During the annual ritual of Earth Hour:
...around one billion people are expected to switch off their lights for one hour as a political statement against climate change and fossil fuels, and in support of carbon cuts and renewable energy.
Bjorn Lomborg thinks the ritual is a feel-good exercise for the rich that does nothing meaningful to improve the planet. Whether he is right to make this judgement is probably too much a matter of opinion to be asked as a question here. But during his argument he makes the very specific claim (I've highlighted the specific part of the claim worth addressing):
In fact, a small decline in electricity consumption does not actually translate into less energy being pumped into the grid, and therefore does not reduce emissions. While any significant drop in electricity demand means a temporary reduction in CO2 emissions, this is partly offset by the surge from firing up coal or gas stations to restore electricity supplies afterward...
Those ‘environmentally friendly’ candles that many participants light? They are a fossil fuel — and burn almost 100 times less efficiently than incandescent light bulbs. (That’s why you won’t ever find a modern hospital using them instead of electricity). Using one candle for each switched-off bulb actually cancels out even the theoretical CO2 reduction; using two candles means that you emit more CO2.
Is he right that lighting one or more candles per bulb turned off cancels out any possible gain from turning off your lights?