Gardeners are finely attuned to short-term changes in nature as well as long-term trends. Here in Seattle, we are fresh off one of the warmest winters on record in the PNW and heading into a summer that could be one of the worst forest-fire seasons ever. Over half the state is in drought. While many PNW gardeners are enjoying good spring harvests of greens and berries at the moment, we’re also casting a concerned eye at our thirstier summer crops, like tomatoes. This is a key moment to talk about climate change and its effect on our plants, yards, and dinner plates. In this series, we will learn what climate change effects to expect in the Puget Sound-area garden, how you can adapt your garden to climate change, and how gardening can ameliorate some of climate change’s negative effects.
To begin, let’s summarize the effects of climate change that we are already seeing today, and will see more of in the future. My favorite source for local climate science is the Climate Impacts Group at the University of Washington. CIG is a scientifically rigorous, well-respected crew that publishes some of the best work on climate change in our region. Their recent publication describes the best Washington climate predictions available from climate models (the sets of equations that climate scientists use to describe climate processes and predict environmental change).
According to CIG, one of the major effects of climate change in our region will be an increase in heat. The average, year-round temperature is expected to increase, and heat extremes (record-breaking hot days) are projected to increase as well. Is this a negative or positive? This is a complicated question to answer. Warmer summers: more likely to cause heat stress in plants (and humans!). Warmer winters: our growing season may extend, winter crops may be more productive, and cold-sensitive perennials may have a better survival rate. A longer growing season may result in new cropping systems (of course, we will need to plan and actually make the switch to these new systems to take advantage).
Precipitation is harder to predict than temperature, especially given the variability between summer and winter precipitation patterns. However, the general expectation in the Pacific NW is that summer precipitation will decrease, and winter precipitation will increase. Decreased summer precipitation, combined with increased summer heat, will make drought stress more of a concern for plants. Winter precipitation may lead to wet spring soils, which could be beneficial to some summer garden species and detrimental to others.
Pests, fungi and weeds are the most difficult to predict, say CIG scientists, especially in the complex system of a garden ecosystem. The most consistent prediction is to expect changes from your usual gardening experience.
In the next post, we will discuss general and specific techniques to adapt your garden to climate change in the Pacific North West. If your interest is piqued, further reading on climate science can be found at CIG, and Cornell has an excellent climate gardening website (although it is mostly for the East Coast).
Rachel Aronson is a professional environmental policy specialist, and avid gardener. She’s most excited for strawberry and tomato seasons, and is growing tomatillos and ground cherries for the first time this year. More of her writing can be found at rachelaronson.net, or @RachelAronson.
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