Our new series “The Heart of the Matter” features interviews with experts on either side of a controversial issue, asking each the same questions to see where and on what grounds their arguments diverge. Participants are asked to limit their responses to 1-3 sentences.
Arguing that global warming is a serious anthropogenic problem is Dr. George Somero, the David & Lucile Packard Professor in Marine Sciences at the Hopkins Marine Station. Arguing for the skeptics is Dr. Roy Spencer, recipient of NASA’s Medal for Exceptional Scientific Achievement and principle research scientist at the University of Alabama in Huntsville. Several environmental scientists at Stanford refused to take part in this exchange, explaining that “there aren’t two sides to climate change.”
1.* The American layman watching the news is likely to hear many different stories: the globe is warming at a rapid rate, the globe is warming at a rate to which we can easily adapt, only parts of the globe are warming, and just recently that there isn’t even a global temperature. Which is it?*
GS: Relative to warming episodes in the past, which have been common throughout the earth’s history, the current rate of warming is extremely rapid and is accelerating as greenhouse effects become more pronounced. Warming rates vary from site to site, with some of the fastest rates of heating occurring in the Polar Regions. It can be somewhat confusing to speak of a “global temperature” because of the varying rates of warming found around the globe; nonetheless, averaged over the earth, the planet has certainly developed a “fever” of about 0.7°C over the past one hundred years.
RS: Each in their own way, most of these statements can be supported. The globally averaged temperature has warmed rapidly in the last 30 years – but some of us think this warming is mostly natural and that it will likely end (for instance, there has been no warming for the last 6 years at this writing). I don’t agree that there isn’t a globally-averaged temperature, though, since we now have near 100% global coverage from satellites…at least for the last 28 years. And there is little doubt that the warming has been stronger in some regions than others, for instance in the arctic.
2.* Is this warming unusual in the history of earth’s climate?*
GS: Highly unusual. As a biologist, I’m concerned about the extent to which evolutionary adaptation to temperature (not to mention adjustment to ocean acidification—potentially a more severe problem for many marine species) can “keep up with” global change. Can slowly evolving species adapt quickly enough to deal with warming and, for many marine species, with acidification of their environments? I’m not very optimistic.
RS: It appears to be unusual compared to the last 500 years or so, but there is abundant temperature proxy evidence that it was just as warm during the Medieval Warm Period during 800 – 1000 A.D. The tree ring-based Mann et al. ‘Hockey Stick’ curve that claimed otherwise has been deeded by a National Academies review panel to be statistically flawed, and in any event it is inconsistent with most other temperature proxies that do show medieval warmth.
3.* Would we expect greenhouse gas emissions to contribute to global warming? The absorptive properties of CO2, for example, would seem to suggest that the more of it in the atmosphere, logically, the more heat that will be absorbed.*
GS: Greenhouse gases like carbon dioxide (CO2) and methane (CH4), which is 20-30 times more potent in trapping heat than CO2, prevent heat from radiating back into space. That’s why they’re called “greenhouse” gases; they function like the glass panes of a greenhouse. Water vapor is the strongest greenhouse gas, and with rising temperatures, the amount of moisture in the air rises too. This is an example of the type of positive feedback effects that play critical roles in global change.
RS: Yes, the infrared absorption properties of carbon dioxide are well understood, but it is also well known that the direct warming from even a doubling of CO2 in the atmosphere would be very small – about 1 deg F. The widespread predictions of much greater amounts of global warming than this have to do with feedbacks in the climate system, which most researchers (but not me) believe will greatly magnify the CO2-only warming.
4.* Are greenhouse gas emissions contributing to global warming? If so, by how much?*
GS: Absolutely—all of the data and the models developed from these data (e.g., the famous Keeling Curve of CO2 levels in the atmosphere) present an iron-clad case for the role of greenhouse gases in climate change. Natural causes of rising temperature, e.g., from changes in solar activity, accounted for essentially none of the approximately 0.7°C rise in temperature since 1900.
RS: There is no way to know for sure, because even a small change in cloud cover (too small to measure over the past several decades) could also explain recent warming, or a small decrease in the efficiency of precipitation systems. But just from a theoretical standpoint, I would have to say that at least some of the warming must be due to the extra CO2 — but I don’t believe we can say with any certainty how much of it is.
5.* How much of these emissions are anthropogenic?*
GS: Almost all types of organisms release CO2 when they respire, so clearly some of the greenhouse gases entering the air and waters are not anthropogenic. However, analysis of the carbon isotope composition of atmospheric CO2 shows that this CO2 is largely from burning of fossil fuels, due in large measure to coal-fired power plants. Human-controlled methane production in rice paddies and from belching and flatulence by cattle and other ruminants is also a major contributor to greenhouse gases. Lastly, greenhouse gases like halocarbons are industrial products, so these are obviously an important anthropogenic source of warming.
