Rising sea levels, the mass extinction of species and the spread of diseases beyond their current range are just some of the potential consequences of global warming. But perhaps one of the most concerning aspects of climate change is that, in general, it is expected to make extreme weather more frequent and intense.
To find out how climate change will affect different types of extreme weather, Newsweek spoke to environmental scientists, who explained the impacts on phenomena such as drought and extreme precipitation; extreme heat, wildfires, hurricanes and tropical cyclones; and tornadoes.
Drought and Extreme Precipitation
The burning of fossil fuels, such as goal and gas, releases carbon dioxide (CO2) into the atmosphere—a greenhouse gas, which traps heat and causes the planet's temperature to rise. This can disrupt the environmental systems which are responsible for precipitation.
For example, warmer temperatures can lead to more water evaporation into the air—and higher retention of that water once there—thus increasing the risk of heavy rainfall. Meanwhile, warmer temperatures can also exacerbate the impacts of drought, according to the Center for Climate and Energy Solutions (CCES.) This is because they lead to an increase in evaporation from soils, drying them out.
Furthermore, droughts are also likely to persist for longer because as soils dry and the number of plants—which release water vapor into the air—is reduced, the feedback effect from this process can lead to further reductions in rainfall, making the situation worse.
Historically, the United States has been vulnerable to drought—think of the infamous Dust Bowl of the 1930s, for example. In more recent times, California experienced one of the worst droughts in its history between 2011 and 2017, which killed more than 100 million trees, according to the U.S. Forest Service.
On the other hand, the 12-month-period ending in April, 2019 was the wettest in U.S. records dating back to 1895, with the contiguous U.S. experiencing an average of 36.2 inches of precipitation, according to data from the NOAA National Centers for Environmental Information.
"What we know is that the so-called hydrological cycle—how water in its various forms moves through the climate system—is amplified under climate change, specifically, warming," Paul Roebber, from the University of Wisconsin at Milwaukee, told Newsweek. "The root cause of this is increased evaporation—drying the land—and the ability of warmer air to contain more water content. This means that both extreme precipitation events and drought are more frequent—and in the latter case, may be more long lasting,"
"The details of how this happens varies widely depending on the type of climate one lives in," he said. "For example, in the upper midwestern U.S., where I am, most of our warm season precipitation is in the form of thunderstorms. With warming, when conditions are right to produce thunderstorms, the amount of available moisture to be 'processed' by these systems is increased, and heavier rainfall events result."
In future, parts of the United States—the northeast, for example—will be receiving more intense and more frequent precipitation than ever before, while others will see an increase in droughts.
"Between 1958 and 2012, the northeast saw more than a 70 percent increase in the amount of rainfall measured during heavy precipitation events, more than in any other region in the United States, while other parts, such as the West Coast, will have more droughts," Maryam Karimi, from the University of Alabama at Birmingham, told Newsweek. "The northeast is vulnerable to climate change and extreme precipitation due to its high density of build environment, population and old infrastructures."
In the American southwest, droughts are very likely to increase, according to Monty Hempel, from the University of Redlands.
"Some droughts, especially in places like California, may be triggered not by overall lack of precipitation but by the fact that less precipitation will fall as snow, leaving less summer run-off from mountains to fill reservoirs," Hempel told Newsweek.
Extreme Heat
Research indicates that climate change will lead to a significant rise in the frequency and severity of extreme heat across the contiguous United States in the coming decades, as the climate warms.
As concentrations of CO2 in the atmosphere rise, the heat-trapping effect of the gas will become more pronounced, leading to hotter hot days, more heatwaves and fewer cold days, on average.
In fact, the Union of Concerned Scientists recently conducted an analysis of current heat trends to make predictions about the future climate for a new study, finding that climate change will lead to a spike in the number of days per year when the heat index—or "feels like" temperature—exceeds 105 degrees Fahrenheit, unless drastic action is taken to curb greenhouse gas emissions.
This means events like the 2018 North American heat wave—which was linked to at least 70 deaths in Quebec, Canada and saw heat advisories issued to more than 60 million people across the continent—will likely occur more often.
"Across the United States we are getting more common and frequent hot days with heat waves that linger around for longer than a week," Karimi said. "Extreme heat is hazardous and results in heat related mortality, morbidity—for example, asthma attacks and cardiovascular diseases—and increased hospital admission."
"Extreme heat also increases the Urban Heat Islands (UHI) effect in the urban environment due to roads, buildings and sidewalks heating up by 40 to 90 degrees Fahrenheit higher than natural surfaces," she said. "Our changing climate has direct impact on heat waves-making them more frequent than ever before. Climate change can worsen extreme heat events by making them last longer with days of extreme heat turning into weeks."
