Enough ado about hockey sticks: the worst is yet to come

Global warming deniers are making another attempt at discrediting the famed "hockey stick" graph, based on a paper (McShane and Wyner 2010) that purports to show mistakes in its statistical methods. While I don't have the statistical chops to assess the validity of either party's math, I did want to make two observations.

First, as others have noted, even if you assume that the new paper is the "correct" version, it doesn't look much different from other hockey stick graphs - if anything, the hockey stick shape in the new study is more pronounced.

More importantly, the hockey stick graph ultimately matters very little for what we should do about CO2, since it only measures past temperatures up to around the year 2000. What we really care about isn't the past temperature increase we've already observed, but rather the much larger future increase that's still to come assuming we do nothing about CO2. And that isn't accounted for in any existing hockey stick graph. I've taken the liberty of (unscientifically) adding this onto the McShane and Wyner hockey stick graph, using a simple average of the IPCC's low-end (1.1 degrees C) and high-end estimates (6.4 degrees C) for 21st century temperature increase:

Looks more like a hockey skate! Despite deniers' strange obsession with the past and lack of concern for the future (perhaps by virtue of their conservatism), the bottom line is this: the reliability of past temperature reconstructions matter very little compared to what we have in store... and it's about to get a whole lot hotter.

If this looks familiar, here's why:

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Cap-and-trade opponents sound like 6-year old Calvin complaining about cleaning his room

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Ending the use of coal overnight: new study shows it's possible

One of the common arguments against climate legislation is that clean energy technology just isn't ready yet. Most often, it's made to defend coal, and usually goes something like this: "Sure, maybe eventually we can replace coal, but right now that would be too expensive. For the next 50 years, we'll need to continue using coal at the same time we're developing cleaner alternative fuels."

This argument has always been illogical. Just because alternatives to coal are expensive now does not mean they always will be, and a major national push would soon bring down costs through economies of scale. But a new study goes even further, showing the "technology not there" argument to be not just illogical, but factually incorrect. In fact, the United States could replace nearly 100% of its coal-fired power generation--and do so almost overnight. How? With natural gas (which emits 50% less CO2 than coal). The Financial Times reports:

The shift from coal-fired generation to gas- fired generation sounds like something that would be lengthy and difficult to accomplish. But a new report by PFC Energy, the consultancy, indicates it is anything but. The report says US gas fired power plants average about 25 per cent utilisation, compared with 70-75 per cent for coal.

So operating existing plants at 72 per cent utilisation would theoretically increase gas demand by 30bn cubic feet per day - a rise of about 50 per cent - and displace almost all coal fired capacity. In doing so, carbon dioxide from the power sector would be cut 50 per cent, according to PFC.

Note that this is referring to existing power plants. In other words, we could completely eliminate the use of coal in this country without building hundreds of new power plants.

Also note that this is a recent development. Just three years ago, the idea of abundant natural gas replacing coal actually was ludicrous, and coal's defenders at least had a point. But that's no longer true. The difference is new technology that has unlocked previously out-of-reach shale gas formations such as the Marcellus Shale in Appalachia.

Providentially, much of the nation's most promising gas potential is in the very states where coal is currently strongest politically: West Virginia, Pennsylvania, and Ohio.

All of a sudden, coal miners who fear job losses from shutting down coal mines now could have gas fields in which to work. Looks like King Coal could have some competition for its most supportive Senators. (Indeed, last month The Hill reported that the natural gas lobby is "pushing new incentives to encourage utilities to switch from coal to natural gas, [and] in doing so, the sector is starting a lobbying fight with the coal industry." All I can say is, go get 'em boys.)

The bottom line: any time you hear someone say that the technology isn't there to switch from coal, you're being fed PR dog food. We don't have to wait for solar and wind costs to come down before abandoning coal, because natural gas is already cheap and abundant - and we can make the switch overnight. All that's needed is political will.

Watts vs. Bolt: Who's the Dumbest Denier?

You have to see this to believe it. Anthony Watts, perhaps the most influential global warming denier, just cited an article from 1989 to prove there's no global warming. You read that right: 1989. Check it out:

Here’s a blast from the past. Dr. James Hansen’s view in 1989 seemed a lot more temperate than it does today. Back then, he’s ready to accede to a study that says something counter to what his theory predicts, saying “I have no quarrel with it”. Today, he uses labels like “deniers” (see here) when such contradictory essays and facts are made public. What a difference 20 years makes...

