Recent Research on the Hurricane - Climate Change Connection
Has Global Warming Affected Atlantic Hurricane Activity? This review by Thomas Knutson of NOAA's Geophysical Fluid Dynamics Laboratory address this question in the context of published research findings. His conclusions are:
i) It is premature to conclude that human activity--and particularly greenhouse warming--has already had a discernible impact on Atlantic hurricane activity.
ii) It is likely that greenhouse warming will cause hurricanes in the coming century to be more intense on average and have higher rainfall rates than present-day hurricanes.
Anthropogenic Effects on Tropical Cyclone Activity - a synopsis page by MIT's Kerry Emanuel that includes a FAQ about global warming and hurricanes, an essay that summarizes recent research, and a reference list.
Interview with Kerry Emanuel from the public radio show Here and Now on September 10, 2008. This short interview covers the basics of the latest research. Listen the audio file (requires Real Audio Player)
Summary Statement on Tropical Cyclones and Climate Change (Acrobat (PDF) 75kB Sep10 08) by the International Workshop on Tropical Cyclones-VI Participants
Real Climate's Hurricanes and Climate Change section summarizes some recent publications, policy and and research.
Hurricane and Cyclone News from Science Daily
Elsner, J.B. (2007). "Climatology: Tempests in Time." Nature 447, 647-649.
Abstract: The frequency of severe hurricanes in the North Atlantic has increased during the past decade. Scrutiny of the prehistoric record left by such storms helps to assess the factors contributing to hurricane activity.A hurricane is a product of its environment: a warm ocean provides sustenance; calm atmospheric conditions nurture an infant storm; and a high-pressure cell in the subtropical atmosphere drives it in a given direction. Increases in oceanic heat from global warming will raise a hurricane's potential intensity, all else being equal.
Elsner, J.B., J.P. Kossin, and T.H. Jagger (2008). "The increasing intensity of the strongest tropical cyclones." Nature 455, 92-95.
Abstract: Atlantic tropical cyclones are getting stronger on average, with a 30-year trend that has been related to an increase in ocean temperatures over the Atlantic Ocean and elsewhere. Over the rest of the tropics, however, possible trends in tropical cyclone intensity are less obvious, owing to the unreliability and incompleteness of the observational record and to a restricted focus, in previous trend analyses, on changes in average intensity. Here we overcome these two limitations by examining trends in the upper quantiles of per-cyclone maximum wind speeds (that is, the maximum intensities that cyclones achieve during their lifetimes), estimated from homogeneous data derived from an archive of satellite records. We find significant upward trends for wind speed quantiles above the 70th percentile, with trends as high as 0.3 ± 0.09 m s-1 yr-1 (s.e.) for the strongest cyclones. We note separate upward trends in the estimated lifetime-maximum wind speeds of the very strongest tropical cyclones (99th percentile) over each ocean basin, with the largest increase at this quantile occurring over the North Atlantic, although not all basins show statistically significant increases. Our results are qualitatively consistent with the hypothesis that as the seas warm, the ocean has more energy to convert to tropical cyclone wind.
Emanuel, K. (2005). Increasing destructiveness of tropical cyclones over the past 30 years. Nature, 436, 686-688.
Abstract: Theory and modeling predict that hurricane intensity should increase with increasing global mean temperatures, but work on the detection of trends in hurricane activity has focused mostly on their frequency and shows no trend. Here I define an index of the potential destructiveness of hurricanes based on the total dissipation of power, integrated over the lifetime of the cyclone, and show that this index has increased markedly since the mid-1970s. This trend is due to both longer storm lifetimes and greater storm intensities. I find that the record of net hurricane power dissipation is highly correlated with tropical sea surface temperature, reflecting well-documented climate signals, including multidecadal oscillations in the North Atlantic and North Pacific, and global warming. My results suggest that future warming may lead to an upward trend in tropical cyclone destructive potential, and-taking into account an increasing coastal population-a substantial increase in hurricane-related losses in the twenty-first century.
Hoyos, C.D., P.A. Agudelo, P.J. Webster, J.A. Curry (2006). Deconvolution of the Factors Contributing to the Increase in Global Hurricane Intensity. Science, 312(5770), 94-97.
