Michael Mann and his colleagues produced research that charted temperatures for the past millennium or so, which showed an almost level but slightly cooling trend line (the shaft of the hockey stick) that suddenly spiraled upward sharply and at an accelerating rate around 1900 (the upturned blade).
4/25/2016 7:27:00 AM Michael Mann:
Man-made climate change
is real The debate should focus on what to do about it
The first in a series of interviews about climate change
The famous climate scientist Dr. Michael Mann has a simple, straightforward message for everyone: manmade climate change is real and significant, and the real debate should focus on solutions to problematic global warming, where he says a range of prescriptions should be on the table.
That said, Mann is not an alarmist. He doesn't fall in line with those who proclaim the sky to be falling tomorrow - the doom-and-gloom crowd - but he does believe steps should be taken and policies fashioned to get a handle on long-term greenhouse gas concentrations.
Mann is a Distinguished Professor of Atmospheric Science and director of the Earth System Science Center at Penn State University, and the author of several books, "The Hockey Stick and the Climate Wars" and "Dire Predictions: Understanding Climate Change." He has also played a central role in the climate debates of the past several decades, most notably as the lead author of 1998 and 1999 papers that resulted in the so-called hockey stick graph of global temperatures.
What is the hockey stick? To greatly oversimplify matters and without attempting to explain the science behind it, Mann and his colleagues produced research that charted temperatures for the past millennium or so, which showed an almost level but slightly cooling trend line (the shaft of the hockey stick) that suddenly spiraled upward sharply and at an accelerating rate around 1900 (the upturned blade).
The only reasonable explanation for such a unique spike in warming would be human activity, in the view of advocates of the theory of anthropogenic global warming, and Mann's work figured centrally in "Climate Change 2001: The Scientific Basis," a part of the United Nations' Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). That assessment proclaimed: "It is likely that the rate and duration of the warming of the 20th century is larger than any other time during the last 1,000 years. The 1990s are likely to have been the warmest decade of the millennium in the Northern Hemisphere, and 1998 is likely to have been the warmest year."
Of course, to say the hockey-stick graph is accepted without controversy would be a monumental overstatement. Critics have challenged Mann's techniques and conclusions as vociferously as he has defended them. No matter who is right, though, the hockey stick analogy has continued to be used and defended by a strong cohort of scientists and others who believe in man-made climate change - indeed, the National Academy of Sciences affirmed Mann's findings in June 2006 - and its ongoing influence in U.N. climate science and governmental policies is incontrovertible.
Here's how the NAS put it in 2006: "The basic conclusion of Mann et al. (1998, 1999) was that the late 20th century warmth in the Northern Hemisphere was unprecedented during at least the last 1,000 years. This conclusion has subsequently been supported by an array of evidence that includes both additional large-scale surface temperature reconstructions and pronounced changes in a variety of local proxy indicators, such as melting on ice caps and the retreat of glaciers around the world."
Mann's work on the hockey-stick graph has been cited as contributing to the IPCC's 2007 Nobel Peace Prize award, which it shared with Al Gore.
Earlier this year, on the Lakeland Times letters-to-the-editor page, Mann debated some of our readers on the issue of climate change. We took the opportunity to give Mann the stage to present his views unfiltered in an exclusive interview with The Times.
What's happening now
Mann says the reality behind climate change is more complicated than what people may read in any given headline, such as those proclaiming the hottest year or month on record.
"We see individual months like this past February, where there was exceptional global warmth, and it's easy to point to that and say, 'It's climate change,'" Mann said. "The real answer is a little more nuanced, as you might imagine, a little more complicated. Climate change is certainly a major part of that - the fact that we have warmed the earth almost a degree Celsius, or 1.6 degrees Fahrenheit, means that there's a much greater likelihood that you will see very extreme warm months like this last February."
Still, Mann said, part of it is almost certainly due to what he called the monumental El Nino the nation experienced this year, by some measures the strongest one on record. The question is - and it's a topic of debate, he said - are El Nino events themselves becoming more extreme because of climate change?
"We don't know the answer to that, and that's very much debated within the scientific community," he said. "There are still some loose ends that we are trying to tie up in our understanding."
Given the many uncertainties in the field, Mann said, it's always worth retreating to "what we know, essentially for certain." And what do they know for certain?