RS: Well, since the rate of increase in atmosphere CO2 is only 50% of what we know mankind produces, it would appear that mankind is mostly responsible for the recent rise.
6.* How much of the warming, then, is anthropogenic?*
GS: As detailed in the recent reports of the Intergovernmental Panel on Climate Change (IPCC), almost all warming in the past century or so is due to human activities (anthropogenic).
RS: Again, I would say that we don’t know. Since the vast majority of the Earth’s greenhouse effect is due to water vapor and clouds, and since weather systems keep the intensity of the greenhouse effect much lower than it could theoretically be (i.e., the atmosphere could hold much more water vapor than it does, which would lead to a warmer Earth), I would say that weather processes act to limit warming by limiting the greenhouse effect. I believe that any additional warming from mankind’s addition of CO2 is damped by weather processes – primarily the action of precipitation systems.
7.* To what extent can we alter the course of the climate?*
GS: Depending on which of the predictions found in IPCC reports and other analyses turn out to be accurate, the answer will range between “somewhat” and “one heck of a lot.” As in most aspects of climate change, a real worry is our inability to predict and evaluate all of the complex interactions that will occur as the planet warms. I think it’s fair to say that, as more interactions are revealed through research, the warming problem is perceived to get worse and worse. I can’t think of any recently discovered interaction that suggests any amelioration of the effects of greenhouse gases.
RS: I don’t believe that mankind has the capability to alter climate very much, and this is because I believe the feedbacks in the system are mostly negative. We certainly have some effect compared to if there were no humans, but the same could be said for forests, too, so I see no philosophical problem with us altering climate to some extent.
8.* Media reports suggest massive increases in hurricane intensity, freakish weather in Europe, droughts, so on and so forth—how much of this is due to global warming?*
GS: Global warming is likely to increase intensities of storms like hurricanes and cyclones, but there is still debate on how strong this effect will be. The physics is pretty simple, however: More thermal energy in the surface of the sea means more evaporation and, thus, stronger hurricanes/cyclones. Greenhouse warming will definitely change wind patterns, and these changes in turn will affect precipitation patterns, the strengths of ocean currents and the amounts of upwelling of nutrient-rich waters in coastal areas. How much of these sorts of changes will be directly attributable to global warming is difficult to predict, however.
RS: I would say virtually none. The most recent research suggests only a slight increase in hurricane strength (if any) from warming, and there is very little evidence that any severe weather events have increase from warming. The only possible exception to this is heavy rain events, which appear to have increased with warming. The fact that storm damage has increased greatly is known to be due to economic growth and the continuing increase in population in coastal areas.
9.* If global warming was not anthropogenic, how would we know?*
GS: To disprove the hypothesis that global warming is largely due to anthropogenic causes, we would have to discover natural forces that could fully account for the approximately 0.7°C rise in temperature over the past century. No one has been able to find any such natural causes, so I think it’s fair to say that human activities have been shown unequivocally the be the “villains” of the story.
RS: We wouldn’t know, unless we have accurate observations (which we don’t) , on a global basis, for at least the last 30 years, at high time resolution (preferably daily) of at least clouds, water vapor, and temperature. The claim that all of our recent warming is due to the extra CO2 is because our observations are simply not good enough to determine whether the warming could, instead, be from some natural process.
10.* Is there a scientific consensus? Is there a scientific debate?*
GS: Climate change “skeptics” who claim there is no scientific consensus on global warming (and a right-wing group supported by Big Oil runs an ad to this effect each week in the New York Times and, I’m sure, many other papers) are basically lying. I don’t know of a single scientist who denies that the planet is warming and the recent IPCC report said that there is at least a 90% chance that anthropogenic effects are to blame. Global warming due to anthropogenic effects is a closed-case; only the details about the magnitude of warming and about the ways to mitigate and adapt to warming’s effects remain under scientific (not to mention political) debate.
RS: There certainly is a scientific consensus that warming has occurred – no one I know of ‘denies global warming’ – even though we all seem to get tagged as ‘global warming deniers’. The big question is, “What has caused the warming?” That is where most of the debate is. But we should also remember that the consensus of the medical community used to be that stomach ulcers are caused by spicy food and stress. The ‘fringe’ idea that bacteria are to blame was ridiculed for twenty years before it was finally accepted. Scientific ‘consensus’ is only resorted to when uncertainty exists.
Interview conducted by email, condensed, and edited by Tristan Abbey.