DarkSyde (DS):
Climate science surely has to be one of the most complex fields I've ever seen as a mathematician. Everything affects everything else. Wasn't one of the original hints leading to modern Chaos Theory an artifact of climate science? What kind of background do you need to get a handle on all that?
DR Michael Mann; Associate Professor, Depts. of Meteorology and Geosciences, Director, Earth System Science Center, Penn. State (MM): We all come into this field from different directions. I double majored in physics and applied math at Berkeley, then obtained my masters in Physics at Yale before deciding to study climate, and switching over to the Dept. of Geology and Geophysics. My Ph.D. advisor at Yale, Barry Saltzman, was one of the original developers of the modern theories of dynamical meteorology (i.e., weather). He co-discovered 'aperiodic deterministic behavior' of the atmosphere (AKA "Chaos Theory") with Ed Lorenz of MIT in the early 60s. The discovery grew out of a set of equations that Barry had developed to describe the problem of thermal convection. Those equations yielded the surprising behavior we know as "chaos". Barry became interested in climate and paleoclimate modeling later in this career, and he infused me and many of his other students with his excitement in this area.
DR Gavin Schmidt; Climatologist, NASA Goddard Institute for Space Studies, New York (GS): I had a similar transition. I started off in applied mathematics at Oxford and London and became more interested in climate questions as I went along. I've ended up managing a climate model development project that touches almost every aspect of the problem - chemistry, cloud physics, oceanography, ice mechanics, orbital dynamics , etc., and so you get exposed to many different disciplines. The most interesting science I've done has involved bridging those interdisciplinary gaps and using knowledge and tools from one branch to tackle problems in the others. Climate modeling is in fact a great integrator of the various groups because you have to learn to speak the same language, otherwise you don't make any progress.
DR Stefan Rahmstorf; Potsdam Institute for Climate Impact Research (PIK), Germany (SR): I actually moved into climate research after working on general relativity theory. But climate is perhaps not as complex as you make it sound. Many factors only play a role on certain time scales. When you look at human time scales, you can forget things like plate tectonics for example. And chaos is only important for the weather, that is fluctuations over days or weeks, while longer-term climatic means are much more well-behaved and easier to calculate.
Antarctica March 22, 2000: A long rectangular section of ice 'calves' away from the Ross Ice Shelf (Red arrows). This massive berg, called B-15, was about 180 miles long by 23 miles wide. B-15 was the first of six large icebergs that broke free of Antarctica's ice shelves from March into May, 2000, and only one in a series that have broken off all around the continent over the last 10 years. Photo courtesy NASA/NOAA
Meteor Blades asks: Real Climate "is a commentary site on climate science by working climate scientists for the interested public and journalists ... The discussion here is restricted to scientific topics and will not get involved in any political or economic implications of the science." That sounds like a tight rope to walk in this day and age! How do you make the call between politics and science?
MM: We are trying to break away from the idea that every climate science question must be parsed and projected onto a pro or anti-Kyoto stance. By avoiding, as best possible, discussion of the policy implications, we keep the discussion focused on scientific uncertainties and conclusions, where we have specific expertise. We are nonetheless more than ready to speak out when we feel that that the science has been misrepresented in the public discourse, whether this be due to honest misunderstandings of the science or, as part of an effort to advance an agenda.
Our criticisms have been aimed at alarmist climate change headlines as well as contrarian global warming is a myth tomes. We've criticized the BBC, as well as Fox News, the Wall Street Journal editorial page, Senator James Inhofe, the British House of Lords, and George Will.
DS: To follow up on MB's question and case in point, as I recall DR Mann and his co-authors of a prominent study published by Nature in 1998, were recently pestered by Rep. Joe Barton (R) of Texas (the leading beneficiary of campaign funds from the oil, gas and utility industries according to the Center for Responsive Politics) to produce all kinds of seemingly trivial documents dating back decades [Excellent background piece by PlutoniumPage]. The justification he used for this demand was criticism of your work by two amateurs from Canada that was heavily promoted by special interest groups and the Wall Street Journal, but not taken seriously by the scientific community. What was that all about?