"We know that the earth is warming up, that we can't explain that warming through natural factors," he said. "We can only explain it when we include the effect of increasing greenhouse gas concentrations from human activity. But there are still puzzles that we're trying to work out. There are still unanswered questions."
One of those questions, and a really interesting one, Mann says, has to do with the ongoing decrease in Arctic sea ice.
"You've got the Arctic warming up faster than the rest of the globe," Mann said. "Because of that, you see fairly dramatic retreats in the ice in the Arctic. Right now, we're on track for the lowest ice year on record. At the end of the summer, when the ice is done melting, it will most likely be the least ice we've seen in the Arctic since we've started measuring - well over a 50 percent decrease from a few decades ago."
So the question is, Mann asks, how might that be impacting the northern hemispheric jet stream?
"There is some evidence that the decrease in the ice in the Arctic can actually change the pattern of the jet stream, and, if you change the pattern of the jet stream, then you start getting things like anomalous drought on the West coast," he said.
And there might be effects on the opposite coast as well.
"We've had some cold winters here back East, not record cold by any measure, but we've had some cold winters, and it's possible that the changes in the pattern of the jet stream are part of that, and it's possible that those changes aren't entirely just natural or random but that they are being influenced by things like the decrease in Arctic sea ice," Mann said.
How do we know it's us?
Assuming that temperatures are on the rise, which Mann says is a scientific certainty, how do we know that rising global temperatures are due to manmade rather than natural causes?
"This is a question that climate scientists have been trying to address for decades now, and there's some pretty rigorous mathematical machinery that has now been developed for addressing questions like that," he said. "There's a technical term for it. It's called Detection and Attribution. Basically, the idea is, can we detect a trend and, if we detect a trend, can we attribute it to some particular set of factors?"
Mann says the main line of evidence for the human role in global warming comes from such detection-and-attribution studies.
"You take a climate model, for example, and you can run that climate model under two different conditions," he said. "You can run it under sort of a pre-industrial control set of conditions, where you're running the model under conditions that prevailed before the advent of fossil-fuel burning and before the increase in atmospheric greenhouse gas concentrations. And then you run the same model at elevated levels of greenhouse gas concentrations, equivalent either to the current day or obviously you can project into the future as well."
The primary focus of interest is the preindustrial control versus current-day simulations, Mann said.
"What you will then do is you will look at some particular attribute - it might be the sea ice in the Arctic, it could be the global average temperature, it could be any number of things - and what you look at is, first of all, is the trend in the observations outside of the range of variability in the preindustrial control?" he said. "Is it larger than what you would expect to arise just from the natural variability that exists in the climate system during a state that hadn't been influenced by increased greenhouse gas concentrations?"
When that has been done, Mann asserts, global average temperatures are shown to have risen far faster than in the era before fossil-fuel burning-and far faster than would have been expected if preindustrial conditions had continued to prevail, even after factoring in natural or internal variability. In other words, a statistically significant change has been "detected," the occurrence of which is unlikely to be the result of internal variability.
"That's half of it: Can you rule out, at a fairly high level of likelihood, that the natural fluctuations could explain the pattern you see in the actual observations," Mann said.
But the scientist isn't done at that point, he continued.
"Then you have to ask, can the simulations, where we've increased the concentrations of the gasses in the atmosphere, can those explain the pattern that we see in the observations?" he said. "And if it passes both of those tests, then we say we both detected a change in the climate and we can attribute it at some level of likelihood."
To say it another way, detection itself says nothing about whether the change can be attributed to an assumed cause. The attribution of the cause of climate change is the next step, the scientific process of establishing the most likely reasons for the change with a defined confidence level. That level depends on the technical details of the analysis, Mann said, and so scientists often employ terms such as "likely" or "very likely" or "extremely likely."
"Typically, when climate scientists use those words, there is a corresponding confidence level to the analysis, but typically, in science in general, we often use a 5-percent confidence level, so what we're saying is, if there's only a 5-percent chance that the natural climate variability could have explained the observed trend, then we say we've both detected it and attributed it to human activity, to the increase in greenhouse gas concentrations," he said.
There are caveats, though, and Mann says he is a skeptic that the models can be inherently trusted on some matters.
