GeoEngineering Could Reduce Total Number of Hurricanes, but Make Katrina Events Happen More Often

Atlantic hurricane surge response to geoengineering

Authors:

Moore et al

Abstract:

Devastating floods due to Atlantic hurricanes are relatively rare events. However, the frequency of the most intense storms is likely to increase with rises in sea surface temperatures. Geoengineering by stratospheric sulfate aerosol injection cools the tropics relative to the polar regions, including the hurricane Main Development Region in the Atlantic, suggesting that geoengineering may mitigate hurricanes. We examine this hypothesis using eight earth system model simulations of climate under the Geoengineering Model Intercomparison Project (GeoMIP) G3 and G4 schemes that use stratospheric aerosols to reduce the radiative forcing under the Representative Concentration Pathway (RCP) 4.5 scenario. Global mean temperature increases are greatly ameliorated by geoengineering, and tropical temperature increases are at most half of those temperature increases in the RCP4.5. However, sulfate injection would have to double (to nearly 10 teragrams of SO2 per year) between 2020 and 2070 to balance the RCP4.5, approximately the equivalent of a 1991 Pinatubo eruption every 2 y, with consequent implications for stratospheric ozone. We project changes in storm frequencies using a temperature-dependent generalized extreme value statistical model calibrated by historical storm surges and observed temperatures since 1923. The number of storm surge events as big as the one caused by the 2005 Katrina hurricane are reduced by about 50% compared with no geoengineering, but this reduction is only marginally statistically significant. Nevertheless, when sea level rise differences in 2070 between the RCP4.5 and geoengineering are factored into coastal flood risk, we find that expected flood levels are reduced by about 40 cm for 5-y events and about halved for 50-y surges.

Cat 3 & 4 Hurricanes Could Batter Northeast US After Global Warming

Scientists today released evidence of historically unprecedented hurricane activity along the northeast coast of what would become the United States between about 800 to 1700 years ago, which was associated with warmer ocean temperatures similar to levels we may expect in coming centuries with climate change and ocean warming.

Geoscientists at the University of Massachusetts Amherst and Woods Hole Oceanographic Institute (WHOI) say new evidence they analyzed in sediment deposits from Cape Cod show that intense hurricanes, possibly more powerful than any storms New England has experienced in recorded history, frequently pounded the region from around 250 A.D. to about 1150.

Jon Woodruff and WHOI researcher Dana MacDonald, currently a visiting scholar at UMass Amherst, with lead author Jeff Donnelly of WHOI, say a warmer climate was associated with more intensity and frequent hurricanes on the U.S. East and Gulf coasts hundreds of years ago. They present a new record of sediment deposits in the current issue of Earth's Future, a journal of the American Geophysical Union.

Woodruff, MacDonald, Donnelly and colleagues report that 23 severe hurricanes hit the New England area between the years 250 A.D. and 1150, the equivalent of a severe storm on average about once every 40 years. Many were likely category 3 storms like Hurricane Katrina or category 4 storms like Hugo that would be catastrophic if they hit the region today, the authors add.

The study, the first to find evidence of historically unprecedented hurricane activity along the northeast coast, extends the hurricane record for the region by hundreds of years. Donnelly says the historical interval was "unlike what we've seen in the last few hundred years."

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Are Cyclones/Hurricanes Really Getting Stronger Under Global Warming?

Validating Atmospheric Reanalysis Data Using Tropical Cyclones as Thermometers

Author:

Kossin

Abstract:

Temperatures in the upper-troposphere of the atmosphere, near the tropopause, play a key role in the evolution of tropical cyclones (TC) by controlling their potential intensity (PI), which describes the thermodynamically-based maximum TC intensity that the environment will support. Accurately identifying past trends in PI is critical for understanding the causes of observed changes in TC intensity, but calculations of PI trends using different atmospheric reanalysis products can give very different results, due largely to differences in their representation of upper-tropospheric temperatures. Without a means to verify the fidelity of the upper tropospheric temperatures, PI trends calculated from these products are very uncertain.

Here, a method is introduced to validate the upper-tropospheric temperatures in the reanalysis products by using the TCs themselves as thermometers. Using a 30-year global dataset of TC cloud-top temperatures, and three widely-utilized atmospheric reanalysis products – MERRA, ERA-Interim, and NCEP/NCAR – it is shown that storm-local upper-level temperatures in the MERRA and ERA-Interim data vary similarly to the TC cloud-top temperatures on both interannual and decadal timescales, but the NCEP/NCAR data have substantial biases that introduce an increasing trend in storm-local PI not found in the other two products. The lack of global storm-local PI trends is due to a balance between temporal increases in the mean state and the poleward migration of TCs into lower climatological PI, and has significant implications for the detection and attribution of mean TC intensity trends.

