Scientists define “climate” as the distribution of possible weather events observed over a length of time, such as the range of temperatures, rainfall totals or hours of sunshine. From this they construct statistical measures, such as the average (or normal) temperature. Weather varies on several timescales – from seconds to decades – so the longer the period over which the climate is analysed, the more accurately these analyses capture the infinite range of possible configurations of the atmosphere.

Typically, meteorologists and climate scientists use a 30-year period to represent the climate, which is updated every ten years. The most recent climate period is 1991-2020. The difference between each successive 30-year climate period serves as a very literal record of climate change.

This way of thinking about the climate falls short when the climate itself is rapidly changing. Global average temperatures have increased at around 0.2°C per decade over the past 30 years, meaning that the global climate of 1991 was around 0.6°C cooler than that in 2020 (when accounting for other year-to-year fluctuations), and even more so than the present day.

A moving target for climate modellers

If the climate is a range of possible weather events, then this rapid change has two implications. First, it means that part of the distribution of weather events comprising a 30-year climate period occurred in a very different background global climate: for example, northerly winds in the 1990s were much colder than those in the 2020s in north-west Europe, thanks to the Arctic warming nearly four times faster than the global average. Statistics from three decades ago no longer represent what is possible in the present day.

Second, the rapidly changing climate means we have not necessarily experienced the extremes that modern-day atmospheric and oceanic warmth can produce. In a stable climate, scientists would have multiple decades for the atmosphere to get into its various configurations and drive extreme events, such as heatwaves, floods or droughts. We could then use these observations to build up an understanding of what the climate is capable of. But in our rapidly changing climate, we effectively have only a few years – not enough to experience everything the climate has to offer.

Extreme weather events require what meteorologists might call a “perfect storm”. For example, extreme heat in the UK typically requires the northward movement of an air mass from Africa combined with clear skies, dry soils and a stable atmosphere to prevent thunderstorms forming which tend to dissipate heat.

Such “perfect” conditions are intrinsically unlikely, and many years can pass without them occurring – all while the climate continues to change in the background. Based on an understanding of observations alone, this can leave us woefully underprepared for what the climate can now do, should the right weather conditions all come together at once.

Startling recent examples include the extreme heatwave in the Pacific north-west of North America in 2021, in which temperatures exceeded the previous Canadian record maximum by 4.6°C. Another is the occurrence of 40°C in the UK in summer 2022, which exceeded the previous UK record maximum set only three years earlier by 1.6°C. This is part of the reason why the true impact of a fixed amount of global warming is only evident after several decades, but of course – since the climate is changing rapidly – we cannot use this method anymore.

Playing with fire

To better understand these extremes, scientists can use ensembles: many runs of the same weather or climate model that each slightly differ to show a range of plausible outcomes. Ensembles are routinely used in weather prediction, but can also be used to assess extreme events which could happen even if they do not actually happen at the time.

When 40°C first appeared in ensemble forecasts for the UK before the July 2022 heatwave, it revealed the kind of extreme weather that is possible in the current climate. Even if it had not come to fruition, its mere appearance in the models showed that the previously unthinkable was now possible. In the event, several naturally occurring atmospheric factors combined with background climate warming to generate the record-shattering heat on July 19 that year.

The highest observed temperature each year in the UK, from 1900 to 2023

Later in summer 2022, after the first occurrence of 40°C, some ensemble weather forecasts for the UK showed a situation in which 40°C could be reached on multiple consecutive days. This would have posed an unprecedented threat to public health and infrastructure in the UK. Unlike the previous month, this event did not come to pass, and was quickly forgotten – but it shouldn’t have been.

It is not certain whether these model simulations correctly represent the processes involved in producing extreme heat. Even so, we must heed the warning signs.

Despite a record-warm planet, summer 2024 in the UK has been relatively cool so far. The past two years have seen global temperatures far above anything previously observed, and so potential extremes have probably shifted even further from what we have so far experienced.

Just as was the case in August 2022, we’ve got away with it for now – but we might not be so lucky next time.

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Simon H. Lee, Lecturer in Atmospheric Science, University of St Andrews; Hayley J. Fowler, Professor of Climate Change Impacts, Newcastle University, and Paul Davies, Chief Meteorologist, Met Office and Visiting Professor, Newcastle University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Wildfire blowups, fire whirls, towering thunderstorms: When fires get large and hot enough, they can actually create their own weather.

