For many of us, a birthday is a time to examine our successes and failures while we decide where we should go from here. Let's keep that in mind as we mark the 35th Earth Day. In fact, before you read any more, do yourself a favor. Have a drink from the tap. Take a deep breath. Maybe enjoy a healthy snack.

Doing any or all of these things should remind you of truths we too often ignore: On the whole, our water is much purer, our air much cleaner and our food much more plentiful than on the first Earth Day back in 1970.

You don't have to take my word for it. Bjorn Lomborg teaches statistics at the University of Aarhus in Denmark, and he's run the numbers. Lomborg, a self-described "old left-wing Greenpeace member," was surprised at his findings. In his 2001 book, "The Skeptical Environmentalist," he details the many ways in which our planet is becoming cleaner and safer.

For example, "the share of people in the developing countries with access to drinking water has increased from 30 percent in 1970 to 80 percent in 2000," he writes. That's an astounding jump, made in the space of just one generation.

Moreover, that increase occurred even as the planet's population grew by hundreds of millions of people. As Lomborg notes, "this means that more than three-quarters of a billion more people got access to clean drinking water and sanitation" during those 30 years.

Those people are also breathing more healthful air.

"We often assume that air pollution is a modern phenomenon, and that is has got worse and worse in recent years," Lomborg writes. In fact, though, "the air of the western world has not been as clean as it is now for a long time."

To prove that, Lomborg uses government statistics to calculate the cost of air pollution. After all, bad air is expensive -- it tends to make people sick, and it tends to shorten lives. Lomborg found that, since 1977, "average air pollution costs have dropped almost two-thirds, from $3,600 to $1,300" in 1999. That demonstrates that our air is getting better -- much better.

And Lomborg notes this is happening even as the American economy more than doubled and as the number of car miles traveled has doubled over the last 30 years. "There is also good reason to believe that the developing world, following our pattern, in the long run likewise will bring down its air pollution."

In addition, our cleaner planet is producing enough to feed billions of people.

"Globally the proportion of people starving has fallen from 35 percent to 18 percent and is expected to fall further, to 12 percent in 2010," Lomborg writes. "Since 1970, the proportion of starving people has fallen in all regions, and it is set to fall even further in all regions."

Since 1961, agricultural output has more than doubled, and it has more than tripled in developing countries. Thus it's cheaper than ever to eat. "The price of food fell by more than two-thirds from 1957 to early 2001," Lomborg notes.

Unfortunately, this sort of good news is rarely heard on Earth Day. The event began in 1970 with environmentalist Paul Ehrlich predicting that overcrowding, hunger and environmental destruction were imminent. He foresaw that in 2000, our American population would be just 22.6 million people and that we'd be scraping by on 2,400 calories a day. Not quite.

The facts, as Lomborg demonstrates again and again, are irrefutable. We're living longer, healthier lives, breathing better air, drinking cleaner water and eating better food than ever before.

A rising economic tide has truly lifted everyone's boat. "Only when we get sufficiently rich can we afford the relative luxury of caring about the environment," Lomborg notes. "Higher income in general is correlated with higher environmental sustainability."

Let's keep the economic and environmental boom going, and we can look forward to celebrating even more success on future Earth Days.

Ed Feulner is president of the Heritage Foundation.