I am spending Earth Day 2009 in Paris, and what a difference a few years makes.

I first spent Earth Day in Paris in 2002, just after moving here to open BSR’s European office. Seven years ago, the U.S. administration’s climate policy basically amounted to saying no to Kyoto. Carla Bruni was an former model finding great success with her first CD. And China’s government was saying—and doing—little to put its economic growth engine on a sustainable path.

As I get ready to address the fourth B4E (Business for the Environment Global Summit), organized by the UN, there are encouraging signs of change.

The U.S. government has rejoined the global debate on what comes after Kyoto, with the likelihood of government action increasing in the wake of last week’s ruling by the U.S. Environmental Protection Agency that it can regulate greenhouse gases. Carla Bruni is now Carla Bruni-Sarkozy, the French First Lady, and will be a co-host of the Champions of the Earth awards dinner at B4E Wednesday night. And China is moving on multiple fronts, using part of its stimulus package to invest in a more environmentally sound infrastructure—not to mention the reported ambition to be the world’s leader in zero or low-emissions vehicles.

Around the world, Earth Day is being marked by gatherings of the green great and good. In China, the China Entrepreneur Club is holding its second annual meeting focused on environmental issues. Fortune’s Brainstorm: GREEN presents two Bills (Clinton and Ford) as it meets in California to grapple with opportunities and impacts of environmental issues on business and the economy. And the U.S. Congress will video link up with B4E's closing session, where business leaders, U.S. Senators John Kerry and Barbara Boxer, the head of the UN Global Compact Georg Kell, and I will discuss prospects for a global deal to manage emissions.

B4E will also showcase innovative technology, consumer engagement, and new business models to reduce the impact of the economic activity we need to pull out of the deep recession. Companies like BT, Alcatel-Lucent, Procter & Gamble, and HP (all BSR members) will join thinkers like John Elkington, Pavan Sukhdev, and Janine Benyus, and public figures including UN Environment Programme Chief Achim Steiner in what should be stimulating debate.

All this activity should not, however, be confused with achievement. There remains considerable evidence that climate change is exceeding the Intergovernmental Panel on Climate Change’s estimates. There are also signs that the recession has dampened public appetite for the changes needed to re-orient our markets to a lower-carbon model.

So while we can say with confidence that April 22, 2009 is considerably more active than April 22, 2002, it remains clear that we have lots of work to do to make the other 364 days a year more impactful.

I’ll be posting from B4E over the next few days, and also report from a BSR member company meeting on water, hosted by Sodexo, here in Paris.