Photo by Brad Smith.

The forecast calls for a “Twitterstorm” Monday, thanks to a couple dozen environmental activist groups, including, Greenpeace International, and the Natural Resources Defense Council.

A “Twitterstorm” isn’t something out of Alfred Hitchcock’s The Birds; it’s a global campaign to raise a ruckus on Twitter by deliberately spreading a message — in this case, the call to end fossil fuel subsidies, or #endfossilfuelsubsidies, as the hashtag call will go out.

Organizers are building a smart network of influential Twitter users to seed their storm. On the eve of the Rio+20 Earth Summit, they’re aiming to break the record for most tweets of a single hashtag in a 24-hour period. As 350’s Jamie Henn writes:

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Justin Bieber currently holds the world record with 322,224, over 223 tweets a minute. Organizers are confident that even if they can’t beat the Biebs they’ll be able to generate enough traffic to dominate the online airwaves during the G20 and in the lead up to Rio+20.

Now, I can already hear the skeptic complaint: How can competing with Justin Bieber possibly be a good use of activist time and energy? Can Facebook and Twitter really spark meaningful political change? Using social media as a platform for activism risks opening yet another round of the debate on this topic that has sputtered for most of the past decade, and that recently peaked with the Arab Spring.

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When you look closely at what these groups are doing with Twitter, however, you see very quickly that there’s nothing simplistic or utopian about it:

Twitter connects world leaders, opinion makers, and regular activists all on one network. If we work together and aim high, we can make sure the right people see and hear this grassroots uprising. We don’t believe the internet will save the world — we believe that people will. Now let’s use this digital bullhorn to make some noise.

It’s not as though thinks, “If you tweet it, you’re done.” Remember, this is the same outfit that organized one of the largest civil disobedience campaigns in U.S. history, stopped the Keystone XL pipeline in its tracks, and circled the White House with a human chain of protest. (Full disclosure: founder Bill McKibben is a longtime member of Grist’s board, and also a friend.)

These people understand that online organizing is a means to an end, not a magic wand. But they also understand that Facebook and Twitter are highly effective in their own way both at reaching people, particularly younger people, and at leveraging media attention.

So I’ll be out there on the Twitter streets Monday, doing my bit for the End Fossil Fuel Subsidies campaign. See you there!