Prof. Katharine Hayhoe

Climate Scientist, Truth-Teller, Christ-Follower
Join me on Bluesky @katharinehayhoe.com
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[Prof. Katharine Hayhoe @KHayhoe]

I don't use X very much any more, but I'd love to see you elsewhere!

For the short & up to date content I used to provide here, see Threads & Bluesky.

For longer commentaries, see LinkedIn & my newsletter.

And for the fun stuff, check out IG + Pinterest.

All links below ⬇️

[Prof. Katharine Hayhoe @KHayhoe]

Looking for more from me than tweets? I regularly share unique content on a dozen other online platforms...and you won't see most of it on Twitter. Browse this thread for direct links and dive in!

[Prof. Katharine Hayhoe @KHayhoe]

@ProjectCuria This is a list of my senators below. None of them hold the positions that you describe.

[Prof. Katharine Hayhoe @KHayhoe]

My friend Jim Stump recently spent five days camping above the Arctic Circle with a group of faith leaders in the very place Big Oil keeps trying to drill ... and what's happening there right now is more hopeful than you'd think.

💸 Good news: When 690,000 acres of the Arctic National Wildlife Refuge went up for oil and gas leasing this June, only two bidders showed up; and neither of them were a major oil company.

🧊 Not-so-good news: The same Arctic that sustains polar bears, caribou, and Gwich'in communities just recorded its hottest year since at least 1900, with winter sea ice hitting the lowest level in the 47-year satellite record.

🌿 What you can do: Jim's group was hosted by the Gwich'in people, who have cared for this land for thousands of years. Learn more about their land and their fight with the two-minute film linked here.

Standing with those on the front lines starts with paying attention; and that support grows when we share their story. 💚 https://t.co/b7xtO1MLHH

[Prof. Katharine Hayhoe @KHayhoe]

Week after week, wildfires & extreme heat continue to devastate communities across North America and Europe ... but there's still good news happening, and inspiring climate action too. Read on!

☀️ Good news: The world's first "solar railway" laid 48 panels between active train tracks in Switzerland to generate 16,000 kWh in its first year. The technology is now expanding to other countries!

🔥 Not-so-good news: Wildfires across France and Spain have driven more than 300,000 people from their homes, in a summer so extreme that this part of France has already seen more days above 40°C in 2026 than in the entire 105 years from 1920 through 2025.

🌱 What you can do: Meet the Climate Joy Project in Ashland, Oregon, where everyday people share how they're putting climate solutions to work!

This week, share one thing you learn here. Conversation matters more than you think 💚 https://t.co/LP7YpOTzwt

[Prof. Katharine Hayhoe @KHayhoe]

@JackC56170306 @BrianTu85458331 @DrKutney BLOCK

[Jonathan R. Robinson @JonRobinNZ]

🌍amazing opportunity here for the right person. Lecturer in Theology and Creation Care. 5 year, full time. at Otago Uni in NZ @KHayhoe might know someone?
https://t.co/RTb7dHER5n

[Prof. Katharine Hayhoe @KHayhoe]

What does it look like when athletes personally experience extreme heat and climate change?

This week, Talking Climate is hosted by two people who can answer that question firsthand: retired pro soccer/football player Imani Dorsey Kunzweiler and current pro Jasmyne Spencer (@Jas_it_Up) - both @ecoathletesteam Champions.

⚽ Good news: Athletes everywhere are speaking up on climate and people are listening. Efforts range from integrating sustainability into college sports to climate-proofing community playing fields.

🌡️ Not-so-good news: The heat is already here, from Imani's near-collapse from heat exhaustion after a match to triathlons cancelled, youth tournaments suspended, and pro games played under wildfire smoke this summer alone.

📣 What you can do: You don't have to be an athlete or a climate scientist to make a difference. The most powerful thing any of us can do is use our voice, sharing our own story or backing teams and events going green.

Check out everything Imani and Jasmyne have to say below, and share it with the athlete, coach, or sports fan in your life to start a conversation this week. https://t.co/Yp0WQwoiov

[Prof. Katharine Hayhoe @KHayhoe]

Last week, Toronto had the worst air quality of any major city in the world. I'm writing this week's newsletter under those same smoke-filled skies.

☀️ Good news: Solar is now so affordable in Australia that three states now offer a free window of electricity midday.

🔥 Not-so-good news: Nearly 900 wildfires are burning across Canada and a new study estimates $23 billion per year in health impacts ... yet the government just approved a new pipeline to carry a million barrels of oil a day for decades to come.

🌬️ What you can do: If the smoke has reached you, stay inside, seal your windows, make or buy a HEPA air purifier, wear an N95 if you have to go out - and let your elected officials know why this is happening and what they can do about it!

See the full newsletter for much more info, including where to check the air quality near you, and share it with someone else who needs to know this week.

https://t.co/PzKLZwHosS

[Prof. Katharine Hayhoe @KHayhoe]

How much is Canada responsible for the wildfire smoke reaching the U.S.?

Right now, nearly 900 wildfires are burning across Canada. Last week, Toronto's air quality was the worst of any major city in the world. But as the smoke spread south to the U.S., many politicians began blaming Canada for poor forest management.

