Climate change isn’t coming to Nashville — it’s already here. And the future might be hotter than we can handle 

Hot Problems

Hot Problems

It doesn't take a climate scientist to realize July 2010 was a hot month in Nashville. You stepped outside, right? For some, the heat was a nuisance, like skin sticking to hot leather seats. For others, it was as serious as sunstroke. But just how hot did it really get? According to data collected by the National Oceanic and Atmospheric Administration (NOAA), the average temperature for July 2010 was 82.4 degrees — 3.3 degrees above normal — making it the 10th-hottest July on record in Nashville.

Wait, that's just the median. On all but six days, the high temperature reached at least 90 degrees, including 14 consecutive days to close out the month. Furthermore, not only did July 2010 come on the heels of the fifth-hottest June on record, it gave way to an August in which the high temperature reached 101 within the first week. If current projections are correct, Nashville won't have to wait long for the next heat wave. And the next. And the next.

Granted, no single weather event or string of hot days should be taken alone as proof of climate change. That includes even our ruinous, once inconceivable May flood. Nevertheless, there is broad consensus in the scientific community that this year's oppressive heat in Nashville and Middle Tennessee is part of a larger trend. What's more, it will accelerate in coming years as temperatures around the globe continue to increase. While Nashville does not face the threat of, say, becoming partially submerged by rising sea waters, as New York City does, scientists say we do face potentially disastrous consequences if we don't adapt.

Released in February, the "Report on the U.S. EPA Southeast Climate Adaptation Planning Workshop" doesn't exactly have a snappy title. A more chilling text, though, you're not likely to read than this projected future of the region. Among its litany of startling assertions: Since 1970, the average temperature in the Southeastern United States has risen 2 degrees Fahrenheit. By 2080, it is expected to rise by as much as 9 degrees.

With it, the frequency, duration and severity of droughts in the Southeast are likely to increase. Reduced oxygen in streams and lakes, caused by higher temperatures, could kill off fish and other aquatic life. The kind of heat wave that once happened 20 years apart could hit the Southeast as often as every other year. It's not just a matter of cranking up the AC. Extremely hot days will occur more frequently — and the hottest of those days will be 10 degrees hotter.

All this building heat is more than a nuisance. Rising temperatures have the potential to set off a chain reaction of consequences, ranging from the inconvenient to the intractable. Greater heat leads to greater stress on the power grid as demand for electricity increases. It also increases demand for water. Decreased water supplies, in turn, can affect economic and natural systems. Native plant and animal species could be hurt by the heat, as could crops and livestock. Heat stress and heat-related deaths, in addition to respiratory problems caused by poorer air quality, present serious public health hazards.

Perhaps ironically, a warmer climate can also lead to more precipitation. Rain falls less frequently, but when it does, it's a deluge. This can trigger a drought-flood-drought cycle, as water evaporates more quickly from the soil when temperatures are hotter. Just last week, the Nashville area went from heat advisories to swiftwater rescues and submerged roads in a span of days.

There is no avoiding climate change entirely, no matter who you are. Those most at risk as temperatures rise are already among our most vulnerable populations: the elderly, the very young, the poor and the homeless. And yet attempts to reduce the carbon emissions responsible for global warming have sputtered. As for regional efforts to move toward adapting to an already warming climate, the EPA report charitably describes them as "nascent."

In other words, we have a long way to go. At the moment, it's tough to say which is more daunting: not knowing what we're heading toward, or having an increasingly queasy sense of what might await us when we get there.

"We know climate is changing, we know temperatures are rising, and we know they are going to continue to change for the next couple centuries," says Jonathan Gilligan, associate professor of earth and environmental sciences at Vanderbilt University. "As the climate warms up, we expect to get more extreme events."

