Pollen Dispersion in Tokyo Begins on Earliest Date on Record; Global Warming Seen As A Cause

The Yomiuri Shimbun

13:19 JST, January 28, 2025

Despite still being the middle of winter, the dispersion of pollen has already begun.

The Tokyo metropolitan government on Jan. 8 confirmed the start of pollen dispersion, the earliest date on record according to a survey that started in 1985. The pollen season is expected to start earlier than usual nationwide, with some areas expected to see high levels of airborne pollen.

Some believe that the early start is partly due to global warming, and experts are calling on people to see a doctor once they experience any symptoms of pollen allergies.

Lines of patients

At Nagakura otorhinolaryngology allergy clinic in Shinagawa Ward, Tokyo, hay fever patients began lining up to see a doctor in mid-January. Normally, such patients would start coming to the clinic around early February.

A 68-year-old a company manager came to the clinic on Jan. 23, having begun to suffer symptoms such as sneezing and having a stuffy nose about two weeks earlier than usual.

“I do hope that the symptoms won’t last until spring,” he said.

Hitoshi Nagakura, director of the clinic, said: “The earlier pollen dispersion starts, the longer the pollen season may last. I hope people will get treatment early, so they can get through it with only mild symptoms.”

‘Conventional wisdom’ overturned

The metropolitan government has installed pollen collectors at observation points in 12 wards and cities. When four or more pollen grains are counted per 1.8 square centimeters on the glass slide of the same collector on two consecutive days, it will determine that pollen has “started to disperse.”

At an observation point in Ota Ward, four pollen grains were counted on Jan. 8 and six the following day. The metropolitan government thus announced that Jan. 8 was the day the pollen dispersion had begun. This was 32 days earlier than last year and 23 days earlier than the previous record — Jan. 31 in 2007.

The amount of pollen is expected to be 20% higher than usual, and the number of days with high pollen counts are expected to total 42, seven more than normal.

In academic circles, pollen dispersion is reckoned to start when the sum of the daily maximum temperatures exceeds 400 C.

However, the sum of daily maximum temperatures this year in central Tokyo was only 86.6 C as of Jan. 8. A metropolitan government official said that the pollen season had started so early that they were wondering if the conventional wisdom still holds.

Nationwide trend

The early start of the pollen season appears to be a trend that will be seen across the country.

According to a survey conducted on Jan. 9 by Weathernews Inc., a weather information company, many users of its app on the Pacific side of Japan reported that they “felt the pollen.”

Pollen dispersion is expected to start a bit earlier than usual in eastern and northern Japan. In western Japan, although the start of the pollen season is expected to be normal, pollen levels may reach their highest in 10 years, as cedar growth has been good due to last summer’s fine weather.

“Global warming is reckoned to be a cause of the earlier pollen dispersion and the rise in the amount of pollen,” a representative of Weathernews said.

According to the Japan Meteorological Agency, the annual average temperature in 2023 and 2024 were both record highs, and the temperature has only fallen below 0 C in central Tokyo on one day so far this season.

Hay fever cases on rise

Hay fever is so prevalent in Japan that it is called a “disease that harms the nation as a whole.”

According to surveys by the Japan Society of Immunology, Allergology and Infection in Otorhinolaryngology and others, the percentage of those who suffer from seasonal allergies has been rising steadily in Japan – from 19.6% in 1998 to 29.8% in 2008 and 42.5% in 2019.

Effective measures to fend off hay fever symptoms include wearing masks, glasses and hats. These reduce the amount of airborne pollen that comes into contact with the eyes and nose. Cleaning the floor with a damp cloth or mop is also recommended.

The Tokyo Metropolitan Institute of Public Health says, “Preventing the intake of pollen into the body as much as possible will help mitigate symptoms.”