Katharine Ricke’s research while affiliated with University of California, San Diego and other places

Climate impacts studies often rely on empirical statistical methods to isolate the effects of changing environmental factors on human outcomes of interest. However, this research may not always account for the ways in which the underlying structure of climate might influence estimates from such models. Here we show how the different characteristic spatial scales of temperature (T) and precipitation (P), as well as the physical relationship between T and P, lead to biased historical and projected impact estimates in standard statistical approaches. Furthermore, we demonstrate how contemporary statistical research designs that exploit local fluctuations may unintentionally mis-characterize the influence of shifts in mean climate on outcomes of interest. Drawing on data from published studies we demonstrate these three issues; we focus primarily on the economic growth literature, though our results also apply to other contexts. We also propose several avenues to correct and bound the magnitude of the identified biases.

Marine cloud brightening (MCB) is a geoengineering proposal to cool atmospheric temperatures and reduce climate change impacts. As large-scale approaches to stabilize global mean temperatures pose governance challenges, regional interventions may be more attractive near term. Here we investigate the efficacy of regional MCB in the North Pacific to mitigate extreme heat in the Western United States. Under present-day conditions, we find MCB in the remote mid-latitudes or proximate subtropics reduces the relative risk of dangerous summer heat exposure by 55% and 16%, respectively. However, the same interventions under mid-century warming minimally reduce or even increase heat stress in the Western United States and across the world. This loss of efficacy may arise from a state-dependent response of the Atlantic Meridional Overturning Circulation to both anthropogenic warming and regional MCB. Our result demonstrates a risk in assuming that interventions effective under certain conditions will remain effective as the climate continues to change.

Many record-breaking climate extremes arise from both greenhouse gas-induced warming and natural climate variability. Marine cloud brightening, a solar geoengineering strategy originally proposed to reduce long-term warming, could potentially mitigate extreme events by instead targeting seasonal phenomena, such as El Ni\~no-Southern Oscillation (ENSO). By exploiting the 2019-2020 Australian wildfire experiment-of-opportunity, we show that simulated marine cloud brightening in the southeast Pacific reproduces observed cloud changes and induces La Ni\~na-like responses. We then explore how cloud brightening timing and duration modifies the 1997-1998 and 2015-2016 El Ni\~no events. We find the earliest and longest interventions effectively restore neutral ENSO conditions and dampen El Ni\~no's impacts. Solar geoengineering that targets climate variability could complement tools such as ENSO forecasting and provide a pathway for climate risk mitigation.

As disruptions from climate change increase, so will the urgency to find shorter-term approaches to ameliorating its harms. This may include calls to implement solar geoengineering, an approach to cooling the planet by reflecting incoming sunlight back to space. While the exact effects of solar geoengineering are still highly uncertain, physical science to date suggests that it may be effective at reducing many aspects of climate change in the short term. One of the biggest concerns about solar geoengineering is the extent to which it may interfere with crucial emissions reductions policies, i.e. mitigation. There are multiple channels by which geoengineering could alter mitigation pathways, both financial and behavioural. Here we define three such linkages and present the evidence available to constrain their potential magnitudes. Because solar geoengineering is not a substitute for mitigation, policies to develop or implement technologies that could be used to carry it out should be designed to accentuate its complementary nature to mitigation and deter the possibility it is used to delay decarbonizing the economy.

The integration of physical and social science data can enable novel frameworks, methodologies, and innovative solutions important for addressing complex socio-environmental problems. Unfortunately, many technical, procedural, and institutional challenges hamper effective data integration – detracting from interdisciplinary socio-environmental research and broader public impact. This paper reports on the experiences and challenges of social and physical data integration, as experienced by diverse Early Career Researchers (ECRs), and offers strategies for coping with and addressing these challenges. Through a workshop convened by the National Center for Atmospheric Research (NCAR) Innovator Program, 33 participants from different disciplines, career stages, and institutions across the United States identified four thematic data integration challenges related to complexity and uncertainty, communication, scale, and institutional barriers. They further recommended individual, departmental, and institutional scale responses to cope with and address these integration challenges. These recommendations seek to inform faculty and department support for ECRs, who are often encouraged – and even expected – to engage in integrative, problem-focused, and solutions-oriented research.

Marine cloud brightening is a solar geoengineering1–3 proposal to cool atmospheric temperatures and reduce some impacts of climate change. To-date, modeling studies of solar geoengineering have primarily focused on large-scale schemes with objectives of stabilizing or mediating changes in global mean temperature4–7. However, these global proposals pose substantial governance challenges8–10, making regional interventions tailored toward targeted climate outcomes potentially more attractive in the near-term. In this study, we investigate the efficacy of regional marine cloud brightening in the North Pacific designed to mitigate extreme heat in the Western United States. We find cloud brightening in a remote mid-latitude region cools our target region more than brightening in a proximate subtropical region, but both schemes reduce the relative risk of dangerous summer heat exposure under present-day conditions, by 39% and 25% respectively. However, the same cloud brightening interventions under mid-century warming produce significantly hotter rather than cooler summers, both in the Western U.S. and other areas of the world. We trace this loss of efficacy to a nonlinear response of the Atlantic Meridional Overturning Circulation to the combination of greenhouse gas driven warming and regional cloud brightening. Our result demonstrates a risk in assuming that regional interventions that are effective under certain conditions will remain effective as the climate continues to change.

The United States government has indicated a desire to advance environmental justice through climate policy. As fossil fuel combustion produces both conventional pollutants and greenhouse gas (GHG) emissions, climate mitigation strategies may provide an opportunity to address historical inequities in air pollution exposure. To test the impact of climate policy implementation choices on air quality equity, we develop a broad range of GHG reduction scenarios that are each consistent with the US Paris Accord target and model the resulting air pollution changes. Using idealized decision criteria, we show that least cost and income-based emission reductions can exacerbate air pollution disparities for communities of color. With a suite of randomized experiments that facilitates exploration of a wider climate policy decision space, we show that disparities largely persist despite declines in average pollution exposure, but that reducing transportation emissions has the most potential to reduce racial inequities.

Research on blocking sunlight needs a dose of realpolitik. Research on blocking sunlight needs a dose of realpolitik. Kate Ricke Kate Ricke