Weather Watch

Climate change is making poison oak stronger

A healthy stand of poison oak along the trail in the Los Osos Oaks State Reserve along Los Osos Valley Road. New leaves are shiny with oil that includes urushiol, the itch causing ingredient.
A healthy stand of poison oak along the trail in the Los Osos Oaks State Reserve along Los Osos Valley Road. New leaves are shiny with oil that includes urushiol, the itch causing ingredient.

The journal Nature Climate Change announced in a paper published this month that 2016 will be the first year in which carbon dioxide (CO2) concentrations in the atmosphere will remain above 400 parts per million (ppm) all year round.

In fact, Hawaii’s Mauna Loa Observatory, which has monitored CO2 concentrations since 1958, reported a level of 407.7 ppm in May, the highest monthly CO2 level ever recorded. For reference, the early measurements taken at the observatory back in the late 1950s were about 315 ppm.

As Adm. David Titley will tell you, “To compare that to something readers may be familiar with, a blood alcohol level of 0.04 percent, or 400 ppm, puts a party-goer well on the way to intoxication. If we increase our blood alcohol to 800 ppm, or 0.08 percent, we are legally impaired.”

Not only are these increased amounts of CO2 producing record high atmospheric and oceanographic temperatures, they’re also causing changes in plant growth.

Our family, like many others, loves to hike the spectacular trails of San Luis Obispo and Santa Barbara counties.

However, the hikers and service groups that maintain these trails — such as the Black Mountain Gang and Central Coast Concerned Mountain Bikers, along with firefighters, rangers and PG&E line crews — have always had to deal with the scourge of a fierce skin irritant called urushiol, a nearly invisible and odorless oil found on poison oak, poison ivy and sumac.

Nearly all plants use CO2 to grow. Some plants use the extra CO2 much more successfully than others. Unfortunately, the Toxicodendron family that encompasses poison oak, ivy and sumac are some of the most effective, allowing them to produce greater amounts of urushiol oil with larger amounts of CO2, according to a U.S. Department of Agriculture study.

Not only does the urushiol become more concentrated, but the plants produce more leaves — a double whammy. A dose as low as 50 micrograms (less than a grain of salt) can cause severe reactions.

If you’re allergic to poison oak, you’re not alone. Between 80 and 90 percent of the U.S. population exhibits an allergic reaction to urushiol, according to the Centers for Disease Control and Prevention and the American Academy of Dermatology. A few individuals are extremely allergic to urushiol, while others can see their degree of reaction change over time.

“While poison oak will not kill you, you may wish it would as the itching can be quite severe,” said Dr. Penny Borenstein, health officer for San Luis Obispo County. “But, with all seriousness, poison oak can be quite dangerous because the allergens can be inhaled, causing lung irritation and scarring, which occurs in firefighters and others who are exposed to the burning plant.”

Even though poison ivy and sumac can grow throughout the lower 48 states, poison oak is most common in California. The old poison oak adage “leaves of three, let them be” is a good way to avoid exposure, but that is often easier said than done. Poison oak can change color throughout the season from a deep green that resembles an oak leaf to fiery hues of red and orange in summer and fall. It can look like a shrub or a vine.

The U.S. Forest Service recommends washing your skin thoroughly with lukewarm water and soap the instant you realize you’ve come into contact with urushiol oil. Also wash everything else that may have touched the poison oak leaves: clothes, shoes, pets, cars, water bottles, everything. You can reduce urushiol’s effects if the oil is washed off before it’s absorbed into the skin. If your reaction is severe, seek medical attention.

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At PG&E, your safety is our highest priority. Summer is here, which means lots of fun in the sun. But, the weather could get extremely hot this week and quickly go from fun to dangerous. Extreme heat can be life threatening. So learn what extreme heat is and how you can protect yourself. Visit for safety tips.

John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and a media relations representative. Email him at or follow him on Twitter @PGE_John.