Existing infrastructure is designed to operate within historical climatic bounds. As these bounds shift, the risk of disrupted operations and damage to roads, railways, ports, and airports will grow. Climate change presents a potentially large source of risk to existing infrastructure, much of which has not been quantified. My work answers critical questions concerning the risk to infrastructure -- particularly aviation and the electrical grid -- in a warming world, and how we can improve infrastructure resilience to climate change.
For example, aircraft takeoff performance is strongly dependent on temperature. As air temperature rises, air density declines, meaning that a wing produces less lift at a given speed. This requires that takeoff speeds be higher on hotter days; for a given airport and aircraft type, there is a threshold above which the airplane cannot takeoff at its maximum takeoff weight and must be weight restricted. My work has shown that as temperatures warm, more frequent weight restrictions may result in significant economic cost to the aviation industry.
As the world warms, heat waves are becoming more frequent, longer lasting, and more severe. Extreme temperatures are already the number one weather-related killer in the US, and as these events become more common, their impacts will likely increase.
Heat stress in humans depends not only on the temperature but also on the humidity. The hottest regions are not necessarily the most dangerous; the body is capable of cooling itself as long as the humidity is low enough to permit evaporative cooling of skin. However, some of the most densely populated parts of the world can be both hot and humid, presenting a major risk to human health. Recent heat waves have killed tens of thousands of people, caused infrastructure damage and crop failure, and dramatically increased energy demand. My work aims to identify the most at-risk regions for heat stress, understand the dynamics that drive the most extreme events, and consider what adaptation strategies could be employed to reduce the impacts of heat. I have shown that in the coming decades, billions of people annually could be exposed to unprecedented heat stress, with millions potentially experiencing heat stress that approaches the limits of human tolerance. In addition, I have demonstrated that heat stress will not be mitigated by land surface drying; in regions where surface moisture content is projected to decline, near-surface humidity is nevertheless expected to rise.
Human societies are heavily dependent on natural ecosystems for food and resources. Climate change is disrupting these ecosystems, with potentially large consequences for forest health, biodiversity, and agriculture. In addition, these ecological changes will in turn further change the climate through land cover change and a modified carbon cycle. My work projects how a warming climate will change ecosystems, and how these changes may affect people.
For example, the Southern Pine Beetle is an invasive forest pest which is killed by cold nighttime temperatures and has historically been confined to the southeastern United States. However, as wintertime minimum temperatures have warmed, the beetle has spread northward along the eastern seaboard and has recently been sighted in New York and Connecticut. I have been involved in work projecting how the beetle may spread in the coming decades; we've found that much of the northeastern United States and southeastern Canada may be climatically suitable for the beetle, with significant consequences for the stability of these boreal forests. This work has been covered in The New York Times, Reuters, and NPR.
The most damaging climate events -- such as storm surge on top of sea level rise, humid heat, or hot drought -- are often multivariate, and can occur even if neither variable is extreme by itself. Due to their multivariate nature, the statistics of these events can change rapidly and unpredictably as the world warms. My work assesses how multivariate extremes are changing, the physical mechanisms that lead to these events, and how they may impact human societies.
The Nile Basin is particularly susceptible to hot droughts, which have contributed to crop failure, famine, and migration in recent decades. I have shown that while precipitation is projected to increase across the Basin, the risk of concurrently hot and dry conditions is also rising, due to higher temperatures and more precipitation variability. On top of this increased risk of concurrently hot and dry conditions, population is rapidly rising across the Basin. My work has shown that this combination of climate and demographic change is likely to result in a vastly increased risk of widespread exposure to hydroclimatic extremes in the coming decades, necessitating adaptation and preparation to avoid humanitarian crises.