CAREER: The Lapse Rate Feedback and Other Mechanisms of High-Latitude Climate Change

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Model simulations of the warming effect of greenhouse gases typically show greater temperature increases over the polar caps than the rest of the globe. This "polar amplification" is consistent with the dramatic temperature increase seen in the Arctic, which has caused a variety of severe impacts on the human and natural systems of the region. Research on polar amplification is thus of practical as well as scientific interest, as the warming and thawing of the polar regions is poorly understood and difficult to predict yet has worldwide consequences.In the education and outreach component of this CAREER award the PI works with undergraduate students to develop computer games that can be used to introduce middle school students to environmental science. The work is based on research showing that appropriately designed games can be used to introduce students to scientific discovery, enticing them to probe a virtual world through formulating, testing, and reevaluating hypotheses. Games have been developed to foster scientific thinking in other disciplines including molecular biology and astrobiology. The work has educational broader impacts both for the broad audience of game players, many of whom may have limited interest in traditional STEM classwork, and for the cross-disciplinary team of undergraduate students who develop the game.The scientific focus of the project is the lapse rate feedback, in which changes in the way temperature varies with height affect the total amount of warming that occurs for a given increase in carbon dioxide (CO2). In the tropics the warming is top heavy, with greater temperature increases at upper levels, and the greater warming aloft helps the atmosphere cool to space more effectively to balance the heat trapping effect of the CO2. But the polar caps typically warm more near the surface, in part due to reductions in ice and snow cover which expose the darker land and sea surface below. This bottom heavy warming requires a greater temperature increase to balance the CO2 increase than would be required if the warming were distributed equally at all levels, thus it contributes to polar amplification.The logic of the polar lapse rate feedback is sound and the effect has been demonstrated in models, but the strength of the feedback is unclear. One consideration is that energy transport into the polar caps could work against bottom-heaviness given that much of the transport occurs aloft. But the net effect of energy transport is unclear as the transport of dry static energy is expected to decrease with warming while latent energy increases as the air becomes more moist. Low cloud changes due to near-surface warming may also reduce the warming effect of the polar lapse rate feedback. These effects are examined through simulations using a hierarchy of models at varying levels of complexity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.