Read Storms of My Grandchildren Online
Authors: James Hansen
Further communication with the editor revealed that even more editing was planned to make the article better correspond to the magazine’s concept. In anger, I withdrew the article, saying that it could be published only on the condition that not a single word was changed. Of course that was unacceptable—and unfortunately, with the paper’s extensive criticisms of IPCC, there was no realistic chance of publishing it in a regular scientific journal—most of the likely referees for the paper were contributing authors of IPCC. I decided that I would prefer to publish it in the gray literature, as a report or on the Web. It was disappointing, yet a relief—I escaped the 3,500-word constraint of
Scientific American
and could make the story more quantitative and complete.
So I prepared a much longer document, still using the title “Can We Defuse the Global Warming Time Bomb?” This paper included most of the charts that I used in my presentation to the White House Council of Environmental Quality on June 12, 2003, and served as a record of that presentation.
The principal contribution of this document was an attempt to define the “dangerous” level of global warming. I concluded that ice sheets were a critical issue—and the more I looked at paleoclimate data, the more I realized how sensitive ice sheets were to even small global mean warming. My inference was that global warming (above that in 2000) should be kept to less than 1 degree Celsius. That limit implied that CO2 would need to peak at about 450 parts per million—or perhaps 475 ppm, if substantial but plausible reductions of non-CO2 forcings were achieved. (As mentioned earlier, I’ve since revised that target limit downward, to 350 ppm.)
In July 2003 I received a request from the Director’s Office at the NASA Goddard Space Flight Center, in Greenbelt, Maryland, to give a presentation to NASA administrator Sean O’Keefe. The director of earth sciences at Goddard, Franco Einaudi, told me that it would be the first earth science presentation to O’Keefe, who had been administrator for more than a year and had already visited Goddard once. On that earlier visit, he declined an offer to attend science presentations, instead choosing to visit the “visualization” laboratory, where he watched a film clip prepared for television viewers of the Winter Olympics; the clip started with a view of the whole Earth from space and then steadily zoomed in to show the Olympics site in Salt Lake City.
The Goddard director offered, as an alternative to my talk, to provide a presentation on Goddard’s Earth observation satellites, but the Administrator’s Office responded that O’Keefe wanted to hear from me about black carbon. I decided to use the contents of my “Time Bomb” document—it included black carbon but in the context of the actions needed to stabilize climate.
I sent a copy of “Can We Defuse the Global Warming Time Bomb?” to Ghassem Asrar, NASA’s associate administrator of earth sciences, who would accompany O’Keefe on his visit to Goddard. As we were assembling in the Goddard director’s office for my presentation, Dr. Asrar showed me the version of the paper that he had given to O’Keefe—Asrar had changed the title to something about “climate change” to make it less “incendiary.”
Sean O’Keefe was a friend and protégé of Vice President Dick Cheney. An accountant by training, O’Keefe had worked in the Department of Defense and on the staff of the Senate Appropriations Committee Subcommittee on Defense. In March 1989, two months after Cheney became secretary of defense, he had O’Keefe successfully nominated for Defense Department comptroller and chief financial officer. Mark Bowen, in
Censoring Science
, notes that O’Keefe was “openly and unapologetically partisan. As one senior insider at the agency [NASA] puts it, ‘In came Sean, and then it became very clear that NASA belonged to Sean, who belonged to Cheney.’” O’Keefe is the only NASA administrator who was not trained in science and engineering.
O’Keefe, a pleasant, soft-spoken person, listened quietly until I showed a photograph of a raging stream of meltwater on Greenland plummeting into a moulin. The chart’s title was “What Determines ‘Dangerous Anthropogenic Interference’?” I took the latter phrase from the 1992 Framework Convention on Climate Change treaty, signed by practically all nations of the world, including the United States. The countries agreed to take steps to keep greenhouse gases at a level that would avert dangerous climate change, with the steps to be defined in binding protocols. The main conclusion of my “Time Bomb” paper was that the stability of the Antarctic and Greenland ice sheets would surely set a low limit on permissible global warming and thus a low limit on greenhouse gases.