Well yes, Anthony, actually it does, because over those 20 years, scientists have been accumulating data, and temperatures have been increasing. That's sort of how you become more sure of something: by collecting evidence over time. The fact that Hansen was "temperate" back in 1989, when the evidence for global warming was less unequivocal, would seem to prove that his current views are based on accumulated evidence rather than conspiracy.

Here's the beginning of the NYT article Watts cites:

January 26, 1989
U.S. Data Since 1895 Fail To Show Warming Trend

By PHILIP SHABECOFF, Special to the New York Times
Correction Appended

WASHINGTON, Jan. 25— After examining climate data extending back nearly 100 years, a team of Government scientists has concluded that there has been no significant change in average temperatures or rainfall in the United States over that entire period.

...

The study, made by scientists for the National Oceanic and Atmospheric Administration was published in the current issue of Geophysical Research Letters. It is based on temperature and precipitation readings taken at weather stations around the country from 1895 to 1987.

So Watts's logic is that 22 years of additional data should not allow James Hansen to become more certain of his conclusions?

This bit of boorishness follows right on the heels of another denier, Andrew Dolt Bolt of Australia, making the bizarre accusation that Apple is behind a new "answers to global warming skeptics" iPhone app. Here was his Twitter post:

Breaking News: Al Gore is funding iPhone apps to create secret new world order. First to be sent to the chambers - me. He must be stopped.

Even many of Bolt's commenters were able to squint through the fog and realize that Apple hosts, not develops, iPhone apps. No one's stopping skeptics from developing their own app.

So I propose a vote. What's dumber: Anthony Watts insinuating that a 21-year-old New York Times article disproves global warming, or Andrew Bolt claiming that Apple is nefariously developing global warming iPhone apps? I report, you decide.

Snowed in

Two feet of snow have cost me two days of my Christmas vacation, and possibly three. After 24 hours and three cancelled flights at Dulles airport, here I am, sitting in a hotel room, waiting to go back to the airport tomorrow to see if I can get on standby.

I've lived in the DC area for a little over two years, and haven't seen more than an inch of slush, much less snow, in my time here.  Everyone I talk to says this is the most snow they've seen in 20 years.

And of course, the irony of the whole thing is that President Obama is flying back from the Copenhagen summit on global warming.

So the question is, how unusual is the snowfall?

Well, according to the New York Times:

Officials in Washington said the storm was likely to produce the area’s heaviest snow since February 2003, when about 16 inches fell on the region.

2003 was also the sixth warmest year on record.  2009 is tied for the second warmest.  The moral of the story is, heavy snowfall can occur even in the presence of global warming.  Don't let the weather fool you.

Duds: a skeptic bombshell that never went off

Climate skeptics are having a field day with a new study on the earth's natural ability to absorb excess carbon dioxide (Knorr, W. (2009), Is the airborne fraction of anthropogenic CO₂ emissions increasing?). Influential skeptic and TV weatherman Anthony Watts calls it a "bombshell" (for more info on Watts, see "You're not a scientist, but you play one in real life"). Essentially the skeptic claim is this: “natural carbon sinks are soaking up human CO2 emissions at a faster rate than previously thought, which suggests that global warming will occur slower than models suggest. The science is not settled!” But is this an accurate interpretation of the study?

Here’s the story in a nutshell. Humans emit a lot of CO2, but only about 40% of that remains in the atmosphere (the airborne fraction, or AF). The other 60% is absorbed by natural carbon sinks, such as oceans, soil, and plants. As CO2 concentrations have increased, the AF has remained constant, meaning that carbon sinks’ ability to absorb CO2 is increasing in line with emissions. However, basic physics predict that eventually carbon sinks will begin to “fill up” with CO2, losing their ability to absorb more. When this happens, the AF will begin to increase exponentially, as carbon sinks absorb less and less CO2—a positive carbon cycle feedback.

The AF has remained constant for decades, but a few studies—Canadell et al (2007), Le Quere et al. (2007), and Schuster and Watson (2007)—have found signs that this carbon cycle feedback was starting to get underway. Canadell, for example, had found that the AF had increased from 40% in 1960 to 45% in 2007, which would signal that less carbon was being absorbed by the biosphere. The climate science website RealClimate notes:

There are uncertainties and caveats associated with each study, but taken as a whole, they provide convincing evidence that the hypothesized carbon cycle positive feedback has begun…

But then came the “bombshell” from Knorr (2009), who found that the AF has not, in fact, increased. The full study is behind a paywall, but you can read the abstract here. If Knorr is correct, it could mean that the studies from 2007 were premature in concluding that carbon cycle feedbacks have begun. The real question is, does this matter? If Knorr is right, does this cast doubt on the consensus view that greenhouse gas emissions from fossil fuels are causing global warming?

