Climate Central is a nonprofit science and media organization created to provide clear and objective information about climate change and its potential solutions.
Hurricane Kilo Crosses Dateline, Becomes Typhoon
The storm formerly known as Hurricane Kilo is now Typhoon Kilo. Well, sort of. The storm is trapped somewhere in the space-time-storm continuum, halfway between typhoon and hurricane, today and tomorrow, eastern and western Pacific.
Satellite loop of Hurricane Kilo as it crosses the international dateline.
It's all very confusing for a storm that, rather than dissipating or taking a northward turn on its trek across the eastern Pacific basin, has stayed the course as a hurricane and crossed over into the western Pacific basin where hurricanes are known as typhoons.
The international dateline is what divides the basins and as luck would have it, Japan's Himawari-8 satellite captured Kilo as the dateline cut right through the center of the hurricane (or typhoon or hurriphoon or whatever you want to call it).
The western half of #Kilo is a typhoon and it's Sept. 2, but the eastern half is a hurricane and it's Sept. 1! pic.twitter.com/iljoimCl1M
— Dan Lindsey (@DanLindsey77) September 1, 2015
The last storm to make the trans-basin trek was Genevieve, which did the feat just last year. With warm water ahead of it, Kilo is likely to stay the course as a typhoon and could even intensify. The storm could threaten Japan next week and it could be one of the longest lasting storms on record.
John, a hurricane that also crossed the dateline to become a typhoon, stuck around for 30 days in 1994. With 12 days under its belt, Kilo still has a ways to go, though.
Better Health a Key Benefit of Renewables, Study Says
Building wind and solar farms helps to reduce the human impact on climate change by displacing noxious emissions from coal-fired power plants. A new study says there’s another important benefit to renewables development: cost savings from cleaner air that saves lives.
Researchers from Harvard University, in a bid to show the monetary value of clean energy projects in terms of improved public health, have found that energy efficiency measures and low-carbon energy sources can save a region between $5.7 million and $210 million annually, based on the accepted dollar value of human life.
A wind farm in Illinois. Credit: Amit Gupta/flickr
Those benefits depend on the type of low-carbon energy involved and the population density of the area surrounding a coal-fired power plant whose emissions are reduced by a clean energy project, according to the study, published Monday in the journal Nature Climate Change.
“This study demonstrates that energy efficiency and renewable energy can have substantial benefits to both the climate and to public health, and that these results could be a big player in a full benefit-cost analysis of these projects,” study lead author Jonathan Buonocore, a research associate at Harvard’s Center for Health and the Global Environment, said. “Additionally, this research shows that the climate benefits and the health benefits are on par with each other.”
Renewables and energy efficiency measures — major components of the Obama administration’s new Clean Power Plan — help displace power plants running on coal and other fossil fuels, which are the leading drivers of climate change. They also help reduce harmful emissions of nitrous oxide, sulphur dioxide and carbon dioxide.
The Harvard study adds to recent research showing that taking global action on climate change could improve public health. An Environmental Protection Agency study published in June found that by the end of the century, 57,000 fewer Americans would die each year from poor air quality if the worst effects of climate change were averted.
“One of the main barriers to replacing the current fossil fuel infrastructure is that not many people and policymakers are aware of the quantifiable health impacts that fossil fuels pose,” Mark Z. Jacobson, a Stanford University civil and environmental engineering professor unaffiliated with the study, said. “This study will educate the public and policymakers more about these impacts, allowing them to compare the full cost of fossil fuels versus renewables and make better decisions about our energy future.”
Using several different computer models to estimate power plant emissions’ cost to public health, the study shows that building wind farms and implementing energy efficiency measures produces the greatest public health benefits.
“This is because these (wind power) installations operated at off-peak times, such as nights and during the spring and fall, and were able to displace greater proportions of coal,” Buonocore said.
Coal-fired power plants are generally used to generate power at all times, regardless of demand. So, coal, which is the electric power sector’s biggest polluter, is the primary source of power in the middle of the night when the fewest people are using electricity.
When people are using the most electricity, such as during the middle of a hot summer day, other lower-carbon sources of electricity, such as natural gas, solar and wind, help meet the higher demand for power. But at night, when demand for electricity is low, natural gas plants are idled and solar panels aren’t producing electricity. At those times, wind and energy efficiency measures can make a big difference by offsetting coal.
