Daily Slice

On March 29, between the hours of 8 p.m. and 9 p.m., hundreds of thousands of people, and countless more businesses across Canada, shut off their lights as a symbolic gesture of concern over global warming. It was perhaps one of the most successful environmental awareness campaigns in recent history.

While organizers of the event correctly pointed out that Earth Hour was mostly about raising awareness, that didn't stop proud proclamations about drops in electricity demand during that hour. Some reports showed electricity demand was down 8.7 per cent for Toronto and 3.5 per cent in Vancouver.

The inconvenient truth, however, is that despite falling energy use, CO2 emissions actually rose during Earth Hour relative to comparable days in the past three years.

The flaw of Earth Hour's publicity campaign is that it fell into the fallacy of equating energy use with greenhouse gas emissions. The two are indeed related, but the relationship is more complex than the simple act of flicking the light switch would suggest.

Turning off a light bulb does not in itself reduce greenhouse gas emissions. Whether or not using electricity produces greenhouse gases depends on which kind of power plant is providing the electricity. If the power grid is predominantly being powered by nuclear fuel or hydroelectricity, there will be little greenhouse gas produced. However, if the power is coming from a coal-fired plant, there will be much more greenhouse gas produced.

In Ontario, power predominantly comes from a mix of nuclear, coal or hydroelectric power while in British Columbia and Quebec over 90 per cent of power comes from clean hydroelectricity. For every megawatt-hour of electricity produced from a coal power plant, a little over 1 tonne of CO2 is emitted.

When comparing power or electricity demand across days, it is important to control for things like weather, the amount of daylight, how many nuclear reactors are running and other possible factors. Using more than four years of hourly data, I estimated how much power would be expected to come from each source, and electricity consumption in each region of Ontario.

In Ontario, the total amount of electricity from coal and the subsequent CO2 emissions were higher during Earth Hour than on any last Saturday in March during the past four years. According to the Independent Electricity System Operator, 3,759 megawatt-hours of electricity were produced from coal in Ontario during Earth Hour, meaning approximately 4,000 tonnes of carbon dioxide were emitted from coal plants in Ontario during the hour.

Compared to the same hour of Saturdays in late spring with similar weather, nuclear operations, and so on, CO2 production was between 5 and 39 per cent higher during Earth Hour than in previous years. A comparison to only the previous Saturday would be misleading, because March 22, 2008, was much colder than the 29th, and weather is a major component in electricity demand. Regardless of what days are examined, the conclusion is that the mix of production sources, and not electricity consumption itself, has the most to do with emissions.
Furthermore, essentially all of the reductions in power production on March 29 came from hydroelectricity power production, and not from coal or natural gas. That is because when demand changes fairly quickly during the course of the day it is usually hydroelectric power that changes output to meet demand, while coal and nuclear remain unchanged.

Again, compared to what power production for all of Ontario normally would have been during Earth Hour, hydroelectricity production in Ontario was 24 per cent below what would be expected, while coal was up 18 per cent. Total power production was in fact above predicted for the entire night partly because power exports to the U.S. were high that night.

Likewise, in British Columbia or Quebec any reduction likely came from largely emission-free hydroelectric power. Even if power production did decline during Earth Hour, the fact remains that this drop did not come from power sources that contribute to global warming.

What really happened to electricity demand in Toronto and Ontario as whole on March 29, 2008 and during Earth Hour? Controlling for other factors, electricity consumption in Ontario as a whole and Toronto was down 5.6 per cent and 6 per cent respectively.

What do these numbers mean? When compared to the general fluctuations in electricity demand over any given day, Earth Hour was not meaningful in the statistical sense. So far this year, there were more than 120 different hours where electricity demand was lower than predicted, by a greater degree than during Earth Hour.

Earth Hour was successful as a symbolic campaign to raise awareness about tackling climate change, but the exercise encourages the mistaken belief that we must reduce electricity consumption in radical ways to cut greenhouse gases.

So what did we really accomplish?