"The caveats of course are that these analyses are only as good as the climate model's ability to faithfully reproduce the natural variability of the climate," he said. "I've actually been a critic when it comes to some of these studies because my feeling is that, in some cases, there are key processes that the models might not be capturing that are important in the real world. Where this really becomes important are some of the more complicated questions, like how is climate change influencing certain types of extreme weather events, or hurricanes, or tornadoes, where the models might not be up to the task of addressing the impact on some of these more subtle phenomena."
Somewhere in the middle
As for those extreme weather events, not to mention other potential calamities that might befall the world, just how catastrophic is global warming and how much time does the Earth have before the effects become ruinous and life-threatening?
To those who doubt that any significant warming is occurring, especially that which might be caused by human activity, the risks posed by a warming Earth are obviously minimal, if there are any at all, and indeed some say a slight rise in global temperature could be beneficial.
To global-warming alarmists, catastrophe for the civilized world is right around the corner-some predict the collapse of civilization by 2040 if nobody does anything-and demands urgent action.
Put Mann in between those two extremes.
"Those who dismiss climate change outright will call me an alarmist," Mann said. "But the funny thing is, I also get attacked from folks on the other side. They are sort of the doomsdayers, and they criticize scientists like me for not being out in the streets announcing (alarmist) headlines. They are genuinely convinced that we are on the verge of catastrophic collapse and they criticize scientists like me for not telling the full story or watering down the scientific evidence."
Frankly, Mann said, the truth is somewhere in between. One of the charges of the IPCC isn't just to assess the scientific evidence for climate change, he said, but to look at its projected impacts and to try and assess what the damages could be and what the costs might be. And so scientists and economists who work in the area of climate science perform cost-benefit analyses and study the costs of implementing mitigation strategies, and they evaluate the costs of not acting as well.
"If you actually look at what the science has to say, the truth really comes in somewhere in between the two extremes in the public debate," Mann said. "We're not about to go off a cliff. Civilization isn't going to end in 10 years. The Arctic sea ice isn't going to disappear in a year, which some have claimed."
That said, that doesn't mean there's no impact, especially if the temperature rises beyond 2 degrees Celsius.
"If you take a sober look at consensus mainstream analyses of projected climate-change impacts, it's fair to say ... there does see to be a consensus arising in the larger discussion that 2 degrees Celsius relative to the preindustrial is a level of warming we probably don't want to go beyond," he said. "That would probably lock in what many of us could agree would be pretty dangerous and essentially permanent changes in our climate. We're talking about the usual things, stronger hurricanes -this last year we saw the strongest hurricane ever in the northern hemisphere and in the southern hemisphere -so the evidence does seem to be bearing this out to some extent."
Just recently, Mann said, the National Academy of Sciences, which he called the most authoritative scientific body in the country and one traditionally viewed as an "honest broker," weighed in with a new report that Mann said connected the dots and showed a link between climate change and certain types of damaging extreme weather events.
"I think in the end one can argue that from a policy perspective a compelling argument can be made that we shouldn't warm the planet more than 2 degrees Celsius and what we saw in Paris last December (an international climate conference in which 195 countries negotiated a draft treaty committing participating nations to a goal of limiting the temperature rise to below 2 degrees Celsius) was a vigorous discussion about how we achieve that," Mann said.
The possible policy approaches to climate change run the gamut of the ideological spectrum, he pointed out. Mann observed that conservatives as well as liberals are pursuing climate-change solutions, and he cited in particular the work of former U.S. Rep. Bob Inglis of South Carolina, a Republican who founded the Energy and Enterprise Initiative at George Mason University after being defeated by a Tea Party challenge in the Republican primary of 2010.
Inglis's group promotes free enterprise solutions to climate challenges, and, among other things, believes climate change can be solved by eliminating energy subsidies, including "the implicit subsidy of the lack of accountability for emissions."
Personally, as a scientist, Mann said it is not his job to advocate for specific policies but rather to help provide the scientific data needed for policy makers to fashion effective strategies.
"(How we achieve the temperature goal is) a matter of policy, and it's a matter of politics, and my personal belief is, I don't see that my role should necessarily be weighing in with prescriptive approaches to solving the problem but rather trying to inform that discussion under an assumption that policy makers and international bodies working with the nations of the world can all agree upon some policy framework for dealing with the problem, whether it takes the form of incentivizing renewable energy or putting some sort of price on the cost of carbon."
Next: Mann talks about the alleged pause in global warming; the Paris accords; the economic costs of various climate change solutions, as well as the costs of doing nothing; methane emissions; and more.
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