Regional haze and other pollution, such as this seen over Chicago, can be reduced by increased use of renewables, possibly saving lives in the process, a new Harvard University study says.
“Coal is a much higher-emission fuel source for electricity than natural gas is, so when coal generation is displaced, a lot of emissions are displaced compared to natural gas or other lower-emissions fuel sources,” Buonocore said. “The total health impacts of air pollution increase as more people are exposed to the air pollution, so benefits are even higher when these air pollution reductions happen in areas with a high population.”
That means regions that already have a lot of low-carbon energy sources benefitted the least from building more renewables while areas with the most coal-fired power generation benefitted the most, especially regions that are very densely populated.
The study found that wind farms built near Cincinnati and Chicago produced $210 million in annual health benefits whereas another wind farm in less-densely populated southern New Jersey produced $110 million in benefits.
The same was true for energy efficiency measures implemented in Cincinnati, which produced $200 million in benefits at off-peak times and $20 million at peak times. In Eastern Pennsylvania, similar measures produced $130 million in benefits at off-peak times and $5.7 million at peak times.
Daniel M. Kammen, director of the Renewable and Appropriate Energy Laboratory at the University of California-Berkeley, who is unaffiliated with the study, said the model the study uses to measure the human health impacts of air pollution is the “gold standard.”
“The U.S. has a very evolved record of examining human health impacts,” he said. “Environmental impacts are harder to quantify.”
Although he called the study “solid,” he said it does not address environmental justice concerns related to the human health toll associated with pollution from coal-fired power plants. The study assumes that everyone across the country is equal, but Kammen said some people are more vulnerable than others, especially low-income minority communities which often are located in areas where power plants are built.
The study “doesn’t highlight the environmental justice inequalities of the system,” he said. “One of the biggest debate issues of social and racial justice is not featured here.”
‘Grey Swan’ Hurricanes Pose Future Storm Surge Threat
Black swans are catastrophic events that no one sees coming, while “grey swans,” as the are known, are extreme events for which there’s no historical precedent, but that could still potentially be predicted. A new study takes this concept into the realm of weather and climate, finding that global warming might sharply increase the odds of grey swan hurricanes and storm surge over the coming century.
While such tempests would still remain relatively rare, they could pose unrecognized but potentially serious threats to coastal areas like Tampa, Fla., and Dubai, with storm surge totals reaching into the double digits when measured in feet.
Damage wrought by Typhoon Haiyan's storm surge, which reached between 15 and 20 feet, in the Philippines in November 2013.
Click image to enlarge. Credit: UNICEF, Jeoffrey Maitem
Overall, the findings of the study, detailed in the journal Nature Climate Change, mesh with the general scientific consensus that tropical cyclones (the generic name for hurricanes) will shift toward higher intensities as the planet continues to heat up.
None of the recent most damaging storms that stick out most in the public memory — hurricanes Katrina and Sandy, Super Typhoon Haiyan — would qualify as grey swans. Even though they all had outsized impacts, they were all known risks given the historical storm records in New Orleans, New York and the Philippines, respectively. Almost the exact scenarios that played out in the first two storms were described years ahead of time by researchers, in fact.
Those weren’t the types of storms that Ning Lin, a civil and environmental engineer at Princeton University, and Kerry Emanuel, a hurricane and climate researcher at MIT, were interested in. They wanted to investigate the odds of storms that don’t appear in the record for a given location, but which could theoretically happen there, as well as how those odds would change with warming.
“I think it’s a great, great question to ask,” Jim Kossin, a hurricane-climate researcher with the National Oceanic and Atmospheric Administration who wasn’t involved with the study, said.
To investigate the question, Lin and Emanuel used a method pioneered by Emanuel where a higher-resolution hurricane model is nested inside a coarser climate model (as climate models can’t resolve individual storms well), and the models are run numerous times so that tens of thousands of storms are generated.
What they were looking for were the storms with long return times (or very low probabilities of happening in any given year) that generated major storm surge.
They looked for such hurricanes in three different places: Tampa, because of its large population; Cairns, Australia, because it is in a cyclone-prone area and in the Southern Hemisphere; and the Persian Gulf, where no hurricane has ever been observed.
