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.”
Comments
"Like with hurricanes, wind shear is an essential ingredient in the storms"
Wind shear boosts tornadoes, but neutralizes hurricanes. Two different animals.
The science does not claim that climate change causes more hurricanes, though warmer seas and blocking patterns may magnify their severity and impacts. Scientists are projecting fewer but more intense hurricanes, and more large precipitation events.
Global warming may in fact reduce the number of tropical cyclones overall, while increasing the number of very intense storms in some basins. While warmer sea surface temperatures favor development and intensification, increased warming of the upper troposphere relative to the surface and increased vertical wind shear are negative factors for hurricane development and intensification. (NOAA)
"Global Warming and Hurricanes" (NOAA 2023):
"Tropical cyclone rainfall rates are projected to increase in the future (medium to high confidence) due to anthropogenic warming and accompanying increase in atmospheric moisture content. Modeling studies on average project an increase on the order of 10-15% for rainfall rates averaged within about 100 km of the storm for a 2 degree Celsius global warming scenario.
"Tropical cyclone intensities globally are projected to increase (medium to high confidence) on average (by 1 to 10% according to model projections for a 2 degree Celsius global warming). This change would imply an even larger percentage increase in the destructive potential per storm, assuming no reduction in storm size. Storm size responses to anthropogenic warming are uncertain.
"The global proportion of tropical cyclones that reach very intense (Category 4 and 5) levels is projected to increase (medium to high confidence) due to anthropogenic warming over the 21st century. There is less confidence in future projections of the global number of Category 4 and 5 storms, since most modeling studies project a decrease (or little change) in the global frequency of all tropical cyclones combined."
"...On a global scale, the frequency of storms hasn't increased. However, cyclones are now more common in the central Pacific and North Atlantic, and less so in the Bay of Bengal, western North Pacific and southern Indian Ocean, the study said.
There is also evidence that tropical storms are becoming more intense and even stalling overland…"
"Analysis reveals how climate change is influencing extreme weather" (Thomson Reuters: Jun 28, 2022)
The IPCC projects that "average peak TC wind speeds and the proportion of Category 4–5 TCs will very likely increase globally with warming. It is likely that the frequency of Category 4–5 TCs will increase in limited regions over the western North Pacific. It is very likely that average TC rain rates will increase with warming, and likely that the peak rain rates will increase at rate greater than the Clausius– Clapeyron scaling rate of 7% per 1°C of warming in some regions due to increased low-level moisture convergence caused by regional increases in TC wind intensity. It is likely that ... the global frequency of TCs over all categories will decrease or remain unchanged." (AR6 11.7.1.5)
Interesting stuff. This dovetails with James Hansen's 'Storms of my Grandchildren' years back and his more recent research on severe storms.
Though ocean tropical cyclones may be getting stronger but less numerous, the evidence to date pegs land-based storms becoming more frequent and intense overall. This correlates with distorted and slowing jet stream patterns / waves which are in turn correlated with a warming Arctic Ocean with longer ice-free summers.
All of this is amplified by the El Nino cycle.
It is painfully clear today that society must plan for adaptation on top of reducing emissions.
This would entail beefing up building codes for energy conservation, providing more generous grants for the resulting necessary improvements to buildings and for outfitting them with heat pumps, superior interior air filtration, district heating systems, and so forth.
Striking up a detailed climate policy framework for cities could be one of the most effective methods to affect change. All of the above grants and code changes should be included in the framework under federal funding agreements with cities, which could be expanded to direct funding for transit and grants for EVs and charging networks in exchange for key changes to zoning bylaws that help urbanize the suburbs.
The preservation of food producing farmland in the surrounding greenbelt would also be key to lowering emissions and enhancing food security, and the feds could offer powerful incentives in that regard. I would go as far to suggest the feds should strike a long term program to incrementally buy up farmland around the major cities then lease back plots to farmers at very reasonable rates who would participate in establishing an extensive array of market gardens within 50 km of our cities.