ARTICLES PUBLISHED ONLINE: 15 JANUARY 2012 | DOI: 10.1038/NCLIMATE1357 The impact of climate change on global tropical cyclone damage Robert Mendelsohn 1 * , Kerry Emanuel 2 , Shun Chonabayashi 1 and Laura Bakkensen 1 One potential impact from greenhouse-gas emissions is increasing damage from extreme events. Here, we quantify how climate change may affect tropical cyclone damage. We find that future increases in income are likely to double tropical cyclone damage even without climate change. Climate change is predicted to increase the frequency of high-intensity storms in selected ocean basins depending on the climate model. Climate change doubles economic damage, but the result depends on the parameters of the damage function. Almost all of the tropical cyclone damage from climate change tends to be concentrated in North America, East Asia and the Caribbean–Central American region. This paper provides a framework to combine atmospheric science and economics, but some effects are not yet modelled, including sea-level rise and adaptation. A lthough several studies argue that climate change has altered tropical cyclones, others argue that the evidence is thin. For example, tropical cyclone intensity has increased over the past 40 years as the climate has warmed 1–3 . However, this recent upward trend is still within natural variability and longer-term records do not reveal changes in underlying frequency or severity 4 . The historic record may simply not be long enough and clear enough to detect how climate may be affecting tropical cyclones; nor is the physical understanding of the phenomenon sufficient to project how future activity might change with climate. In particular, there remains significant debate about how rising greenhouse-gas concentrations affect tropical cyclones. There is also evidence that the damage from extreme events and specifically tropical cyclones is increasing over time 5 . One explanation for this trend is that there are just more people and assets in harm’s way 6,7 . Until the influence of rising vulnerability from income and population is properly controlled, it is difficult to know whether the trend in damage is due to a trend in the underlying hazards. This paper develops a tropical cyclone integrated assessment model. The model begins with an emissions scenario for the next century. Given this emissions scenario, several climate models are used to project how climate might change by 2100. A tropical cyclone model is used in conjunction with the climate models to predict how the frequency, intensity and location of tropical cyclones change in each ocean basin of the world. The paths of the resulting tropical cyclones are followed until they strike land whereupon a damage function is used to estimate the damage caused given the intensity of each cyclone and what is in harm’s way. Although each component of the model will undoubtedly improve over time, the model provides a guide for how to combine atmospheric science and economics to estimate tropical cyclone damages. There are several innovations in this modelling exercise. With the exception of one study 8 , the tropical cyclone damage literature previously linked climate to tropical cyclones using a single reported statistical relationship between wind speed and sea surface temperature 9 . Consequently, previous studies assumed that climate change has the same effect on all tropical cyclones 10–12 . This 1 Yale School of Forestry and Environmental Studies, 195 Prospect Street, New Haven, Connecticut 06511, USA, 2 Massachusetts Institute of Technology, Department of Atmospheric Science, 77 Mass. Ave. Cambridge, Massachusetts 02139, USA. *e-mail:robert.mendelsohn@yale.edu. paper models how storm frequency, intensity and location may change in each ocean basin 1 . The previous literature assumes that tropical cyclone damage increases proportionally with gross domestic product (GDP) 8,10–12 . This study tests that assumption with an empirical analysis of global data. The previous literature has relied on wind power to measure storm intensity 8,10–12 . This paper reveals that minimum barometric pressure predicts damages more accurately than maximum wind speed. Impact of climate on tropical cyclones For each climate scenario, a synthetic set of 17,000 storms is examined to capture detailed information about the frequency, path and intensity of storms in each ocean basin. Given the present climate, the properties of these synthetic storms are consistent with observed data 3 . Figure 1 provides a map of a sample of these synthetic storms. The predicted storm frequencies and intensities match historic data. We measure storm intensity using minimum pressure. The storms are most intense over warmer waters (near the Equator). As storms veer over cooler water (towards the poles) or land, they lose their intensity. Storms also lose their intensity if they get too close to the Equator. Figure 2 shows how climate change affects tropical cyclone power, which is the cubed cumulative wind speed of each storm over its entire track. The results vary a great deal across ocean basins. The results also vary across the climate models. Power consistently increases only in the northwestern Pacific. All of the other ocean basins experience both increases and decreases in power. Some climate models predict particularly large increases in power in the North Atlantic. Average effects are more moderate in the other ocean basins as the changes cancel each other out across different climate models. These large regional inconsistencies among the climate model results are consistent with other variables such as tropical precipitation, which differ widely across models on regional scales. Forecast of baseline damage The present annual global damage from tropical cyclones is US$26 billion (which is equal to 0.04% of the gross world product (GWP) 13 . This is the expected damage per year given NATURE CLIMATE CHANGE | ADVANCE ONLINE PUBLICATION | www.nature.com/natureclimatechange 1 © 2012 Macmillan Publishers Limited. All rights reserved.