The short answer is no. I don’t have the scientific training to figure out which study is correct, but I do understand logic, and here’s what you need to know about carbon cycles.

First, the study's conclusion makes no claims about FUTURE carbon cycle feedbacks—it simply finds that carbon sinks' ability to absorb CO2 has not declined in the PRESENT. Claiming that Knorr casts doubt on models predicting accelerating future growth in CO2 concentrations makes the logical fallacy of extrapolating future trends from current results—the same error that led financial firms to conclude that housing prices would always increase.

Second, keep in mind that the current climate consensus is summarized within the 2007 IPCC report. On the other hand, the studies that Knorr critiques were published AFTER the IPCC report came out; therefore, if Knorr is correct in proving these studies wrong, his findings cannot logically have any bearing on the accuracy of the IPCC’s conclusions. At worst, Knorr simply returns us to the state of science when the IPCC report was written. In other words, skeptics are attacking a straw man.

Let me elaborate. For the Knorr study to make a dent in the armor of global warming theory, the findings it attacks would have to be included in, and critical to, the most widely accepted climate models. This is not the case. Studies like Canandell cannot have been included in the models on which the consensus is based, since they were published AFTER those models were created.

Moreover, while these studies gave us reason to believe global warming could occur faster, no one claimed they were certain, so it is inaccurate to claim that Knorr is throwing a bomb at the consensus. RealClimate, for one, emphasizes the difficulties with modeling carbon cycle feedbacks, because there are multiple physical processes that work in opposite directions. For example, as CO2 concentrations increase, the ocean’s ability to absorb CO2 also increases. At the same time, rising temperatures decrease the ocean’s ability to absorb CO2 (think of a warm soda can losing its carbonation). So the trick is to figure out when one process begins to dominate the other, and that’s hard to do:

We have to keep in mind that it is a tricky business to invert the atmospheric CO₂ concentration to get sources and sinks. The history of this type of study tells us to wait for independent replication before taking this result to the bank… I guess it’s fair to say that models are not decisive in their assessment about which of these two factors should be dominating at present.

In other words, none of these findings had been independently verified, and certainly not risen to the level of consensus. In fact, before Canandell, most models apparently predicted a declining airborne fraction, meaning that Knorr’s study is actually in line with IPCC models:

Carbon cycle models (13 of them, from the SRES A2 scenario) also predict that the atmospheric fraction should increase, but not yet. For the time period from 1960 to 2000, the models predict that we would find the opposite of what is observed: a slight decrease in the atmospheric fraction, driven by increasing carbon uptake into the natural world. Positive feedbacks in the real-world carbon cycle seem to be kicking in faster than anticipated, Canadell et al conclude.

In any case, according to Jones et al (2007), it is incorrect to conclude that a constant AF disproves carbon cycle feedbacks (don’t ask me why—I’m just copying and pasting to prove that the consensus supposedly being attacked by Knorr is a straw man):

It is commonly assumed that no change in airborne fraction implies no change in the carbon cycle. This is not true. It is also commonly assumed that if AF is rising, this implies we’ve detected a climate feedback on the carbon cycle. This is also not true. In reality, the AF depends not only on this years emissions and natural fluxes, but the time history of the carbon cycle, which in itself depends on the time history of the emissions. A different rate of emissions will imply different response of AF. This is true regardless of any feedbacks from climate.

The bottom line is that while Knorr (2009) may cast doubt on the conclusion that carbon cycle feedbacks have already begun, that conclusion is hardly pertinent to the consensus on global warming. The most far-reaching conclusion a skeptic could logically draw is that global warming is as bad as we thought (and not worse than we thought).

In other words, Anthony Watts isn’t a scientist, but he plays one in real life.

NOTE: Obviously I am not a scientist, and have probably gotten some points wrong (and probably left some out as well). If you ARE a scientist with expertise in the area, please leave a comment, and I can send you a link to a Google Document that you can edit.

