Some holidays, such as Veteran's Day and Memorial Day, are a time for reflection. Others, like July 4th and Thanksgiving, are a time for celebration. This year, we ought to add Earth Day to the list of days to celebrate -- but only if we rename it Growth Day.

As in "economic growth." Believe it or not, nothing's better at cleaning up the environment and keeping it clean.

Many on the radical left dispute this, of course. Indeed, they fault the industrialized nations for allegedly endangering our planet. Yet the opposite is true. That's why the major environmentalist movements are all based in Western countries, where people are wealthy enough to be concerned about the world around them -- and have the wherewithal to protect it. Our own country provides a perfect example.

Almost all the settlers who arrived here hundreds of years ago were subsistence farmers. They cleared hundreds of millions of acres of trees. According to the Pennsylvania Department of Conservation and Natural Resources, "A single household could consume 20 to 40 cords of wood annually." Economic growth changed all that.

First, we progressed from wood to coal. This allowed us to begin replacing millions of trees. Plus, coal was more efficient and easier to transport than wood, so it took less to produce more energy.

But even coal is fairly dirty, and of course digging it out of the ground affects the environment. So the country moved on to natural gas. It was safer, easier to get and cleaner burning.

The economic growth made possible in part by these new fuel sources allowed people to leave their farms and make a living in manufacturing and service industries. That translated into higher incomes. Today, the United States has a per capita income of $37,600. Our crops literally feed the world, even though fewer than three out of every 100 Americans are farmers.

If we want the rest of the world to be as clean as we are, we should shun the guerrilla tactics of the radical environmental activists. What's needed are the free-market ideas that have fueled our economic growth and led to prosperity. Studies show that air and water pollution start plummeting once per capita income in a country reaches more than $3,500 a year.

In the meantime, of course, Americans are still giving environmentalists plenty to complain about, because we drive gasoline-powered cars. But with technology improving our vehicles all the time, they're not really the disaster some claim.

Our environment has improved markedly over the last three decades, even as the population rose 30 percent, the number of licensed vehicles jumped 87 percent, and vehicle miles traveled increased more than 125 percent.

Consider, too, the jobs generated by cars. They include everything from high-paying manufacturing, repair and sales jobs to entry-level gas station attendant positions. Plus, by allowing us to get around quickly and easily, cars enabled people to move out of crowded cities into suburbs, where they're in closer contact with nature.

And let's not forget what autos replaced: horses. Back in the days when horse-drawn carriages were the main means of transportation, our streets were filled with manure. This waste was itself a dangerous form of pollution.

Horses required tons of hay, which meant thousands of acres of farmland were needed to grow food for animal use, not human consumption. The invention of the car actually helped clean our streets, clear our air and free land for more productive use.

People are more likely to be concerned about the environment when they have the time to appreciate nature. That's a luxury still not enjoyed in poor nations, where too many people eke out a living through subsistence farming.

The best way to clean up our planet and keep it clean is to generate worldwide economic growth and lift everyone to the same level of prosperity Americans take for granted. Let's get started on April 22, the new international Growth Day.