a chapter 9 with the same title in the 2001 IPCC report. FYI, the real report is here: https://www.ipcc.ch/ipccreports/far/wg_I/ipcc_far_wg_I_full_report.pdf

If you want to see what the actual scientists actively working in the field are saying go read the IPCC AR4 WG1 report. Pay close attention to the time frames and other conditions they put on their projections. I think you'll find their projections are rather conservative.

So, when exactly did this change occur? Obviously it had to be before the establishment of the Intergovernmental Panel on Climate Change back in 1988. Certainly long before Science magazine published Barrett and Gast's article titled Climate Change back in 1971, I assume. Probably even before the publication of Gilbert Plass's study The Carbon Dioxide Theory of Climatic Change back in 1956.

Please, enlighten us. When did this "name change" occur to avoid all of this ridicule?

Erm, have you checked google, or are you just repeating talking points?

Because the IPCC has pretty much all of their data available. Here is the data used in AR4. Whereas the math appears to be over at the paper itself.

Erm, have you checked google, or are you just repeating talking points?

Because the IPCC has pretty much all of their data available. Here is the data used in AR4. Whereas the math appears to be over at the paper itself.

There are climate predictions, the first from the IPCC was made in 1990, and it claimed the "temperature anomaly" in 2010 would exceed 4 degrees +- 0.3 degrees, in business as usual scenario.

No it didn't. It projected an average warming rate of 0.3 degrees C/decade for the 21st century (range of 0.2 to 0.5 C/decade) under business-as-usual emissions, with the actual rate being lower than the average during the early decades and higher during the later decades. See Section 1.0.3 of the report.

I don't think they explicitly spelled out what it would be in 2010, but you can see projections under high, medium, and low sensitivity scenarios in Figure 6.11.

Look at the "BaU" curve in Fig. 6.11b, the middle scenario. (This is "business as usual". I don't know whether their BaU scenario agrees with the actual emissions since 1990.) Eyeballing the amount of warming from 1990 to 2010 looks like about 0.25 C warming, to my eye, when I zoom the figure. Much closer to the actual warming than your claim.

And of course, it's kind of a fair question to wonder why every IPCC report has erred on the same side, until AR4 dropped that nasty business of actually predicting climate

No they didn't. They said that what they do is projections not predictions, which means that the predictions are conditional on assumed emission scenarios. This is the same as what every IPCC assessment report has done.

Anyway, I see two main possibilities here: (1) you're lying about what the IPCC said, or (2) you're uncritically repeating someone else lying about what the IPCC said. In either case, you're "not accurately describing the state of climate science", and perhaps you can see why such statements get "villified".

There are climate predictions, the first from the IPCC was made in 1990, and it claimed the "temperature anomaly" in 2010 would exceed 4 degrees +- 0.3 degrees, in business as usual scenario.

No it didn't. It projected an average warming rate of 0.3 degrees C/decade for the 21st century (range of 0.2 to 0.5 C/decade) under business-as-usual emissions, with the actual rate being lower than the average during the early decades and higher during the later decades. See Section 1.0.3 of the report.

I don't think they explicitly spelled out what it would be in 2010, but you can see projections under high, medium, and low sensitivity scenarios in Figure 6.11.

Look at the "BaU" curve in Fig. 6.11b, the middle scenario. (This is "business as usual". I don't know whether their BaU scenario agrees with the actual emissions since 1990.) Eyeballing the amount of warming from 1990 to 2010 looks like about 0.25 C warming, to my eye, when I zoom the figure. Much closer to the actual warming than your claim.

And of course, it's kind of a fair question to wonder why every IPCC report has erred on the same side, until AR4 dropped that nasty business of actually predicting climate

No they didn't. They said that what they do is projections not predictions, which means that the predictions are conditional on assumed emission scenarios. This is the same as what every IPCC assessment report has done.

Anyway, I see two main possibilities here: (1) you're lying about what the IPCC said, or (2) you're uncritically repeating someone else lying about what the IPCC said. In either case, you're "not accurately describing the state of climate science", and perhaps you can see why such statements get "villified".

You keep saying that, but it doesn't make it any more true. GCMs are programmed with the basic assumption that CO2 drives global average temperature, more specifically through assumed feedback effects on water vapor (which is a much stronger greenhouse gas). I welcome you to show me any existing GCM which does not assume this.

Feedback effects of are not "assumed," but are based upon established physical properties of CO2 and water, such as the effect of temperature on CO2 solubility and evaporation of water.

You're really stretching yourself thin here. The null hypothesis is the assertion that there is no relationship (causal or otherwise) between to things. It is not the "zero hypothesis".