Powerful, Destructive Tropical Cyclones Moving North and South,

Powerful, destructive tropical cyclones are now reaching their peak intensity farther from the equator and closer to the poles, according to a new study co-authored by an MIT scientist.

The results of the study, published today in the journal Nature, show that over the last 30 years, tropical cyclones — also known as hurricanes or typhoons — are moving poleward at a rate of about 33 miles per decade in the Northern Hemisphere and 38 miles per decade in the Southern Hemisphere.

"The absolute value of the latitudes at which these storms reach their maximum intensity seems to be increasing over time, in most places," says Kerry Emanuel, an MIT professor and co-author of the new paper. "The trend is statistically significant at a pretty high level."

And while the scientists who conducted the study are still investigating the atmospheric mechanisms behind this change, the trend seems consistent with a warming climate.

"It may mean the thermodynamically favorable conditions for these storms are migrating poleward," adds Emanuel, the Cecil and Ida Green Professor of Earth and Planetary Sciences at MIT.

The implications are serious, since the movement of peak intensity means regions further north and south of the equator, which have not previously had to face many landfalls by violent cyclones, may now have greater exposure to these extreme weather events. That, in turn, could lead to "potentially profound consequences to life and property," the paper states. "Any related changes to positions where storms make landfall will have obvious effects on coastal residents and infrastructure."

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Tropical Cyclones Warm Ocean, May Cause Positive Feedback Cycle

Sea surface height evidence for long-term warming effects of tropical cyclones on the ocean

Authors:

1. Wei Mei (a)
2. François Primeau (a)
3. James C. McWilliams (b)
4. Claudia Pasquero (c)

Affiliations:

a. Department of Earth System Science, University of California, Irvine, CA 92697;

b. Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095; and

c. Department of Earth and Environmental Sciences, University of Milan-Bicocca, I-20126 Milan, Italy

Abstract:

Tropical cyclones have been hypothesized to influence climate by pumping heat into the ocean, but a direct measure of this warming effect is still lacking. We quantified cyclone-induced ocean warming by directly monitoring the thermal expansion of water in the wake of cyclones, using satellite-based sea surface height data that provide a unique way of tracking the changes in ocean heat content on seasonal and longer timescales. We find that the long-term effect of cyclones is to warm the ocean at a rate of 0.32 ± 0.15 PW between 1993 and 2009, i.e., ∼23 times more efficiently per unit area than the background equatorial warming, making cyclones potentially important modulators of the climate by affecting heat transport in the ocean–atmosphere system. Furthermore, our analysis reveals that the rate of warming increases with cyclone intensity. This, together with a predicted shift in the distribution of cyclones toward higher intensities as climate warms, suggests the ocean will get even warmer, possibly leading to a positive feedback.

Model Predicts Less Storms like Sandy

Model projections of atmospheric steering of Sandy-like superstorms

Authors:

1. Elizabeth A. Barnes (a,b)
2. Lorenzo M. Polvani (b,c)
3. Adam H. Sobel (b,c)

Affiliations:

a. Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523;

b. Division of Ocean and Climate Physics, Lamont-Doherty Earth Observatory, Palisades, NY 10964; and

c. Department of Applied Physics and Applied Mathematics and Department of Earth and Environmental Sciences, Columbia University, New York, NY 10027

Abstract:

Superstorm Sandy ravaged the eastern seaboard of the United States, costing a great number of lives and billions of dollars in damage. Whether events like Sandy will become more frequent as anthropogenic greenhouse gases continue to increase remains an open and complex question. Here we consider whether the persistent large-scale atmospheric patterns that steered Sandy onto the coast will become more frequent in the coming decades. Using the Coupled Model Intercomparison Project, phase 5 multimodel ensemble, we demonstrate that climate models consistently project a decrease in the frequency and persistence of the westward flow that led to Sandy’s unprecedented track, implying that future atmospheric conditions are less likely than at present to propel storms westward into the coast.

Time Lapse of Sandy Hitting Manhattan

Water Temperatures Warm Enough For Hurricanes

The first month of the 2009 Atlantic hurricane season drew to a close without so much as a tropical storm, but that isn’t unusual. According to the National Hurricane Center, the 1944-2002 average for named storms in June was only about 0.75, which means they don't occur every year. When they do form, it is usually the Gulf of Mexico that brews them up, and this image of sea surface temperatures on June 30, 2009, shows why.

Based on a blend of observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) on NASA’s Aqua satellite and MODIS on the Terra satellite, the image shows temperatures that are generally warm enough to sustain hurricanes in yellow, orange and red. The waters of the Caribbean Sea (south of Cuba), the Gulf of Mexico, and the Atlantic off the Southeast coast were all warm enough to fuel hurricanes, while most of the tropical Atlantic between the Americas and Africa was still too cool.

No time to comment. Well, ok, very fast. Now imagine that pic with the surface water temps shifted 5 C up.