Checked out the allergy medication section at your neighborhood pharmacy lately? Chances are it's nearly bare, with the few remaining boxes of Claritin, Zyrtec, Sudafed and Benadryl tossed about as if the shelves have been pillaged by marauding, sneezing and sniffling Vikings.

Blame it on a dry winter, hotter-than-normal spring -- possibly even climate change: This year has been a particularly rough one for allergy sufferers battling the pollen that early blooms have sprayed into the air.

"The weather here has been so bipolar that my allergies think that it has been springtime since December," said Sarah Sohm, of South San Jose.

And the worst is yet to come because grass pollen -- known to trigger the most severe pollen allergies -- will soon inflict its misery.

Every spring, the allergy season kicks off when trees such as oak, sycamore, juniper and birch unleash pollen granules into the air. While the particles may seem harmless to some, the immune systems of allergic people mount an all-out attack by releasing loads of histamine -- the culprit behind the watery, itchy eyes, nose and throat that allergy sufferers have come to loathe. Those with asthma have an even tougher time because allergens like pollen can make symptoms much worse.

Every year, Bernita Alfonzo of Walnut Creek, along with her teenage son, brace themselves for the onslaught of allergy symptoms that could trigger an asthmatic response if they aren't careful.

When Alfonzo visited her local CVS pharmacy on Saturday afternoon, she found that fellow allergy sufferers had cleared out most of the shelves. But she was lucky to find some Zyrtec on sale.

A transplant from upstate New York, Alfonzo began experiencing allergies only after her family moved to the East Bay. She said her asthma was a direct result of severe allergies. "It traveled down (from my sinuses) into my chest," Alfonzo said.

This spring, drier- and warmer-than-average weather kicked off the season early. So pollen counts are soaring from Martinez to Morgan Hill.

Some fear that climate change -- caused by the increasing concentration of greenhouse gases released into the atmosphere -- is leading to earlier and longer allergy seasons.

The time of the year that plants bud and flower is intimately linked to "accumulated warmth over time," Dr. Richard W. Weber of National Jewish Health, a medical research institute in Denver, Colo., wrote recently in the Annals of Allergy, Asthma & Immunology. "Global warming could therefore speed flower development, resulting in earlier blooming."

Weber compared multiple studies that showed clear relationships between warming trends and the release of pollen.

Dr. Alan Goldsobel of the Allergy and Asthma Associates of Northern California has treated allergy and asthma patients for 25 years. "What we've seen so far this year is very high levels of pollen from trees," said Goldsobel, who has one of San Jose's two official pollen collectors in his office.

Resembling flytraps for pollen, the rotating collectors have microscope slides smeared with Vaseline. Researchers periodically examine the slides to determine how much and what kinds of pollen are circulating in the atmosphere.

"Starting a month or two ago, juniper and cedar trees were releasing pollen," Goldsobel said. "And most recently, sycamore trees have been bothering a lot of people, but also pine and oak trees."

The high levels of pollen have translated into a steady stream of allergy and asthma sufferers marching into Goldsobel's office.

"Some patients are having more severe symptoms this year than previous years, maybe even as of a few weeks ago," Goldsobel said.

And, unfortunately for allergy sufferers, the tree pollen season is only the beginning.

"The biggest thing in this area is grass," said Dr. Sean McGhee, head of the allergy clinic at Lucile Packard Children's Hospital at Stanford. And grass pollen, the most common and severe contributor to pollen allergies, won't be released for another month or two, McGhee said.

He has seen higher numbers of patients with asthmatic symptoms this season. "Pollen itself doesn't cause asthma," but it exacerbates its symptoms, McGhee said. "We're starting to see people whose asthma was really well-controlled, but then things have gotten bad in the last month or so."

While avoidance of the allergen is the best way to prevent symptoms, anyone who goes outside is likely to come in contact with the high levels of pollen now in the air.

For patients who don't respond well to medications, allergy shots are another alternative. But many allergy sufferers will just have to suck it up until July, when the grass pollen season dies down.

According to McGhee, Bay Area residents allergic to pollen do have it lucky in one regard: The fall ragweed season in Northern California isn't as bad as in other parts of the country.

Staff writers Katie Nelson and Dan Nakaso contributed to this report. Contact Jessica Shugart at 408-920-5782. Follow her at Twitter.com/jessicashugart.