I'm a life-long conservationist. On the first Earth Day I was in the fourth grade. With the help of my mom I crafted a letter to President Nixon urging increased protection for our nation's air and water.

In college I studied geology. In the years before graduate school, I worked as a teacher and later spent many years in the wilderness areas of North America as an instructor with the National Outdoor Leadership School. When I entered graduate school at the University of Montana School of Forestry I had two children and was serious about my career and the environment.

Though I work for a foundation with "economics" in its name, I've had only one course in the subject. Like many of the federal judges and law professors who attend our seminars, I remember difficult math and lots of graphs with crossing lines. It's not an accident my master's is in forestry.

But now I write and speak on using economics to achieve environmental goals. And I believe that one can't begin to understand (let alone develop constructive solutions to) environmental problems without knowing a few basic economic concepts. Here are the three I find especially helpful.

First, individuals make decisions based on incentives and information. When they are insulated from the costs of their actions, or denied access to the benefits, problems follow like mud after rain.

Consider voting. A majority of American voters are ignorant of national politics. Most can't even name their congressional representatives. Here's why: Even though the outcome of an election for a U.S. senator or representative is very important, one individual vote is rarely, if ever, decisive. Since voters never bear the full costs or reap the full benefits of their vote, spending time following particular issues or a candidate is simply not worth the effort.

But when the same individual bears the full costs of her actions, her behavior is much different. For example: Many of my Green friends consider SUVs bad; they contribute to global warming and endanger those in smaller, lighter vehicles. But SUV owners intuitively understand the "lug nut rule," i.e., the more lug nuts on a wheel the greater the mass of the vehicle. All things equal, in accidents, more mass equals more safety.

Suburbans are safer than Subarus, the two most popular cars in Montana. A Geo Metro gets over 40 highway miles per gallon. Despite the environmental benefits, none of my environmentalist friends own a Metro, not even those without kids. When buying a vehicle they have stronger incentives to consider: their safety, convenience, and comfort, over statistical impacts of CO2 on unknown parties in the distant future.

The second key point: Decisions are made at the margins. We rarely face all-or-nothing choices. Marginal decision making requires looking at the detail - the additional costs and benefits from any particular action. Here's an example borrowed from the late theologian and economist Paul Heyne.

The love of your life calls at 8 p.m. the night before your big chemistry test. He wants to go to a movie. You tell him you need to study. He asks, "Is chemistry more important than me?" Your response, "Only at the margin." You've decided that an additional few hours with your chemistry text is more important than the movie with him tonight.

The same process applies to environmental protection. A dollar spent to improve air quality is one less dollar available to protect endangered species.

The third point is the social analogue to the law of gravity. The law of demand states: When the price of a good rises, the quantity demanded falls. One doesn't raise the asking price of a house that's been languishing on the market for months. The number of potential buyers varies inversely with the price.

This law of demand explains our increasing consumption of petroleum. Domestic new-car fuel economy has increased 114 percent since 1974 and light truck fuel economy has increased 56 percent. But fuel consumption has not declined and, in fact, people are driving twice as many miles. Why is this true? It's simple. As efficiency goes up it costs less to drive. Until the burden of driving rises high enough to reduce demand, consumption will continue to grow.

There are, of course, non-economic aspects to environmental problems. Politics, law, and especially ethics are important. But we'll make more progress on environmental issues when we have an understanding of basic economics.

Until recently, I didn't understand the contributions of economics to ecology. It's no accident that the Greek word "oikos" is the root of both.