Storms of My Grandchildren (15 page)

If the Times article is correct, he [Hansen] is going further than he has in the past, thereby placing himself at significant personal risk this evening. NASA does not have any control, input, or even insight into a decision by the Office of Special Counsel to prosecute Hatch Act violations. [The Hatch Act is the federal law that restricts participation by government employees in many aspects of partisan political activity. It does not limit the right to vote and express opinions about candidates and issues.]…In view of the timing, the content of the Times article, and the current flap with the Office of the Special Counsel [about a possible Hatch Act violation at Kennedy Space Center], I think it would be advisable for Dr. Hansen, for his own sake, to consider modifying his speech to eliminate the political elements. This is not a direction from NASA management, which has not expressed an opinion on the speech, at least not to my knowledge. This is simply offered in my capacity as an ethics counselor solely for the purpose of ensuring that, whatever Dr. Hansen does, he understands the ramifications of it, and, if he deems it appropriate, takes steps to mitigate the risk to himself.

That advice did not seem credible. I was using vacation time for the trip and was paying for the hotel and airfares. I was not about to change my mind. I had already gone through a struggle with self-doubt that chilly morning at 4:30 A.M. as I was dodging traffic while crossing the street on my way home after working extra late, realizing that I would get only an hour’s sleep. Why, I wondered, was I doing such an almost surely fruitless thing? Wasn’t I tilting at windmills?

It would be nice, for the sake of this book, if I had thought of my grandchildren at that moment. Instead, I thought of a cryptic four-word enigma that had stuck with me for decades. It was advice from Donald Hunten, who, along with Richard Goody, had been the father of the Pioneer mission to Venus. Hunten is small in stature but very authoritative. He speaks with a gravelly voice, seeming to push the words out from deep within his throat. I presumed Hunten had been responsible, at least in part, for the selection of our experiment to measure the Venus clouds as part of the Pioneer mission. Thus in 1978, when I wanted to resign as a principal investigator on Pioneer Venus so I could study Earth’s climate full-time, I felt that I should seek Hunten’s approval. I remember his advice as four gruff words: “Be true to yourself.” What did that mean? Venus or Earth? I was not about to query him further.

I told that story later in a commencement address at my hometown high school in Denison, Iowa, suggesting that the students make their own interpretation. Perhaps Hunten only wanted me to think, to be sure that what I did was consistent with values I would like to have.

In any case, I had written my talk to be given at the University of Iowa carefully and was not going to change it. My aim was to explain the science as well as I could, and also make clear the way things were working in Washington.

My Iowa talk was titled “Dangerous Anthropogenic Interference: A Discussion of Humanity’s Faustian Climate Bargain and the Payments Coming Due.” Humanity’s Faustian bargain with fossil fuels, I suggested, has more far-reaching consequences, and, as we’ll see in later chapters, some protagonists play a more shameful role than was the case in the bargain the grasping Dr. Faustus struck with the devil.

My talk included a discussion of the way science works, information on the greenhouse effect from Venus and Mars, an evaluation of climate sensitivity from paleoclimate data, and an analysis of ongoing climate change. The full version of the talk is on my Web site. Here I include observational data updated to 2009, and I focus on the most important uncertain aspect of the global warming story: the degree to which aerosol cooling is offsetting greenhouse gas warming—the Faustian climate bargain that humanity inadvertently entered into via the aerosol cooling effect.

The net human-made climate forcing—warming due to greenhouse gases, offset by uncertain aerosol cooling—is represented by the solid area in figure 10, which is the probability distribution for the net forcing. The most likely net forcing is close to Sophie’s 2 watts. But there is a substantial chance that Connor’s 1 watt could be closer to the truth. Does it matter which one is right, or closer to being right? Yes, it matters a lot!

If the net forcing is 2 watts, aerosols have been masking about one third of the greenhouse forcing. So if humanity makes a big effort to clean up particulate air pollution (say, reducing human-made aerosols by half), the net forcing will increase by only a quarter, from 2 to 2.5 watts. The additional global warming would not be welcome, but it might not be earthshaking.

On the other hand, if the net forcing is only 1 watt, that is, if aerosol forcing is −2 watts, that means aerosols have been masking most of the greenhouse warming. In that case, if humanity reduces particulate pollution by even half, the net climate forcing would double. That increased forcing, combined with a continued greenhouse gas increase, might push the planet beyond tipping points with disastrous consequences. The current smaller net climate forcing already is causing a notable recession of mountain glaciers around the world, affecting freshwater availability, shifting climatic zones, increasing fires and flooding, promoting the loss of Arctic sea ice and vulnerable coral reefs, accelerating mass loss from the Greenland and Antarctic ice sheets with rising sea level, and putting pressures on many species, leading to a danger of mass extinctions.

The importance of knowing the actual aerosol forcing is thus obvious. The missing aerosol measurement was the principal objective of the Climsat mission, which I proposed at the Gore-Mikulski roundtable meetings in 1989 and 1990. Measurement of the aerosol forcing involves determining the effect of aerosols on clouds via precise simultaneous polarimetry data for reflected sunlight and interferometric data for emitted thermal radiation.

The satellite mission never took place, but little is gained by crying over spilled milk. What we can do, in the absence of adequate aerosol measurements, is look instead for a measurable signature of the net climate forcing. The most fundamental effect of net climate forcing is on Earth’s energy balance. If the net climate forcing is positive, Earth must be gaining more energy (as absorbed sunlight) than it is losing (as emitted heat radiation). If the climate forcing stabilizes, the energy imbalance gradually declines as the planet warms up in response to the forcing and increases its heat radiation to space. The energy imbalance remaining at any time reveals the portion of the net climate forcing that has not yet been responded to.

So if we measure Earth’s current energy imbalance, we can determine the amount of global warming still “in the pipeline.” Direct measurement of the imbalance would require continuous monitoring by several satellites measuring radiation outgoing in all directions to an absolute accuracy of about a tenth of a watt. That is impractical. But a precise measurement can be inferred indirectly—from the rate at which heat is being stored in available reservoirs on Earth. The dominant reservoir, by far, is the ocean. For this reason I have argued for the past two decades that the single most important geophysical measurement is change of ocean heat content. If we can measure how much the oceans are warming, we will know not only how much additional global warming is in the pipeline but also how much we must reduce the human-made climate forcing if we want to stabilize climate.

In 1997 a number of colleagues and I published a paper (“Forcings and Chaos in Interannual to Decadal Climate Change”) that concluded Earth was out of energy balance by at least + 0.5 watt. Our conclusion was based on a comparison of climate model simulations with analysis of global ocean temperatures by the National Oceanic and Atmospheric Administration’s Sydney Levitus. The result was tentative because ocean temperature measurements were spotty, especially in the deep ocean and at high latitudes, and because it was uncertain whether the temperature data were sufficiently accurate. Large, probably unrealistic temporal fluctuations in Levitus’s analyzed ocean heat content data suggested the possibility of errors due to instrumental changes or incomplete sampling of the ocean.