Communities across the globe got a sobering snapshot this week of what the future is likely to hold more of: extreme weather getting even more extreme thanks to climate change.
Historic rainfall and flooding in Texas and Oklahoma left thousands homeless and dozens of people dead. India is in the midst of a prolonged heat wave that has already claimed more than 1,800 lives. Wildfires in Alberta consumed hundreds of square miles of forest while creeping closer to Canada's tar sands, shutting down production of the carbon-intense fossil fuel.
More natural disasters may be on the way. Firefighters across the American West are bracing for a record-breaking wildfire season due to sustained drought. Federal scientists predicted Wednesday that once the U.S. hurricane season begins June 1, the East Coast could see as many as 11 named storms out of the Atlantic Ocean, including two hurricanes rated in the major categories, 3-5. Sea levels, rising as the globe warms, could increase the amount of damage from even smaller storms.
Scientists have long balked at attributing natural disasters directly to climate change. They often conclude that global warming has made an extreme event more likely, and exacerbated the conditions that make them more damaging. Warmer ocean waters and air, for example, fuel stronger tropical storms. Heat waves or soil dried by drought—which makes it harder for water to be absorbed when it does finally arrive—increase the chance of devastating flooding. They also say the events are examples of what's to come. Researchers are confident climate change will cause more extremes—more droughts, wildfires, heat waves, flooding and coastal storms, among other disasters—over the next century.
Climate change "affects all weather and storms," said Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research in Boulder, Colo. "They cannot not be affected. The risk of drought and flood is greater, and so are heat waves and wildfires. There is excellent evidence for all of these things happening."
Here is a roundup of what the latest science says about climate change and extreme weather:
India is typically hot in May as warm, dry winds from the west are prelude to monsoon season. But this heat wave, with temperatures reaching 116.6 degrees F, is shattering records, melting roads and exhausting an already unreliable electrical grid. The Indian government has warned people to stay inside for the hottest midday temperatures, but for some, skipping work isn't an option. More than 1,800 deaths have been attributed to the heat and hospitals are struggling to care for the sick.
Scientists estimate that approximately 75 percent of the world's hottest days are the result of climate change, according to an April study in the peer-reviewed journal Nature Climate Change. A 2013 analysis of extreme weather events on four continents found that climate change significantly increased the severity and likelihood of the five major heat waves that occurred that year.
And as heat waves increase in severity and length, and populations increase in the hottest regions, the number of Americans exposed to extreme heat could quadruple by 2070, according another Nature Climate Change study published earlier this month. The hot temperatures have significant health implications, such as worsening asthma, causing heatstroke and even death.
Heavy rain can seem like a godsend to the wide swath of the American West suffering from a multiyear drought, but there can be too much of a good thing.
After five years of drought, Texas got nearly a week of rain leading up to Memorial Day, soaking the state's parched soil. So when 11 inches of rain fell in Houston Monday night, the land couldn't absorb any more water. The resulting flood submerged entire neighborhoods and swept away cars and houses. Officials reported 21 dead and many more remain missing. To make matters worse, more rain is on the way this weekend. This flooding, which has also plagued Oklahoma, comes two years after floods devastated Colorado. The United Kingdom, Eastern Europe, India, Pakistan and Bangladesh have also experienced record-breaking floods in recent years.
Warm air can hold more moisture than cool air, so it makes sense that as global temperatures rise, rain events drop more precipitation. Forty of the lower 48 states have seen an increase in heavy downpours since 1950, according to an analysis of 65 years of rainfall data by Climate Central, a nonprofit climate news and research organization. Heavy downpours increased 31 percent in the Northeast from the 1950s, and 16 percent in the Midwest.
In drought-stricken regions, where the land is parched and hardened, sudden downpours can be dangerous. If a storm dumps too much precipitation too fast after a dry spell, the rain won't absorb into the soil. Instead it runs quickly off, creating flash floods.
In coastal communities, flooding has become commonplace as sea levels rise. Neighborhoods flood with high tides or small rain events.