Yes it is: The "no relationship" hypothesis is that the derivative dy/dx = 0 (where x and y are two different measurements) . Nothing to do with causality--simply that a plot of y vs. x has a true slope of zero. Of course, if the slope is zero, then there is no evidence upon which to base a causal hypothesis relating x to y. But the converse is not true: a nonzero slope does not establish a causal relationship. In the case of CO2 and temperature, the null hypothesis of zero slope is readily excluded by simple statistics. There is a correlation between temperature and CO2; the question is why. For this question of causality, there is no null hypothesis, because the null hypothesis has already been excluded.

Pray tell, what would the "zero hypothesis" of "smoking causes lung cancer" be? That there is no difference between the measurement of smoking and the measurement of lung cancer?

I've answered this question before. Did you miss it? Of course, there is no null hypothesis about "smoking causes cancer," because null hypotheses apply only to statistics, and statistics does not address questions of causality. But there are certainly null hypotheses that can be formulated regarding the relationship between smoking and cancer. Examples would be: "There is zero difference in the incidence of lung cancer in smokers and nonsmokers" or (for more quantitative data regarding smoking) "the derivative dy/dx (where y is the incidence of lung cancer and x is the number of cigarettes smoked)" is equal to zero."

Again, you're not fighting with a competing model here, you're competing with the null hypothesis that there is no causal relationship between CO2 and global average temperature. Trying to put your model above strict scrutiny is clever, but not convincing.

Again, you are back to special pleading based upon your failure to understand that a question of causality cannot be a null hypothesis. The null hypothesis of no statistical relationship between temperature and CO2 is excluded. A causal model, whether "natural" or otherwise, must indeed be subject to strict scrutiny--which means you must do what climate scientists have done (and what the self-styled "skeptics" have so far failed to do): define a specific model of climate that makes definite predictions, and carry out observations to test those predictions.

You lie like a dog. Throughout this entire conversation, you have completely been unable to make any specific statement of what observation of CO2 and global average temperature, on any time scale, would falsify your hypothesis. Having a mathematical model that cannot hind cast such events as the MWP, or LIA, or Holocene optimum, much less forecast within any sort of error range, is no great feat.

There have been numerous papers published on the quality of hindcasts from the models (a good summary can be found in the IPCC report)--but you are hardly equipped to criticize the quality of those hindcasts unless you can offer a model that does a better job. Once again,

If you want to convince us as to the veracity of your hypothesis, provide proof that can be scientifically verified.

The way that we scientifically verify something is to start off with a falsifiable hypothesis statement, and then to ruthlessly try to falsify our hypothesis. We *look* for evidence that we're wrong.

If you want to convince us of the veracity of the AGW or CAGW hypothesis, start off with your falsifiable hypothesis statement that you're willing to defend. Else, we've got no option than to fill the empty shirt with straw to argue against.

If you wish to falsify the hypothesis, simply repeat the experiment done by Tyndall and publish the result

Tyndall's hypothesis is simple and testable - gases have different absorption spectrums. Asserting that on faith, from this finding alone, you can extrapolate to "humans releasing CO2 will cause measurable and catastrophic global warming" is ludicrous.

If, on the other hand, you wish to falsify the models , then explain in detail what the problem with the model(s) is: what forcing do the models fail to account for?

The problem with the models is that they make basic assumptions that are unfalsifiable, such as "CO2 drives global average temperature". If the models are scientific, they should have falsifiable hypotheses for *every* one of their assumptions...care to share that particular list with me for any GCM of your choice?

Then you agree that there is no such effect?

And therefore you agree that this current warming phase is caused by anthropogenic emissions?

What, so if you agree that there are no unicorns, then you agree that this current warming phase is caused by anthropogenic emissions? The two have no relation to each other!

While cleverly trying to place AGW as the null hypothesis (by assuming it is true, and then asserting that it can only be falsified if a hypothetical mystery force is found to exactly counteract it), you're simply moving the pea under the thimble. Try again!

Why not? What climate effect do the models fail to account for? Please be precise.

Really? How about clouds? From the IPCC:'

http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch1s1-5-2.html

"In spite of this undeniable progress, the amplitude and even the sign of cloud feedbacks was noted in the TAR as highly uncertain, and this uncertainty was cited as one of the key factors explaining the spread in model simulations of future climate for a given emission scenario. This cannot be regarded as a surprise: that the sensitivity of the Earth’s climate to changing atmospheric greenhouse gas concentrations must depend strongly on cloud feedbacks can be illustrated on the simplest theoretical grounds, using data that have been available for a long time."

How about the climate effect of butterflies? How about the climate effect of phytoplankton blooms? How about the climate effect of any number of invasive species?

I mean, really, you think the GCMs actually contain simulations of every last thing that can effect climate? Really?

Watt's obviously doesn't know what a feedback is. (Do you?)