O’Keefe interrupted me to say that he did not think I should use the “dangerous” phrase, because we did not understand climate well enough to say what constituted danger. I probably
should
have disputed his admonition—our ignorance of what constitutes danger is actually a reason to focus on that topic. But nobody wanted to see a disagreement with the administrator, and I could readily admit that our understanding of ice sheet behavior was rudimentary, so the ensuing discussion was brief and not heated.
O’Keefe did not “order” me to never again use the “dangerous” phrase; it was only polite but unequivocal advice. Franco Einaudi remembers O’Keefe’s admonition as simply a mild rebuke. Yet it was O’Keefe’s only interjection during my entire talk, it was crystal clear, and he was the administrator.
During the return trip to New York I at first felt bad about the exchange—and my failure to take issue with the administrator’s advice. Of course, arguing the point would not have altered his opinion. But this matter raised a question: Given the fundamental nature of the “dangerous” phrase in the Framework Convention, why was there not greater explicit attention to it in the scientific literature? I decided that I would try to draw more attention to this “dangerous” issue.
I added some clarification and another figure to the “Time Bomb” document and sent the resulting version to be posted on the rather obscure Web site naturalSCIENCE. At about the same time, I received a proposal from the
Scientific American
editor: They were willing to publish this entire “Time Bomb” document on their Web site as well as a condensed version in
Scientific American
—with no changes, only condensation.
This second go-round with
Scientific American
worked out better. The editor said that he was busy on another project, so an alternate editor would work with me on extracting the condensation. I guessed that the change of editors was intended to minimize the chance that I would fly off the handle again.
The word limit for my
Scientific American
article was increased to 4,500 words, but I knew I would need still more space to adequately discuss why I thought ice sheets are closer to dangerous disintegration than IPCC assumed. An opportunity to supplement the
Scientific American
discussion was provided by the coincidence of an invitation from Steve Schneider, editor of the journal
Climatic Change
, to write an editorial essay, and a request from the State Department to attend a European Union–United States climate workshop in Bologna, Italy. I used my spare time on that trip to write the essay “A Slippery Slope: How Much Global Warming Constitutes ‘Dangerous Anthropogenic Interference.’”
People ask me why the “Slippery Slope” paper acknowledges Harlan Watson for facilitating the paper. It is because he used his gold card to get me into his airline’s first-class lounge in Munich, where I spent a six-hour layover writing half the paper. Watson was heavily criticized for being the face of the Bush administration’s rejection of the Kyoto Protocol. But I will show quantitatively in chapter 9 that Watson’s assertion that the protocol “was more about being seen to agree than about actual action” was dead on the mark. And I will argue that there is a great danger that our governments will follow a similar ineffectual path in the next international agreement, unless the public places strong pressure on them.
Publication of “Slippery Slope” took a year. The editor decided, because the paper challenged IPCC and conventional wisdom, that there should be a commentary on it, which he obtained from Michael Oppenheimer and Richard Alley. Then my essay in
Climatic Change
took another half year to be published, because of old-fashioned typesetting procedures.
What I was trying to address in this essay were IPCC estimates that if greenhouse gas emissions increased on a business-as-usual path, sea level might rise about a foot (30 centimeters) or perhaps a foot and a half in a century. Such a sea level rise would be more than a nuisance but hardly a disastrous global alteration of shorelines. The IPCC picture seemed to allow plenty of time to study the matter more carefully, and perhaps agree on ways to adapt to such changes. Sea level rise, in the panel’s estimates, would be due to the melting of mountain glaciers and the expansion of ocean water as it became warmer.
