We have to cope. A comprehensive new study finds the best ways to cool down cities with Canadian scientist Scott Krayenhoff. First we explore the dragon: can the world feed itself as we heat up the planet? When crops go bad, society can go off the rails. Long-time expert David Lobell on climate and crop damage. It’s must-listen radio for anyone who eats.
The new paper led by David Lobell says:
“,,, estimates of global calorie supply and demand elasticities indicate that a 5% shock to total calorie supply leads to a 30% increase in prices and a decline in consumer surplus of ~$180 billion “
Listen to or download this Radio Ecoshock show in CD Quality (57 MB) or Lo-Fi (14 MB)
STILL HOT!
Parts of Canada, the UK and the Northeast U.S. go from summer heat to November-like cold overnight. But most of the world is rocking hot!
Texas: summer heat wave in early Spring, like 112 degrees Fahrenheit and 115 in Mexico, that’s 44 to 46 C. It was not much cooler up North. Temperatures hit 100°F in North Dakota and northern Minnesota, with “tropical nights” (defined as above 68 F or 20 C.) Huge wildfires in Minnesota and just across the border…
Canada’s Manitoba has almost twice the number of wildfires compared to average for the last 20 years. Two people died, thousands were ordered to evacuate. A treasured parkland was threatened. Winnipeg was 96.8 in the shade – 36 C in the Middle of May. This is all crazy stuff, but never mind that global warming. We have pipelines to build. It’s jobs and money while the house burns down.
Professor Eliot Jacobson points out
“May 9th, 2025 was the hottest May 9th on record globally, with daily records dating back to 1940. And yes, this means that May 9, 2025 was likely the hottest May 9th in the last 120,000+ years.”
May 10th was the hottest May 10th during all human existence. Just the facts.
Even stranger, the weather could switch from sizzling hot to snow in a couple of days. Is it just me, or is that becoming more common? Scientists noticed, checked it all out, and published the paper “Rapid flips between warm and cold extremes in a warming world”.
They say:
“Of the global areas defined by the Intergovernmental Panel on Climate Change, over 60% have experienced more frequent, intense, and rapid flips since 1961, and this trend will expand to most areas in the future. “
Paul Beckwith has a video out on that.
Did I mention the strange dry spring in the UK – along with the worst UK wildfire season on record, already, by April.
And now we have “thirstwaves” – defined as “Prolonged Periods of Agricultural Exposure to Extreme Atmospheric Evaporative Demand for Water”. They say, quote:
“Not only have thirstwaves increased in severity, but the likelihood of no thirstwaves occurring during the growing season has significantly decreased.”
We all know the rule that a 1 degree C rise in global mean temp means 7% more water vapor in the air. But not really. It means 7% more CAPACITY (or demand) for water in the air. When it’s much less than that, the air sucks water from plants and the soil as it passes over. That is a “thirst-wave”. Atmospheric demand for water makes a guest appearance in our next interview.
FLASHBACK
On May 16, 1972, 53 years ago, great American climate pioneers like Charles Keeling and Wally Broecker met at the “Carbon and the Biosphere” symposium held in New York State. Carbon dioxide in the atmosphere then was about 327 parts per million. Here in 2025, that became 430 ppm, more than a hundred parts per million more carbon dioxide up there in just 50 years. That isn’t safe for anybody.
CAN WE FEED OURSELVES DURING THE CLIMATE SHIFT?
DAVID LOBELL
“Will climate change compromise the ability of humanity to feed itself?”
Will climate change damage key crops like wheat, soybeans or rice? Has it already reduced yields? That is part of the life-work of Dr. David Lobell. David is Professor at Stanford University in the Department of Earth System Science – and Director of the Center on Food Security and the Environment. Lobell received the MacArthur “genius” award and was elected to the National Academy of Sciences.
With co-author Stefania Di Tommaso, Lobell just published a major review of climate impacts on food production. Published April 2025 in PNAS, the title is “A half- century of climate change in major agricultural regions: Trends, impacts, and surprises”. We all eat. We all need to know.
Listen to or download this 25 minute interview with David Lobell in CD Quality or Lo-Fi
For some crops, the authors find “the average season now would have been extremely rare” without warming. Others, like maize, wheat and barley in the European Union “indicate that even the coolest growing season in the present day is warmer than the warmest season that would have occurred 50 y[ears] ago.” And that is already in the past, with worse to come.
THE U.S. “WARMING HOLE”
Then more surprises. Despite dramatic warming for crops in countries, this study finds the United States and Canada are an exception. There is even talk of a U.S. “warming hole”.
I find at least two dangers to Canada and the United States lagging behind other countries when it comes to climate and crops. First, it may further delay climate action in North America, even while others suffer.
Second, do we know if this “warming hole” is temporary, whether it could suddenly catch up to general warming? David Lobell suggests because this pattern is pushed by warming, it is likely to continue during further warming. But we can’t be sure.