Abstract: To better understand the change in global hurricane intensity since 1970, we examined the joint distribution of hurricane intensity with variables identified in the literature as contributing to the intensification of hurricanes. We used a methodology based on information theory, isolating the trend from the shorter-term natural modes of variability. The results show that the trend of increasing numbers of category 4 and 5 hurricanes for the period 1970-2004 is directly linked to the trend in sea-surface temperature; other aspects of the tropical environment, although they influence shorter-term variations in hurricane intensity, do not contribute substantially to the observed global trend.
Knutson, T.R., J.J. Sirutis, S.T. Gamer, G.A. Vecci, and I.M. Held (2008). "Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions." Nature Geoscience, 1, 359-364.
Increasing sea surface temperatures in the tropical Atlantic Ocean and measures of Atlantic hurricane activity have been reported to be strongly correlated since at least 1950, raising concerns that future greenhouse-gas-induced warming could lead to pronounced increases in hurricane activity. Models that explicitly simulate hurricanes are needed to study the influence of warming ocean temperatures on Atlantic hurricane activity, complementing empirical approaches. Our regional climate model of the Atlantic basin reproduces the observed rise in hurricane counts between 1980 and 2006, along with much of the interannual variability, when forced with observed sea surface temperatures and atmospheric conditions. Here we assess, in our model system, and find that Atlantic hurricane and tropical storm frequencies are reduced. At the same time, near-storm rainfall rates increase substantially. Our results do not support the notion of large increasing trends in either tropical storm or hurricane frequency driven by increases in atmospheric greenhouse-gas concentrations.
Knutson, T.R. and Tuleya, R.E. (2004). Impact of CO2-induced warming on simulated hurricane intensity and precipitation: Sensitivity to the choice of climate model and convective parameterization. J. Clim. 17, 3477-3495.
Abstract: Previous studies have found that idealized hurricanes, simulated under warmer, high-CO2 conditions, are more intense and have higher precipitation rates than under present-day conditions. The present study explores the sensitivity of this result to the choice of climate model used to define the CO2-warmed environment and to the choice of convective parameterization used in the nested regional model that simulates the hurricanes. Approximately 1300 five-day idealized simulations are performed using a higher-resolution version of the GFDL hurricane prediction system (grid spacing as fine as 9 km, with 42 levels). All storms were embedded in a uniform 5 m s-1 easterly background flow. The large-scale thermodynamic boundary conditions for the experiments- atmospheric temperature and moisture profiles and SSTs-are derived from nine different Coupled Model Intercomparison Project (CMIP2+) climate models. The CO2-induced SST changes from the global climate models, based on 80-yr linear trends from +1% yr-1 CO2 increase experiments, range from about +0.8° to +2.4°C in the three tropical storm basins studied. Four different moist convection parameterizations are tested in the hurricane model, including the use of no convective parameterization in the highest resolution inner grid. Nearly all combinations of climate model boundary conditions and hurricane model convection schemes show a CO2-induced increase in both storm intensity and near-storm precipitation rates. The aggregate results, averaged across all experiments, indicate a 14% increase in central pressure fall, a 6% increase in maximum surface wind speed, and an 18% increase in average precipitation rate within 100 km of the storm center. The fractional change in precipitation is more sensitive to the choice of convective parameterization than is the fractional change of intensity. Current hurricane potential intensity theories, applied to the climate model environments, yield an average increase of intensity (pressure fall) of 8% (Emanuel) to 16% (Holland) for the high-CO2 environments. Convective available potential energy (CAPE) is 21% higher on average in the high-CO2 environments. One implication of the results is that if the frequency of tropical cyclones remains the same over the coming century, a greenhouse gas-induced warming may lead to a gradually increasing risk in the occurrence of highly destructive category-5 storms.
Kossin, J.P., K.R. Knapp, D.J. Vimont, R.J. Murnane, and B.A. Harper (2007), A globally consistent reanalysis of hurricane variability and trends, Geophys. Res. Lett., 34, L04815.
Abstract: Recently documented trends in the existing records of hurricane intensity and their relationship to increasing sea surface temperatures suggest that hurricane intensity may be increasing due to global warming. However, it is presently being argued that the existing global hurricane records are too inconsistent to accurately measure trends. As a first step in addressing this debate, we constructed a more homogeneous global record of hurricane intensity and found that previously documented trends in some ocean basins are well supported, but in others the existing records contain trends that may be inflated or spurious.
