Deadly Hurricane Helene, wildfires in the Amazon, an extreme monsoon downpour in India, a heat wave during the Summer Olympics, and other dangerous and devastating weather events in 2024 were all made more likely and damaging by climate change, scientists have found.
Climate scientists quantified the link by running thousands of simulations in climate models, some that included and some that did not include the effects of human-caused climate pollution in the atmosphere. They also examined past and present weather data to see how the probability of these kinds of events has changed in a hotter world.
This approach, known as attribution science, is a relatively new branch of climate science. It has enabled scientists to conclude that human-caused climate change made many recent extreme weather events much more damaging, deadly, and expensive than they would otherwise have been.
Climate change increased Hurricane Helene’s and Milton’s potential destructiveness
Hurricane Milton, which formed in the Gulf of Mexico in early October, offers an example of how climate change amplifies extreme weather. As a result of high water temperatures, the storm rapidly intensified from a tropical storm to reach Category 5 status. The scientists at Climate Central estimated that those unusually warm sea surface temperatures were made up to 400 to 800 times more likely by climate change.
Hurricane Helene made landfall on September 26, 2024, near Perry, Florida, as a Category 4 with 140 miles per hour winds. The storm is being blamed for 247 deaths, with hundreds more still missing, making it the fourth-deadliest U.S. hurricane since at least 1963. And a new study published in Nature found that the death toll associated with hurricanes is dramatically underestimated, perhaps by hundreds of times, due to knock-on effects lasting for over a decade.
Early estimates have placed the economic costs of the storm at up to $47 billion.
On Wednesday, the attribution science group World Weather Attribution released an analysis of how climate change affected Hurricane Helene. Their main findings:
- Hurricanes as intense as Hurricane Helene are today about 2.5 times more likely in the region: They would be expected to occur on average every 130 years in a preindustrial climate but now have a one-in-53 chance in any given year.
- Hurricane Helene’s wind speeds on the coast of Florida were about 13 miles per hour or 11% more intense due to climate change.
- Climate change increased Hurricane Helene’s rainfall by about 10%. This level of rainfall that led to catastrophic flooding in the Appalachians has shifted from a once-in-115-year event to a once-in-70-year event today as a result of climate change.
- The high sea temperatures that fueled Hurricane Helene were made 200 to 500 times more likely by climate change.
“Yet again, our study has shown that hurricanes will keep getting worse if humans keep burning fossil fuels and subsequently warming the planet,” Friederike Otto, lead of World Weather Attribution and senior lecturer in climate science at Imperial College London, said in a news release. “Americans shouldn’t have to fear hurricanes more violent than Helene – we have all the knowledge and technology needed to lower demand and replace oil, gas, and coal with renewable energy.”
A 5% increase in hurricane winds increases a hurricane’s destructive power by about 50% since hurricane damage grows exponentially with intensity. Thus, the 11% increase in Helene’s winds found by the World Weather Attribution group likely made Helene’s winds more than twice as destructive.
And it is hurricane winds that drive storm surge, so although surge was not evaluated directly in the group’s report, it can be inferred that the destructive surge from Helene was made worse by climate change (apart from the separate long-term increase in both surge and everyday water levels caused by warming-induced sea level rise).
A separate rapid analysis by scientists at Lawrence Berkeley National Laboratory estimated that climate change caused over 50% more rainfall during Hurricane Helene in some parts of Georgia and the Carolinas and that global warming made the high amount of rainfall up to 20 times more likely in these areas.
Percentage increase in Hurricane Helene rainfall caused by global warming. (Image credit: Lawrence Berkeley National Laboratory)
Climate change is incredibly costly
The recent studies show that climate-worsened extreme weather events are imposing immense costs to lives, health, and finances across the world.
Home insurance costs have more than doubled in the U.S. over the past two decades, and many insurance companies are exiting states like Florida and California that are especially vulnerable to climate-worsened extreme weather like hurricanes and wildfires. The Federal Emergency Management Agency, or FEMA, is running out of money to fund its efforts to help communities recover from extreme weather disasters.
The faster the world can curb climate-warming pollution and reach net zero emissions, the less damaging future extreme weather events will be. But people will also need to prepare for the types of weather extremes that are most common in their areas, knowing that they will continue to worsen until climate change stops.
Extreme heat ‘virtually impossible’ without global warming
Worsening heat waves are the most direct consequence of pumping climate-warming pollution into the atmosphere. By trapping more heat at Earth’s surface, the pollution increases the average temperatures all around the world and makes extreme heat waves hotter and more frequent. Heat waves are the deadliest type of extreme weather in the United States. And heat-related deaths are often dramatically undercounted because coroners usually attribute deaths to direct causes like heart attacks, and not necessarily the triggering factors like heat stress.
