- Carbon capture and storage (also called sequestration). This is something that actually removes GHGs from the atmosphere. An obvious example is planting trees. Plant enough of them, and you can make up for GHGs that are difficult or impossible to eliminate. You need a lot of forest to achieve a meaningful impact, though - about 11 hectares (28 acres) per tCO2e. After implementing our Pathway to Net Zero Carbon, Guelph's 2050 emissions are expected to be 93,000 tCO2e (down from 1,032,000 tCO2e in 2016). To offset all that you'd need to add a million hectares, an area about twice the size of Prince Edward Island. (Based on Natural Resources Canada reporting, Canada's 226 million hectares of managed forests were a net sink of 20 million tCO2e in 2016. There's a pretty big "yes, but" behind that number though - if you also consider in the impact of wildfires and insect infestations, our forests have actually been a net source of emissions.)
- Clean electricity purchase. Our Pathway to Net Zero Carbon assumes that the provincial electricity grid will still be generating some electricity from natural gas plants by the target year of 2050. That generation is expected to be responsible for just about all of our GHG emissions, so one way to balance that would be to make sure that the only electricity that we import into the city is from renewable sources like hydroelectricity, wind, and solar photovoltaics. This is done using a power purchase agreement.
- Carbon offsets. Also called carbon credits, these are an accounting artifact - they let you buy the carbon-reducing attributes of a project that otherwise has nothing to do with you. As an example, I travelled overseas by air back in March and offset the resulting carbon emissions by purchasing credits from Gold Standard. The money I provided helped to fund a project like low-smoke cook stoves in Darfur, a wind power project in Rajasthan, or planting biodiverse forests in Panama. The going rate for these projects is between $13 and $25 per tCO2e. At that price, offsetting our 2050 city-wide emissions will cost between $1.2 and $2.3 million.
Like your tax return, you can think of it as an accounting ledger - two columns. (See illustration on the right.)
On one side we have activities that emit the airborne pollution that is unhealthy to breathe and causes climate change - like emissions from tailpipes or chimneys.
On the other side of the ledger we have activities that pull those bad things out of the atmosphere - like when productive forests use carbon dioxide to grow, and the trees store that carbon dioxide in their bodies.
Net zero means we make changes on both sides of the ledger. We reduce what goes out - by biking more often, using more renewables and consuming less energy overall. And at the same time we increase what we’re pulling in - by maintaining healthy green space or using carbon capture and storage technologies.
Summing up, the idea is to reduce as much as you can, then offset what you can't. That gets you to net zero carbon.