Summertime

Alfred Lord Tennyson tells us that in spring, a young man’s fancy lightly turns to thoughts of love.

Well, I’m here to tell you that even approaching 70, that spring-thing still works.

But in recent years, my thoughts each summer have often gone in a different direction…back to a conversation in my office something like a decade ago.

My visitor then was Alexander E. (Sandy) MacDonald.

Sandy merits a special word or two here. He directs NOAA’s Earth System Research Laboratory and serves as NOAA’s Deputy Assistant Administrator for Research Laboratories and Cooperative Institutes. He holds the patent for Science on a Sphere^TM, a truly extraordinary education and outreach tool for helping the public visualize the Earth system and how it functions[1]. He’s an exemplar for federal scientist-leaders.

That Presidential rank award, recognizing only the very best of the best?

Sandy’s merely won it three times.

And you know what? These few words and the achievements they hint at, the creativity and vision they acknowledge, don’t begin to paint the picture of this man. We don’t have space for a full account, but let’s summarize it this way. The people who know him the best, like and respect him the most.

Back to that conversation. Sandy, then director of NOAA’s Forecast Systems Laboratory, was in my office at AMS and discussing abrupt climate changes on a regional scale. He touched on the Arctic Ocean, melting of the ice cap, and disruption of ocean circulation. He was building an argument that it’s not the slow trends in the averages per se but the risk of triggering tipping points that should put society on alert. He was articulating the importance and indeed urgency of sustained progress in Earth observations, science, and services. But for some reason the memorable piece, the piece I carried with me, was the idea that the central United States might switch rather suddenly from its historic regime as breadbasket to the world to something closer akin to the interior of Australia.

For ten years or so I’ve been carrying that last snippet around in the back of my mind. And over that same span, every summer, when we’d have a hot, dry spell somewhere in the United States, I’d wonder, “Is this what Sandy was talking about?” In each of those ten years, the dry spell would break, we’d get a dumping of rain, and my mind would turn to other things.

Until this summer. For weeks now, the headlines have been screaming about the drought and heat, and the geographic extent and duration of both. More recently, the coverage has expanded to the impacts on this year’s corn and soybean crops, and the ripple effect on livestock prices, ethanol supplies and more, not just in the United States, but worldwide.

Time to reach out to Sandy…  

I got lucky. He called back, and a couple of days ago we had a brief but enjoyable chat.

Sandy, do you remember our conversation those few years back? Can you remind me of the details?

Of course he could. Part of the reason was that around that same time he’d written them up in the summer of 2001 in a short article for the NAS/NRC publication ISSUES in Science and Technology, entitled The Wild Card in the Climate Change Debate.

Here’s the relevant excerpt: “Some of the regional climate change scenarios could interact with other regional changes. It is valuable to ask why central Australia is dominated by desert, whereas the North America interior is the richest agricultural land in the world. Australia is somewhat closer to the equator, which results in subtropical sinking air causing increased surface heating and evaporation. The temperatures become so high that the moisture is baked out at the beginning of the growing season. In many of the global warming scenarios, this process would operate in the U.S. interior. For the great agricultural zone that extends from the eastern slope of the Rockies to the Atlantic, the GFDL model predicts a 30 percent reduction in soil moisture for a doubling of carbon dioxide (shortly after mid-century) and a 60 percent reduction for a quadrupling (in the next century). Loss of the Arctic ice cap would change the amount of cool air entering North America, whereas a warmer Atlantic ocean would increase summer convection adjacent to the eastern half of the United States. Both of these changes would make North America more like Australia. It should be pointed out, however, that not all the models predict the creation of a permanent dustbowl in the eastern United States. Some predict increased precipitation.

I was once told that the 60 percent reduction in eastern U.S. summer soil moisture seen in the GFDL model was not a serious worry. “If it happens,” I was assured, “we’ll just have to irrigate the place.” Others may not take nature’s richest gift to the North American continent so lightly. The prospect of summer dryness, with its associated large impact on U.S. agriculture, should capture the attention of policymakers. And such a change would not be short lived. A reasonable timescale for this new dust bowl would be hundreds to thousands of years.

Currently, there is agreement neither among the models nor the scientific experts about the likelihood of these regional climate changes; they must be regarded as low-probability possibilities. Then again, it is unlikely that there will be a fire in your house in the middle of the night. Yet you protect yourself against this low-probability event by installing smoke detectors. Highly credible climate models could be our global change smoke detectors. The regional changes described above may have a low probability, but we should do everything possible to predict them while we have time to act.”

In our call this week, Sandy added some conjecture about the processes contributing to such a possible tipping point. One such is plant evapotranspiration. So long as plant roots are deep enough at every stage throughout the growing season to reach needed soil moisture, they’ll grab all the water they can, and they’ll evaporate relatively large amounts of that water through their leaves. This in turn provides the boundary-layer moisture flux needed to form the clusters of thunderstorms that deliver much of the warm-season precipitation over the Midwest. But when hot, dry spells bake soil moisture out of the upper layer to such an extent plants can no longer access it, then the surface vegetation ceases to drive this cycle. Sandy was careful to add that occasional wet years can change this picture (think an especially heavy snowfall over a winter season, for example). So the model picture is not one of unrelenting bad news year upon year, so much as one where crop failures might become more common…and possibly more harsh.

Several aspects of the ISSUES paper and the conversations were striking. First, Sandy was careful to note when it came to the climate modeling he was drawing on the work of others, especially Syukuro Manabe, who was responsible beginning as early as the 1960’s to model the effects on climate of CO₂. Second, he used the model results not to make a forecast but rather to reveal potential risk. Third, he wasn’t prescriptive with respect to policy options, but did suggest that one part of a risk management strategy might be to learn more. Fourth, he saw learning more as requiring: detailed observations from both satellite and surface-based platforms, and balanced, sustained attention to research and modeling.

A final note: if you have time and inclination, read his original paper. You might find yourself struck by the civil, measured tone, the refusal of a temptation to overstate, the caveats. The ideas are current, but the language seems foreign to today’s ears, inured as we have become to exaggerated claims and confrontational rhetoric.

Might not have been a cooler world back then, but certainly less hot-tempered.