July 22, 2024, was the planet’s hottest day on record. According to an analysis by Climate Central, nearly half of all people on Earth that day experienced dangerous temperatures that were made at least three times more likely by climate change. The organization also estimated that between June and August, more than 2 billion people – or one-quarter of the global population – faced at least 30 days of dangerously hot temperatures, also made at least three times more likely by climate change.
The 2024 Summer Olympics in Paris were also affected by an extreme heat wave throughout the Mediterranean region. The event’s organizers were forced to retrofit the eco-friendly athlete housing with 2,500 air conditioning units. An analysis of the heat wave by World Weather Attribution estimated that this extreme heat would have been virtually impossible without human-caused global warming. But in today’s hotter world, similar extreme heat waves are expected about once per decade in this region.
In the spring and early summer, Mexico and a vast area extending from Israel and Palestine in the west to the Philippines in the east also experienced extreme heat waves. During this period, Mexico reported over 100 heat-related deaths and thousands of cases of heat stroke. In Gaza, extreme heat worsened the living conditions of 1.7 million displaced people.
World Weather Attribution estimated that climate change made the Mexico heat wave about 1.5°C or 2.7°F hotter and 35 to 200 times more likely to occur. In the Philippines, the event would have been impossible without human-caused climate change, the scientists found. Climate change also made the heat in west Asia five times more likely to occur.
A 10- to 30-fold increased likelihood of drought in the Amazon
In dry regions of the planet, global warming can amplify droughts and wildfires because higher temperatures increase evaporation, which dries out soil and vegetation.
These conditions have played out this year in the Amazon rainforest, which a recent study in Nature reported has seen a threefold increase in the number of days per year with hot and dry extreme fire weather conditions. Another study published earlier this year in Nature found that by 2050, these conditions could expose 10% to 47% of the rainforest to sufficient stress to trigger a tipping point and cause a collapse to a degraded forest condition or a grassy savanna with few remaining trees.
This year, wildfires have burned more than 32 million acres in the Brazilian rainforest and Pantanal wetlands to the south, releasing a combined 150 million tons of carbon dioxide. That’s about one-third as large as Brazil’s annual fossil fuel climate pollution. The World Weather Attribution team estimated that climate change has increased the likelihood of droughts in the Amazon by a factor of 10 to 30. What would have been a relatively severe natural drought is an exceptional drought today due to global warming. As a result, the 2024 Amazon wildfires became about 40% more damaging and four to five times more likely to occur.
The two largest Italian islands of Sicily and Sardinia have also suffered from extreme drought conditions since May due to exceptionally low rainfall and high temperatures. The two islands have been rationing water since February, and yet water reservoirs are almost empty. Sicily declared a state of emergency in May.
The World Weather Attribution team concluded that these intense hot and dry conditions would have been almost impossible to occur without human-induced climate change, and similar conditions will become more frequent and intense in a warmer world.
More intense, deadly rainstorms
French military engineer and physicist Nicolas Léonard Sadi Carnot discovered 200 years ago the relationship between temperature and vapor pressure. His discovery was subsequently used to estimate that for every 1°C (1.8°F) of warming, Earth’s atmosphere can hold about 7% more water vapor. As a result, there’s more water available in the air to fall as precipitation during storms and potentially cause flooding. When it rains, it’s more likely to pour.
In September, central Europe saw by far the most intense rainfall recorded in the region, directly affecting nearly 2 million people. The scientists at World Weather Attribution conservatively estimated that this event was twice as likely and 7% more intense due to global warming. And if the world reaches 2°C of global warming, such events are expected to be 5% more intense and 50% more likely to happen than today.
In northern Kerala, India, an extreme monsoon downpour on July 30 triggered massive landslides that killed hundreds of people. It was the region’s third heaviest one-day rainfall event on record. World Weather Attribution estimated that global warming increased the intensity of this event by 10% and that similar events will become another 4% more intense if the world reaches 2°C of global warming.
And in late April and early May, over 16 inches of rain fell in Brazil’s southernmost state of Rio Grande do Sul, leading to more than 90% of the state being affected by flooding. These unprecedented floods displaced 600,000 people, led to over 150,000 being injured and over 169 fatalities. World Weather Attribution estimated that climate change has made this kind of event about twice as likely to happen and 6-9% more intense. If the world reaches 2°C of global warming, this type of extreme flooding will become twice as likely to occur and 4% more intense than today.
Jeff Masters contributed to this article.