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Calvin & Hobbes take on Superfreaks, part 2

Calvin & Hobbes just have so much to say about the world. In a past post (What do Calvin & Hobbes and SuperFreaks have in common?), I'd pointed out how trusting the authors of Superfreakonomics on a geoengineering solution to global warming would be like trusting a 6-year-old to fix your plumbing. If Levitt and Dubner think technological control over Nature can solve our problems, I think Nature will have some surprises in store for them:

Assuming that we can engineer Nature to fit our lifestyles doesn't make Levitt and Dubner courageous geniuses. Although Bill Waterson certainly is one.

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Don't believe global warming scientists? Ask an economist

On the heels of my post yesterday which looked at what the Market believes about global warming (verdict: it's true and it's terrible), there's a new poll out today confirming that it's not just scientists who nearly unanimously buy the climate consensus: 84% of economists also agree that global warming poses significant risks to the economy. In the New York Times:

A New York University School of Law survey found near unanimity among 144 top economists that global warming threatens the United States economy and that a cap-and-trade system of carbon regulation will spur energy efficiency and innovation.

“Outside academia the level of consensus among economists is unfortunately not common knowledge,” Richard Revesz, dean of the law school, said during a press conference Wednesday. “The results are conclusive – there is broad agreement that reducing emissions is likely to have significant economic benefits.”

The law school’s Institute for Policy Integrity sent surveys to 289 economists who had published at least one article on climate change in a top-rated economics journal in the past 15 years. Half of those economists responded anonymously to a dozen questions that solicited their opinions on a range of issues, from the impact of climate change on particular industries to how the benefits of reduced greenhouse gas emissions should be calculated.

The survey found that 84 percent of the economists agreed that climate change “presents a clear danger” to the United States and global economies – hitting agriculture the hardest – even though the severity of global warming remains unknown.

Only 5.6 percent disagreed with that statement while 7.6 percent were neutral and 2.8 percent had no opinion.

Interesting point #1: Agriculture will be the industry hurt most by global warming. To scientists, this isn't news. Anyone who follows climate science already knows that global warming will turn the Midwest into a permanent dust bowl of drought and decay. But it should be a wakeup call to agricultural interests and Midwestern Senators currently opposed to climate and clean energy legislation. Kansas Sen. Sam Brownback, for example, fears that cap-and-trade will hurt Kansas farmers by raising energy prices. Memo to Sen. Brownback: cheap energy doesn't help crops grow when there's no rain.


Interesting point #2: Uncertainty increases, not decreases, the case for action NOW. Again, this is not news to anyone who follows climate science and economics. But the Superfreaknonomics authors, or the hack Jim Manzi over at nationalreview.com, should take note of this:

Seventy-three percent of the respondents agreed that the uncertainty surrounding the severity of climate change raises the economic value of implementing measures to reduce greenhouse gas emissions.

The reason is simple: the costs of climate change range from large to civilization-destroying, while the worst-case costs of implementing cap-and trade look something like this. The economic crisis has taught us not to discount "long-tail" probabilities which, though unlikely to occur, would be almost too terrible to imagine if they did.

Interesting point #3: 98% of economists agree cap-and-trade will boost innovation and efficiency in the economy. This is a truly critical finding. Economics 101 teaches that economies grow not by keeping the price of goods cheap, but by inventing more products and producing them using fewer unit inputs. Unsurpisingly then, placing a price or cap on carbon would force companies to find ways of producing their goods using less energy, spurring a tidal wave of innovation and economic growth. And 92% of economists agree that market-based mechanisms like cap-and-trade are the best way to accomplish this goal. In fact, according to the poll, "most economists would support the cap‐and‐trade structure proposed by the main legislative options now pending before Congress."


So to the skeptic who thinks scientists are making up global warming: now you have two free market sources whose word you can take. Ask reinsurance company Munich Re, who believes climate change will be so destructive to property that they're pushing a $400 billion project to combat CO2. Or you can ask free market economists, 84% of whom believe global warming will damage the economy, and 98% of whom believe cap-and-trade will spur innovation and efficiency.

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Don't believe in global warming? Ask an insurance company

Skeptics of climate science believe first and foremost in the primacy of free markets over all other reason. Their fervency is so absolute that free market platitudes supersede any evidence, no matter how objective, to the effect that markets aren’t perfect. Thus, if there’s a problem that may need a government solution, skeptics are willing to disbelieve any evidence of that problem’s existence, latching on instead to any half-baked talking points that suggest things are fine. Convince yourself that all science is political, and it’s easy to dismiss out of hand all evidence contrary to your beliefs, shielding dogma from science.

