Last year, Sydney switched off many its lights as people joined in the first Earth Hour.
This year, cities and smaller settlements from scores of countries joined in. By all accounts it has been a great success. It's only a symbolic event, but awareness and willingness to change are the first steps.
Power generation represents one major source of carbon emissions (I've seen figures like 30%, but it would surely vary a lot), so cutting electricity usage by 5%, as was estimated in Sydney, is only token, but still symbolic.
Of course the challenge is to turn this growing public goodwill into effective action, something our politicians often seem to struggle with. There are so many who say how large the problem is, but the economic costs of not acting will be even greater - the Stern report and other sources quoted by the European Union estimate that the cost of not acting now on climate change will be about 5-20% of global GDP, whereas the cost of acting will be less than 1% of GDP.
"All" it will take is for all of us to be willing to vote for, and continue to support, politicians who will make the painful decisions that will cost us now, to save our children and grandchildren far more. Surely we can do that much?