[Source Chris Mooney] "Just within the last 6 months, research based on actual data in the Atlantic Ocean has come out that says the whole concept of global warming may be exactly wrong, could be totally 180 degrees wrong."--Joe Barton (R-Texas) 2001
MM: Well, this relates to the work that my colleagues, Ray Bradley and Malcolm Hugues, and I published in the journal "Nature" in the late 90's. We developed a method to combine natural archives, so-called "proxy" records such as tree-rings, ice cores, and corals, to reconstruct climates in past centuries, before we had widespread instrumental measurements available. The primary advance provided by our study was that we were able to piece together the various pieces of evidence in such a way that we were able to reconstruct the actual regional patterns of past temperature change. This allowed us insights, for example, into the behavior of the El Nino phenomenon in past centuries as well as the average temperature over the entire Northern Hemisphere for the past 600 years. Another advance over previous work was that our method also allowed us to estimate the uncertainties in the reconstructions.
We later extended the work to the past 1000 years. One of the key conclusions of our work was that it was likely that the 1990s had been the warmest decade over the past 1000 years. However, this conclusion was hardly unique to our study, and this conclusion was not the most novel aspect of our study. What was most novel, in fact, was the reconstruction of regional patterns and the insight that provided into phenomena such as El Nino. Well, more than a dozen different studies since have come to the same conclusion as we did regarding the anomalous warmth of the last decade. In fact, the most recent such study published just last year in Nature by an independent group of scientists indicates that the late 1990s were likely the warmest decade in at least the past two thousand years.
The "Hockey Stick" diagram. Each colored line represents different studies conducted by different researchers, all converge on the same disturbing conclusion: Our planet is warming up and the trend appears to be increasing over the last century
While our work was important, it represented only one in many studies coming to the same conclusion, and all of these studies collectively represent just one small part of a large number of independent lines of evidence indicating a human influence on climate in recent decades. Our Northern Hemisphere temperature reconstruction, since termed the "Hockey Stick" by a colleague of mine, due to the sharp 20th century warming (the "blade") that occurs at the end of the 1000 year record, became an icon of the evidence for global warming in large part because it was a simple, easily depicted indication of climate change, and was prominently featured in the summary for policy makers of the 2001 report of the U.N. intergovernmental panel on climate change. Even though several other studies, as shown in the report, came to the same conclusion, the iconisation of our work made it a target for special interests who thought that they could sow doubt about the vast amount of science that indicates that human-caused global warming is a real phenomena, by attacking our study by whatever means possible, regardless of how vicious or dishonest.
The original criticisms of our work have been completely discredited now, and as I mentioned above, numerous independent studies have confirmed our original. We dealt with the technical issues involved in past posts at RealClimate here and here. To be sure, our original work is hardly the last word on the subject and new data and improved methods are continually being published by many groups including my collaborators and me. The science has advanced well beyond where it was nearly ten years ago when we started our original work, focusing instead now on the detailed comparisons of model-predicted and reconstructed spatial patterns of climate variables in past centuries, and interpretation of past changes in terms of various factors such as changes in solar output and volcanic eruptions, as well as recent human influences. In fact the whole focus by our attackers on an almost decade old piece of work instead of the current state-of-the-art demonstrates clearly that the aim of these manufactured 'controversies' is political and not scientific.
As for the larger issues involved, my co-authors and I were fortunate to have so many distinguished scientists, scientific organizations, editor writers, and politicians of principle from both parties all speak out so clearly and so forcefully, on our behalf. You can see the various letters of support and editorials here and here and I believe they speak best for themselves.
GS: I think the most worrisome thing about the whole affair was not that Congress was taking a serious interest in the policy implications of the science of climate change (that would be great!), but that a congressional committee was involving itself in the minutiae of the science itself - that is, trying to second guess the work that these scientists and others in the field are doing. Something they just weren't qualified to do. Many of the editorials written used terms such as "witch hunt", "inquisition", and "McCarthyism" to describe Barton's expansive requests for irrelevant information (funding sources over their whole careers, all correspondence with the public, etc.). Senator McCain even described the episode as "a kind of intimidation, which threatens the relationship between science and public policy" adding "That behavior must not be tolerated". I think the New York Times summed it up well with "It's going to be hard enough to find common political ground on global warming without the likes of Representative Joe Barton harassing reputable scientists who helped alert the world to the problem in the first place". The communication of relevant science to policy makers is always going to be complicated, but that is one of the good reasons why bodies like the National Academies and the IPCC exist to provide policy relevant summaries of the science.
DS: Obviously the planet has been warming up since the end of the last ice Age over ten thousand years ago. But on a more recent time scale, is global climate changing, and if so, what is the consensus on the direction and rate of change?