Landsea, C.W., B.A. Harper, K. Hoarau, J.A. Knaff (2006). Can We Detect Trends in Extreme Tropical Cyclones? Science, 313(5786), 452 - 454.
Abstract: Subjective measurements and variable procedures make existing tropical cyclone databases insufficiently reliable to detect trends in the frequency of extreme cyclones.
Liu, K. and M.L. Fearn (2000). Reconstruction of Prehistoric Landfall Frequencies of Catastrophic Hurricanes in Northwestern Florida from Lake Sediment Records. Quaternary Research, 54, 238-245.
Sediment cores from Western Lake provide a 7000-yr record of coastal environmental changes and catastrophic hurricane landfalls along the Gulf Coast of the Florida Panhandle. Using Hurricane Opal as a modern analog, we infer that overwash sand layers occurring near the center of the lake were caused by catastrophic hurricanes of category 4 or 5 intensity. Few catastrophic hurricanes struck the Western Lake area during two quiescent periods 3400-5000 and 0-1000 14C yr B.P. The landfall probabilities increased dramatically to ca. 0.5% per yr during an "hyperactive" period from 1000-3400 14C yr B.P., especially in the first millennium A.D. The millennial-scale variability in catastrophic hurricane landfalls along the Gulf Coast is probably controlled by shifts in the position of the jet stream and the Bermuda High.
Mann, M.E., Woodruff, J.D., Donnelly, J.P., and Zhang, Z. (2009). Atlantic hurricanes and climate over the past 1,500 years. Nature, 460, 880-883.
Note: this article was also referenced by NPR:
Hamilton, J. (2009). Recent Hurricanes Not Matched Since Middle Ages. National Public Radio, 12 August 2009.
Abstract: Atlantic tropical cyclone activity, as measured by annual storm counts, reached anomalous levels over the past decadehttp://www.nature.com/nature/journal/v460/n7257/full/nature08219.html#B1. The short nature of the historical record and potential issues with its reliability in earlier decades, however, has prompted an ongoing debate regarding the reality and significance of the recent rise. Here we place recent activity in a longer-term context by comparing two independent estimates of tropical cyclone activity over the past 1,500 years. The first estimate is based on a composite of regional sedimentary evidence of landfalling hurricanes, while the second estimate uses a previously published statistical model of Atlantic tropical cyclone activity driven by proxy reconstructions of past climate changes. Both approaches yield consistent evidence of a peak in Atlantic tropical cyclone activity during medieval times (around ad 1000) followed by a subsequent lull in activity. The statistical model indicates that the medieval peak, which rivals or even exceeds (within uncertainties) recent levels of activity, results from the reinforcing effects of La-Niña-like climate conditions and relative tropical Atlantic warmth.
Mock, C.J. (in press). "Tropical Cyclone Variations in Louisiana, U.S.A. since the Late Eighteenth Century." G-Cubed.
Plentiful documentary and pre-twentieth century instrumental data from Louisiana, U.S.A. provide a record of continuous tropical cyclones, with daily resolution dating back to the late eighteenth century. The reconstruction provided new specific information for 83 storms prior to 1872. Parts of the early and mid nineteenth century exhibit greater tropical cyclone and hurricane activity than at any time within the last few hundred years. A major hurricane that impacted southeast Louisiana in August 1812 is very likely the closest landfalling hurricane known to impact New Orleans. The longer temporal perspective provides insight on historical hurricane impacts and information on assessing future hurricane mitigation strategies concerning potential worst-case scenarios.
Nyberg, J., B.A. Malmgren, A. Winter, M.R. Jury, K.H. Kilbourne, and T.M. Quinn (2007). "Low Atlantic hurricane activity in the 1970s and 1980s compared to the past 270 years." Nature, 447, 698-701.