First they used the models to see what level of storm surge a 10,000-year storm (or one with a 1-in-10,000 chance of happening in any given year) would have for each location. For Tampa, which is highly susceptible to surge because of shallow waters and low-lying land, this was 19 feet. The highest surge ever measured there was the 15 feet generated by the 1848 Tampa Bay hurricane.
For Cairns, which is situated in far northern Queensland and has had several close calls from storms in recent years, the 10,000-year surge was a similar 18 feet, and for Dubai, on the Persian Gulf, it was 13 feet.
About 80 percent of New Orleans was flooded when Hurricane Katrina's storm surge overwhelmed the city's levees.
Credit: Kelly Garbato/flickr
Warming fairly drastically increased the odds of each of these events in the models, with Tampa’s current 10,000-year storm becoming anywhere from a 2,500-year to a 700-year storm by the end of the century (assuming high greenhouse gas emissions).
The Dubai case was particularly astounding to the researchers given that the models suggested even a moderate-intensity storm could generate an extremely high surge, and that under the right circumstances, a strong storm could reach intensities far greater than even the most intense storm on record with a surge up to 23 feet (though these would be 3 to 20 times rarer than a 10,000-year storm).
“Those results are quite surprising,” Lin said, given that no storm has ever been observed in the Persian Gulf “and we got very intense storms there.” (While the Gulf’s waters are very warm, a boon to hurricanes, the area’s low humidity and high wind shear aren’t conducive to storm formation.)
These are “alarming results in terms of just how much those return periods change,” Kossin said. But he cautioned that what such results might mean for disaster planning was a point for future study, since such storms would still be quite rare.
Also, unlike the bulk of climate models to date, the increase in odds of extreme storms found in the study stems both from a shift toward more intense hurricanes as well as an overall increase in hurricane frequency. Most models to date have suggested that global hurricane numbers might decline.
Lin said that she and Emanuel want to use other models to investigate the same issue and see what they turn up.
Also not factored in to the results of this study is sea level rise, which is considered the surest influence of warming on future hurricane impacts. Even if hurricanes change very little over the coming century, sea level rise means that storm surge events will be worse than they are today.
Large Wildfires Are Now More Common and Destructive
The West continues to be a fiery inferno as August fades into September. Wildfires have exploded across the region this month.
There have been 117 large wildfires to date including 70 large fires that are still burning. Those fires along with thousands of smaller blazes have contributed to 7.8 million acres burned in the U.S., a record for this time of year.
Washington has officially had its most destructive wildfire season on record, including its largest wildfire in state history. In Alaska, 5.1 million acres have burned. Even if all the fires went out across the West tomorrow, this year would still rank as the seventh-most destructive wildfire season in terms of acres burned. But with the season set to continue for at least another month, 2015 will continue to climb the charts, though whether it displaces 2006 for the record remains to be seen.
That puts it right in line with trends since the 1970s of more large fires and more acres burned by these large wildfires as the West dries out and heats up according to an updated Climate Central analysis. Climate change is one of the key drivers helping set up these dry and hot conditions favorable for wildfires.
Spring and summer — two key seasons for wildfires — have warmed 2.1°F across the West, on average. Some states, particularly those in the Southwest, have warmed even faster. Add in shrinking snowpack that’s also disappearing earlier, and you have a recipe for a wildfire season that’s now 75 days longer and more devastating than it was in the 1970s.
There’s been a notable increase in the large wildfires — defined as those 1,000 acres or bigger. A Climate Central analysis of U.S. Forest Service data through 2014 shows that large fires are three-and-a-half times more common now than they were in the ‘70s. They also burn seven times more acreage in an average year.
The biggest changes are in the Northern Rockies. Large wildfires are now 10 times more common than they used to be and the area burned is up to 45 times greater in Idaho, Montana and Wyoming.
Fire is a natural part of most ecosystems but a century of fire suppression, the expansion of homes, roads and infrastructure, and climate change have altered the order of things. Now there’s more fuel in the woods and hotter and drier conditions that can help fires explode with dire consequences.
Air quality in downwind communities (some a thousand miles away) also suffer from the smoke. At least twice in the past 12 years, cities like Los Angeles and San Diego were forced to deal with Beijing-level air pollution caused by southern California wildfires.
Intense burns can leave soil barren and inhibit the regrowth of forest. They can also erode forests’ ability to store carbon and actually turn them into a source of carbon emissions. That’s already occurring in California, there are concerns that could happen in Alaska this year and it could be coming soon to a forest near you.
Climate Central's Todd Sanford provided data analysis for this story.
Atlantic Storm Sets Records as 3 Others Span Pacific
Tropical Storm Erika may have fizzled out, leaving Florida’s 10-year hurricane-free streak still running, but there is plenty of other tropical cyclone activity afoot: Once again this year, there is a string of storms spanning the Pacific, while over in the Atlantic, a hurricane has formed further east in the tropics than any other on record.
The GOES West satellite snapped this image of the three storms spanning the Pacific on Aug. 27, 2015. From left to right, the are: Tropica Storm (now Hurricane) Kilo, Hurricane Ignacio and Tropical Storm (now Hurricane) Jimena.
Click image to enlarge. Credit: NOAA
Like many Atlantic storms, Hurricane Fred began as what is called an easterly wave — basically an area of low pressure that, as hurricane researcher Brian McNoldy put it in a blog post, “can serve as the seed for hurricane formation.”
But typically this transformation takes time to occur, if it occurs at all.
“Only a small percentage of easterly waves EVER develop into a tropical cyclone, let alone immediately off the coast,” McNoldy, of the University of Miami, said in an email.
What likely allowed Fred to do so was an area of much warmer than average sea surface temperatures off the coast of Africa right now, McNoldy said.
Fred first became a tropical depression in the wee hours of Sunday morning; less than four hours later it intensified into a tropical cyclone. It became a hurricane just over 24 hours after it first formed, the furthest east a storm has done so in the tropical Atlantic.
The quick intensification resulted in the first ever hurricane warning for the Cape Verde Islands, which are just off the African coast. (The islands have been hit by two hurricanes before, though prior to the modern system of hurricane watches and warnings.)
Fred, and Erika before it, formed despite a strong El Niño that has otherwise helped keep a lid on Atlantic activity this season.
“So far, the Atlantic is behaving like one would expect in an El Niño year: suppressed,” McNoldy said. “The seasonal activity is at almost 60 percent of average for this date. For comparison, the western Pacific is at 240 percent of average, and the central/east Pacific is at about 200 percent of average.”
This stark difference between ocean basins comes from the different effects El Niño has in different regions. In the Atlantic, it tends to lead to more subsiding air and higher wind shear (or winds that go in different directions and speeds at different heights in the atmosphere), both of which tamp down on storm activity. In the Pacific, though, it leads to a more conducive atmospheric environment and warmer ocean waters, which provide hurricanes with fuel.
Two impressive #Fred images: 1st ever satellite pics of a #hurricane over Cape Verde, and waves pounding Ilha de Sal. pic.twitter.com/TZzFcejO4I
— John Morales (@JohnMoralesNBC6) August 31, 2015
Particularly noteworthy is the spate of storms that have formed or traveled near the Hawaiian Islands, the latest of which is Hurricane Ignacio. So far the island chain has avoided any direct hurricane hits from the two storms that passed through its neighborhood this year. Last year, three storms threatened the islands.
Hawaii is expected to see more tropical cyclones in the future because of global warming, one of the few clear regional signals to have emerged from climate models. The increase is expected to occur because of more conducive conditions in the central Pacific that will allow both more storms to form there as well as eastern Pacific storms to survive longer.
Ignacio is one of three storms across the Pacific now. The other two are Hurricane Jimena, which is well away from land between Mexico and Hawaii, and Hurricane Kilo, located near the International Date Line. All three are Category 4 storms, the first time such a line-up has been observed in the Pacific.
This isn’t the first time this season that multiple storms have been lined up across the Pacific: Back in July, four storms spanned the ocean basin.
How hurricane activity in other regions, like the eastern Pacific or the Atlantic, might change with warming is an active area of research right now. In the flurry of hurricane-climate change research in the decade since Hurricane Katrina, scientists have come to largely agree that while some areas may see an uptick in storms, global tropical cyclone activity may decline. But of those storms that do form, more are likely to be on the more intense end of the spectrum.
U.S. Seeks Greater Focus on Ocean Warming
By Oliver Milman, The Guardian
The U.S. government has urged the international community to focus more on the impact of climate change on the oceans, amid growing concern over changes affecting corals, shellfish and other marine life.
The U.S. will raise the issue at United Nations climate talks in Paris later this year. The UN’s Intergovernmental Panel on Climate Change (IPCC) will be asked to devote more research to the issue.
“We are asking the IPCC in their next series of reports to focus more on ocean and cryosphere [ice ecosystem] issues,” David Balton, deputy assistant secretary for oceans and fisheries at the U.S. State Department, said.
“In my judgment, more attention needs to be paid to the climate change effects upon the ocean areas of the world,” Balton said. “We need to keep pushing up until the Paris conference and beyond.
“Ultimately, we need to change the way we live if we’re to keep the planet in the safe zone.”
Around half of all greenhouse gases produced by the burning of fossil fuels and other activities are absorbed by the world’s oceans, which are warming steadily.
This has caused sea levels to rise and the oceans to become around 30 percent more acidic than in pre-industrial times. In acidic water, corals and shellfish struggle to form skeletons and shells.
An Australian-led study released this week, which examined the impact of climate change on 13,000 marine species, found that while some fish may be able to move into cooler areas, others face extinction due to warming waters. Species on the Great Barrier Reef are considered to be at particular risk.
U.S. government scientists have voiced their concern over recent signals that marine life is under pressure. An enormous toxic algal bloom nicknamed the “blob”, stretching from the Gulf of Alaska to the coast of Mexico, has been linked to the deaths of 30 large whales washed up on Alaskan coasts.
More than 250,000 Pacific salmon have died or are dying, meanwhile, due to warm temperatures in the Columbia river. Scientists predict that up to 80 percent of the sockeye salmon population, which swim up the river from the ocean to spawn, could ultimately be wiped out.
Warming water causes outbreaks of disease among some fish, as well as triggering problems high up the food chain by reducing the number of small prey fish.
“This year is looking an awful lot like what climate-change predictions for the future look like,” said Toby Kock, a scientist at the U.S. Geological Survey.
Another government scientist, Dr. John Stein, science and research director at National Oceanic and Atmospheric Administration (NOAA) Fisheries, said people were “having to change the way they do things right now” because of changes to the oceans, citing the decision by some U.S. shellfish farmers to move their operations.
Stein, who is based in Seattle, added that there was a “fair amount of political challenge” in talking about climate change.
“On this coast you can talk about climate change, in certain parts of the country you cannot,” he said, in reference to a reported ban by the Florida governor of any reference to climate change by public officials.
“We have a very diverse Congress and there are some of them that are true deniers and I don’t know if we’ll ever be able to reach them,” Stein said. “But you can talk to a broader section of Congress about severe drought and flood and they will listen.
“Sometimes you have to craft your message in a way that gets resonance.”
Michael Gravitz, director of policy at the Marine Conservation Institute, a U.S.-based nonprofit, said: “It’s likely the IPCC has done less on oceans than the general atmosphere and we hope that will change.”
Gravitz said overfishing was another blight on ocean ecosystems, with just 10 percent of the world’s fish populations not under significant stress.
Reprinted from The Guardian with permission.
Climate Change Poses Risk to Great Barrier Reef Species
By Joshua Robertson, The Guardian
Species native to the Great Barrier Reef are more likely to face extinction through climate change than marine life elsewhere that can adapt by “invading” new regions, according to new research.
The largest study to date on the impacts of climate change on marine biodiversity found that many species would cope by finding new waters.
Studies have shown "high levels of extinction risk in local marine populations" thanks to human impact and climate change.
Credit: AIMS/EPA/The Guardian
However, tropical species with narrower ranges were more likely to die out in a rapidly warming climate, the international research team found.
And the unknown effects of “invaders” encroaching on “natives” would pose “unprecedented challenges” for conservation, they warned.
One of the researchers, John Pandolfini from University of Queensland’s ARC center of excellence for coral reef studies, said the richness of marine biodiversity would change markedly and vary considerably region to region.