That expectation is shared by many other scientists, including Noah Diffenbaugh, a lead author of the study "Intensification of Hot Extremes in the United States," which was published this year in the journal Geophysical Research Letters. Examining a variety of climate models, the study predicts "warm-season drying and intensification of hot extremes throughout much of the U.S." Speaking by phone, Diffenbaugh, assistant professor of environmental earth system science at Stanford University, tells the Scene that extreme heat waves used to occur in the Southeast once every 50 years. Soon, they could happen three to five times in a single decade. And as time goes on, the heat will continue to rise — well within a lifetime for many of us. Looking at various climate models, Diffenbaugh says, "For the decade of the 2030s, the season that was the hottest in five decades ... in the Southeastern U.S. occurs somewhere between five and eight times in a single decade."

And as time goes by, not only do heat waves happen more frequently, the extremes get more extreme.

"Looking at the hottest temperatures of the year, year after year — say, the hottest 5 percent of maximum daily temperatures," Diffenbaugh says, climate models show the Southeast can expect "something on the order of a doubling" in how often the mercury hits those record-setting marks.

"Whether it's the extreme event of the five-decade period, or what is now the extremes of each year, they both show more frequent occurrence in the Southeast by the decade of the 2030s," Diffenbaugh says. Talk about cruel summers: What are now the hottest of hot days in Nashville could become the norm in as little as 20 years.

Climatologist Heidi Cullen's recently published book The Weather of the Future arrives at similar conclusions by similar means. "All weather is local," she writes, "and ... in the future, all climate change will be local too."

But (to coin a phrase) is this change we can believe? Perhaps it seems counterintuitive to start planning our lives around the prognostications of a few dozen climate model computers. Yet it's important to note that not only are temperatures already rising, past computer models have been surprisingly accurate. In 1988, James Hansen ran computer simulations trying to predict what would happen in the next 30 years under various greenhouse gas emissions scenarios. Actual temperatures between then and now have been extremely close to his "most likely" scenario, which took into account both greenhouse gas emissions and the cooling effects of other things like airborne pollution.

As Vanderbilt's Gilligan notes, this doesn't mean we can be 100 percent confident in everything the models tell us. Specific storms, hurricanes and tornadoes are very difficult to predict, because of myriad contributing factors. Temperature, however, can be forecast much more reliably.

"Increasing greenhouse gases will cause the planet to warm up," Gilligan says. "This is such basic physics that for the planet not to warm up would mean something is very wrong with the basic laws of thermodynamics from the 1800s. You can trust models very well that temperatures will rise significantly over most of the planet and that there will be big changes to weather and climate patterns."

The biggest change headed our way: new definitions of "extreme."

"For years," former Vice President Al Gore tells the Scene via email, "many scientists used the analogy of 'loaded dice' to describe the increased likelihood of more frequent extreme weather events — like the 1,000-year rainfall event we had here in Nashville at the beginning of May. But some of these same scientists are now saying that the 'loaded dice' analogy misses an important point: The climate crisis is now beginning to cause totally unprecedented events. We are not only loading the dice, we are, in effect, painting more spots on the dice. Instead of rolling 11s and 12s, we are now rolling some 13s and 14s."

No one's fate hinges more directly on the roll of those dice than farmers. As anyone knows who watched their victory garden succumb this summer to the agony of defeat, food-bearing plants are sensitive to heat. The hotter the climate gets, the more frequent and severe droughts become. With drought comes pressure on agriculture. While gradually increasing temperatures aren't likely to devastate our local agricultural economy in a single dramatic incident — farmers already have to plan for fluctuating temperatures from season to season — they could eventually cause significant shifts in the types of crops that are grown here, and the way those crops are raised.

First, the good news. According to Nick Gawel, superintendent of Tennessee State University's Nursery Research Station in McMinnville, "Most of our major agronomic crops are middle-of-the-climate type crops." These major crops — soybeans, corn, cotton and tobacco — are at the moment pretty far from any kind of heat-related tipping point.

"Most of what we grow is not on the edge," Gawel says. Many crops have already been tested in terms of heat tolerance, and heartier varieties that are currently grown in hotter climates to our south, as in Texas and Florida, could be introduced here.

"If temperatures do climb," Gawel says, "we have the advantage here in Tennessee that, OK, we just need to look south a little bit to see what their conditions are there, and what is growing, what are their control measures, what are their issues."

