Spring is in full swing, but many in New Hampshire have seen their allergies starting earlier.Weather and climate trends are worsening allergy season.”We are seeing global trends with allergy seasons getting longer because we think of global warming as a factor,” Dr. Erin Reigh, with Dartmouth Hitchcock Medical Center, said.Research shows that earlier spring and longer periods of freeze-free days for parts of the U.S. have meant that plants have more time to flower and release allergy-inducing pollen.”It’s also likely that the allergy season will increase in duration,” Reigh said.A Dartmouth Hitchcock doctor talks about when to take allergy pills and the best way to tell the difference between an allergy and sensitivity in the player below:A study from the National Academy of Sciences found that pollen concentrations have increased by more than 20% across North America since 1990, and the season is about 20 days longer.Each year in New Hampshire, there are an average of eight more days above 32 degrees compared to a century ago, and that’s giving pollen a head start.”There’s no question that in New England, we’ve seen that happen within the last decade or so,” Riegh said.Researchers said that by the end of the century, the U.S. pollen season could begin 40 days sooner, and the pollen count could climb by 250%.A Dartmouth Hitchcock doctor talks about the timing of pollen release during the day and when tree pollen ends in the player below: