A go-to argument of the modern breed of climate-change deniers is that carbon dioxide is good for plants and what’s good for plants is good for humans. Well, sure, a greener planet actually could be beneficial for humanity. But let's not ignore the many not so beneficial effects. Seasonal-allergy sufferers could give you at least one.

Hay fever and the like may not be the most devastating illnesses in the world, but they have a real cost in terms of dollars and human misery. Due to its effect on plants, a hotter planet is making these seasonal allergies worse. Even if not the direst effect of climate change, it does add to the growing list of harms humanity has inflicted on itself by refusing to take climate seriously for so long. And every little bit hurts.

Pollen counts will be higher than average at times this year in parts of 39 U.S. states, AccuWeather predicted last week. Tree, grass and weed pollen each have different seasons, with peaks stretching from the spring all the way into the fall. These seasons will be a little bit longer and more intense than usual this year. That’s more opportunity for those of us with pollen allergies — about a quarter of all U.S. adults and a fifth of all children, according to the Centers for Disease Control (RIP) — to feel miserable.

It’s becoming a new normal. “The trend of more intense allergy seasons getting a jump start earlier in the spring and lasting later into the fall follows the overall trend line of warmer and wetter spring seasons in America,” AccuWeather Senior Meteorologist and Climate Expert Brett Anderson said in an emailed release. “Pollen counts are on the rise and seasonal allergies are getting worse for millions of people as our climate continues to warm.”

A hotter planet increases the risk of all sorts of ailments. Extreme heat makes everything from heart disease to mental illness much deadlier, as my Bloomberg Opinion colleague Lisa Jarvis has written. Hotter, wetter weather encourages the spread of mosquitoes, Earth’s deadliest creatures, as another one of my Bloomberg Opinion colleagues, Lara Williams, has noted. They carry malaria, dengue fever, Zika virus and more. And who knows what paleolithic plagues wait in the permafrost to be thawed?

Allergies, in contrast, may sound relatively benign. But they make it harder for people to work, study, sleep and otherwise function normally. All of this imposes a real economic cost — $18 billion per year, according to the American College of Allergy, Asthma & Immunology, and four million missed work days per year, according to the Allergy & Asthma Network, a nonprofit group. For the almost 25 million American asthma sufferers, pollen can trigger life-threatening attacks. Some 3,500 Americans die from asthma every year, according to the ACAAI.

We need to prepare for an even wheezier future. Since 1970, temperatures in meteorological spring (the calendar months of March to May; not to be confused with astronomical spring, which started on March 20) have warmed in 234 of 241 U.S. cities studied by Climate Central, a nonprofit research group, by an average of 2.4 degrees Fahrenheit.

Warmer and longer springs and delayed fall frosts mean longer growing seasons for all kinds of plants, including those that produce pollen. Between 1990 and 2018, the North American pollen season grew by 20 days and became 21% more intense, according to a 2021 study in the Proceedings of the National Academy of Sciences. Human-caused climate change was the main culprit, the study found.

Given the extreme heat of the past seven years, it’s no shock this trend has continued. Between 1970 and 2024, the growing season has lengthened in 172 of 198 U.S. cities studied by Climate Central, by an average of 20 days. Reno, Nevada, has gained more than three months of freeze-free days. Many other cities got more than a month, including Toledo, Atlanta, Minneapolis and my hometown of Columbia, South Carolina.

Longer growing seasons might sound like a feature of climate change, not a bug. Certainly those climate change deniers insist easier farming will be the only consequence. And some regions that are now too cold for crops may eventually benefit, but others will become too hot to farm. And in places where farms are currently located, floods, droughts, heatwaves and other symptoms of a chaotic climate make it harder to grow healthy plants. Fewer freeze days also encourage blight and pests that attack crops. Although the planet is greener today than it was decades ago, that is mostly due to industrial farming and tree plantations, not the urban parks and wild forests that would be more helpful to humans.

Meanwhile, warmer weather encourages many plants to not only produce more pollen, but to make that pollen even more allergenic, according to the Environmental Protection Agency (RIP). Correlation isn’t causation, but the incidence of seasonal allergies stands at 25% for adults, compared with 10% of all Americans in 1970, according to the U.S. Global Change Research Program.

Allergy sufferers probably know how to deal with this by now. That includes limiting time outdoors during the worst of the pollen seasons and improving indoor-air quality. People with asthma need to be prepared for attacks. It sounds simple, but it involves time, energy and money that could be spent on more productive things, like starting up a Midwestern Champagne business. President Donald Trump could help by ending his administration’s assault on climate and health science.

The best thing we can do for everybody is to stop burning the fossil fuels that are heating up the planet and causing all this misery. Those climate deniers would have us give up that fight. In their view, not only is climate change beneficial, but combating it is just too costly and destructive to our way of life. In fact, its real physical and financial costs grow exponentially every day we ignore it.

_____

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Mark Gongloff is a Bloomberg Opinion editor and columnist covering climate change. He previously worked for Fortune.com, the Huffington Post and the Wall Street Journal.

_____

©2025 Bloomberg L.P. Visit bloomberg.com/opinion. Distributed by Tribune Content Agency, LLC.