The same basically goes for livestock, says Richard Browning, research associate professor and small animals specialist at Tennessee State University. "I don't see any reason why we wouldn't be able to adapt," Browning says.

Even so, extended droughts could still stir up their fair share of trouble for agriculture. You don't need to go further than your local farmers' market to hear talk of how recent extreme heat has made cows unwilling to milk. Heat can affect growth and mortality rates as well as lactation.

"If we see a consistent increase in temperature over time," Browning says, "then certainly we will start to see some shifts, either in management of these animals, or in the genetics we're using." Also problematic is that much of Tennessee's agricultural land is not irrigated. Extended droughts could result in lower production, slower growth and lower survival rates, and this could be economically disruptive. The price of wheat, for example, shot up recently as a result of devastating drought in Russia — prompting President Dmitri Medvedev to proclaim, "What's happening with the planet's climate right now needs to be a wake-up call to all of us."

Staring down acres of parched land, farmers could be forced to choose between installing irrigation systems or changing their business model. Small farms operating on razor-thin profit margins could be forced to shut down entirely. Chandra Reddy, dean and research director of TSU's School of Agriculture and Consumer Sciences, says that if prolonged droughts become a regular feature of the local climate, "You are going to have [an] extremely different strategy for what we grow and what we raise here."

Additionally, farmers might switch over to more profitable crops to offset increased water costs. "Most of the time, when you spend money on irrigation, people produce more valuable crops like vegetables or rice, or sugar cane," Reddy says. "Even cotton would be more valuable than corn or soybeans."

That could mean an eventual shift in the crops grown in Tennessee. Sorghum, millet and sugar cane, which are currently grown further south, are among the crops that could find their way to local fields if the temperatures continue to rise. With them, though, would come new insects and new plant diseases hitherto unknown to the region. It will be up to research universities, Browning says, to help lead the way in determining what kinds of adaptations will be needed, and in developing methods to help farmers cope with the changes.

Even if our agricultural industry is able to adapt, Tennessee is likely to face problems related to water — an element that can wreak havoc both in scarcity and overabundance. A statement released earlier this month by the Tennessee Commissioner of Environment and Conservation's Water Resources Technical Advisory Committee hints at just how problematic extended droughts could be for our area.

"[S]ome areas of the state are growing fast enough that utilities there are competing for water even in times of plenty," the committee said. "We know now ... that utilities along the main stem of the Cumberland River in fast-growing Middle Tennessee are using more water than the main stem alone can supply."

Since there is already pressure on our water supply, increased demand created by hotter temperatures will only further stress the system. Are we headed toward water rights allocations, as in New Mexico? Will we all be driving dirty cars and taking Navy showers, as we did in the weeks after the 2010 flood? Whatever happens, Tennessee's water infrastructure might be as vulnerable to climate change as it is vital to our adaptation.

"In '07, when we had the big drought," TSU's Browning says, "they were telling livestock producers they couldn't use the water for their livestock, and they had to find other sources, and it became a real issue. So certainly there's going to have to be some planning if that becomes an annual issue. ... Certainly there will have to be some policies."

At the very least, state officials are thinking about how those policies might take shape. Though it didn't mention climate change specifically, the Water Resources Advisory Committee released a statement of goals and principles Aug. 2 that showed awareness of the issue: "Drought conditions, increased demand, economic growth, and competition for water use in the 21st century emphasize the critical need for a continued water use management program in Tennessee." Similarly, a state water supply pilot study coordinated by the Tennessee Department of Environment and Conservation aims to "account for climate change, droughts more severe than those in the record, and inaccuracies in streamflow and precipitation estimates."

Another, less obvious reason water could be at the center of Tennessee's climate change problems: its role in producing the power we'll need to stay cool — and in some cases, alive. As Vanderbilt's Gilligan puts it: "We need water to make electricity — we have a lot of hydroelectric, but even nuclear and coal-burning plants need cooling water. ... We've run into problems in the past when, in the summer, the water temperature in the streams, combined with the decreased levels due to the higher temperatures, [has meant] they have to hold back on the power."