The paper says:
“The persistence of the warming hole for multiple decades, the fact that it relates only to daytime but not nighttime temperature, and the fact that it extends from April to October combine to suggest that at least part of the warming hole is a response to greenhouse forcing and thus would continue into the future. “
THIRSTY AIR
Watching repeated triple-digit heat waves, we might think extreme heat is killing crops. But the authors found a more serious threat. It is “vapor pressure deficit”. It often happens during high heat the air can hold much more water than it does. The dry atmosphere tries to suck moisture from plants and the soil. That, rather than heat, might be the true cause of crop damage.
This is from a press release about the paper:
“The analysis showed that 45% of summer cropland and 32% of winter cropland experienced warming that was more than two standard deviations above interannual variability. Water stress measures increased in most temperate areas but not in most tropical areas. Climate change trends have caused global yields of wheat, maize, and barley to be 10%, 4%, and 13% lower, respectively, compared with estimated yields without climate change; the detrimental effects of drying and warming likely outweighed the beneficial effects of increased CO2.
However, benefits of rising CO2 for rice and soybeans likely outweighed climate-related losses, leading to net increases in yield. Climate models that were run on initial conditions from 50 years ago overestimated warming and drying in North America and underestimated water stress increases in most temperate regions. According to the authors, the underestimation of water stress may explain why some crop adaptations, guided by climate models, have not performed as expected.”
COOLING CITIES
SCOTT KRAYENHOFF
We know cities will get even hotter. How can we stay comfortable, without burning more fossil fuels? A team of experts led by Dr. Timothy Jiang of Pacific Northwest National Lab investigated common cooling ideas, from making roads white to living green roofs. What works best in most climates? We get answers – and a new mantra for urban development – with co-author Scott Krayenhoff. Scott is Associate Professor at the University of Guelph School of Environmental Sciences.
Listen to or download this 24 minute interview with Scott Krayenhoff in CD Quality or Lo-Fi
“Prioritizing urban heat adaptation infrastructure based on multiple outcomes: Comfort, health, and energy” was published in PNAS, May 5, 2025.
Let’s start with expectations of extreme heat in three cities, and then go to the best solutions. The classic case is Phoenix in the desert heat of Arizona. From this paper, in the scenario of 4.5 degrees C of global mean temperature rise, the hottest week of the year in Phoenix would see temperatures going from 109.9 F currently, 43.3C – to 114 F or 45.6 C.
GET STREET TREES (where possible)
The biggest discovery in this new paper is the winning benefit of street trees. India has known this for a long time. At least at late as the 1980’s, India’s major roads were lined by giant trees with massive shade for the people and animals moving along by foot, with cars, trucks, buses, and auto-rickshaws mixed in.
In 2018, I spoke with Professor Mat Santamouris in Australia. He launched a drone that measured 158 degrees F (70 degrees C) on the upper level of a car park in Darwin. People said it felt like a “river of fire”. But just below, at ground level under a tree the temperature was almost 30 degrees Fahrenheit cooler. People know trees work.
There are also the psychological benefits of trees. People like them and may be less stressed by the heat in a landscape offering shade. Birds and many other creatures depend on trees – and we become part of that slightly enriched biosphere.
In 2020, Scott led an article on “Street tree impacts on pedestrian-level climate”. He has been working on urban heat solutions for years.
SEE ALSO: “Dynamically downscaled projection of urban outdoor thermal stress and indoor space cooling during future extreme heat” Authors Timothy Jiang, E Scott Krayenhoff, Sept 1, 2023
TORONTO
“UTCI increases of 2.7 (6.2) °C are expected for Toronto, and of 2.2 (3.8) °C for Miami, under RCP 4.5 (8.5), on top of contemporary UTCI values of 32.9 °C and 35.8 °C, respectively.” Jiang, Krayenhoff et al 2025
This translates to daytime temperatures increasing 4 degrees F during the hottest week of the year in Toronto, in the best scenario. That Universal Thermal Climate Index (UTCI), goes from about 91 degrees F. to 95 F during the hottest week. But it could be as high as 101 degrees F during days of the hottest week, by the year 2100 in the worst case.
Personally, this may be an underestimate. Remember the IPCC never considered or modeled global warming above 8.5 degrees C, which is possible with cascading tipping points or complete failure to reduce or sequester carbon. For a few weeks, Toronto might get as hot as Phoenix is now, but with more humidity.
“In the case of Toronto, heat adaptation strategies are projected to become more effective in EoC [End of Century] climates since SoC [Start of Century] climates do not reach heat stress thresholds as often.”
STILL, TREES WIN
“…street trees strongly outperform the other strategies. When averaged across the three cities and time periods, the magnitude of daytime heat stress reduction associated with street tree expansion was almost four times greater than cool roofs, ten times greater than green roofs, and nineteen times greater than cool paving. “ Jiang et al 2025
That’s it for this week. I’m Alex Smith. Thank you for listening and caring about the world.