When people talk about global warming, they usually refer to the number of tonnes of CO2 that are put into the air.
Since I can’t imagine what a tonne of CO2 gas looks like, I called Richard Ubbens, City Arborist with the City of Toronto, and asked him how many trees would it take to offset a tonne of CO2. During daylight hours, trees inhale CO2 and exhale oxygen. The carbon from the CO2 is converted into wood and leaves.
Ubbens said that in Toronto, a tree eight centimetres in diameter will absorb three kilograms of CO2 in a year. In other words 333 of these large saplings will remove a tonne of CO2 from the air in a year.
Putting it another way, that same 8-centimetre tree will remove the CO2 emitted by a car driven for 16 kilometres (assuming a mileage of 12.7 kilometres a litre).
So, if you put 20,000 kilometres on your car in a year, it would require 1,250 trees to absorb the CO2 you are putting out.
Ralph Torrie, of Torrie Smith Associates in Ottawa, offers a third perspective. Every time you drive 8,000 kilometres, your car will emit its weight in CO2 (assuming your car weighs 1.5 tonnes).
Now, think of how many cars there are on your block and how many trees would be needed to absorb their emissions. Then add the emissions from other combustion engines. Plus emissions from coal-fired generating plants. And oil and gas furnaces. And wood fires.
Another way of looking at the problem is through parts per million (ppm) of CO2 in the atmosphere. From the end of the last ice age, about 11,500 years ago, until the beginning of the Industrial Revolution, there were about 280 ppm in the atmosphere. We know that from testing ice bubbles trapped in glaciers. By 1958 there were 315 ppm.
In 1989, there were 360 ppm and, according to a new book by Wayne Grady (The Quiet Limit of the World: A Journey to the North Pole to Investigate Global Warming, Macfarlane Walter & Ross, Toronto, $29.95) the amount of CO2 in the atmosphere was increasing by 1.8 per cent a year. The rate of increase slowed during the recession, but it has since rebounded.
At some point above 400 ppm, says Grady, palm trees start growing on Baffin Island, sea levels rise 75-metres, and the world is drastically altered by new deserts, washed out croplands, inundated coastal cities, some rivers drying up and others expanding enormously. In other words, a new system of world weather at an inconceivable economic cost.
In the midst of all this bad news, however, there are pockets of hope. For example Toronto’s Cityhome is retrofitting 1,150 of its 7,500 housing units and, in the process, is reducing CO2 emissions by 5,500 tonnes a year.
That’s like taking about 1,467 cars off the road (assuming each travels about 20,000 kilometres a year). Or adding 1.7 million large saplings to Toronto’s forest.
Cityhome was created by the city in 1973 to build and rent affordable housing. The buildings being retrofitted have multiple units that were individually heated by electricity. Cityhome is switching to natural gas-fired, central, hot-water heating.
Richard Pearson, manager of maintenance and technical services for Cityhome, says calculations of CO2 reductions are based on lowering the demand on Ontario Hydro’s coal-fired generating plants.
What makes the retrofit especially attractive, he says, is that it’s going to save Cityhome money. The project will cost about $6 million, but will cut annual heating costs by $392,000.
The retrofit became possible when the city allocated Cityhome 10 per cent of the infrastructure grants received from the federal and provincial governments. As a result, Cityhome had to pay only $1.9 million for the retrofit, and that gives it a payback of just under five years.
It’s intelligent arrangements such as this that have allowed Toronto to cut its emissions since 1990 by 6 per cent, and to place first in the world (edging out Berlin by a whisker) in the battle to reduce global warming.