And that's just the scarcity side of the water equation. Between droughts, we could be inundated with more water than we can handle, seesawing between Mad Max and Waterworld. While precipitation is much harder to predict, and models disagree about just how it will play out in the future, a warmer climate means more water evaporating into the air. And while scientists may not able to predict precisely when and where that water will fall, greater heat in the atmosphere creates a greater likelihood for heavy rain. (See chart above.)

"Make no mistake," Heidi Cullen writes in The Weather of the Future, "global warming increases the likelihood of floods."

Randall Gentry, director of the University of Tennessee's Institute for a Secure and Sustainable Environment, says changing storm patterns can have significant regional impacts. "Let's say that during a given month, a region, on average, typically gets 10 inches of rain over 30 days cumulatively," Gentry says. "Under climate change, the patterns of delivery can be altered such that the 10 inches is received in more intense storms." These storms could overwhelm a system calibrated to less extreme downpours.

"Engineers design infrastructure on the basis of frequency of events or risk," Gentry says. "So a one-in-50-year probability storm could occur on a much more frequent basis ... and do great damage."

Given that 50-year heat waves have the potential to become every-other-year heat waves, it is within the realm of possibility that our 1,000-year flood could be more like a 20-year flood by the time this year's kindergarteners finish college. Taken as an isolated event, the great Nashville flood of 2010 could have happened even if the climate is not changing. But a warming climate will increase the likelihood of extreme weather — and make it even more devastating. As Vanderbilt's Gilligan says, citing a NOAA report, the recent drought in Russia happened as part of a natural event called a "blocking high." However, he says, "if the same weather conditions took place in combination with the kind of climate change we are confident will occur over the coming century, the results would be much more severe than what we see this year." In other words, Russia's next heat wave might not only come sooner, it could be even worse — and so might our next flood.

"It's clear that long-familiar patterns are being disrupted, and the extreme events are becoming both more extreme and more frequent," Gore says. "Moreover, the changes — like larger downpours — are absolutely consistent with what the scientists have long warned us would accompany global warming."

As Eric Pooley, author of the new book The Climate War, puts it: "In a warmer world, that kind of thing will happen more often. So if you liked the Nashville flood, you're going to love living in a warmer world."

"There's not been a lot of attention to climate change impacts on Tennessee," says Thomas J. Wilbanks, research fellow at Oak Ridge National Laboratory (ORNL). Wilbanks co-authored a chapter on adaptation for the Intergovernmental Panel on Climate Change, which, along with former Vice President Gore, was awarded a Nobel Peace Prize in 2007 for their efforts on the issue. "So much of the attention has been on coastal areas and the arid West," he says. "... We don't know as much about what climate change means for Tennessee as we need to."

What we do know, with a high degree of certainty, is that Tennessee — like the rest of the world — will keep getting hotter. And as an urban center, Nashville is susceptible to the "heat island effect," which makes for higher temperatures in cities (as much as 5.4 degrees during the day and 22 degrees at night) than in rural and surrounding areas.

Efforts in the U.S. toward climate change mitigation — action to significantly reduce greenhouse gas emissions and slow global warming — have stalled. A climate bill, weak and carbon cap-less as it was, died in the Senate earlier this month, even as millions of barrels of oil still foul the waters of the gulf. So if solving the problem is off the table, at least for now, that leaves coping with it.

"We need to deal with adaptation," Pooley says. "Especially now that the Senate has made it clear that it won't act now, and the likelihood is it won't even be in a position to discuss serious climate action for another couple of years, depending on what happens in the midterm elections."

And the time for getting serious is short. "I think it's already clear that the climate crisis has very real and serious implications for Middle Tennessee and the United States as a whole," Gore says. As ORNL's Wilbanks warns, "If it turns out that climate change is more severe, or more rapid — and we seem to be on that track at the moment — then it starts to get tougher to look at adaptations that don't involve fairly big decisions, as opposed to gradual, incremental decisions."

