We all love those beautiful, mild days when the temperatures range between the mid-60s and mid-80s, when the air is clear and the humidity low. They’re perfect for a backyard barbecue, for a hike or run, or walking the dog.
If you already think we don’t have enough of these days, brace yourself for some bad news. Beautiful days will likely become even rarer in the coming years as a consequence of climate change.
“It’s the type of weather that matters to everyday lives,’’ says Sarah Kapnick, a research scientist with the National Oceanic Atmospheric Administration, and co-author of a new study that examines the effects of climate change on mild days. “It’s the type of weather we hope for, and plan for.”
While numerous climate studies in recent years have examined the influence of global warming on extreme weather events — heat waves, superstorms, flood and drought — there has been little attention directed at the impact of climate change on the weather we enjoy the most.
“People often use the frog-in-boiling-water metaphor to show how gradual, long-term changes in climate can sneak up on us,’’ said Henson, who was not involved in the study. “But it’s everyday climate, not the extreme events, that affects our day-to-day life the most. As with other aspects of climate change, there will be winners and losers when it comes to mild weather — but globally, what we lose could exceed what we gain.”
The research suggests the number of mild days will decrease as a result of warming. The current worldwide average of 74 mild days a year will drop by four days by 2035, and 10 days by 2100, according to the study.
“Mild weather is something everyone knows, experiences and has memories of,” says Karin van der Wiel, a Princeton University postdoctoral researcher at NOAA’s Geophysical Fluid Dynamics Laboratory and lead author of the study. “Our study shows that human-caused climate change is going to lead to changes in mild weather all over… The changes are happening now, and where people live.’’
Losing mild weather potentially could harm tourism, construction, transportation, agriculture and outdoor recreation, since all of them rely on specific weather patterns. In addition to the economic costs, there also could be health impacts, since mild days in summer can act to break up deadly heat waves.
Scientists predict the biggest losses will occur in tropical regions due to rising heat and humidity. Parts of Africa, Asia and Latin America could see as many as 50 fewer days of mild weather annually by 2100.
Those who live farther from the equator, including the United States, and many mountainous areas around the world, will likely see more mild days. These areas include communities along the Canadian border in the Northeast, Midwest and Northwest, as well as many parts of Canada. Some U.S. cities could lose mild days during the summer months, but gain them during cooler periods.
“There are very few parts of the country that actually see gains in mild weather,” Kapnick says. “One of the cities with the largest increases, for example, is Seattle, but those increases by the end of the century aren’t occurring in summer, but in spring and fall. Los Angeles too will have losses in the summer, but gains from spring and winter increases.”
The researchers used high-resolution climate models to examine the changing patterns of mild weather globally, as temperatures rise due to the buildup of greenhouse gas emissions in the atmosphere.
“We used a climate model to simulate the current climate,” van der Wiel explains. “In that simulation we counted the number of mild days. Then, we increased greenhouse gases in the climate model to simulate the future effects of climate change. This leads to increasing temperatures, changes in humidity, changes in precipitation over the whole world and with very specific patterns. In this new, future climate, we counted the number of mild days again. We could then calculate the change — increase or decrease — of mild weather days for each location globally.”
Kapnick adds: “Looking at the current climate also allowed us to measure how the number of mild days naturally varies from year to year to know that the changes in mild days in the future are larger than these natural variations.”
The study projects that parts of England, northern Europe and Patagonia and South America could gain as many as 15 mild days annually by the end of the 21st century. Although, in some of those regions, mild weather will drop off during the summer months, while becoming more abundant during fall, winter and spring.
“We’ve already seen a warmer climate pushing some plant and animal species poleward, but the human population is growing the fastest at lower latitudes, where we may see the biggest loss of mild days,’’ Henson says. “We humans are an enormously adaptive species. Plants and animals don’t have the luxury of turning on the air conditioner or changing their wardrobe to stay comfortable.
“This study implies that our warming climate will swap out some of the nicest summer weather in the United States in exchange for a greater number of comfortable cold-season days,” he adds. “Whether that’s a good trade depends on where you live and what kind of weather you enjoy. This is especially true in the Sunbelt, where the U.S. population is growing the fastest. People in the South and Southwest often stay indoors during the worst of their summer heat and head outside when it’s milder. But many folks are busy with work and school during those southern cool seasons.”
He points out that, over time, heat and humidity “may encroach on the total number of mild days in the southern United States,” adding: “What happens when the mild weather that helped draw Americans to the Sunbelt gets eroded?”
The scientists hope their work will encourage more studies, believing that additional information will prove especially important for business and industry, as well as for physical and mental health, leisure and urban planning.
Moreover, “further research [can tell us] how mild days impact peoples’ emotions, psychology and maybe even their decisions,” van der Wiel says.
Marlene Cimons writes for Nexus Media, a syndicated newswire covering climate, energy, policy, art and culture.