When it rains, it pours. When it's dry, it's parched. When it's hot, it lasts.
These are some of the impacts climate change is already bringing to the United States, with more extremes to come in the future, according to the National Climate Assessment report released yesterday.
With 30 chapters, multiple appendices and a user-friendly website, the report comprehensively documents climate change impacts across the United States.
It even includes a frequently asked questions section -- a sort of "everything you always wanted to know about climate change but were afraid to ask."
"It is much more comprehensive than we did before with a lot more detail looked at," said Donald Wuebbles, a climate scientist at the University of Illinois who also helped lead the report.
While the assessment has more data on certain topics, like the link between extreme weather and climate change, and sea-level rise impacts, it also reiterates the message of past climate reports from the Intergovernmental Panel on Climate Change, the American Association for the Advancement of Science and the previous National Climate Assessment, which came out in 2009.
That message: Climate change is happening, it's human-caused, and without action, the impacts will be bad.
"Has the basic message changed? No," Wuebbles said. "But the message is stronger because we have that much more data."
Weather extremes linked to climate
The assessment makes a stronger link between extreme weather events and climate change than the past one did. That is because the science of attribution of weather events to climate change has improved, said Wuebbles.
Heat waves have become more frequent and intense, while cold waves have become less so. This is expected to continue and intensify as the climate warms. Heavy downpours are also trending up, particularly in the Midwest and Northeast.
Other weather trends cannot be directly attributed to climate change yet but are noted in the report. "The intensity, frequency, and duration of North Atlantic hurricanes, as well as the frequency of the strongest (Category 4 and 5) hurricanes, have all increased since the early 1980s," the assessment states.
Winter storms have also increased in frequency and intensity, and their tracks have shifted northward. There are not yet clear trends in intensity and frequency of tornadoes, hail and thunderstorm winds, but those are still being studied.
"It is intuitively clear that they have a connection here, but the causality relationship has not been made," said Robert Corell, a lead author of the assessment chapter on research and a principal at the Global Environment Technology Foundation.
National water trends go toward extremes
The assessment projects a future of wet and dry extremes, although it cites many national trends with water resources, as well.
For example, the length of dry spells is expected to increase in most locations.
Short-term droughts lasting a few months also are expected to intensify in most U.S. regions, while long-term droughts are more of an issue in specific hot spots, like the Southwest and southern Great Plains.
In Southwestern and Western watersheds, like the Rio Grande and Sacramento-San Joaquin River Delta, runoff reductions of roughly 15 percent could occur in the next 50 years, according to the assessment.
Very heavy precipitation events -- during which rain falls in massive daily spurts -- have increased nationally and are projected to increase in all U.S. regions. "Heavy precipitation events that historically occurred once in 20 years are projected to occur as frequently as every 5 to 15 years by late this century," the assessment says.
This dynamic will create ongoing challenges with runoff contamination and with stormwater, sewage and drainage infrastructure, which is already overwhelmed in many older cities, the scientists said. Sea-level rise and storm surges further could threaten coastal freshwater aquifers and wetlands.
The report documented other regional differences since the 1920s, such as an increase in flooding magnitude in the Midwest and Northeast, while the Southwest has followed an opposite trend.
Annual precipitation and river flows have increased in the Midwest and Northeast. In the future, hydropower is expected to decline in the southern United States and increase in the Northeast, although the assessment says that technology innovations with turbines may alleviate some of those constraints.
Meanwhile, Florida, the Mississippi Valley, the Great Plains and the Great Lakes region likely will face greater challenges with groundwater, because of a high reliance on it for water supplies combined with climate impacts.
For this reason, the report calls for a national framework for groundwater monitoring and better scientific analysis of the groundwater-climate link.
"Nearly all monitoring is focused in areas and aquifers where variations are dominated by groundwater pumping, which largely masks climatic influences," the report states.
Sea-level rise pegged at 1 to 6 feet by end of century
The report goes further than previous editions by predicting upper and lower bounds for sea-level rise through the end of the century. Oceans could rise by up to 6 feet, the authors predict, affecting millions of U.S. coastal residents who live within 4 feet above the high-tide line.
On the lower end, seas are almost certain to rise at least 1 foot just from the melting of smaller mountain glaciers and thermal expansion of seawater.
The report's authors stress that 6 feet of sea-level rise by 2100 is an extremely unlikely result. But it can't be ruled out.
"When you really look at the science, it's hard to say it's impossible for it to be 6 feet," said Josh Willis, a climate scientist at NASA's Jet Propulsion Laboratory. "The way the upper bound is calculated is if every possible thing went wrong that could, you'll get 6 feet."
The major contributors to sea-level rise of that magnitude would be Greenland and Antarctica, he said, which contain enough ice to raise sea levels by more than 250 feet combined. If West Antarctica alone melted, it would raise the ocean by 10 feet.
"Six feet seems like the most reasonable upper bound based on what the ice can do," he said.
Sea-level rise and storm surges also have the potential to cripple transportation infrastructure like coastal airports, ports and harbors, rail lines, tunnels and bridges. Thirteen of the nation's 47 largest airports have at least one runway within reach of moderate to high storm surge, the report states.
The report also highlighted impacts of permafrost thawing on Alaska roadways, which can cause roads to slump and runways to sink. These impacts can also be reduced through adaptation, like infrastructure redesigns and transportation planning, the report states.
Ag sees crop failures, temperature changes
The report also outlines dire impacts for agriculture, including failed cherry crops in Michigan, high nighttime temperatures in the Corn Belt, heat stress in livestock and food price spikes.
The signs of climate change are right in front of us, says the assessment's chapter on agriculture, one of the few comprehensive reports to explicitly point to certain events -- like the 2012 drought -- as an example of the consequences of climate change.
