Las Vegas Sun

September 28, 2022

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Climate change creating boom of allergy-causing plants

Plant life’s pollen assault on desert dwellers is only going to get more pronounced, experts say

Itchy eyes and swollen sinuses — these are the signs of spring in Las Vegas.

And parts of summer.

Oh, and a bit of fall, too.

It wasn’t always like this. There was a time when people suffering from respiratory illnesses flocked to the Mojave Desert to escape allergens. But then their neighbors planted olive and mulberry trees, and what was once a haven became hell for a growing number of residents.

If climatologists and botanists are right, it wasn’t all the landscapers’ fault. Rising temperatures and carbon dioxide emissions also played key roles. If those trends accelerate as projected, Mother Nature will persecute valley allergen sufferers in new and tortuous ways.

As Las Vegas blossomed into a grassy oasis, the air and climate were changing in ways that made the plants happy. The amount of carbon dioxide, the chemical compound that plants inhale, increased dramatically and temperatures gradually increased, expanding the growing season. That, in turn, led to more pollen and pollen-producing plants.

Today about 25 percent of Las Vegans suffer from seasonal allergies, according to local allergist Dr. Jim Christensen.

“The adage is true: If you aren’t allergic, come to Vegas and you will be,” Christensen said. “On top of all those pollen-producing plants, nonallergic rhinitis (nasal inflammation) can affect anyone — anywhere, anytime. We have triggers like cockroach feces, dust and low humidity that cause irritation and allergylike symptoms.”

Wind can exacerbate the problem, blowing pollen that triggers allergies and dust that simply irritates the eyes and nose.

Still, allergies in Southern Nevada are not considered severe enough to give us significant notoriety, even as summers get drier and plants put out more pollen in a carbon-rich environment.

The National Wildlife Federation’s recent report about allergy “hot spots” that are expected to become downright unbearable in coming years mentions Las Vegas only in passing.

The others have ragweed, which scientists expect to put out more pollen and bloom longer as the climate warms and carbon increases.

Las Vegas doesn’t have ragweed, but that doesn’t mean much for the quarter of Las Vegans allergic to other fast-growing weeds: Bermuda grass, mulberry trees, oleander, privet and other pollen-spewing plants that do grow here.

Climatologists and plant scientists say they are not certain just how climate change and carbon-level increases will affect these plants, but they wouldn’t bet on things getting better, just different.

The desert Southwest is warming. Since the 1950s, the average annual temperature has risen 7 degrees and carbon levels about 25 percent. That trend is expected to continue in the Mojave with warmer winters, warmer nights and drier summers.

The valley is in a new paradigm: Carbon levels and temperatures are rising, seasons shift and plants are reacting in unpredictable ways.

“The more complicating thing, when you talk about allergens, is each plant has its own day in the sun, so to speak,” said Kelly Redmond, a Western Regional Climate Center climatologist. “You get different combinations of plants at different times of year. They’ve evolved to get a competitive advantage and they’re picking up on triggers in the atmosphere. It’s likely they won’t all respond in the same way (to climate change and carbon increases).”

It could mean more pollen and for longer. It could also mean the somewhat reliable allergy seasons turn into an unending chain of misery as they begin to overlap. Allergy sufferers can even hold out hope that it could mean the death by heat exhaustion of every hated allergy-inducing plant — but that seems to be the least likely effect for the foreseeable future.

Plants tend to like warm, carbon-rich environments. It’s why the ancient bristlecone pines atop Mount Charleston are growing like teenagers and olive trees planted 50 years ago seem to splatter even more fruit across sidewalks on the valley floor.

The valley is seeing worsening allergy seasons because of it. Allergy-causing weeds are growing more thickly and for longer periods, UNLV plant researcher Scott Abella said.

Some plants can’t use the increase in carbon and shed it by throwing out more pollen, he said.

The warming winters mean some plants are having longer growing or flowering seasons, while others may not be able to adjust to the higher temperatures and could die off.

“It’s like if a human gets a fever,” Abella said. “Because our bodies are tuned to a limited range of temperatures, we immediately notice when we’re too cold or too hot. And it’s only a small range. That’s what’s happening (in the plant world). In a certain sense, the biological community has a collective fever, but all the plants have a different range. They don’t respond the same way to everything.”

In Las Vegas, like most places, a crucial third factor comes into play: water. In some places, drops in precipitation could stress or kill allergen-producing ornamental plants.

But here, the water for such plants doesn’t come from the sky — it’s pumped from the Colorado River.

Most of the allergen-inducing plants aren’t native trees and shrubs watered by rain, but exotics planted by humans and kept alive via sprinklers. That makes them more independent of rainfall patterns, Abella said.

That water originates, mostly as snow, in the mountains of New Mexico, Colorado, Arizona and other Great Basin states. These places are expected to see precipitation fall as quick-evaporating rain, not the deep snow pack needed to sustain most of the Southwest, Redmond said.

Less water in the river means less water in Las Vegas.

Southern Nevada Water Authority General Manager Pat Mulroy has said that if the water supply situation gets dire, and new sources are not tapped, shade-providing trees will be spared. But lawns could be outlawed across the valley.

For those allergic to Bermuda grass, it’s not such a grim prospect.

For those whose allergies are triggered by dust, it just means more misery.

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