Because I believe that environmental organizations have ducked the immigration-population issue too long, I am running for the board of directors of the Sierra Club. I am not part of a slate; I represent only myself and the issues I care deeply about.

One of the most important challenges of public policy is to recognize when an old world is obsolete and a new one in place. If I could have left anything carved on the state capitol in Denver after my 12 years as governor, it would be something like this: Beware of solutions appropriate to the past but disastrous to the future.

A pressing environmental question faces America: What is our demographic destiny? How big a country do we want to become? How many people can live satisfied lives within our borders? These issues will not go away and will only grow more complicated. Environmental organizations must add population and immigration to their list of issues and concerns. It is environmental mal-practice not to, and the Sierra Club has never faced up to this issue.

Our natural American birth rate will lead to a stable population around 2050. But with the current level of immigration our population will be approximately 500 million on its way to a billion. I have yet to meet an American who wants one billion neighbors. What possible public policy advantage would there be to an America of 500 million? Do we lack for people? Do we have too much open space, parkland and recreation? What will 500 million Americans mean to our environment?

We have a chance to stabilize America’s population or we can double it and double it again: The key driver is immigration. If we continue with our present policy of mass immigration (America takes twice as many immigrants as the rest of the world combined) we will continue to grow and grow and grow. The geometry is relentless.

The first census, 1790, found 4 million Europeans in America. In 1990, 200 years later, we had approximately 260 million Americans. That means we had six doublings of the original European population. (4,8,16,32,64,128, 256). Please note that two more doublings (we have already had five in our short 200 years) gives us over a billion people sharing America. Can you imagine an America of one billion people that you would want to leave to your grandchildren?

Of course, immigration has been good for America, and yes, we are all immigrants. But is that the extent and depth of the argument? Population compounds every environmental issue we face. Where will we draw inspiration when America is paved, polluted and overpopulated?

There are approximately 5 billion people in the world who live below the American poverty level, and polls show literally billions of them want to come to America. Immigration is no longer a solution to the problems of the world. The best gift this country could give to the world would be to develop a sustainable, equitable, environmentally benign nation that could serve as an example of sustainability to the world. America before immigration "reform" averaged approximately 250,000 immigrants a year. Returning to those historic numbers would take a great step toward leaving our children a sustainable America.

My candidacy, and the candidacy of some other people -- whom I have never met, never talked to, and never heard of -- has caused consternation among some Sierra Club old-timers. For the record, I am not an animal-rights activist but a hunter and fisherman who goes fishing in Alaska on a regular basis. To those who charge that anyone interested in immigration limits must be a racist, let me say that I organized the NAACP at the University of California and served as its first vice president. My first job out of law school was for the Colorado Anti-Discrimination Commission, and I have received numerous brotherhood awards. When we had little money, we paid for my wife to go to Selma, Ala., to take part in a march for civil rights to show our support.

It is past time for us to move from name-calling and toward sustainability, and that means addressing the twin questions of consumption and population. And it is time that the Sierra Club confronted these issues.

Richard D. Lamm is a contributor to Writers on the Range, a service of High Country News (hcn.org). He was the Democratic governor of Colorado for 12 years and is now director of the Center for Public Policy and Contemporary Issues at the University of Denver.