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Climate Science for Sustainability in the Future Greenhouse/Hothouse

David Feary, School of Sustainability and School of Earth and Space Exploration, Arizona State University at the Tempe Campus

My upcoming course—Climate Science for Sustainability—is a 200-level course offered with the intent of providing sustainability and earth science majors with an understanding of fundamental climate dynamics. The motivation for offering this course came from student representations to the effect that an understanding of Earth's present and future climate is an essential component for societal decisions affecting and promoting sustainability. With the diversity of possible future employment options for sustainability graduates, they felt that an understanding of the basics of climate science and dynamics would be essential. One upfront admission—I have not yet taught this course, so this discussion will be focused on the intent and philosophy of the course, rather than on experience with teaching it or descriptions of the refinements that come from student feedback.

The geological record shows that throughout Earth's geological history, this has tended to be a warm planet dominated by 'greenhouse' or 'hothouse' conditions, with relatively brief periods of cooler 'icehouse' climates (see figure). One of the important—and perhaps somewhat unusual—components of the course is an emphasis on the need to understand climate dynamics of warm or hot worlds, based on analysis of Earth's different climate states contained in the geological record of the 'deep' past—more than 30 million years ago. While it is relatively easy to dismiss the climates of such distant times as not being relevant to modern societies, in fact we are likely to see atmospheric CO2 concentrations by the end of this century—in less than 90 years !!!—that Earth hasn't experienced since 34-35 million years ago, long before the formation of northern hemisphere ice and prior to formation of most of the southern hemisphere Antarctic icecap.

The evolution of hominins has occurred entirely within one of these cooler icehouse periods, during the past 7-8 million years. As anthropogenic CO2 builds up in the atmosphere, it appears likely that humans will move Earth's climate into different dynamic states where we have much more limited understanding of the drivers and feedbacks, compared to the more detailed and higher resolution (but still far from perfect) understanding provided by tree rings, ice cores, coral reefs, and historical records. The implications for humans are clear—at the same time as there is increasing societal pressure to interact with the natural environment in a more sustainable manner, we will have to grapple with the need to adapt and/or mitigate a very uncertain and potentially highly challenging climate future of our own making.

Some of the past climate examples to be considered are the essentially ice-free world of the Cretaceous, as an example of a warm period, and the hot periods of the Paleocene-Eocene Thermal Maximum and the Middle Eocene Thermal Maximum. The course also looks at heat transport in the oceans and atmosphere, and the way that Earth's natural processes—e.g., plate tectonics—can make major modifications to climate states. One important aspect is consideration of rates of change, with the rates of entering and leave hot episodes being compared with modern rates of change for atmospheric greenhouse gas concentrations. This will be associated with considerations of climate feedback (e.g., albedo) as well as climate tipping points, thresholds, and transitions. The potential for rapid sea level rise—of the order of 10-20 meters in less than 500 years—will also allow consideration of the longevity of a populated southern Florida and other low-lying coastal locations.

While it is somewhat easier to assess and prepare for the science backgrounds of earth science majors, one of the challenges with this course will undoubtedly be the exceedingly diverse backgrounds of sustainability majors. This group of students is are targeting future careers with disciplinary combinations that encompass biodiversity and habitats, climate, social transformations, energy, materials and technology, governance and policy, international development, urbanization, and water. With diverse backgrounds and variable understanding of earth systems, I am particularly struggling with the level at which to pitch the course.

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