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Muller writes: "Call me a converted skeptic. Three years ago I identified problems in previous climate studies that, in my mind, threw doubt on the very existence of global warming. Last year, following an intensive research effort involving a dozen scientists, I concluded that global warming was real and that the prior estimates of the rate of warming were correct."

Muller concludes that temperatures will continue to rise. (photo: EcoWatch)
Muller concludes that temperatures will continue to rise. (photo: EcoWatch)

The Conversion of a Climate-Change Skeptic

By Richard A. Muller, The New York Times

29 July 12


ALL me a converted skeptic. Three years ago I identified problems in previous climate studies that, in my mind, threw doubt on the very existence of global warming. Last year, following an intensive research effort involving a dozen scientists, I concluded that global warming was real and that the prior estimates of the rate of warming were correct. I'm now going a step further: Humans are almost entirely the cause.

My total turnaround, in such a short time, is the result of careful and objective analysis by the Berkeley Earth Surface Temperature project, which I founded with my daughter Elizabeth. Our results show that the average temperature of the earth's land has risen by two and a half degrees Fahrenheit over the past 250 years, including an increase of one and a half degrees over the most recent 50 years. Moreover, it appears likely that essentially all of this increase results from the human emission of greenhouse gases.

These findings are stronger than those of the Intergovernmental Panel on Climate Change, the United Nations group that defines the scientific and diplomatic consensus on global warming. In its 2007 report, the I.P.C.C. concluded only that most of the warming of the prior 50 years could be attributed to humans. It was possible, according to the I.P.C.C. consensus statement, that the warming before 1956 could be because of changes in solar activity, and that even a substantial part of the more recent warming could be natural.

Our Berkeley Earth approach used sophisticated statistical methods developed largely by our lead scientist, Robert Rohde, which allowed us to determine earth land temperature much further back in time. We carefully studied issues raised by skeptics: biases from urban heating (we duplicated our results using rural data alone), from data selection (prior groups selected fewer than 20 percent of the available temperature stations; we used virtually 100 percent), from poor station quality (we separately analyzed good stations and poor ones) and from human intervention and data adjustment (our work is completely automated and hands-off). In our papers we demonstrate that none of these potentially troublesome effects unduly biased our conclusions.

The historic temperature pattern we observed has abrupt dips that match the emissions of known explosive volcanic eruptions; the particulates from such events reflect sunlight, make for beautiful sunsets and cool the earth's surface for a few years. There are small, rapid variations attributable to El Niño and other ocean currents such as the Gulf Stream; because of such oscillations, the "flattening" of the recent temperature rise that some people claim is not, in our view, statistically significant. What has caused the gradual but systematic rise of two and a half degrees? We tried fitting the shape to simple math functions (exponentials, polynomials), to solar activity and even to rising functions like world population. By far the best match was to the record of atmospheric carbon dioxide, measured from atmospheric samples and air trapped in polar ice.

Just as important, our record is long enough that we could search for the fingerprint of solar variability, based on the historical record of sunspots. That fingerprint is absent. Although the I.P.C.C. allowed for the possibility that variations in sunlight could have ended the "Little Ice Age," a period of cooling from the 14th century to about 1850, our data argues strongly that the temperature rise of the past 250 years cannot be attributed to solar changes. This conclusion is, in retrospect, not too surprising; we've learned from satellite measurements that solar activity changes the brightness of the sun very little.

How definite is the attribution to humans? The carbon dioxide curve gives a better match than anything else we've tried. Its magnitude is consistent with the calculated greenhouse effect - extra warming from trapped heat radiation. These facts don't prove causality and they shouldn't end skepticism, but they raise the bar: to be considered seriously, an alternative explanation must match the data at least as well as carbon dioxide does. Adding methane, a second greenhouse gas, to our analysis doesn't change the results. Moreover, our analysis does not depend on large, complex global climate models, the huge computer programs that are notorious for their hidden assumptions and adjustable parameters. Our result is based simply on the close agreement between the shape of the observed temperature rise and the known greenhouse gas increase.

It's a scientist's duty to be properly skeptical. I still find that much, if not most, of what is attributed to climate change is speculative, exaggerated or just plain wrong. I've analyzed some of the most alarmist claims, and my skepticism about them hasn't changed.

Hurricane Katrina cannot be attributed to global warming. The number of hurricanes hitting the United States has been going down, not up; likewise for intense tornadoes. Polar bears aren't dying from receding ice, and the Himalayan glaciers aren't going to melt by 2035. And it's possible that we are currently no warmer than we were a thousand years ago, during the "Medieval Warm Period" or "Medieval Optimum," an interval of warm conditions known from historical records and indirect evidence like tree rings. And the recent warm spell in the United States happens to be more than offset by cooling elsewhere in the world, so its link to "global" warming is weaker than tenuous.