SR: Let me chime in here, as ice ages are my field of research. They are caused by regular changes in Earth's orbit, the so-called Milankovitch cycles. These cycles affect how much sun arrives on each part of the globe in each season. The last ice age ended because solar radiation in summer in northern continents increased strongly between 20,000 and 10,000 years ago - that melted the big ice sheets away. Since then, the climate has entered the 'Holocene' period and has been pretty stable (with possibly a slight long term cooling) and during which humans invented agriculture and civilization developed. More recently, we've entered another strong warming period, this time due to human influence: by our emissions we've increased the levels of carbon dioxide, an important greenhouse gas throughout Earth's history, to levels unprecedented for at least 650,000 years. So far we've only seen the feeble beginning of this warming: the planet has warmed 0.7 C since the beginning of the 20th Century. That's not much compared to the end of the last ice age, when the planet warmed by about 5 C. But those 5 C took about 5,000 years - that's only 0.1 C per century. If the steep rise of carbon dioxide in the atmosphere continues we have to expect 3, 4 or even 5 C warming during this century - as much again as at the end of the last ice age, but up to fifty times faster.
View of the Blomstrandbreen Glacier in Svalbard in 1922 Vs 2002. Photo courtesy of Svalbard Images: Copyright © Greenpeace. For more stunning photo comparisons, see Gary Braasch's Glacier melting gallery
DS: What is the evidence that human activity is playing a role?
GS: Well starting at the top, there is no doubt that the greenhouse effect is what keeps the planet's surface much warmer than it would be without it (around 30 deg C warmer). There is also no doubt that greenhouse gas concentrations have increased over the last 100 years due to human activities. Measurements from space and through the atmosphere have shown that the increased greenhouse gases are doing what we expect them to, and so they are definitely causing the planet to warm. However the situation is complex - there are natural things that cause climate to change - volcanic eruptions, changes in the sun, other human-related changes such as deforestation or air pollution that also affects climate, as well as the 'noise' associated with the chaotic nature of the weather. But, when we put all these things together what we find is that only explanations that include the greenhouse gas changes are able to explain the vast majority of the trends that we can see in the observations (warming oceans, land, melting glaciers, reducing Arctic sea ice, cooling stratosphere, etc.). This is a pretty robust result.
Left January 31 to right March 7th, 2002. A portion of the Larsen B Ice Shelf collapses and breaks up. The missing region in the last photo represents an area equivalent to the state of Rhode Island. Photos courtesy NASA/NOAA
MM: Let me follow up on that, because I'd like to correct a myth often promoted by climate change "contrarians" who have claimed that the dominant (indeed only) piece of evidence for human effects on climate is the 'hockey stick' study we mentioned above. While the attacks against the hockey stick are specious, the argument that the science supporting human influence on climate hinges entirely on these reconstructions is simply wrong. We have discussed the issue in some detail on RealClimate; Myth vs. Fact Regarding the Hockey Stick and What if the Hockey Stick Were Wrong?.
Indeed, there are many independent lines of reasoning supporting a role for human influences on the dramatic recent warming including; the close relationship between observed and model-predicted patterns of climate change during the 20th century, the dramatic retreat in recent decades of mountain glaciers that have existed for many thousands of years, and simple theoretical considerations regarding the basic physical properties of greenhouse gases, all of which is accompanied by greenhouse gas concentrations that are now known to be higher than any period in at least the past 650,000 years.
DS: What are the biggest immediate dangers of these developments?
GS: If the dangers were all immediate, I doubt this would be as contentious an issue! It's precisely because of the long time scales that are involved - the oceans take time to warm up, ice sheets need time to melt, and our society takes a long time to change its habits - that this is such a problem. It's not like ozone depletion or acid rain, where a few sources were producing the bulk of the problem and results were seen almost as soon as things changed. Fossil fuels are much more fundamental to society than aerosol cans ever were! Going back to what those dangers are, I would rate the possibility of significant ice sheet melt and consequent sea level rise as the biggest danger, followed by changes to rainfall patterns that will occur as climatic zones shift poleward and which could severely impact ecosystems and agriculture. Up until now, the climate changes that have occurred have been at the level of annoyances rather than catastrophes, but the projections of business-as-usual scenarios take us a long way past what we have seen so far.
DS: What about hurricanes, does global warming affect tropical storm frequency and intensity, and if so, can you tell us in what way?