He said the study of almost 13,000 species “gave us hope that species have the potential to track and follow changing climates but it also gave us cause for concern, particularly in the tropics, where strong biodiversity losses were predicted.”
“This is especially worrying, and highly germane to Australia’s coral reefs, because complementary studies have shown high levels of extinction risk in tropical biotas [local marine populations], where localized human impacts as well as climate change have resulted in substantial degradation,” Pandolfini said.
The modeling relied on blending “climate velocity trajectories” – a measurement which combined the rate and direction of shifting ocean temperatures over time – with information about what temperatures and habitats species can tolerate.
CSIRO professor Elvira Poloczanska said the study showed that climate change would drive a new sameness in marine life populations across the world.
“Ecological communities which are currently distinct, will become more similar to each other in many regions by the end of the century,” Poloczanska said.
University of the Sunshine Coast researcher David Schoeman said the model suggested there was still time to prevent major climate-driven extinctions outside the tropics.
“Results under a scenario in which we start actively mitigating climate change over the next few decades indicates substantially fewer extinctions than results from a business-as-usual scenario,” Schoeman said.
However, the prospect of new blends of marine life populations through climate-driven migration was “possibly more worrying.”
“We have little idea of how these new combinations of species in ocean systems around the world will affect ecosystem services, like fisheries,” he said. “We should be prioritizing ecological research aimed specifically at addressing this question.”
Pandolfi said the broad geographic connections of climate change effects shown by the study underlined the need for international cooperation on conservation.
Climate Velocity and the Future of Global Redistribution of Marine Biodiversity is published in Nature Climate Change.
Reprinted from The Guardian with permission.
Carbon Emissions From Power Plants Hit 27-Year Low
As states begin the long task of reducing greenhouse gas emissions from electric power plants to comply with new federal climate policy, a 27-year low in carbon dioxide emissions earlier this year shows the U.S. may be heading toward meeting its emissions goals.
U.S. power plants emitted less carbon dioxide — 128 million metric tons — in April than at any point in since April 1988, according to new U.S. Energy Information Administration data.
Click image to enlarge. Credit: EIA
That continues a long-term trend of declining electric power sector carbon dioxide emissions in the U.S. that began after they peaked at about 250 million metric tons in the summer of 2007. April is the month each year when power plants emit the least carbon dioxide because heating and cooling demand is very low in the early spring.
“April is the so-called shoulder season between heating load and air conditioning load,” EIA analyst John Cogan said.
The 27-year low in power plant carbon emissions comes as the U.S. Environmental Protection Agency has finalized the Clean Power Plan. The plan requires states to cut carbon emissions from existing power plants running on fossil fuels by generating more electricity from renewables and natural gas and by making buildings more energy efficient, among other measures.
The plan’s goal is to reduce those plants’ carbon emissions 32 percent by 2030. Coal-fired power plants are the nation’s largest source of greenhouse gas emissions driving climate change.
April’s low emissions numbers happened because, for the first time in history, electricity production from natural gas surpassed electricity produced from coal, which produces greater than 70 percent more carbon emissions than natural gas when it is burned. That happened only for one month, but as more coal-fired power plants are retired because of environmental regulations and low natural gas prices, the EIA expects more and more electricity to be produced from natural gas. Electricity production from natural gas has tripled since April 1988.
Click image to enlarge. Credit: EIA
“I think it’s indicative of the transition that’s underway in the power sector,” said Dan Bakal, electric power program director at Ceres, a sustainability think tank that has researched each state’s preparations to comply with the federal climate policy. “The Clean Power Plan will solidify that kind of transition and accelerate it a little bit.”
Each passing month increases the probability that natural gas will once again surpass coal as the nation’s dominant fuel for electricity production, especially as more coal-fired power plants are retired, he said.
Alternative energy sources were also factors in the downward trend of carbon emissions this year, according to the EIA. Nuclear power generation was 3 percent greater during the first four months of this year over the previous year and renewable power production increased 2 percent during that time over the first four months of 2014.
Cogan said EIA’s long-term projections show much greater decarbonization of electricity nationwide.
“With the Clean Power Plan, that would continue that trend,” he said.
