Storing Carbon is Cool

By Todd Burley, Lisa Ciecko, and Craig Chatburn

The City of Seattle has signed on to the Paris Climate Accord and is committed to reducing our greenhouse gas emissions as part of a global community. Much of our effort is dedicated to reducing our carbon emissions through transportation and building improvements, yet it is also important to absorb and retain atmospheric carbon. This is called carbon sequestration, and as the manager of almost 12% of Seattle’s land, it is right up Seattle Parks and Recreation’s alley.

Carbon can be absorbed from the atmosphere in a number of ways, including new technologies that “strip” it from the air. However, natural methods of carbon storage are very effective and pertinent to parks. In fact, trees, wetlands, soils and oceans have been doing a great job of balancing the carbon cycle for millions of years. The science if simple – plants take in carbon, store it in their bodies, and pass it on to the soil to be stored.

Seattle Parks and Recreation supports carbon sequestration through planting trees and restoring forests, improving soil health, and restoring and protecting wetlands and near-shore habitat.

Did you know that a 45-foot tall tree can store a ton of carbon in 40 years? The longer the tree lives, the longer the carbon is stored. Over the past decade, SPR’s Green Seattle Partnership has worked diligently to restore our urban forests with native evergreen trees and shrubs that will renew the complex ecosystem still found in places like Seward Park. In the last 15 years, GSP has planted over 300,000 trees in Seattle’s natural areas! SPR also works to maintain the trees we have, and replaces each tree removed with at least two others. Urban trees are a critical part of reducing the impacts of climate change, particularly in the cities they grow in. 

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But healthy trees aren’t the only part of the story. Healthy and stable soil is also a significant contributor to carbon sequestration (watch this soil carbon sequestration video or go deep with this academic paper on soil carbon). Carbon in the soil is absorbed by fungi and other living things and held in place underground. In fact, even gardeners can contribute to carbon sequestration by building healthy soils. In our parks, we work hard to compost weeds in place, leave grass clippings in place, retain fall leaves as free mulch and minimize tilling. We let logs decompose on site wherever possible and add wood chip mulch to support a natural soil biome and keep the carbon stored underground.

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Finally, “blue carbon” is another important part of carbon sequestration in Seattle. Like soils on land, soils in wetlands and nearshore ecosystems do a great job of absorbing and storing carbon from the atmosphere. In fact, because much of this substrate become anaerobic over time, carbon can be stored in these systems for millennia, undisturbed. Wetlands, estuaries, and near shore coastal ecosystems are extremely rich and productive, and as such can sequester significant amounts of carbon.  

Cities like Seattle are working hard to reduce our contribution to climate change through emissions reductions but sequestering the carbon already in the air is important as well. Seattle Parks and Recreation, as the manager of most of Seattle’s green spaces, can have a significant impact in this area. Whether it is in plants, in the soil, or under water, we think storing carbon is pretty cool.