Pooley is more blunt. "Local impacts may be where people do start to focus on the problem," he says. "The trouble is, by the time the impacts are dramatic enough to get their attention, it'll be too late."

One bright spot is that demand for renewable energy in Tennessee is strong — exceeding TVA's present ability to produce it. "The Southeast is a national leader in looking at energy from biomass as a regional source — such things as switchgrass that grow on marginal lands," Wilbanks says. "... I think the encouraging thing is the strong regional demand for green power."

While experts disagree on what the best mechanism for implementing adaptation measures would be — with some arguing for top-down federal mandates, and others for more state- and municipality-level initiative — time is not on our side. Research is already under way or being planned, pilot programs are in motion, and awareness of climate change among public officials is generally high, but there is no centralized effort for adaptation in place at a federal, state or city level. There is no statewide coordination among research universities, the office of the State Climatologist, the Tennessee Department of Ecology and Conservation and other state agencies, nor between city governments. That may be OK for the time being. But it won't help when the accelerated heat waves begin — and the science says they will come, whether we're ready or not.

"The pervasive denial of these scientific realities — these inconvenient truths — allows the polluters to continue threatening the future of human civilization," Gore says, "including our way of life here in Middle Tennessee."

Even if climate models are not as detailed as we might like, we still have real problems staring us down if we don't plan accordingly. And those models could get more precise soon. A project called the Ultra High Resolution Global Climate Simulation at ORNL is working to develop programs that can model climate in greater detail. The National Center for Atmospheric Research is also working on a report, due next year, that would contain more localized predictions.

But a lack of high-def projections is not a barrier to adaptation. "In most cases, risk management doesn't require precise forecasts of impacts, because a risk management strategy tries to equip a community or a region or a firm to deal with a variety of possible futures," says ORNL's Wilbanks.

Florida has developed a state climate action plan. King County, Wash., New York City and Keene, N.H. (population: 22,834), have drafted adaptation plans. In Wilbanks' view, Nashville would do well to develop one of its own.

"It doesn't have to be expensive," Wilbanks says. "It can involve a lot of people in the community." Coming up with an adaptation plan, he says, "would show real leadership on the part of the state of Tennessee."

So where does that leadership stand in Nashville?

"Climate change is a real issue that cities have to think about," Mayor Karl Dean tells the Scene. And Dean has thought about it, even if there's no Nashville Climate Action Plan per se.

"We have taken a number of measures in the last couple of years that, even without climate change, are good for the city and the quality of life here, but will also help protect us against the risks that are predicted to accompany changes in our environment," Dean says.

Measures already under way include an energy-efficiency retrofit program, incorporating funds through the federal Weatherization Assistance Program. The Clean Water Infrastructure Program, passed last year before the historic flooding, created dedicated funding for Nashville stormwater projects, including $500 million for water and sewer systems over the next five years and $50 million for stormwater capital projects.

According to the mayor's press secretary, Janel Lacy, "We are also working on a Green Infrastructure Master Plan that will start us down the road of including green stormwater collection features throughout Nashville." Dean has also called for an "Open Space Master Plan," set to be completed by the end of this year, which would "provide for strategically placed green spaces that also will help absorb stormwater and protect our natural resources."

Craig Owensby of the Metro Planning Department says, "There's a lot going on ... not necessarily specifically about warming, but about building a more sustainable community." Buildings that use less energy, for example, reduce electricity consumption, which can help reduce stress on the power grid during heat waves. More compact communities can help reduce travel times and carbon emissions, while more green space can help divert stormwater from streets. Whether sustainability development can keep pace with temperature rise, and adequately compensate for the effects of climate change, remains to be seen.

It also remains to be seen — even with an environmentally conscious Metro government — whether we really will be prepared for a Nashville in which 117-degree days are a fact of life. Then again, maybe next July won't be as hot as this one. Maybe the climate models are wrong. Maybe a decades-long upward temperature trend will suddenly level out on its own. Maybe we really do have 1,000 years until our next flood.

Maybe. But are we willing to bet our city on it?


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