The careful analysis by our team is laid out in five scientific papers now online at That site also shows our chart of temperature from 1753 to the present, with its clear fingerprint of volcanoes and carbon dioxide, but containing no component that matches solar activity. Four of our papers have undergone extensive scrutiny by the scientific community, and the newest, a paper with the analysis of the human component, is now posted, along with the data and computer programs used. Such transparency is the heart of the scientific method; if you find our conclusions implausible, tell us of any errors of data or analysis.

What about the future? As carbon dioxide emissions increase, the temperature should continue to rise. I expect the rate of warming to proceed at a steady pace, about one and a half degrees over land in the next 50 years, less if the oceans are included. But if China continues its rapid economic growth (it has averaged 10 percent per year over the last 20 years) and its vast use of coal (it typically adds one new gigawatt per month), then that same warming could take place in less than 20 years.

Science is that narrow realm of knowledge that, in principle, is universally accepted. I embarked on this analysis to answer questions that, to my mind, had not been answered. I hope that the Berkeley Earth analysis will help settle the scientific debate regarding global warming and its human causes. Then comes the difficult part: agreeing across the political and diplomatic spectrum about what can and should be done. your social media marketing partner


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+7 # hammermann 2012-07-30 00:00
His continued skepticism is unwarrented- untrue that the the 2012 searing spring was matched by cold elsewhere- I think it was hottest spring in history over the world. Heartening some of these fools are seeing the light, but maybe their universities were about to dump them.
+9 # Trueblue Democrat 2012-07-30 04:38
Three years ago there might have been a chance to prevent our planet from reaching the tipping point. Today, it's probably too late, thanks to sellout artists like OK Senator Inhofe and the weak kneed phonies who infest US mass media -- such as Richard Muller.

From this date on, anyone who finally wakes up and smells the pollution will truly be a deathbed convert.
+19 # universlman 2012-07-30 05:42
Perhaps those who came late to the party should have less say about what "can and should be done."

I say in the coming fall election, purge candidates like Romney who pander to the deniers. We need leaders who are in touch with reality.
+7 # the wizard 2012-07-30 05:49
But Pox News is reporting a different story, albeit fake, but different and therefore it will carry equal weight with the corporate stooge media.
+1 # amos365 2012-07-30 06:55
Engines that run on carbon dioxide might help.
+2 # NAVYVET 2012-07-30 07:04
This guy tries to have it both ways. He's a poor scientist. Skepticism is fine, but it's NOT synonymous with covering the butt.
+6 # bingers 2012-07-30 08:03
No surprise here, fewer but more intense storms were predicted years ago. And tornadoes in upstate NY? hmmm
+8 # xflowers 2012-07-30 08:07
Berkeley Earth had to quickly post their papers on line if they didn't want to be left in the dust (quite literally.) I'm glad to see the turnaround in this former skeptic; but as he says, the difficult task, made more difficult by years of denial I would add, is what to do. That's the next big fight. In spite of the turnaround of opinion, my guess is it will be hard to find agreement on what to do as long as we are governed by short term economic policy rather than sound scientific policy. The battle will now shift to predicting effects of global warming, which Muller has already begun in paragraphs eight and nine. The truth is, no one can predict with certainty the ultimate outcome of climate change or the extent of causation between global warming and immediate weather events. All that science can present us with is possible outcomes. So that will be the next battleground between those who call for action and those who resist it.
+10 # genierae 2012-07-30 09:06
Such a lukewarm analysis doesn't help much. Since the global warming deniers have most of the money, they also have most of the power over congress. Don't look for a change of heart from these people, they have forgotten they have a heart. Consciousness-r aising is what will save us, every one of us who is awake must speak out for the sake of our environment. The future of this planet depends on us, we are the ones that we have been waiting for.
+3 # Jorge 2012-07-31 11:37
Congress is dominated by Sociopaths (except for a few like Bernie Sanders). TV is owned by the right-wingers and talk radio is 91% right-wing (per Thom Hartmann). Universities and regulatory agencies have been under attack by the ultra-conservat ives. Help appears to be in the form of expansion of Truthout and RSN (George Soros needs to buy some newspapers/TV/r adio stations) and more public involvement in Occupy and translate that action into third-party successes/chang es.
+6 # bsmith 2012-07-30 10:02
Until the raised Atlantic waters caused from arctic ice sheet melting flood the halls of congress, nothing will be done.
+3 # Jorge 2012-07-31 11:40
The 1%, including Congress, will have their own fortified retreats on high ground. Some may leave the country.
+2 # xflowers 2012-07-30 12:21
Read this article in The Washington Post to see one of the new battlegrounds. Also notice the Koch brother's involvement and Romney's promise not to renew tax credits. The bogus argument will run something like the risk of climate change doesn't merit the investment.

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