This is an invitation to help start a movement--to take one spring day and use it to reshape the future. Those of us who know that climate change is the greatest threat civilization now faces have science on our side; we have economists and policy specialists, courageous mayors and governors, engineers with cool new technology.

But we don't have a movement—the largest rally yet held in the U.S. about global warming drew a thousand people. If we're going to make the kind of change we need in the short time left us, we need something that looks like the civil rights movement, and we need it now. Changing light bulbs just isn't enough.

So pitch in. A few of us are trying to organize a nationwide day of hundreds and hundreds of rallies on April 14. We hope to have gatherings in every state, and in many of America's most iconic places: on the levees in New Orleans, on top of the melting glaciers on Mt. Rainier, even underwater on the endangered coral reefs off Key West. ...