This week we've been looking at the trees around us. They raise many questions, which we'll tackle in bite-sized chunks over the coming weeks. Today we're asking, how many trees would it take for Australia to offset all our emissions? Let's go.
How much carbon do trees absorb?
As trees grow, they absorb carbon dioxide from the air. That's why they're called 'carbon sinks'. The amount they absorb is complicated and to be honest, it's above my paygrade. But we did find some rules of thumb as a guide:*
How many trees would we need to offset our carbon emissions?
Australia created 465.9 million tonnes of CO2e* emissions in the last year. If we apply the midway point of the Chief Scientist's estimate (4.6 tonnes / year), we would need roughly 102 million ha of forest to absorb it all. That means forest with continuous canopies across an area the size of Victoria and NSW combined.
How many trees do we have?
Australia's most recent State of the Forests Report says we have 40.8 million ha of native forest with at least 50% cover.* That leaves a forest shortfall of about 60 million ha. According to Global Forest Watch, our sum of 'tree cover loss' for every year between 2001 and 2022 is 8.9 million ha. (If you think that sounds low, please read the footnotes!)* The vast majority of that was from fires. The chart below shows hectares of annual 'tree cover loss' by driver. The charts beneath that show the same data on separate axes, to make the smaller categories easier to read. Source: Global Forest Watch.
Circle of life as a carbon atom
Of course, this simplistic back-of-the-envelope calculation fails to account for numerous complexities in the carbon cycle. Longstanding forests are more valuable than new growth as carbon sinks. If trees burn or are cut down, the carbon dioxide they were storing is released. According to estimates from the Copernicus Atmospheric Monitoring Service, Canada's devastating wildfires this year have led to 410 million tonnes of carbon emissions. For context, the country's total annual emissions in 2019 were 733 million tonnes. This eloquent explainer lays out the cyclical journey of a single carbon atom as nature intended: moving from a blade of grass, into the body of an animal, released into the air after the animal dies, and absorbed back into a tree. The basic rhythm of the natural carbon cycle hasn't changed. What has changed, is the amount of CO2 in the air, as humans dig up geological carbon that was locked underground in the form of oil, coal and gas, and burn it.
Other questions
In future Tree Issues, we want to examine: • Arguments for and against tree-planting as a climate solution.• How reliant on trees is Australia's path to net zero?• How many trees will offset your own vehicle emissions? If you want to add to this list, please let us know.