How a hotter planet revs up our weather

We know climate change is making extreme weather events like wildfires and hurricanes more severe, but what may be less obvious is how changes in the climate — caused largely by the burning of fossil fuels — connect to weather patterns.

It’s a question Rachel White thinks about often. The atmospheric scientist and assistant professor at the University of British Columbia said making the climate connection between some extreme weather events, like heat waves, is simple, while others like tornadoes are more complex.

“There's some extremes — like heat waves, extreme precipitation and the strength of hurricanes — that are so clearly linked to temperature. It's really clear, and there's very little uncertainty about the impact that climate change, increasing temperatures, is going to have on those extremes,” she explained.

However, there are other weather events that “are affected by temperature, but also affected by other things,” she said.

Canada has seen a slew of weather-related disasters this past year. Nova Scotia was hit by hurricane Fiona last fall — the most costly catastrophe ever recorded in Atlantic Canada. Its largest-ever wildfires tore through the province in May, followed by devastating flash flooding in late July. Most of British Columbia is currently experiencing its highest levels of drought.

Wildfires across the country have forced communities to evacuate, while others deal with poor air quality from the smoke. Meanwhile, a tornado touched down in Ottawa last week less than a month after storms caused structural damage in the area.

Politicians have stressed these events are the result of a warming climate. This past week, B.C.’s Emergency Management and Climate Readiness Minister Bowinn Ma said the province’s fires are the result of climate change. In July, federal Natural Resources Minister Jonathan Wilkinson said climate change was to blame for the “worst wildfire season on record.”

But what does that really mean? Here’s the breakdown on how wildfires, hurricanes, floods, tornadoes and heat waves are caused — or not — by climate change.

Wildfires

The warmer the temperature, the more water is pulled out of the soil, which makes wooded areas more dry. That makes it easier for fires to catch, explained White.

As NASA puts it: “Current climate models indicate that rising temperatures will intensify the Earth's water cycle, increasing evaporation. Increased evaporation will result in more frequent and intense storms, but will also contribute to drying over some land areas.”

However, dry conditions aren’t the only things that cause wildfires. White says wind also plays a big role in spreading wildfires, “and there's just less certainty about exactly how the winds are going to change because of the warming temperatures.”

Along with the impacts of climate change, human interaction contributes to wildfires. While there have always been wildfires, modern logging practices that fracture the landscape with roads and leave large piles of brush are creating conditions that lead to fire spreading.

Hurricanes

Warmer air also pulls more moisture from the ocean, which leads to more moisture in the atmosphere, explained White.

“Sea surface temperatures are warmer. And so what happens with hurricanes is you end up with a lot of convection,” she explained. Convection is when warmer air and water air rise over colder air, fuelling hurricanes with more rain and stronger winds.

“So, when there is a hurricane, it can grow more. But there has always sort of been an uncertainty around general hurricane numbers — will there be more hurricanes? Will there be fewer hurricanes? And the problem is, there are so many pieces that go into what causes a hurricane and helps it grow,” said White.

Like with tornadoes, wind is an important part of the puzzle, she said. While a hurricane needs fuel, it also needs wind to propel it. Climate change means more uncertainty around winds, meaning it's unclear whether more or less hurricanes will develop.

“And so whether there's going to be more of them or fewer of them, it's still kind of quite uncertain,” she said. “But we do have confidence that when there is a hurricane, there's just more energy available for it. So they're more likely to be stronger.”

Floods

Increases in the amount of water in the atmosphere also drive higher flooding, fuelling rains that fall more intensely and for longer. This is compounded by factors like drought or fire, which can harden the soil and make it harder for the environment to absorb the water dumped on it during intense rainfalls. Other factors like logging can also compound this issue.

Tornadoes

While there has been an increase in documented tornadoes in Canada, White said that doesn’t necessarily mean they are increasing in intensity.

Western University’s Northern Tornadoes Project counted 117 tornadoes in 2022, which tied with the previous year for the most documented tornadoes on record. Like with hurricanes, wind shear is an essential ingredient in the storms, and White stresses there is mystery around how it is changing due to a warming climate.

However, “climate change is playing a role,” she said, while also noting that the increase in tornadoes could be due to scientists and storm chasers paying closer attention to the events.

Ultimately, “we don’t really know” how climate change is playing a role in tornadoes, said White, but she said scientists are working hard to understand the connection.

Think of it like a domino effect

At the same time, many of the extreme weather events caused or made worse by climate change can interact with each other and make conditions worse, such as hurricanes creating more ideal conditions for fires to spread.

“Fires in areas where hurricane Fiona downed trees have the potential to move faster and burn more intensely, making them potentially more difficult to contain and control. At this time, needles, twigs, leaves, etc., support fire ignition and spread,” the Nova Scotia Department of Natural Resources and Renewables said in May.

In turn, wildfires can make it harder for the ground to absorb rain, which can lead to more intense flooding. In British Columbia in 2021, wildfires — which damage tree roots needed to stabilize the soil — contributed to landslides, which can dam rivers and make flooding worse.

“There's enough things that we are certain about that, for me, the uncertainty around exactly how much worse climate change will make wildfires and whether it'll affect tornadoes and those pieces, that uncertainty is sort of almost more of a reason to act,” said White.

“There's so many things that we are certain about, and the idea that it could be even worse: that is a reason … that this isn’t a risk worth taking.”