Apparently you know know what a feedback is either...or at least you can't come up with any falsifiable hypothesis for determining whether or not a given climate factor is a feedback or a forcing :)

From the paper cited:

"the cloud radiative cooling effect through reflection of short wave radiation is found
to dominate over the long wave heating effect, resulting in a net cooling of the climate system of 21 Wm2."

Go ahead, explain how IPCC models that depend on clouds having a net heating of the climate system jive with this.

http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch8s8-6-3-2.html

"The Partial Radiative Perturbation (PRP) method, that excludes clear-sky changes from the definition of cloud feedbacks, diagnoses a positive global net cloud feedback in virtually all the models (Colman, 2003a; Soden and Held, 2006). "

I challenge you to present me one published paper where a climate scientist tells me what I can and can't do. Or even where they merely suggest restrictions of what a person can do.

http://www.ipcc.ch/publications_and_data/ar4/wg3/en/contents.html
There you go.

No, they needed to address the existing evidence which contradicted their work.

Sounds like a double standard - there's lots of existing evidence against the hockey stick, or various multi-meter sea level rise predictions, but nobody has expected people writing papers with the warmist point of view to fully address existing critiques to their work.

If there is strong support for a hypothesis "A" and you write a paper saying "not-A", it needs to contain some explanation for why all those previous papers were wrong and you're right

Wasn't that the entire *point* of Spencer's paper? He was challenging hypothesis "A" *with* his paper.

How would you falsify the hypothesis that adaptation is cheaper than mitigation?

Well, at the simplest level, I'd look for comparative societies in the past - but the problem in regards to CO2 is that we have no confidence, whatsoever, that mitigation is even possible. So the *first* thing I'd have to come up with is a falsifiable hypothesis that mitigation is *possible*.

How would you falsify the hypothesis that mitigation is even possible?

If you were living in the projected path of a hurricane, would you demand a lab experiment to show that it was going to hit before agreeing to evacuate?

Of course not. But if I was living in an area that experienced hurricanes, and someone demanded that I plan to evacuate ten years from now in July for two weeks, I'd demand a falsifiable hypothesis showing this kind of long term planning is necessary or accurate, or, I'd just wait for an actual storm with an actual predicted track was being observed by our satellites.

I refer you (again) to IPCC AR4.

Like this: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch8s8-3-2-2.html

"It is likely that the relatively poor Southern Ocean simulation will influence the transient climate response to increasing greenhouse gases by affecting the oceanic heat uptake. When forced by increases in radiative forcing, models with too little Southern Ocean mixing will probably underestimate the ocean heat uptake; models with too much mixing will likely exaggerate it. These errors in oceanic heat uptake will also have a large impact on the reliability of the sea level rise projections. See Chapter 10 for more discussion of this subject."

Sounds like they have very little idea as to where sea level is going to be in 200 years, at any point in the globe.

Yes, we both agree that climate's not weather and that long-term regional/global climate models don't make accurate local weather predictions. Neither do local weather models make long-term global climate predictions.

What I think we disagree on, and please correct me if I've misunderstood you, is that *weather* matters to humans, *climate* does not. A human never experiences the average global temperature, or even "climate" - they experience *weather*. In the same way, phone numbers are used by humans, but average phone numbers, either for geographic areas, or averaged for a family over time, are *not* usable (or even useful).

so while (say) a 1m sea-level rise might not seem like much, it's going to vastly increase the frequency of catastrophic events -- for instance, your hundred-year floods may now be ten-year floods.

That's an assertion, not a fact. What kind of falsifiable hypothesis would you put forward regarding frequency of catastrophic events?

Some information on Bangladesh: http://wattsupwiththat.com/2011/01/03/bangladesh-the-poster-child/

"Flooding disasters are seasonally the result of excessive run-off, and occasionally due to unfortunate

an argument that the model was too simple is, in general, disingenuous

As I said -- if you want a peer-reviewed rebuttal, you'll have to wait (but not much longer) for it to get through GRL's publication pipeline...

You seem like a reasonable person, and perhaps you've never stated that the "science is settled", but that has been the mainstream argument for a while.

I'm happy that the science is sufficiently settled for action to be warranted now.

To summarize: climate is unknowable to any level of detail important to humanity, and while humans certainly affect their surroundings (as all living beings do), the level of that effect is on the boundary of undetectable.

I'm still not sure that I get your meaning (surely large-scale changes in climate -- i.e. the more knowable ones -- are more important to humanity that small-scale ones?). But I really don't know what makes you so sure we're on the "boundary of undetectable". We're already up to CO2 concentrations not seen for 20 million years -- do you really think that's not going to have an effect?