It's true that local and regional forestry practices matter. Leafy deciduous trees hold moisture and can act as natural fire breaks; so clearing them for conifer monocultures can leave forests at higher risk to burn. But fire suppression, a big issue in the dry forests of the western U.S. where putting out frequent fires let fuel pile up, isn't a major factor here. Canada's remote boreal forests already burn naturally, in less frequent but higher-intensity fires.

The single biggest reason for the record-breaking *increases* in the area burned by wildfires that are causing all this smoke isn't land management. It's human-caused climate change.

As the world warms, winters are no longer cold enough to kill off tree-eating beetles. Their populations explode, leaving millions of acres of dead trees ready to burn. Warmer winters also mean less snowpack, so soil dries out earlier and the fire season runs longer. And climate change has more than doubled the frequency of hotter, drier fire weather across Canada and increased the frequency of the lightning strikes that spark most fires in northern Alberta and BC.

Every one of those four dials is being turned in the same direction by the same thing: the heat-trapping gas emissions from burning fossil fuels. And that's where the numbers start to tell a different picture.

The United States has emitted more carbon than any country in history: around 435 billion tonnes since the 1800s. That's close to a quarter of all the carbon humans have ever put into the air, 12 times Canada's total and still 50% more than China's 285 billion tonnes.

Look at it by company instead of by country, and 88 of the world's largest fossil fuel producers are responsible for the emissions that led to more than a third of the forest area burned across western North America since 1986. At the top of that list is Saudi Aramco, followed by US companies Chevron and ExxonMobil. The first Canadian company, Suncor, doesn't appear until number 76 ... but that could change, as Canada is building more pipelines!

Bottom line? If politicians want to clear the smoke from our skies, tell them the most effective place to start is by cutting the emissions that are driving these fires - no matter which side of the border we're on.

Sources, I'm a scientist so you know I have them: Doubled fire weather risk (World Weather Attribution, 2023). Fire suppression near communities (Parisien et al. 2020, Nature Communications). Climate-beetle-fire connections (e.g. Woo et al. 2024, Ecosphere). Climate-driven lightning increases in northwestern Canada (Burrows et al. 2024, Atmosphere-Ocean). Cumulative CO₂ by country (Our World in Data). 88 producers behind 1/3+ of western N. American area burned (Dahl et al. 2023, Environmental Research Letters). Company ranking (Carbon Majors). And for an exhaustive review of how we know human emissions are driving climate change, see the next post in this thread.

https://t.co/Spedt9SMaI

[Prof. Katharine Hayhoe @KHayhoe]

I am the author of a study that looked at how climate change would impact wildfire around the world, 20 years ago.

Our results clearly showed that some places would increase while others would decrease – which is not a good thing for fire adapted ecosystems either.

Western North America was one of the strongest increase signals, and that’s exactly what’s happening.

Please update your understanding here before commenting on this topic again. It is all our responsibilities to refrain from spreading misinformation, even if inadvertently. https://t.co/9F2lv2aC49

[Prof. Katharine Hayhoe @KHayhoe]

@Pcrawjr Snow trends are happening over Climate time scales.

If you’d like to learn the difference between Weather and Climate, I have a handy video.

https://t.co/4iCYNylOL3

[Prof. Katharine Hayhoe @KHayhoe]

Frustrated that you can't reply to this post? This is why.

Follow me on Bluesky or LinkedIn if you want to engage.

[Prof. Katharine Hayhoe @KHayhoe]

How much is Canada responsible for the wildfire smoke reaching the U.S.?

Right now, nearly 900 wildfires are burning across Canada. Last week, Toronto's air quality was the worst of any major city in the world. But as the smoke spread south to the U.S., many politicians began blaming Canada for poor forest management.

It's true that local and regional forestry practices matter. Leafy deciduous trees hold moisture and can act as natural fire breaks; so clearing them for conifer monocultures can leave forests at higher risk to burn. But fire suppression, a big issue in the dry forests of the western U.S. where putting out frequent fires let fuel pile up, isn't a major factor here. Canada's remote boreal forests already burn naturally, in less frequent but higher-intensity fires.

The single biggest reason for the record-breaking *increases* in the area burned by wildfires that are causing all this smoke isn't land management. It's human-caused climate change.

As the world warms, winters are no longer cold enough to kill off tree-eating beetles. Their populations explode, leaving millions of acres of dead trees ready to burn. Warmer winters also mean less snowpack, so soil dries out earlier and the fire season runs longer. And climate change has more than doubled the frequency of hotter, drier fire weather across Canada and increased the frequency of the lightning strikes that spark most fires in northern Alberta and BC.

Every one of those four dials is being turned in the same direction by the same thing: the heat-trapping gas emissions from burning fossil fuels. And that's where the numbers start to tell a different picture.

The United States has emitted more carbon than any country in history: around 435 billion tonnes since the 1800s. That's close to a quarter of all the carbon humans have ever put into the air, 12 times Canada's total and still 50% more than China's 285 billion tonnes.