From Katrina, an ‘Amazing’ Decade of Climate Research
During the summer of 2005, Columbia University climate scientists Adam Sobel and Suzana Camargo were planning a workshop on a topic to which only a handful of scientists had given much thought: how the warming climate might alter hurricane activity.
“It seemed to us sort of like a small, sort of obscure field,” Sobel said, so the pair didn’t expect a large showing. But then Hurricane Katrina hit New Orleans on Aug. 29, 2005, helping to galvanize scientific interest in the subject. By the time their workshop was held in March 2006, they had five times the expected turnout, Camargo said, amid a surge in research that changed the direction of some careers.
“You could see the impact of Katrina on everyone’s thinking,” Sobel said.
Katrina, along with two blockbuster studies that bookended the disaster, marked the beginning of a decade of rapid growth in a once tiny subfield that has since become one of the most visible in climate science.
Hurricane Katrina as it spun up over warm Gulf of Mexico waters in August 2005.
“It’s been exciting ever since then,” Sobel said. While there have been growing pains and sometimes heated disagreements, researchers have made considerable advancements in their understanding of how climate and hurricanes interact in the decade since Katrina, and have reached a general consensus on what the future might bring.
There are still plenty of unanswered questions, of course, which researchers hope to chip away at by the time the 20th anniversary of Katrina rolls around.
“There’s been an amazing rate of progress in the last 10 years. I think the next 10 years will be greater,” Gabriel Vecchi, a climate scientist with the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory, said.
Setting the Stage
Kerry Emanuel, an atmospheric scientist at MIT, was one of the few scientists who had looked at the question of how hurricane activity might change in a warming climate prior to Katrina. In a 1987 paper, he suggested that warming would lead to more intense, and therefore more potentially destructive, hurricanes (still one of the basic precepts of hurricane-climate research).
In early August 2005, just weeks before Katrina, Emanuel, who had been working on other issues, came back to this idea, with a paper in the journal Nature that took his earlier work a step further. It suggested that not only would warming lead to more intense and destructive hurricanes in the future, but that this was already happening, helped along by some natural climate variations. When Katrina struck later that month, interest in his study surged and Emanuel found himself pulled into the cacophonous media coverage.
A separate study by another group followed in mid-September, adding fuel to the fire. This study, in the journal Science, came to a similar conclusion as Emanuel: That of the hurricanes happening in the global oceans, more were becoming Category 4 and 5 storms than was the case three decades earlier.
The two high-profile studies, whose conclusions seemed to be so viscerally demonstrated by Katrina, propelled the issue of warming and hurricanes into the public, and scientific, eye, virtually overnight. But they also created some backlash from other scientists, like NOAA hurricane researcher Chris Landsea, who criticized the papers for relying on a flawed hurricane record.
“And I think that just made the whole field explode,” Camargo said. “They started huge debates.”
Arguments ensued in the scientific literature and at meetings in what might be thought of as the growing pains of an emerging field that combined two disciplines, weather and climate, that had effectively been speaking different languages.
“Scientifically it was a tumultuous time,” Vecchi said, but it spurred “a really strong and vibrant effort” to focus on the topic, drawing in many scientists, including some who hadn’t previously thought much about the subject, like Vecchi himself.
Ten years later, the differences of those early years have largely been hammered out and considerable progress has been made in understanding hurricanes and how they relate to the larger climate.
There is “a lot that has been really learned since then,” Landsea said.
Hurricanes feed off of warm ocean waters, which provide them with the water vapor that fuels the heat engine at their core. So when scientists first started thinking about how such storms might be affected by a changing climate, they reasoned that because the excess heat trapped by greenhouse gases was warming the oceans, that would lead to more, and more intense, storms.
New Orleanians walk throught floodwaters pushing boats in areas inundated by Hurricane Katrina on Sept. 2, 2005.
Click image to enlarge. Credit: Jocelyn Augustino/FEMA
But what researchers discovered as they delved into the subject was that the issue was significantly more complex than that. Many other factors that can affect whether a hurricane forms and how strong it becomes — such as atmospheric moisture and winds — can also be influenced by the changing climate.
“We can’t just simply say that the oceans are getting warmer and therefore this is what tropical cyclones will do,” Jim Kossin, an atmospheric scientist with NOAA, said.
