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Forest fire damage reaches the edge of the Coldwater River just outside Merritt, B.C., in early June. The use of trees as carbon saviours is threatened by the worsening trend of wildfires.Melissa Tait/The Globe and Mail

Who doesn’t like trees? Planting them is a rare climate policy with support across the political spectrum. Many plans to cut emissions, whether government or corporate, include a promise to plant trees, a lot of them. As one ecologist quipped: “There’s no anti-tree lobby.”

The planet has an estimated three-trillion trees – and after centuries of concerted effort to cut as many down as possible, there’s now a frenzy of reforestation proposals. There’s Trillion Trees, a program backed by the conservation groups like the World Wildlife Fund. The World Economic Forum in 2020 promoted a plan to “grow, restore and conserve” a trillion trees. Australia wants to plant one billion over a decade. And in Canada’s 2019 federal election, the Liberals promised two billion by 2030.

These numbers are at once big and small. Ottawa says two billion trees would cover an area of 11,000 square kilometres, twice the size of Prince Edward Island. But PEI is a fraction of a fraction of one per cent of Canada’s land mass. And two billion trees is only 40 per cent more than the number of trees expected to be planted absent any new policy. Canada’s forests are estimated to be home to more 300 billion trees – so adding two billion more, while worthy, is basically a rounding error.

The Liberals’ “2BT” program officially started in late 2020, with a promised investment of $3.2-billion over a decade. While benefits of trees are many – they sure make cities nicer places to live – climate is at the fore of all the recent promises. “There is no path to net-zero emissions that does not involve our forests,” the Trudeau government said.

All those new trees are supposed to deliver, by 2050, an annual cut to greenhouse gases of 12 megatonnes. Canada’s emissions in 2020 were 672 MT, so 12 MT is less than 2 per cent of the current total. Even the Trudeau government’s big planting strategy knows that trees, via their ability to remove carbon dioxide from the air through photosynthesis, are only a small part of GHG reductions.

And planting trees at a massive scale, enough to suck up significant GHGs, is a lot harder than it sounds.

Just 29 million trees went in the ground in 2021, the first planting year of Ottawa’s two billion tree plan. Three-quarters of the trees won’t be planted until the back half of the decade.

Tree planting as a carbon-reduction strategy has been hyped for years, with its serious limitations rarely acknowledged – remember, there is no anti-tree lobby. But a commentary last year in Nature, looking at Microsoft’s net zero investments, including “offsets” against emissions, found decidedly mixed results. The report included a reminder that current strategies to abate global warming by removing and storing carbon represent “a tiny proportion” of required cuts to GHG emissions.

In other words, the real heavy lifting on climate change is going to have to come from emitting less carbon through burning less fossil fuels and major investments in clean energy.

And the use of trees as carbon saviours is threatened by another worsening trend: Wildfires. “We’ve bought forest offsets that are now burning,” a Microsoft official said last year. Offset programs – a company planting a number of trees to theoretically be able to negate its carbon emissions – assume some fires over time. But fires have been so severe of late that a new study finds the buffer built into forest offsets in the United States, supposed to account for a century of fires, is already almost all burned up.

Trees store carbon; burning them releases it. Two of the worst fire years in British Columbia came in 2017 and 2018, with 26,000 square kilometres burned. That’s almost five times the size of PEI, and more than double the planned land for the 2BT program.

What’s more, according to B.C. data, those two fire years released 360 MT of GHGs – more than half of Canada’s total annual emissions. Add in last year’s fires – B.C.’s third-worst ever – and that’s at least another 100 MT of GHGs. And there will be sequels, because global warming is likely to make fires more common and more extreme.

Who doesn’t like trees? Planting two billion more trees in Canada, and a trillion worldwide, is a great idea. But don’t oversell it. It represents a small part in the hard work of slowing climate heating.

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