Tall and Old or Dense and Young: Which Kind of Forest is Better for The Climate?

In 2007, Richard Branson, the British business magnate, offered a $25 million prize to anyone who can invent a device capable of removing significant volumes of carbon dioxide from the atmosphere.

Andy Kerr, a noted Oregon environmentalist, drew a picture of a tree and sent it in. After all, a tree performs the job of sucking carbon out of the air far better than any technology yet devised by humans. But Kerr didn’t win, foiled by contest rules specifying the winner must be the inventor of such a device, and it’s certain neither Kerr nor anyone else invented the tree. An artificial tree might win if it could perform the implausible feat of inhaling CO2.

Kerr’s idea, however, was rooted more in the climate benefits provided by an entire forest rather than just a single tree. These benefits can be enormous, according to “Natural Climate Solutions,” a paper published in 2017 in the Proceedings of the National Academy of Sciences.

The paper asserts better management of forests, wetlands and farmland can provide 37 percent of the cost-effective climate mitigation needed through 2030. Forests alone can provide 18 percent of the mitigation, according to a statement published last year by the Climate and Land Alliance and signed by an international group of 40 scientists.

“The ‘natural technology’ of forests is currently the only proven means of removing and storing atmospheric CO2 at a scale that can meaningfully contribute to achieving carbon balance,” the 40 scientists said. “The world’s forests contain more carbon than exploitable oil, gas, and coal deposits, hence avoiding forest carbon emissions is just as urgent as halting fossil fuel use.”

Last year, the United Nations’ Intergovernmental Panel on Climate Change (IPCC) warned we have only until 2030 to act if we hope to limit global warming to moderate levels.

Forests cool the atmosphere by inhaling CO2 through the process of photosynthesis and storing or sequestering it in roots, trunks, branches, needles and leaves. Half a tree’s weight is carbon. Although every backyard vegetable garden absorbs some amount of carbon, a rainforest takes in exponentially more. For this reason, rainforests and other large terrestrial ecosystems made up of dense vegetation are known as “carbon sinks.”

Kerr lives at the edge of a temperate rainforest straddling the west coast of North America from the redwoods of Northern California into Alaska, the largest contiguous temperate rainforest in the world. Few ecosystems anywhere match its capacity to absorb and store carbon. Trees in the temperate rainforest, among the tallest in the world, live for 800 years or more.

The expansive Amazon tropical rainforest of South America is one of the world’s largest carbon sinks. But on a per-acre basis, the Amazon is not nearly as efficient at absorbing carbon as the coastal temperate rainforest. The Douglas fir forests of Oregon and the hemlock and cedar forests of Alaska store about twice as much carbon per acre as the Amazon. The giant redwoods of Northern California, which store seven times as much, are regarded as the most carbon dense forests in the world.

The temperate rainforest is a “carbon storage powerhouse,” says John Talberth of the Portland, Ore.-based advocacy group Center for a Sustainable Economy (CSE). “If allowed to mature, Pacific Northwest forests can capture and store more carbon than almost any terrestrial ecosystem on Earth.”