Overall, it is thought that warming will indeed lead to a shift to more intense hurricanes over the course of the 21st century, by anywhere from a few percent to 10 percent, but that overall global hurricane numbers might drop, though by how much is uncertain.
Two of the most robust projections for future hurricanes are that storm surge will be worse, thanks to rising global sea levels, even if hurricanes themselves don’t change, and that storms will bring heavier rains thanks to increased moisture in the atmosphere.
Leaps in climate model resolution and computer power have helped lead to some of these conclusions, allowing scientists to probe how different hurricane ingredients and patterns of warming seem to affect future storms.
They have learned, for example, that how some ocean areas warm relative to others might make a difference in how hurricane activity changes there, Vecchi said.
Researchers also have a better grasp of the proverbial “known unknowns” — the pieces they know are missing from the puzzle that hamper the conclusions they can draw. For example, globally there are around 90 tropical cyclones (the generic name for hurricanes) every year, but scientists have no idea why and what governs the overall global frequency of storms.
Another hindrance is the relatively short period of hurricane records and their imperfect nature. Satellites have only been monitoring global activity since the 1970s, and even then they can only estimate a hurricane’s intensity, so our records of the past are limited in what they can tell us about the potential future, and work over the last decade has clarified some of these limits.
But overall, “there’s more and more consensus,” that there will be a change in hurricane activity globally, but that it won’t become discernable until the end of the century, Camargo said.
The Next 10 Years
That increasing consensus doesn’t mean that scientists have all the answers on what changes we might see in hurricane activity as the climate continues to warm.
There is still room for a breakthrough in our basic theoretical understanding of hurricanes, Sobel said, such as why hurricane numbers seem to be capped globally. “As long as we don’t have that, I think it’s a big hole in what we can say,” he said.
School buses swamped by the floodwaters following Hurricane Katrina.
Click image to enlarge. Credit: Liz Roll/FEMA
And then there are what Camargo calls the “next level of questions.” For example, what role another human-caused factor, aerosol pollution, might play in influencing hurricane activity. Some posit that it could be behind the dip in Atlantic hurricane activity in the 1970s and 1980s (with the subsequent rise the result of pollution controls), but others argue it’s natural variability. Vecchi expects more clarity on this issue by the time another decade has passed.
Some findings over the next 10 years could be a surprise, as was a recent finding that suggested hurricane tracks were shifting slightly poleward.
“Sometimes we don’t even know the question until the answer shows up,” Kossin, who conducted that research, said. “None of us really expected that, it’s just something that we found.”
But there are some questions that scientists “maybe won’t be able to have [an] answer” for, Camargo said, such as how the threat to a particular city like Miami might change.
The imperfect hurricane record is likely to remain that way for some decades, limiting what can be gleaned from it, and making computer models even more important, Sobel said. In particular, it is important to know what the models can and can’t do well. Researchers do expect continued improvements in models and computer power.
“In the hurricane business that matters more than anything else,” Sobel said.
Whatever the decade leading to the 20th anniversary of Katrina brings, “I would guess that the next 10 years will be just as exciting as the last 10 years,” Emanuel said.
And in the meantime, “the things that we know are sort of enough now” that even with the questions that remain, we still have a fair idea of what the future will bring, Sobel said. And all of the things that researchers do know about what to expect from hurricanes down the road, he added, “don’t make us feel good.”
Alyson Kenward Talks ‘Danger Days’ on WVM Radio
Our senior scientist and research director, Alyson Kenward, spoke with West Virginia Morning's Ashton Marra about the high number of "danger days" that West Virginia's capital city, Charleston, will face as the world warms.
Climate change is about to make danger days a lot more common over the next 15 years. Charleston, W.Va., for example, is set to take on the title of Danger Day Capital of the U.S. by 2050, potentially facing 168 days a year of dangerously hot weather. "It's the humidity in a place like Charleston that is really driving the number of danger days that Charleston's going to face," Kenward said.
Of the 144 U.S. cities Climate Central analyzed, only 12 of them averaged more than one danger day per year since 1950. Most of those cities are clustered in the South where humidity tends to be worst in the morning while temperatures peak in the late afternoon.
This interactive is available for embed. Get the code >>