Climate Change and the Coast Redwood 

Monday, May 3rd, 2021

We all know that climate change is having and will continue to have a dramatic impact on our planet. But knowing exactly what that impact will be can be a tricky business. Our planet’s weather patterns are the result of a delicate balance of a multitude of factors. And so, tracking how increasing global temperatures will impact specific regions takes a lot of scientific inquiry. Even more complicated is understanding what climate change’s impact on specific species will be. That being said, I wanted to take this opportunity to talk about what we know about climate change’s impact on one of the most iconic species on the planet and the species most heavily associated with the North Coast of California – the Coast redwood.

The Coast redwood (Sequoia Sempervirens) is the tallest species of tree on earth and one of the longest living. Despite their impressive size and age, coast redwoods only naturally occur in a 50km wide belt along the coast of Northern California and extreme Southern Oregon. The reason is that they depend on a unique set of conditions that exist in that range in order to thrive. Some scientists believe that because of climate change, those conditions could change and that the range of Coast redwood could shrink even further in the future.

Coast redwoods depend on two main ingredients in order to grow to their incredible sizes, lots of moisture and lots of sun. Farther north than where they are currently located (Oregon and above) there’s plenty of water but not enough sunlight. Farther south (Mid and Southern California), there’s plenty of sunlight but not enough water. Only in the perfect Goldilocks zone of the redwood region do the right conditions exist to produce these magnificent trees.

The secret is our summer coastal fog. Our region’s dependable summer fog allows Coast redwoods to retain enough moisture during the dry summer months to keep from drying out, while simultaneously still allowing enough sunlight through. The fog prevents the redwoods from unnecessarily losing water due to transpiration while simultaneously providing water in the form of fog drip. Fascinatingly, Coast redwoods (along with many other plant species native to our region) are uniquely adapted to absorb water directly from fog through their leaves. This dependence on fog is why Coast redwoods don’t extend farther inland. Fog doesn’t travel that far from the coast.

That’s why it’s so concerning that researchers believe that climate change could reduce the total amount of fog that occurs along our coast. Very basically, our coastal summer fog is caused by low lying, relatively warm, moist air flowing east over the very cold Pacific Ocean. As the air flows over the cold ocean, it cools and the moisture in the air condenses. Then, when the air gets close to land, warm air flowing west from inland California flows over the moist air flowing east and squeezes the moist air even more until eventually it forms a low lying fog.

Recent research has analyzed the impact of climate change on air currents over California and the result is troubling. In the future, fog will shift northwards, penetrate less far inland, and occur less frequently. This research is supported by an analysis of the frequency of fog over the past one hundred years. The researchers analyzed the number of days per year that there were fog warnings at north coast airports such as the Arcata-Eureka Airport. The result was that there has been a 33% reduction in the amount of fog since the early 20th century. Another study projecting the change of fog into the future concluded that under a middle-of-the-road climate scenario for California, there would be no suitable habitat for Coast redwoods south of the San Francisco Bay by the year 2030. And that, as the earth continues to warm, that contraction will extend further north all the way into Southern Humboldt County, particularly affecting more inland coastal redwoods which will no longer be blanketed in fog in the summer.

The news is not all bad. Some research has indicated that coast redwoods located particularly close to alternative sources of water, such as streams, may be able to continue to exist after the fog disappears. But overall, this prediction is incredibly troubling. So, the next time you attend a climate march, decide to take public transit instead of your car, or eat a salad instead of a cheeseburger, remember that you’re helping to preserve some of the oldest, tallest trees on the planet.