Robin Collins and Bill Bhaneja (editors)
The Urban Tree Planting project is part of a larger climate crisis amelioration effort being investigated in a series of video discussions by the Canadian Pugwash Group. It focuses on responding to excess atmospheric carbon and adapting to climate change. Both carbon capture (sequestration) and eliminating production of additional carbon emissions are necessary to reach Canada’s Paris Agreement levels—cutting 45% of CO2 by 2030 with the goal of reaching net zero by 2050.
A ‘carbon sink’ is part of nature’s breathing machinery—the forests absorb carbon dioxide from the atmosphere and release oxygen. During forest fires or natural decay, this process is reversed. A forest then starts lowering its carbon sink capacity, emitting a large amount of stored carbon, sending it billowing into the air.
Some 40% of Canada’s land base is covered by trees, which is about 9% of the earth’s total canopy. Over 90% of Canada’s forests are owned by the public (crown land and provincially) and only about .02% of our forests have been deforested (cleared), and that removal rate has been declining.
One idea for responding to excess carbon in the atmosphere is to grow a trillion or more trees worldwide. “Assisted migration”, a related proposal, would deliberately move select tree species to locations that may climatically suit them in the future. Places to plant more trees however are not unlimited. Successful forestation requires programs deploying tried and true practices (site preparation, —- tree planting, seeding, tending, and forest management operations.)
In stark competition with remediation efforts such as this, the International Energy Association (IEA) says that in the last decade installed coal-fired power generation doubled because of population growth and industrialization in the developing world. And to put that more graphically: Coal accounts for 1/4 of global CO2 emissions with China currently building 100 new coal plants.
While China is the worst culprit by far in terms of total national carbon production (almost 9,900 megatons, compared to 4,745 for the USA), Canada (at ~670) is not off the hook. In fact, our per capita carbon load is twice that of China’s. A study of Canadian Greenhouse emissions by source shows (2017) the oil and gas and transportation sectors are the largest greenhouse gas (GHG) emitters. Together, they accounted for about half of our total.
Canada has committed itself to zero GHG emissions by 2050. That makes it urgent to work on all fronts to bring emissions down through reducing carbon from energy and non-energy sources, as well as seeking effective management of Canadian forests to increase their carbon storing capacities.
The Canadian government has a plan to plant two billion trees (a 40% annual increase over and above current planting rates) over ten years. Currently Canada plants an estimated 137 million trees a year out of a total of 1.9 billion planted globally. According to the Canadian Forest Service estimate, those additional trees here could cut 12 megatons (Mt) of carbon dioxide annually—“the equivalent of taking over 2 million gasoline-powered cars off the road each year.” Reaching net zero carbon by 2050 means eliminating ~670 Mt in under thirty years (that’s approximately 37 irreversible Mt per year from 2022 to 2030.)
The Canadian Pugwash Group and Project Save the World, which is affiliated with Peace Magazine, are looking at four core projects, including planting urban, suburban, and accessible rural-road trees, and ensuring that they are maintained by municipalities and their citizens. The scale of the greenhouse gases (GHG) problem, however, requires a global effort. Our project should be seen in that light as a very modest but useful contribution.
PROTECT GRASSLAND AND PEAT
If direct carbon capture is the priority, then according to a 2021 paper by Ronnie Drever, Susan Cook-Patten et al., “Natural Climate Solutions for Canada”, avoiding conversion of grassland and peatland disturbance, adding cover crops, together with improved forest management should be our focus in Canada. The authors looked at 24 pathways and costed them for likely results by 2030 and 2050. Preventing conversion of grassland to cropland represents the “single largest opportunity for Canada,” primarily though preservation of soil carbon. The scale of its impact is explained by the “large net area of planted and native grassland and pastures.”
The side benefits of trees in populated areas, beyond a marginal expectation for sequestration, are likely the primary contribution of urban tree planting programs.
Aesthetics, fruit-growing and mental health benefits aside, urban woods are good for removing pollutants and smog, and a few well-placed trees can significantly reduce the power levels required for air conditioning (by way of shading), heating (by wind breaking) and temperature insulation (dead-spacing around buildings from shrubs and bushes).
Tree planting is complex and no panacea. As retired tree scientist David Price points out, it can involve protection of old-growth forests “where they have a decent chance of survival”, targeted replacement of those stands that fail but before they rot, and a particular “focus on maximizing the [carbon] sink value of the harvested material.” This means using carbon-rich tree lumber for building construction and furniture manufacturing while minimizing waste at cull and tree-farm sites. These are not notable outputs of urban tree planting efforts, therefore.
There is an urgent need to raise public awareness of adverse impacts of climate change and how urban forests might play a role in the greening of neighbourhoods. Better coordination between municipal, federal, and provincial governments will be essential to streamline and help stimulate and fund effective measures as quickly as possible.