In these extreme fire situations, firefighters’ ordinary methods to directly control the fire don’t work, and wildfires burn out of control. Firefighters have seen many of these risks in the enormous Park Fire burning near Chico, California, and other wildfires in summer 2024.

But how can a fire create weather?

I’m an atmospheric scientist who uses data collected by satellites in weather prediction models to better anticipate extreme fire weather phenomena. Satellite data shows fire-produced thunderstorms are much more common than anyone realized just a few years ago. Here’s what’s happening.

The wildfire and weather connections

Imagine a wildland landscape with dry grasses, brush and trees. A spark lands, perhaps from lightning or a tree branch hitting a power line. If the weather is hot, dry and windy, that spark could quickly ignite a wildfire.

When vegetation burns, large amounts of heat are released. This heats the air near the ground, and that air rises like a hot air balloon because hot air is less dense than cool air. Cooler air then rushes in to fill the void left by rising air.

This is how wildfires create their own wind patterns.

What happens next depends on the stability of the atmosphere. If the temperature cools rapidly with elevation above the ground, then the rising air will always be warmer than its surroundings and it will keep rising. If it rises high enough, the moisture will condense, forming a cloud known as a pyrocumulus or flammagenitus.

If the air keeps rising, at some point the condensed moisture will freeze.

Once a cloud has both liquid and frozen water particles, collisions among these particles can lead to electrical charge separation. If the charge buildup is large enough, an electrical discharge – better known as lightning – will occur to neutralize the charges.

Whether a fire-induced cloud will become a thunderstorm depends on three key ingredients: a source of lift, instability and moisture.

Dry lightning

Wildfire environments typically have limited moisture. When conditions in the lower atmosphere are dry, this can lead to what’s known as dry lightning.

No one living in a wildfire-prone environment wants to see dry lightning. It occurs when a thunderstorm produces lightning, but the precipitation evaporates before reaching the ground. That means there is no rain to help put out any lightning-sparked fires.

Fire whirls

As air rises in the atmosphere, it may encounter different wind speeds and directions, a condition known as wind shear. This can cause the air to spin. The rising air can tilt the spin to vertical, resembling a tornado.

These fire whirls can have powerful winds that can spread flaming ash, sparking new areas of fire. They usually are not true tornadoes, however, because they aren’t associated with rotating thunderstorms.

Decaying storms

Eventually, the thunderstorm triggered by the wildfire will begin to die, and what went up will come back down. The downdraft from the decaying thunderstorm can produce erratic winds on the ground, further spreading the fire in directions that can be hard to predict.

When fires create their own weather, their behavior can become more unpredictable and erratic, which only amplifies their threat to residents and firefighters battling the blaze. Anticipating changes to fire behavior is important to everyone’s safety.

Satellites show fire-created weather isn’t so rare

Meteorologists recognized the ability of fires to create thunderstorms in the late 1990s. But it wasn’t until the launch of the GOES-R Series satellites in 2017 that scientists had the high-resolution images necessary to see that fire-induced weather is actually commonplace.

Today, these satellites can alert firefighters to a new blaze even before phone calls to 911. That’s important, because there is an increasing trend in the number, size and frequency of wildfires across the United States.

Climate change and rising fire risks

Heat waves and drought risk have been increasing in North America, with rising global temperatures more frequently leaving dry landscapes and forests primed to burn. And climate model experiments indicate that human-caused climate change will continue to raise that risk.

As more people move into fire-risk areas in this warming climate, the risk of fires starting is also rising. With fires come cascading hazards that persist long after the fire is out, such as burn-scarred landscapes that are much more susceptible to landslides and debris flows that can affect water quality and ecosystems.

Communities can reduce their vulnerability to fire damage by building defensible spaces and firebreaks and making homes and property less vulnerable. Firefighters can also reduce the surrounding fuel loads with prescribed fire.

It’s important to remember that fire is a natural part of the Earth system. As fire scientist Stephen J. Pyne writes, we as humans will have to reorient our relationship with fire so we can learn to live with fire.

Kyle Hilburn, Research Scientist in Atmospheric Science, Colorado State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.