The problem of extreme heat could have significant implications for public health and the productivity of workers in many areas, as well as for important ecosystems.
"It is likely to increase in both frequency and severity to the point that air conditioning for those in poverty becomes a recognized issue of human rights," Hempel said. "Meanwhile, forest die-back and other ecological disruption may prove more devastating as irreversible losses."
Wildfires
Climate change will lead to hotter, drier conditions in many regions, which can increase the risk and severity of wildfires.
There are several factors which can contribute to the risk of wildfires—including soil moisture, temperature, the amount of plant cover, type of plants, and availability of fuel—all of which are influenced by variations in the climate. Where people are choosing to live and how forests have been managed are also important.
Furthermore, warmer and drier conditions, can provide better conditions for fires to spread, making them harder to extinguish.
In the U.S., large wildfires are burning almost double the area that they did in the 1970s, while the average fire season lasts about 78 days longer, according to the CCES. Last year, California experienced the deadliest and most destructive wildfire season in its history, which burned a total of nearly 2 million acres.
"Drought and heat predispose forests and other ecosystems in the already-dry western U.S.—and many other places globally—to wildfires. As we have seen, these events are getting more common, larger and more intense," Wendy McIntyre, from the University of Redlands, told Newsweek.
Hurricanes and Tropical Cyclones
As the world warms, ocean temperatures will also increase—a process which, scientists predict, will lead to an increase in the intensity of hurricanes. The warmer the temperature of the sea surface that a hurricane is moving over, the stronger the storm will become, because heat energy in the water acts almost like a fuel.
Just last month, Hurricane Dorian—which caused catastrophic destruction in the Bahamas—equaled the record for the most powerful Atlantic hurricane ever to make landfall.
Furthermore, global sea level rises—which are being driven by climate change—will mean that coastal storms become more destructive, due to the increased risk of storm surges. The damage that these events cause will only be exacerbated by the fact that climate change is expected to lead to a rise in hurricane rainfall given that warmer air holds more moisture.
While hurricanes are expected to become more intense in future, scientists are still not sure whether climate change will lead to an increase or decrease in their frequency.
"For hurricanes, which derive much of their energy from sea surface temperatures, we expect to see more Category 4 and 5 events, but the overall frequency of all hurricanes is less clear, and may actually decline in some areas," Hempel said.
Timothy Krantz, from the University of Redlands, noted that the atmosphere and oceanic circulation are both energy-driven systems.
"Add more energy to the system and the circulations pick up more energy, creating higher 'highs' and lower 'lows.' Wind is atmosphere moving between high and low pressure centers, so wind speeds will also be more extreme," Krantz told Newsweek. "The lowest pressures ever recorded in hurricanes have all been in the last several years, with Hurricane Dorian being tied for lowest pressure ever recorded in the North Atlantic."
Tornadoes
Tornadoes are formed—usually in thunderstorms—when warm, moist air, which rises, meets cooler air, creating atmospheric instability. Changes in wind direction and speed—known as wind shear—in combination with this instability creates the distinctive rotating column. Currently, the link between climate change and tornadoes is unclear, due to inconsistent data on the phenomenon.
"There is no consensus on how climate change may affect this," Roebber said. "Based on the previous arguments regarding heat, moisture and drought, there are regions where thunderstorm activity will increase and others where it may decrease. Likewise, these same factors will likely increase the strength of these storms where they do occur, which would increase effects such as damaging winds."
"Tornadoes, however, also require organization by the broader winds—called vertical wind shear—and in many areas, shear will decrease," he said. "However, this is on average and so there may be days where all the ingredients are in place and there is more energy available for these storms, so on those days, conditions would be more severe. Hence, the uncertainty on what will happen."
Can we link single extreme weather events to climate change?
So, if extreme weather is expected to become more common for the most part, are we able to link single events to climate change?
"You can never say that 'this event happened because of climate change,'" Roebber said. "What you can say, and we already have been able to say for some events, is that 'the chances of an event like the one that just occurred having happened has increased because of climate change.' It is really about the changing risk. Traffic accidents happen whether or not there are a lot of cars on the road, but certainly increases in traffic density increase the likelihood of an accident."
"As an example, some studies have been done regarding the flooding from Hurricane Harvey. We know that the probability of that amount of rainfall in that part of the U.S. has increased dramatically from historical norms," he said. "We cannot say that Harvey was, itself, the result of climate change. From a social policy point of view, this distinction is irrelevant, what matters is the increased risk."
However, just because it is difficult to directly link climate change to single extreme weather events does not mean that these cause and effect relationships do not exist, according to McIntyre. "Nor should we rest easy because it is not easy to explain," she said.