GS: This is exactly the kind of climate question that people are interested in (particularly last summer!) and where our public role as scientists is most crucial. I think that what we've written on this topic in particularly shows how useful something like RealClimate is. Our article Hurricanes and Global Warming - Is there a connection? even got us on the Sunday New York Times Op-Ed page.
MM: The short answer is that we can never blame any one single event (e.g. Hurricane Katrina) specifically on global warming. But we can draw some conclusions in a statistical sense regarding the links between hurricane activity and global warming. We likened the situation to rolling loaded dice: you could construct a set of dice where sixes occur twice as often as normal. But if you were to roll a six using these dice, you could not blame it specifically on the fact that the dice had been loaded. Half of the sixes would have occurred anyway, even with normal dice. Loading the dice simply doubled the odds. In the same manner, while we cannot draw firm conclusions about one single hurricane, we can draw some conclusions about hurricanes more generally. But there are a number of complex scientific issues at play here. One of the key issues is the distinction you raise in your question between "frequency" and "intensity".
Model simulations don't show any clear evidence that the overall frequency of tropical storms and hurricanes in the tropical Atlantic will increase as a result of human-caused climate change. The simulations do however indicate that the distribution of tropical storms is likely to shift towards stronger storms (e.g. more category 4 and 5 Hurricanes) as the ocean surface warms. In fact, very basic fundamental physical reasoning leads to that same conclusions. Even here, however, there are potential complications. For example, we know that the El Nino phenomenon reduces Atlantic hurricane formation. So if El Nino's are to become more frequent and stronger in an enhanced greenhouse world (which some climate model simulations predict), we might expect this to counteract the effect of increasing Sea Surface Temperatures (SSTs). However, taking all of the available scientific evidence, it is probably fair to say that global warming will likely make - and quite possibly already is making - those hurricanes that form more destructive than they otherwise would have been. There are some initial observations that point that way, but we haven't yet been able to make a clear attribution.
Some climate models predict a dramatic warming trend over the next few hundred years as a result of increased greenhouse gases. This phenomena could lead to more powerful tropical storms. Full abstract here; Illustration courtesy IPCC
Stirling Newberry (SN) asks: What is being done to link the results of climate change studies with studies showing the emergence of 'peak oil' and other supply constraints?
GS: Oil is not the only fossil fuel. There are enough known coal and natural gas supplies (And methane hydrates) to keep those emissions of CO2 climbing for a long while. So while supply constraints that increase prices may lead to greater efficiencies in energy utilization, there is no reason to think the climate problem will consequently fix itself.
SN: Most of us accept the fact that humans have contributed a great deal to global warming, but can anything we do short of shutting down all fossil fuel burning reverse the trend?
SR: From a natural science point of view, we can say that we can stabilize CO2 concentration around 450 ppm if we gradually reduce global emissions by about half until 2050. There is some uncertainty in the carbon cycle here, but a reduction between 40% and 70% should do the trick. That would allow us to meet the policy target of the European Union, which is stopping global warming at 2 ºC above preindustrial. Politically, we are in fact committed to do something like this: there is a binding treaty, the United Nations Framework Convention on Climate Change of 1992, which almost all nations, including the US, have signed. It obliges nations to stabilize greenhouse gas concentrations at a level that avoids a dangerous human interference with the climate system. Many conferences of course now debate where climate change starts to be "dangerous", e.g., the conference "Avoiding Dangerous Climate Change" that Tony Blair called in Exeter last year. We're now moving outside the natural science topics we discuss on our site, but allow me add that economists and energy experts have worked out detailed scenarios how these emission reductions can be achieved with minimal impact on the economy - see for example the report by the German government's Advisory Council on Global Change, of which I'm a member.
DS: This is all both fascinating and disturbing, but sadly far beyond the scope of what a single interview could possibly illuminate. To wrap up, are there any orgs you would suggest the interested layperson might contact or want know about to learn more?
MM: That's a big reason we started Realclimate in the first place! This information isn't always easy to find, usually buried on page A30 in local papers, if covered at all. And too often what is out there is either highly technical or flatly wrong. But a couple of good places to start would be the U.N. Intergovernmental Panel on Climate Change and the U.S. National Academy of Sciences.
Gavin Schmidt, Michael Mann, and Stefan Rahmstorf, along with Eric Steig, William Connolley, Ray Bradley, Rasmus Benestad, Caspar Ammann, Thibault de Garidel, David Archer, and Ray Pierrehumbert, blog on climate related environmental issues at www.Realclimate.org
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