So to convince skeptics, we'll have to try a different tactic. If we can’t ask a scientist, we’ll need to go straight to the source skeptics trust most: the Market (capital M). If the Market always has the answer, It (capital I) should be able to tell us whether global warming is real. And the best way to find out what the Market says about global warming is to ask the company that has the most to lose from it.

Munich Re is the largest reinsurance company in the world, with 2008 revenues of $46 billion. As a reinsurance company, Munich Re is in the business of insuring insurance companies. Yes, insurance companies buy insurance too: to protect themselves against the risk of a major disaster. It's simple: when a single house burns down here and there, it doesn’t threaten an insurance company’s solvency. But when a major catastrophe such as a hurricane strikes, that's a different story—with thousands of customers wiped out all at once, the company may not be able to handle the barrage of claims. Hence the need for reinsurance, and Munich Re sells more policies than anyone in the world.

So if looming environmental change were threatening to increase the incidence of such profit-destroying disasters, you’d think the company which stands to foot the bill would want to know something about it. And with an army of actuaries to assess those risks, you’d think it would be pretty well positioned to figure out those risks and do something about it.

And Munich Re is doing something, spearheading a massive $400 billion initiative to transform the Sahara desert into a solar power plant for Europe. Funded by a consortium of companies, it’s called the Desertec initiative, and it aims to scatter dozens of concentrated solar power plants throughout the desert, transporting the power across the Mediterranean to Europe via high-capacity cables. Munich Re is hoping this technological marvel will help to avert climate catastrophe and rescue its profits:

[Peter Höppe, Munich Re's head of climate change] said Munich Re had been concerned about the potential impact of climate change on the insurance business since the early 1970s. Extreme weather events related to climate change are already a reality and have the potential to be uninsurable against within a few decades, pointing to a possible crisis for the industry, he said.

"To keep our business model alive in 30 or 40 years we have to ensure things are still insurable," he said.

Munich Re also plans to invest in the new initiative and Höppe said banks were confident that they could raise sufficient funding to make the project work.

Concerned about climate change since the early 1970s? That wasn’t Al Gore or a university research scientist speaking—that was an executive at one of the largest risk management companies in the world. And it’s not just PR greenwashing—Munich Re is investing its own capital in a project, outside of its core business, of almost unimaginable scale. This isn’t even like certain American utilities supporting cap-and-trade in order to put less efficient rivals at a disadvantage. Rather, it’s a company whose business it is to predict natural disasters doing what it takes to prevent more of them from happening.

Put another way, this is not a case of a company trying to convince the public to buy its climate-friendly products (e.g. solar panels, wind turbines, etc.) - it's a company aiming to stop climate change and its damaging effects. A solar panel maker can create a market for its products by hyping global warming; at the end of the day, what matters is not global warming's reality, but customers' belief in that reality. Munich Re, on the other hand, couldn't care less what anyone believes - all it cares about is what nature will do to the properties insured by its clients. If global warming turns out to be false, spending time and capital abating it through Desertec would be a waste. In other words, Munich Re has a vested interest in climate change science being wrong, but it has nonetheless concluded that the science is right, and that spending billions of dollars abating global warming is a wise investment. This is about an unbiased assessment as it gets.

So when the world’s largest reinsurance company, the firm with the most money riding on its ability to predict disasters, acknowledges the reality and seriousness of global warming, it puts the skeptic in quite a pickle. If markets are always right, then shouldn’t we trust Munich Re about global warming? Because teabaggers have a certain word for people who don’t trust free market firms to make the right decisions. And it starts with S.

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What do Superfreaks and Calvin & Hobbes have in common?

The sequel to Freakonomics is creating quite a stir in climate science communities - specifically, its poorly-researched chapter on global warming. Besides regurgitating a number of well-debunked climate skeptic myths, the chapter's more insidious suggestion is that there's no need to do the hard work of reducing emissions because there's a cheap, easy fix: injecting billions of tons of sulfur dioxide into the atmosphere to reflect heat from the sun, or "geoengineering."

Hmmm. Two laymen who have no idea what they're doing think they have an easy solution to a problem they know nothing about? What could possibly go wrong? I think these cartoons say it all:





Hacksaw? How about just hacks.