To clarify: average global temperature has zero relevance for anything experienced by humans - perhaps it is an interesting artificial statistic, but because we are affected by specific distributions of temperatures, not some imaginary average, it provides little functional use.

If you truly believe that average global temperature has no relevance, why on earth are we discussing a paper about it?

(If you are interested in regional-scale effects of global temperature rise, they are dealt with in some detail (976 pages) in Section 2 of the IPCC's fourth assessment report.)

Realclimate is difficult to take seriously - simply asserting that a model is too simple seems a critique

They don't "simply assert" that the model is too simple; they point out that has "no realistic ocean, no El Niño, and no hydrological cycle, and it was tuned to give the result it gave". A model without an ocean does seem rather over-simplified to me.

In any case, that's far from being the only issue: "The basic material in the paper has very basic shortcomings because no statistical significance of results, error bars or uncertainties are given either in the figures or discussed in the text. Moreover the description of methods of what was done is not sufficient to be able to replicate results." No error bars and insufficient detail to reproduce? Doesn't sound very much like science.

...that should be heeded by the various climate modelers out there who don't have any sort of realistic cloud modeling at all.

I'll grant you that clouds are not yet fully understood, but the IPCC models do take account of them.

Appeal to unnamed authorities. "Respected climate scientist" is not a title which is required to falsify a hypothesis, or critically examine a scientific proposition.

The authorities were named at the top of the article I linked to; Drs. Kevin Trenberth and John Fasullo. I was answering your question as to why "argument against it somewhere on the intarwebs" was sufficient to cause so much trouble for this paper: some of the arguments against it were solid, and they were solid in part because they were constructed by people who had expertise in the relevant field. Not all "arguments on the intarwebs" are created equal.

Speaking of which, how would you concisely state a falsifiable hypothesis of Catastrophic Anthropogenic Global Warming?

Perhaps embarrassingly, I'd never come across that term before reading your comment, and (while the general idea is clear) I've been unable to find a solid definition for it -- particularly important since the term "catastrophic" is often used differently in scientific and general contexts. Do you have a definition handy?

By the way, since you appended the "Catastrophic", I take it that you regard the hypothesis of Anthropogenic Global Warming (sans "Catastrophic") to be adequately proven?

This has nothing to do with Mann's study of paleoclimate records. All of his data is available. Mann's study has been replicated time and time again using different data and different methods for reconstruction. The results are solid.

Check the literature and ignore the media. The literature is motivated to find truth. The media is motivated to sell advertisements - and possibly there are other motivations depending on the media in question. If you are able, you would do well to go straight to the literature. I recommend starting with the IPCC AR4 WG1. It is about six years out of date but is a good summary of the literature at the time.

This is the problem that I have with climate change scientists and proponents. While we cannot be averse to the notion that what we do affects our own climate, the question is how and by how much? Despite all protestations to the contrary that evidence is simply not there, and when you question it the above is a classic example of what the discussion boils down to - surely if we are doing something then it must have an effect.

You appear to be ignorant of (a) all research into atmospheric feedbacks and forcings and (b) all research into climate modelling. There's a substantial body of work out there (hint: Google Scholar is your friend) ... perhaps you should read some of it. As for the question of how and how much, the IPCC report has a good summary of multi-model predictions, which in turn was based on Tebaldi et al., 2004, Greene et al., 2006 and Furrer et al., 2007 ...

Currently, we know that the earth is warming, and warming substantially faster -- and to a greater extent -- than any time previously in the last 800,000 years. We know that CO2 can act as a forcing on global temperatures (and thanks to extensive research in the 50s and 60s we know this very accurately). We know that human activity has substantially increased the atmospheric concentration of CO2. We know that other GHGs can also act as forcings or feedbacks. We know that the temperature rises we are currently seeing fit extremely well with the prediction that current climate change is a result of human activity increasing the concentration of GHGs in the atmosphere. Furthermore, we do not know of any other cause that could explain the temperature rise we are observing. We know that models based on research into atmospheric forcings accurately model current and past climates, and also predict a rapid and significant temperature increase if we continue to increase the concentration of GHGs in the atmosphere.

The most parsimonious explanation by far, based on current research, is that increasing the concentration of GHGs in the atmosphere has resulted in significant, rapid warming and will continue to cause significant, rapid warming.

http://www.ipcc.ch/publications_and_data/publications_and_data.shtml

Stick it up your pipe and smoke it.

Troll?

Here's a citation for my statement that there's a wide range of values believed possible for CO2 sensitivity:
http://www.ipcc.ch/publications_and_data/ar4/syr/en/mains2-3.html

Researching someone before trusting them is inarguable basic critical thinking,

Hmm. Well, here's a hypothesis: the claims made by global warmists will not not come true.

Winner!

http://www.ipcc.ch/