How hurricanes threaten forests — and the carbon markets that depend on them

A single hurricane barreling into New England forests can undo decades of carbon storage, a new study has found.

As climate change heats oceans and fuels hurricanes, worsening storms with higher-speed winds are reaching ever deeper into the region’s woodlands, according to findings published on Wednesday in Global Change Biology. Now, just one big storm can knock down as many as 10 percent of standing trees in the heavily forested region.

Small increases in wind speed led to exponential increases in damage, the researchers found. An 8 percent increase drove up the number of high-destruction areas by more than 10 times; a 16 percent increase by more than 25 times.

The findings spell trouble for forest carbon markets, which aim to sell “credits” generated by storing carbon from the atmosphere in the growing bodies of trees.

With so many corporations looking to carbon credits as a means to “offset” their greenhouse gas emissions, the carbon credit market — of which forestry is a major part — is expected to grow to $100 billion by the end of the decade, and a quarter trillion by midcentury, according to Morgan Stanley.

As they grow, U.S. forests currently pull down the equivalent of about 15 percent of the nation’s fossil fuel emissions, according to the Department of Agriculture. The agency and state partners have sought to encourage markets in which landowners can sell the carbon stored in their growing forests on regional and international markets.

There is a lot of controversy over whether carbon offsets truly reduce emissions. But any version of carbon offset schemes rests on the idea that carbon is being permanently removed from the atmosphere — which requires the trees to keep standing.

“If we are going to rely on forest carbon as a primary tool to mitigate climate change—which seems to be the dominant direction that policies and voluntary/compulsory carbon markets are going in—we have to adequately account for the risks to this forest carbon from disturbances,” said coauthor Shersingh Joseph Tumber-Dávila of Dartmouth College and Harvard Forest.

Tumber-Dávila’s work shows that forest carbon storage companies face insolvency, rather like a bank without enough capital reserves to cover a sudden run on deposits.

“Current carbon market policies are incredibly insufficiently buffered against these risks, with a single hurricane having the capacity to emit the equivalent of 10[-plus] years of carbon sequestration from New England Forests,” he said.

To put those numbers into perspective, he noted that in California’s regulated carbon market — the U.S.’s largest — “less than 3% of carbon credits are set aside to mitigate catastrophic risks.”

If the trees fall — in storms or fires — those carbon offsets are wiped out. That’s been a serious problem for West Coast companies like Green Diamond, which received millions of dollars from tech companies seeking to offset their fossil fuel use with forest protection — only to have destructive wildfires fueled by climate change rip through their forests, according to Oregon Public Broadcasting.

That project, the broadcaster reported, ”depended on live trees. Year after year, they would act like worker bees, collecting carbon dioxide and — with the aid of the sunlight and water — use photosynthesis to store more of it in their wood.”

But in one fire, the company lost live trees that held down 3.3 million metric tons of carbon dioxide — the equivalent of the annual emissions from the tailpipes of 700,000 cars.

The Global Change Biology study expands this survey beyond wildfires and into the damage caused by storms.

Unlike that done by fires, however, this damage isn’t instantaneous: fallen trees take up to two decades to become a net source of emissions — countering the carbon stored by the forest regrowing around them — and up to a century to fully break down.

Nonetheless, the writers expressed caution about the future of New England’s forests on a heating planet — not to mention their utility as a financial instrument for companies unable to cut emissions.

A single storm, Tumber-Dávila noted, “is likely to deplete what is set aside for risks over 100 years.”

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