Not only will weather affect crop growth, but it will encourage invasive species and pests, lower the quality of forage for livestock and lead to changing land uses across the country, the report says.
"The rising incidence of weather extremes will have increasingly negative impacts on crop and livestock productivity because critical thresholds are already being exceeded," states the assessment's subchapter on drought and heat damage.
For the first time, the report highlights the problems caused by fewer chilling hours for fruits like cherries and plums, a problem that shriveled the 2012 cherry crop in Michigan, causing an economic impact of $220 million.
To adapt, farmers will need to select varieties that need fewer cold hours to survive.
They will also need to develop ways to chemically manipulate plants to withstand the lack of chill, said Jerry Hatfield, a lead author of the chapter and a laboratory director for the Agriculture Department's Agricultural Research Service. Rezoning growing areas is another possibility.
"Being prepared for these things and understanding this is extremely critical," he said.
Soils erode, dry with change
It's also the first time that soil erosion has been discussed in the report. Soil erosion from heavy precipitation can remove dirt from fields, taking it to waterways or roads.
Not only does erosion harm crop potential, but soil loses its ability to hold carbon and act as a CO2 sink. Maintaining soil organic carbon by tilling the ground less and planting cover crops can both help boost crop yields and store carbon underground. Subsurface drainage can prevent soil from washing away in heavy rains.
Soil helps food and fiber grow, but also helps with flood mitigation and the biological control of pests, and provides physical support for roads and buildings, said the assessment.
"What it really says is that we need to be adopting conservation practices to help us protect our soil resources ... in the very short term," said Hatfield. "How do we get conservation practices that are very aggressive in protecting our soil and water in place, and with producers, to make sure we are not increasing our soil erosion?"
The report also notes that warmer temperatures will deplete soil moisture, possibly making drought worse. In the long term, said Hatfield, farmers will need to look at how to adapt cropping systems to variable weather.
The five-year farm bill passed in February contained several soil conservation measures, such as provisions that prevent farmers from getting crop insurance on acres that have been converted from grasslands or wetlands. Yet growers still lack the incentives to take care of their soil, said Claire O'Connor, an agricultural water policy analyst at the Natural Resources Defense Council.
USDA's Risk Management Agency should create a pilot program that would provide discounted crop insurance premiums to growers who demonstrate practices that minimize soil erosion, said O'Connor (ClimateWire, May 2).
"After the Dust Bowl, we learned that farmers have the best insurance under their feet," she said in a teleconference last week, adding, "The longer we wait, the harder the job will be."
Forests face challenges, but also solutions
The assessment puts into context the negative impacts of climate change on forests -- wildfires, bark beetle infestations, and losses of carbon dioxide into the atmosphere -- but balances those with solutions.
"If there's an emphasis, it's that there's something that we can do," said David Cleaves, the Forest Service's climate change adviser. "You can do something about it, if you use the best science and apply it on the ground."
Western forests, most of which lie on public lands, will see an increase in wildfire activity as drought and heat are compounded by decades of fire suppression policy. These policies have prevented natural fire regimes from regulating the amount of wood in forests and thus their propensity to burn.
Forests and wood products in the United States act as a substantial carbon sink, capturing and storing more than 227.6 million tons of carbon per year -- about 16 percent of the country's fossil fuel emissions.
The capacity of forests to hold carbon is expected to peak by the middle of the century and drop steadily through the end of the century, as drought, pests and fires kill off more trees, according to the Forest Service's 2012 Resource Planning Act assessment (ClimateWire, Dec. 19, 2012).
Conversion of forests to other land uses, mostly urban or agricultural land, is one of the biggest sources of carbon loss in forests today. This could be mitigated by encouraging economic activity in forests.
"The fate of our carbon sequestration resource depends on the ability and the incentive to see forests in forests," said Cleaves. In other words, he added, the country must recognize the economic benefits of forests in comparison to other land uses.
Forest bioenergy could serve as an energy source that could replace fossil fuels, said the report, although uncertainties remain. Backers of bioenergy say that maintaining forests to provide wood for electricity protects the carbon sink, rendering biomass energy carbon-neutral.
But opponents say the lag time between emissions of biomass and absorption from trees is too long for the energy source to be considered carbon-neutral. U.S. EPA is currently developing an accounting methodology to accurately measure net biomass emissions.
Scientists push for action
In presenting the report to the media and the public, scientists stressed the consequences but also the fact that adaptation is possible, particularly if measures to reduce emissions are taken soon.
"We can take steps to reduce greenhouse emissions to avert some of these possible outcomes," said Radley Horton, an assessment author and a scientist at Columbia University's Center for Climate Science Research.
Researcher Katharine Hayhoe, a report co-author and climate scientist at Texas Tech University, said the assessment offers people a clear example of the consequences of the choice to burn fossil fuels. Hayhoe likened this to understanding the consequences of eating fast food daily.
"If we didn't know that eating pizzas and hamburgers every day was bad for our health, why wouldn't we eat them?" she said. "If we didn't have these consequences shown to us, why would we change?"
Many researchers also pointed out steps that are being taken at the local and state levels to prepare for climate change, such as installing larger culverts or permeable pavement to deal with floods or putting in green roofs and urban canopy to mitigate the heat island effect. Measures like these are also cataloged in the assessment.
They also, however, stressed that those are not yet enough.
Vicki Arroyo, executive director of the Georgetown Climate Center at Georgetown Law, said she found the assessment very "user friendly," particularly online, and thought it did open up space to talk about action on climate change.
"It's pretty clear it paves a way for a more robust conversation that we really need to have in this country on how are we going to prepare for these massive changes," Arroyo said.