But IPCC sea level change estimates did not include any contribution from Greenland or Antarctica. Its rationale: Global warming might speed melting at the edges of ice sheets, but a warmer atmosphere would also increase winter snowfall, which would thus make the central part of the ice sheets thicker. Indeed, as I wrote the “Slippery Slope” paper in 2003, the most recent global climate model results—from one of the best models in the world, with the highest resolution—were published in the
Journal of Geophysical Research
. They concluded that the ice sheets would grow as the world became warmer, thus tending to make sea level fall.
Hmm, is something wrong with that picture? As the planet warms, ice sheets get bigger? Actually, that is conceivable, for a limited period. Rapid atmospheric warming could cause a prompt snowfall increase that exceeds increased ice loss at the ice sheet periphery, if changes of ice sheet dynamics begin slowly. The problem is that most existing climate models pretty much
assume
that result will occur, by treating ice sheets as if they were giant rigid ice cubes that melt only slowly. Models, at best, produce answers consistent with the assumptions put into them.
The diagram I included in the essay (similar to
figure 7
) was intended to aid discussion of processes that are not adequately represented in global climate models. It also provides a different way to think about the sea level problem. It focuses on the planet’s energy imbalance—where the excess energy goes and why it is important for ice sheets.
Earth’s energy imbalance is tiny. In 2003 I estimated that it was between 0.5 and 1 watt per square meter. The latest data suggest about 0.5 watt, averaged over several years and averaged over the planet. Yet this small energy imbalance is the most important number characterizing the state of our climate. It defines how much more global warming is “in the pipeline” without further change of atmospheric composition, and it tells us how much we must alter human-made climate forcings if we want to restore the planet’s energy balance and thus, to first order, stabilize climate—topics we will dig into in later chapters.
For the moment, it’s important to note that climate models have a hard time estimating the imbalance because it depends on the net climate forcing, and the big aerosol forcing is unmeasured. Thus our best measure of Earth’s energy imbalance comes from toting up observed changes of energy in its reservoirs—the ocean, atmosphere, land, and ice. It turns out that the lion’s share of the excess incoming energy, about 90 percent, goes into the ocean.
Let’s first make a calculation along the lines that IPCC assumes, namely with the ice sheet melting as if it were a giant ice cube. In that case, how much of the ice would melt due to human-made heating, which we take as, say, 1 watt per square meter? It is an easy calculation—most of the energy is needed for the phase change from ice to liquid. That requires 80 calories of energy for each gram of ice (if you are a youngster in a physics class today, rather than an old guy like me, you would say that it requires about 335 joules of energy—either unit is okay). If the average melt season is four months long and covers one third of Greenland, then the extra melt due to 1 watt of heating is about 20 cubic kilometers of water—enough to raise global sea level 0.05 millimeter (5 millimeters in a century). Hmm—not very much. Moreover, climate models find that global warming increases winter snowfall by more than that, so the net effect would be a sea level decrease as Earth becomes warmer.
How do we know this picture is wrong? Earth’s paleoclimate history shows the contrary: As Earth gets warmer, ice sheets get smaller and sea level rises. Indeed, sea level sometimes rises as much as several meters per century. Where does the energy to melt the ice so fast come from? The explanation surely must involve the huge reservoir of energy provided by the ocean and it must include ice sheet dynamics.
Let’s consider the amount of energy being soaked up by the ocean. As a round number, which we can scale later to any fraction that we want, let’s say that Earth’s energy imbalance is 1 watt per square meter, with 90 percent of the energy going into the ocean. If all that energy were used to melt ice, sea level would rise 10 centimeters per year (or 10 meters, about 33 feet, per century). For an Earth energy imbalance of 0.5 watt, these numbers would be half as large.
A 1- to 2-meter sea level rise would be disastrous for hundreds of millions of people. So if even a fraction of the excess energy going into the ocean finds its way to the ice sheets, we are in trouble. I argue that Earth’s history demonstrates that there are efficient ways to transfer energy between the ocean and ice. Furthermore, observations suggest that these mechanisms are beginning to come into play today.