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Sam Seidel, 52, had never had pollen allergies. But recently he came down with a nagging throat cough, right about the time a “sheen of yellow haze” descended on his gray Chevrolet Volt.

A coincidence? Maybe. But Seidel was curious. Perhaps his resistance to the airborne irritant had reached its breaking point, overwhelmed by this spring’s bumper crop of the sticky powder.

At least his vehicle is probably safe.

“If anybody was trying to break into my car we wouldn’t have to dust for fingerprints, we’d have it already,” quipped Seidel, who lives in Cambridge.

For millions of people, high pollen counts are a perennial woe, and one that has kicked into high gear in the Boston area recently. But pollen seasons are getting longer and more intense, as allergy sufferers will surely attest, a trend specialists have linked to global warming.

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“There’s really good research showing that allergy seasons are getting more severe, and more people are developing allergies, because of climate change,” said Dr. John Costa, medical director of the allergy clinic at Brigham and Women’s Hospital.

Higher concentrations of carbon dioxide in the atmosphere provide plants with more food, making them larger and leading to more pollen, sniffling, and sneezing, research has shown.

Jennifer M. Albertine, a visiting lecturer in environmental studies at Mount Holyoke College, grew timothy grass in a greenhouse with elevated carbon dioxide and ozone levels to try to simulate what might happen to the common pollen producer if carbon dioxide levels increased to 800 parts per million, roughly double what they are now.

The plants produced about 2.5 times as much pollen.

“It’s plant food, right? So when you have more carbon dioxide, the plants are going to grow bigger,” she said. “And when you have bigger plants, you have more pollen.”

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Beyond that, spring comes earlier now. Frost comes later. The growing season is longer.

“Plants that couldn’t live in our climate are now able to live in our Northeast,” Costa said.

Making matters worse were April’s record rains, which allowed grass and vegetation to flourish.

In the past few weeks, pollen counts have increased because it has been dry, Costa said. Rain weighs down pollen, sending it to the ground. In dry, gusty weather, pollen flies into the air.

So rain offers a reprieve, but at a cost.

“We will pay for it eventually,” Costa said.

The gender of trees also plays a role, said Naomi Cottrell, principal of the Boston landscape architecture firm Crowley Cottrell.

For years, cities and towns asked landscape architects to avoid planting female trees, which bear fruit or seed pods that can litter sidewalks and muck up car windshields. Instead they planted male trees, which emit pollen.

Male trees have become so prevalent that plant nurseries, bowing to supply and demand, overwhelmingly stock male saplings, Cottrell said.

“I think we have to be more educated about the severity of asthma and allergies,” she said.

The answer is likely a better gender balance, and a greater diversity of plants, Cottrell said.

In the meantime, pollen will continue to wreak havoc on allergies. Dr. Andrew MacGinnitie, clinical director of the Boston Children’s Hospital division of immunology, provided a few pointers — limit exposure by closing the windows and turning on the air conditioning, which can filter out pollen; shower before bed to wash the accumulated pollen away; and take an over-the-counter antihistamine, or use a nasal spray.

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People should see a doctor when “they can’t concentrate in school, they can’t go to work, they have trouble sleeping because they are so congested or their allergies are so bad,” MacGinnitie said.

But not everyone sneezing when the trees start to flower is having an allergic reaction, said Dr. Caroline Sokol, principal investigator at the Center for Immunology and Inflammatory Diseases at Massachusetts General Hospital.

New allergies can develop for people in their 20s and 30s, she said. But as people reach their 40s and 50s, some experience allergy-like symptoms that are not actually allergies.

“It looks just like allergic rhinitis [hay fever], but it’s not caused by allergic immune responses,” Sokol said.

If that’s the case, antihistamines won’t help — try using a steroid nasal spray and limiting exposure to pollen, Sokol said.

Many people dread pollen season well in advance, but others have been caught off guard by its punch this spring. At first, Aurora Dominguez, 33, thought she had a cold. But as her eyes kept itching and watering, she realized it was allergies. She had to make a last-minute run to the pharmacy for antihistamines “just to get through the day.”

“That had never happened before,” said Dominguez, who lives in Arlington and has noticed patches of pollen on the Minuteman Bikeway by her home.

Not everyone suffers through the season, however.

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Steve Peterson manages Perfection Car Wash in Watertown and is not allergic to pollen. He said he looks forward to this time of year and the caravan of cars blanketed with greenish-yellow powder.

“We’re doing very well,” he said. “It’s been a bad year for pollen, that’s for sure.”


Gal Tziperman Lotan can be reached at gal.lotan@globe.com. Follow her on Twitter @tzigal. Lauren Fox can be reached atlauren.fox@globe.com.