The year 2023 was marked by extraordinary heat, forest fires and weather disasters.
In the US, an unprecedented heat wave gripped much of Texas and the Southwest, with highs well above 37.8 degrees Celsius throughout July.
Historic rains in April flooded Fort Lauderdale, Florida, with 2 feet of rain in 24 hours. A wave of severe storms in July sent water flooding into towns in Vermont and New York. Another powerful system inundated the Atlantic coast in December with a hurricane-like storm surge and heavy rainfall. California suffered floods and mudslides from a series of atmospheric rivers early this year, then was hit by a tropical storm in August – an extremely rare event there.
Wildfires devastated Hawaii, Louisiana and several other states. And Canada’s worst fire season on record sent thick smoke across much of North America.
Globally, 2023 was the hottest year on record, and it wreaked havoc around the world. El Niño played a role, but global warming is at the root of the world’s increasing extreme weather.
How exactly is global warming related to fires, storms and other disasters? I am an atmospheric scientist who studies the changing climate. Here’s what you need to know.
Dangerous heat waves and devastating forest fires
When greenhouse gases, such as carbon dioxide from vehicles and power plants, build up in the atmosphere, they act like a thermal blanket that warms the planet.
These gases let in high-energy solar radiation while absorbing the outgoing low-energy radiation in the form of heat from the Earth. The energy imbalance at the Earth’s surface gradually increases the surface temperature of the land and oceans.
The most immediate consequence of this warming is more days of abnormally high temperatures, as many countries saw in 2023.
Extreme heat waves are affecting large parts of North America, Europe and China, breaking many local records for high temperatures. Phoenix went 30 days with daily high temperatures of 110°F (43.3°C) or higher and recorded the highest minimum overnight temperature, with temperatures never dropping below 97°F (36.1°C) on July 19.
Although heat waves result from weather fluctuations, global warming has raised the baseline, making heat waves more frequent, intense, and longer lasting.
That heat also causes forest fires.
The increased evaporation removes more moisture from the soil, causing the soil, grasses and other organic matter to dry out, creating favorable conditions for wildfires. All it takes is a lightning strike or spark from a power line to start a fire.
Canada lost much of its snow cover in early 2023, allowing the ground to dry and major fires to burn throughout the summer. The ground was also extremely dry in Maui in August when the town of Lahaina, Hawaii, caught fire and burned during a storm.
How global warming is causing extreme storms
As more heat is stored as energy in the atmosphere and oceans, not only does the temperature rise, but the amount of water vapor in the atmosphere can also increase.
When that water vapor condenses into liquid and falls as rain, a large amount of energy is released. This is called latent heat and is the main fuel for all storm systems.
When temperatures are higher and the atmosphere contains more moisture, that extra energy can create stronger, longer-lasting storms. This is the main reason for the record-breaking storms in 2023. Nineteen of the 25 weather and climate disasters that caused more than $1 billion in damage each in early December 2023 were major storms, and two more were floods caused by major storms.
Tropical storms are similarly fueled by latent heat from warm ocean water. That is why they only form when the sea surface temperature reaches a critical level of about 27 degrees Celsius.
With 90% of the excess heat from global warming being absorbed by the ocean, global sea surface temperatures have risen significantly, reaching record-breaking levels by 2023.
Higher sea surface temperatures can lead to stronger hurricanes and longer hurricane seasons. They can also lead to faster intensification of hurricanes.
Hurricane Otis, which struck Acapulco, Mexico in October 2023, was a devastating example. The storm exploded in strength and quickly grew from a tropical storm to a destructive Category 5 hurricane in less than 24 hours. With little time to evacuate and buildings not designed to withstand a storm of that strength, more than 50 people died. The hurricane’s intensification was the second-fastest on record, surpassed only by Hurricane Patricia in 2015.
A recent study found that maximum intensification rates of tropical cyclones in the North Atlantic increased by 28.7% between the 1971-1990 average and the 2001-2020 average. The number of storms that grew from a Category 1 storm or weaker to a major hurricane within 36 hours has more than doubled.
The Mediterranean also experienced a rare, tropical-style cyclone in September 2023, providing a warning of the magnitude of future risks – and a reminder that many communities are unprepared. Storm Daniel became one of the deadliest storms of its kind when it hit Libya. The heavy rains overwhelmed two dams, causing them to collapse and killing thousands of people. The heat and increased moisture over the Mediterranean Sea made the storm possible.
Cold spells are also related to global warming
It may seem counterintuitive, but global warming could also be contributing to a cold snap in the US. That’s because it changes the general circulation of the Earth’s atmosphere.
Earth’s atmosphere is constantly moving in large-scale circulation patterns in the form of wind belts near the surface, such as the trade winds, and jet streams at higher levels. These patterns are caused by the temperature difference between the polar regions and the equatorial regions.
As the Earth warms, the polar regions are warming more than twice as fast as the equator. This can change weather patterns, leading to extreme events in unexpected places. Anyone who has ever experienced a “polar vortex event” knows what it feels like when the jet stream drops south, bringing with it cold Arctic air and winter storms, despite generally warmer winters.
In short, a warmer world is a more violent world, with the extra heat causing increasingly extreme weather conditions.
This article is republished from The Conversation, an independent nonprofit organization providing facts and analysis to help you understand our complex world.
It was written by: Shuang-Ye Wu, University of Dayton.
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Shuang-Ye Wu does not work for, consult with, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.