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The cold logic of hockey sticks

It's fitting that so much of the "debate" over global warming concerns a sport played on

ice: hockey sticks, to be precise. For the non-initiated, "hockey stick" in climate-speak means any temperature reconstruction that shows relatively steady temperatures for 1000 years, followed by rapid warming in the last 100 (the "blade" of the hockey stick). We've been over this before, but global warming deniers just can't criticize hockey sticks enough.

The most recent spat comes from TV weatherman Anthony Watts, who claims that a recent study by some Canadian scientists, Rolland et al, proves all hockey sticks wrong. Watts asserts that according to the study, which uses insects called "midges" as proxies for temperature in a small region of Canada, we had more global warming between about 1100 and 1400 AD than we do today. Here's the temperature graph he shows:

If you just glance at the graph, it appears that the hockey stick is broken, and temperatures have been higher in the geologically recent past than today. Look a little closer though, and you realize the study says no such thing, as it refers only to summer temperatures in a single island in Canada, not global climate change. The study's conclusion states:

The paleolimnological study of this northern Southampton Island lake provides information and extends the spatial understanding of Northern Hemisphere climatic events(Medieval Warm Period and Little Ice Age) in the Foxe Basin region. Both chironomid-based August air temperature inferences and sedimentological assemblages suggest that Southampton Island was affected by a regional warming between cal yr AD 1160–1360 and a regional cooling between cal yr AD 1360–1700. These results compare well with both archaeological studies made on Southampton Island and paleoclimatic studies. (More about the medieval warm period can be found here.)

So the paper makes no claims about *global* climate. Rather, it was testing how accurately a certain method of analysis could estimate past temperatures. It was already well-understood that there was *regional* warming in parts of the northern hemisphere during the time period in question, and the authors' midge analysis confirmed previous findings. For Watts to wave it around triumphantly as if it's the "latest" crack in global warming is misleading.

In fact, if Watts had read the study, he would have seen this in the very first paragraph:

Evidence of rapid climate change at northern latitudes has focussed research efforts on arctic environments. Due to possible feedback mechanisms, such as snowand sea ice extent (albedo), these regions are believed to be particularly sensitive to global warming... Many studies have already shown that some arctic areas have undergone major modifications of their annual thermal budget during the second half of the last century. They specifically showed an increase of surface air temperatures during summer, and a drastic reduction of winter sea ice cover thickness and summer extent (Johannessen et al.,1995,1999; Dickson, 1999; Rothrock et al., 1999; Comiso, 2002). On the other hand, regions surrounding the Foxe Basin, the Hudson Bay, and the Hudson Strait are so far only slightly affected by such global warming effects.

In other words, the authors acknowledge the reality of "rapid" global warming, with the potential for large feedbacks, and were trying to understand why one region in the arctic might be anomalous to this trend. To infer from the study that the medieval warm period was a global warming trend equivalent to today's is to commit several errors of logic.

But for the moment, let's assume that Watts' assertion was true, and temperatures today are similar to the "medieval warm period." Would it matter?

The reason the "medieval warm period" is important to Watts and his ilk is that in their interpretation, it shows that today’s temperatures are not out of the ordinary. If temperatures were just as high in the past as they are today, what do we need to worry about?

But there's a fallacy in that reasoning – what matters is not how high today's temperatures are compared with the past, but rather how high they’ll be 50-100 years from now. It's not where we are; it's where we're going.

We know that increasing carbon dioxide in the atmosphere warms the climate (check here for the best explanation out there). We also know that CO2 is already at a higher concentration than during the medieval warm period - indeed, than at any point in the last 400,000 years, and likely the last 15 million; since it takes a few decades for temperatures to catch up with CO2 levels, we've still got a few degrees of warming in the pipeline even if we stopped emitting CO2 today. And if we keep going like we are, it won't stop there: we'll double the preindustrial level of CO2 by 2050, and triple it by 2090. In fact, the last time CO2 levels were as high as they were today, the earth was 5 to 10 degrees Fahrenheit hotter, sea level was 75 to 120 feet higher, and there was no permanent ice cap in the Arctic and very little ice on Antarctica and Greenland. And we're poised to triple that level.

So even if Watts proved that the earth was as warm 700 years ago as it is today, it is completely irrelevant, because we're about to get a whole lot hotter if we don't act now. Any time you hear someone "debunk" the hockey stick, just remember, it doesn't matter.

Medieval warm period debunking global warming? The only thing that's medieval is Anthony Watts's grasp of logic and science.

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