Look at it by company instead of by country, and 88 of the world's largest fossil fuel producers are responsible for the emissions that led to more than a third of the forest area burned across western North America since 1986. At the top of that list is Saudi Aramco, followed by US companies Chevron and ExxonMobil. The first Canadian company, Suncor, doesn't appear until number 76 ... but that could change, as Canada is building more pipelines!

Bottom line? If politicians want to clear the smoke from our skies, tell them the most effective place to start is by cutting the emissions that are driving these fires - no matter which side of the border we're on.

Sources, I'm a scientist so you know I have them: Doubled fire weather risk (World Weather Attribution, 2023). Fire suppression near communities (Parisien et al. 2020, Nature Communications). Climate-beetle-fire connections (e.g. Woo et al. 2024, Ecosphere). Climate-driven lightning increases in northwestern Canada (Burrows et al. 2024, Atmosphere-Ocean). Cumulative CO₂ by country (Our World in Data). 88 producers behind 1/3+ of western N. American area burned (Dahl et al. 2023, Environmental Research Letters). Company ranking (Carbon Majors). And for an exhaustive review of how we know human emissions are driving climate change, see the next post in this thread.

https://t.co/Spedt9SMaI

[Prof. Katharine Hayhoe @KHayhoe]

https://t.co/ovSpzr8T22

[Prof. Katharine Hayhoe @KHayhoe]

When we see climate changing, we don't automatically jump on the human bandwagon, case closed. No, we rigorously examine and test all other reasons why climate could be changing: the sun, volcanoes, natural cycles, even something we don't know yet: could they be responsible? ..

[Prof. Katharine Hayhoe @KHayhoe]

@libs_hatefacts I have a PhD in Science. I guess you’re a lib who hates facts?

[Prof. Katharine Hayhoe @KHayhoe]

Bluesky is the new science Twitter: new study concludes

For the past decade, Twitter has been a primary home of scientists on social media. In recent years, new leadership at Twitter has made substantive changes that have resulted in increases in the prevalence of pseudoscience, conspiracy theory, and harassment on the platform, causing many scientists to seek alternatives. [including me]

Survey results overwhelmingly confirm that changes to Twitter have made the social media platform no longer professionally useful or pleasant, and that many scientists have abandoned it in favor of Bluesky.

Results show that for every reported professional benefit that scientists once gained from Twitter, scientists can now gain that benefit more effectively on Bluesky than on Twitter.

https://t.co/u9Hm6EzMXm

[Prof. Katharine Hayhoe @KHayhoe]

Climate denial may sound different in Spanish, Italian, or German—but the arguments are remarkably similar.

In this episode of Cold Facts, Hot Takes, I’m responding to comments on my recent conversation with Dr. Andrea Hinwood, Chief Scientist for the @UNEP . The replies range from familiar claims that climate change is a hoax or a natural cycle to accusations of corruption, conspiracy, and even threats against me and my family.

Behind many of these comments is something deeper than disagreement over scientific evidence.
Researchers call this “solution aversion”: rejecting the problem because the solutions feel threatening. But climate change is a far greater threat to our freedom, finances, and way of life than the solutions they fear.

Watch now: https://t.co/kBHBluM9UH

If you like what you see and want more, support my work on Substack or Patreon to see the more... personal attacks 😳

Substack: https://t.co/syAbRyDwoG
Patreon: https://t.co/aGZVSeok7n

[Prof. Katharine Hayhoe @KHayhoe]

Most people assume caring about climate change makes them the odd one out. But that isn't true! And by keeping silent, we perpetuate that myth.

☀️ Good news: Inspired by the 89 Percent Project, 136 Japanese news outlets are teaming up to show people that the vast majority of the country wants stronger climate action.

🌡️ Not-so-good news: Recent heatwaves have buckled US highways, burst the concrete on part of Germany's Autobahn, and melted the asphalt around Leipzig's tram tracks - real life examples of how our infrastructure was built for yesterday's climate, not today's.

🏠 What you can do: As temperatures soar and wildfire smoke chokes the air, consider climate-proofing your home for a warming world.

Read more below - and share what you learn with someone else this week!

https://t.co/ML9NBQpT8F

[Prof. Katharine Hayhoe @KHayhoe]

@ChrisGloninger He’s not a climate scientist.

[Prof. Katharine Hayhoe @KHayhoe]

For decades, coastal mangrove forests have been decimated by development. But just this past week, forty years of satellite data confirmed something remarkable ...

🌿 Good news: Mangrove forests worldwide are now growing back faster than they're disappearing, with forty years of NASA satellite data showing the decline has reversed thanks to conservation, restoration, and regrowth.

💰 Not-so-good news: A new study finds biodiversity loss carries a steep price tag that financial markets haven't priced in, with $83 trillion in assets potentially mis-priced and some countries facing GDP losses over 15% by 2030.

🌡️ What you can do: Reuters just launched an interactive tool showing how much hotter today is than normal wherever you live. Look up your city and use what you find to start a conversation today!
https://t.co/G4UdlWd9kK

[Prof. Katharine Hayhoe @KHayhoe]

@NoSunscreenGirl If you were real, you could read the thread and learn why your claim was wrong.

Can you do it? I bet not.