The issue is the heat island effect — the way that different materials absorb, release, or reflect heat when they’re exposed to sunlight. Urban areas, with all their paved roads, parking lots, and asphalt roofs, tend to create a much hotter microclimate compared to all the healthy plants in rural areas.
“Using an infrared thermometer to measure the difference in temperature between mown paths and the unmown areas in my garden,” he said in a tweet in June.
The attached photos show a side-by-side comparison using the same thermometer on the same day.
The photo of the unmowed area showed the thermometer reading 25.5 degrees Celsius, or just under 78 degrees Fahrenheit. But the temperature of the mown part of the lawn was a whopping 34.3 Celsius (around 94 degrees Fahrenheit) — almost 10 degrees hotter in Celsius and almost 20 degrees higher in Fahrenheit.
Another user chimed in with an even more dramatic comparison: “Our grass versus neighbor’s plastic.” The natural grass came in at 76.5 degrees Fahrenheit, while the synthetic turf reached 126.5 degrees Fahrenheit, 50 degrees hotter than the ordinary lawn next door.
All of the heat being created by frequently-mowed lawns and plastic turf has real effects on people and the environment.
People are more likely to experience dehydration and heat stroke in higher temperatures, which can be deadly. Meanwhile, these conditions are unhealthy for wildlife and even the grass itself, as one commenter illustrated with a photo of their regularly-mowed lawn.
But apparently, homeowners can turn this effect around just by mowing less. “Now this is interesting,” said one commenter — a major understatement.
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