In 1970, millions of people all across the country participated in events attempting to raise awareness about the environment. That first Earth Day birthed the modern-day environmental movement. It is still considered by many as the largest grass-roots event in American history, and young people are given a lot of credit for making it happen. In fact, Earth Week was created by a committee of mostly students from the University of Pennsylvania.

On Thursday, Earth Day will turn 40, and it is experiencing somewhat of a midlife crisis. Over the years, environmentalism has gone from the fringe of political concerns into the mainstream, but environmental and ecological catastrophe looms dangerously close. We find ourselves in an even more precarious situation now than then. The overwhelming scientific consensus is clear, and it is simply this: If we further delay bold action on climate change, our options won’t be whether we can avert it, but rather how to deal with and manage climate catastrophe.

In light of the global economic crisis we are beginning to emerge from, environmental concerns have at times taken a back seat. So on this year’s Earth Day we are confronted with two immense, yet inextricably linked, problems: Resurrecting the economy and solving climate change.

And nothing short of a great transition, a transformation of our economy, and our relationship to the environment is needed to address these challenges.

The United States is still in a deep economic hole. Unemployment, underemployment, and long-term unemployment are at levels not seen since the Great Depression. For many the economic recession that began in 2007 only served to weaken a fragile sense of economic security. The remnants of this economic collapse will be felt long after the country’s Gross Domestic Product gradually picks up.

But throughout the world, we see a slightly different picture — economy recovery fueled by such major developing countries as China and India.

These countries are on a path on which more and more people will consume goods and resources the way citizens in developed countries do. Using more cars and building more homes, living in über-urban metropolises. Imagine if the millions of people transitioning from poverty to the middle class in China, India, and Brazil mimicked American consumer habits. Maybe more iPods and Nikes, but more coal plants. This scenario is simply unsustainable.

Current human activity is placing irreparable stress on the Earth; it would be hard to fathom the consequences if these processes were to be multiplied. But millions of people are still living under harsh poverty and billions more seek better fortunes. And it would be unfair and immoral to deny them this possibility. Western countries have developed and polluted for centuries; we could never truly pay and account for our ecological debt.

Our challenge on this Earth Day is to envision a world in which we can meet the needs of the present without compromising the ability of future generations to do the same. Or in other words: a more sustainable economy, environment, and society.

On this Earth Day, as we participate in a cleanup or make an extra effort to recycle, we should also think about how we can create clean energy jobs for the unemployed. Or how we might help deliver electricity and clean water to people living without it in sub-Saharan Africa. It’s a vision for a society and a world where we can solve environmental and economic challenges sufficiently, while learning to think of ourselves as more of a community.

Forty years ago there was no environmental movement. Yet young people concerned about what they didn’t see around them and concerned about the lack of urgency among elected officials with regard to conserving the environment created a movement. And a broader cultural shift toward sustainability, towards sustainable development is what we need today.