Hurricane activity in the North Atlantic Ocean has increased significantly since 1995. This trend has been attributed to both anthropogenically induced climate change and natural variability, but the primary cause remains uncertain. Changes in the frequency and intensity of hurricanes in the past can provide insights into the factors that influence hurricane activity, but reliable observations of hurricane activity in the North Atlantic only cover the past few decades. Here we construct a record of the frequency of major Atlantic hurricanes over the past 270 years using proxy records of vertical wind shear and sea surface temperature (the main controls on the formation of major hurricanes in this region) from corals and a marine sediment core. The record indicates that the average frequency of major hurricanes decreased gradually from the 1760s until the early 1990s, reaching anomalously low values during the 1970s and 1980s. Furthermore, the phase of enhanced hurricane activity since 1995 is not unusual compared to other periods of high hurricane activity in the record and thus appears to represent a recovery to normal hurricane activity, rather than a direct response to increasing sea surface temperature. Comparison of the record with a reconstruction of vertical wind shear indicates that variability in this parameter primarily controlled the frequency of major hurricanes in the Atlantic over the past 270 years, suggesting that changes in the magnitude of vertical wind shear will have a significant influence on future hurricane activity.
Saunders, M.A. and A.S. Lea (2008). "Large contribution of sea surface warming to recent increase in Atlantic hurricane activity." Nature, 451, 557-560.
Atlantic hurricane activity has increased significantly since 1995, but the underlying causes of this increase remain uncertain. It is widely thought that rising Atlantic sea surface temperatures have had a role in this, but the magnitude of this contribution is not known. Here we quantify this contribution for storms that formed in the tropical North Atlantic, Caribbean Sea and Gulf of Mexico; these regions together account for most of the hurricanes that make landfall in the United States. We show that a statistical model based on two environmental variables - local sea surface temperature and an atmospheric wind field - can replicate a large proportion of the variance in tropical Atlantic hurricane frequency and activity between 1965 and 2005. We then remove the influence of the atmospheric wind field to assess the contribution of sea surface temperature. Our results indicate that the sensitivity of tropical Atlantic hurricane activity to August - September sea surface temperature over the period we consider is such that a 0.5 °C increase in sea surface temperature is associated with a ~40% increase in hurricane frequency and activity. The results also indicate that local sea surface warming was responsible for ~40% of the increase in hurricane activity relative to the 1950-2000 average between 1996 and 2005. Our analysis does not identify whether warming induced by greenhouse gases contributed to the increase in hurricane activity, but the ability of climate models to reproduce the observed relationship between hurricanes and sea surface temperature will serve as a useful means of assessing whether they are likely to provide reliable projections of future changes in Atlantic hurricane activity.
Swanson, K. L. (2008), Nonlocality of Atlantic tropical cyclone intensities, Geochem. Geophys. Geosyst., 9, Q04V01, doi:10.1029/2007GC001844. http://www.agu.org/pubs/crossref/2008/2007GC001844.shtml
The assumption that tropical cyclones respond primarily to sea surface temperatures (SSTs) local to their main development regions underlies much of the concern regarding the possible impacts of anthropogenic greenhouse warming on tropical cyclone statistics. Here the observed relationship between changes in sea surface temperature and tropical cyclone intensities in the Atlantic basin is explored. Atlantic tropical cyclone intensity fluctuations and storm numbers are shown to depend not only upon SST anomalies local to the Atlantic main development region, but also in a negative sense upon the tropical mean SST. This behavior is shown in part to be consistent with changes in the tropical cyclone potential intensity that provides an upper bound on storm intensity. However, Atlantic tropical cyclone intensity fluctuations are more nonlocal than the potential intensity itself and specifically vary along with Atlantic main development region SST anomalies relative to the tropical mean SST. This suggests that there is no straightforward link between warmer SSTs in the main development region and more intense tropical cyclones.
Trenberth, K. (2005). Uncertainty in Hurricanes and Global Warming. Science, 308(5729), 1753 - 1754.
Abstract: The marked increase in land-falling hurricanes in Florida and Japan in 2004 has raised questions about whether global warming is playing a role. In his Perspective, Trenberth explains that the observational hurricane record reveals large natural variability from El Niño and on multidecadal time scales, and that trends are therefore relatively small. However, sea surface temperatures are rising and atmospheric water vapor is increasing. These factors are potentially enhancing tropical convection, including thunderstorms, and the development of tropical storms. These changes are expected to increase hurricane intensity and rainfall, but the effect on hurricane numbers and tracks remains unclear.