California and much of the American West has been embroiled in a multiyear drought that's endangered the nation's agricultural sector and threatened the drinking water supply for millions. Mountain snowpacks that typically supply water throughout the spring, summer and fall are at historic lows, as are dozens of reservoirs. California Governor Jerry Brown ordered a 25 percent cut in water usage statewide, and some farmers agreed to ration their water use by 25 percent as well.
Scientists have disagreed whether this drought is the result of climate change, but they do agree that warming global temperatures have increased the severity and length of the disaster. The entire region is experiencing far below average rainfall. Hotter temperatures mean that most precipitation that does fall in the mountains, does so as rain, not snow, which causes smaller snowpacks that act as critical water reserves. Higher temperatures also dry out the soil and plants.
Parts of Africa have also increasingly experienced severe periods of drought in the last decade, causing widespread humanitarian crises and violent conflicts over water and food.
Later this century, the American Southwest and Central Plains will likely experience catastrophic "megadroughts" worse than any in the last millennium, according to a study published in the peer-reviewed journal Science Advances. The droughts could be as severe as the Dust Bowl of the 1930s, but lasting 35 years instead of just a few, said the study.
As the U.S. braces itself for the start of another hurricane season, scientists and community leaders are struggling to figure out how climate change might be changing the storms' intensity, frequency, and movements.
The link between the two is still not entirely clear. Increases in the number of the most intense hurricanes and cyclones in recent decades correlate with warmer ocean waters and air, indicating global warming may be fueling stronger storm systems. Superstorm Sandy in 2012 caused an estimated $68 billion in damages and killed 285 people on the East Coast. Typhoon Haiyan swept across the Philippines in November 2013 with 194 mile per hour winds, flattening towns and killing more than 6,300 people. Scientists are also examining whether warmer temperatures could be extending the length of hurricane season across the globe. Tropical Storm Ana made landfall May 10, three weeks before the official start of the season.
Rising sea levels also mean that less powerful cyclones with smaller storm surges can cause just as much damage as large-scale storms did just a few decades ago.
"The best climate scientists in the world are telling us that extreme weather events like hurricanes are likely to become more powerful," President Obama said during a visit to the National Hurricane Center on Thursday. "When you combine stronger storms with rising seas, that's a recipe for more devastating floods."
Sixty-three wildfires raged in Alberta, Canada this week, one of which alone scorched 67 square miles of forest. Fossil fuel producers working in Alberta's oil sands shut down 10 percent of their production and evacuated thousands of workers as the fire crept closer to their operations.
The U.S. wildfire season is now two months longer than it was in the early 1970s. Wildfires occur nearly four times as often, burn six and a half times the land, and last five times as long as they did in the 1980s, according to a study in the journal Science. The average number of wildfires per year scorching more than 1,000 acres of land jumped from 180 in the 1980s to 250 in the 2000s, according to Climate Central.
Increasing global temperatures suck more moisture from the ground and vegetation and diminish mountain snowpacks, leaving forests ripe for fire risk—a situation that seems certain to get worse the longer policymakers delay taking action on climate change.
The warmer temperatures have also caused pine beetles, an insect that eats wood, to expand their range and reproduce twice a year instead of once. As the population moves from one forest to the next, it leaves behind dead trees to act as kindling when a forest fire starts.
The increased wildfires can also cause flash flooding and mudslides when rain finally comes. This is because there is no vegetation on the ground to slow down the water as it rushes downhill.
Texas and Oklahoma didn't experience only flooding this week, but several tornadoes as well, adding to the region's devastation. While the link between climate change and flooding is well understood, the science is unclear when it comes to twisters. Part of the problem is that historical tornado data isn't reliable, making it difficult to compare current trends with past decades to see whether the storms have increased in severity or frequency.
However, one study published in the peer-reviewed journal Climate Dynamics last year found that the number of days each year with large outbreaks of tornadoes seem to be increasing as the atmosphere warms from human activity. The chance of having a day with 32 tornadoes or more has doubled since 1980, though such days are still rare, the study found.
InsideClimate News reporter David Hasemyer contributed to this report.