"during Earth Hour, any significant drop in electricity demand will entail a reduction in CO2 emissions during the hour, but it will be offset by the surge from firing up coal or gas stations to restore electricity supplies afterward."

Note: Offset. Not negated.

"And the cozy candles that many participants will light, which seem so natural and environmentally friendly, are still fossil fuels—and almost 100 times less efficient than incandescent light bulbs. Using one candle for each switched-off bulb cancels out even the theoretical CO2 reduction; using two candles means that you emit more CO2."

So if you use a candle and if you use more than one candle for every single light switched off, then you're emitting more CO2.