Vecchi, G. A., and T. R. Knutson, 2008: On estimates of historical North Atlantic tropical cyclone activity. Journal of Climate, 21(14), 3580-3600. http://www.gfdl.noaa.gov/reference/bibliography/2008/gav0802.pdf
In this study, an estimate of the expected number of Atlantic tropical cyclones (TCs) that were missed by the observing system in the presatellite era (between 1878 and 1965) is developed. The significance of trends in both number and duration since 1878 is assessed and these results are related to estimated changes in sea surface temperature (SST) over the "main development region" ("MDR"). The sensitivity of the estimate of missed TCs to underlying assumptions is examined. According to the base case adjustment used in this study, the annual number of TCs has exhibited multidecadal variability that has strongly covaried with multidecadal variations in MDR SST, as has been noted previously. However, the linear trend in TC counts (1878–2006) is notably smaller than the linear trend in MDR SST, when both time series are normalized to have the same variance in their 5-yr running mean series. Using the base case adjustment for missed TCs leads to an 1878–2006 trend in the number of TCs that is weakly positive, though not statistically significant, with p = approx.0.2. The estimated trend for 1900–2006 is highly significant (increase of approx.4.2 storms century) according to the results of this study. The 1900–2006 trend is strongly influenced by a minimum in 1910–30, perhaps artificially enhancing significance, whereas the 1878–2006 trend depends critically on high values in the late 1800s, where uncertainties are larger than during the 1900s. The trend in average TC duration (1878–2006) is negative and highly significant. Thus, the evidence for a significant increase in Atlantic storm activity over the most recent 125 yr is mixed, even though MDR SST has warmed significantly. The decreasing duration result is unexpected and merits additional exploration; duration statistics are more uncertain than those of storm counts. As TC formation, development, and track depend on a number of environmental factors, of which regional SST is only one, much work remains to be done to clarify the relationship between anthropogenic climate warming, the large-scale tropical environment, and Atlantic TC activity.
Vecci, G.A. and B.J. Soden (2007). "Effect of remote sea surface temperature change on tropical cyclone potential intensity." Nature, 450, 1066-1070.
The response of tropical cyclone activity to global warming is widely debated. We find that changes in local sea surface temperature are inadequate for characterizing even the sign of changes in potential intensity, but that long-term changes in potential intensity are closely related to the regional structure of warming; regions that warm more than the tropical average are characterized by increased potential intensity, and vice versa. We use this relationship to reconstruct changes in potential intensity over the twentieth century from observational reconstructions of sea surface temperature. We find that, even though tropical Atlantic sea surface temperatures are currently at a historical high, Atlantic potential intensity probably peaked in the 1930s and 1950s, and recent values are near the historical average. Our results indicate that - per unit local sea surface temperature change - the response of tropical cyclone activity to natural climate variations, which tend to involve localized changes in sea surface temperature, may be larger than the response to the more uniform patterns of greenhouse-gas-induced warming.
Vecchi, G.A., Swanson, K.L. and Soden, B.J. (2008). Whither Hurricane Activity? Science 332, n. 5902, p. 687-689
Summary: Alternative interpretations of the relationship between sea surface temperature and hurricane activity imply vastly different future Atlantic hurricane activity.
The authors explored the relationship between sea surface temperature and an index of Atlantic hurricane activity (specifically Emanuel's Hurricane Power Dissipation Index). If there is a causal connection between tropical Atlantic SST and hurricanes, then Atlantic hurricane activity would be expected to increase dramatically in the 21st century as a result of anthropogenic climate change. However, another way to examine the relationship is to consider the relative SST in the Atlantic compared to other ocean basins. If the relative SST is the more relevant driver of hurricane activity, then future Atlantic activity (i.e., power dissipation) is not likely to be dramatically different from present-day levels.
Webster, P.J., G.J. Holland, J.A. Curry, H.R. Chang (2005). Science, 309(5742), 1844 - 1846.
Abstract: We examined the number of tropical cyclones and cyclone days as well as tropical cyclone intensity over the past 35 years, in an environment of increasing sea surface temperature. A large increase was seen in the number and proportion of hurricanes reaching categories 4 and 5. The largest increase occurred in the North Pacific, Indian, and Southwest Pacific Oceans, and the smallest percentage increase occurred in the North Atlantic Ocean. These increases have taken place while the number of cyclones and cyclone days has decreased in all basins except the North Atlantic during the past decade.