The world's population has grown more in the past 50 years than it has grown in the total history of humankind. Yesterday, the United Nations marked this phenomenon by declaring that the world's population has surpassed 6 billion people. And that number is rapidly increasing.

Every 12 to 13 years, another billion people are added to the population, almost all of them in developing countries. More than 1 billion people are between 15 and 24 years of age, and they belong to the largest generation ever to grace the Earth. They are the largest group entering reproductive age ever, and the choices they make about family planning and contraception will have enormous impact not only on population but also on every aspect of the environment affected by population. The United Nations has projected that the Earth's population could be 7 billion, 9 billion or 11 billion in 50 years, depending on the decisions made now by this generation of young people. There are another 2 billion young people in the generation right behind them.

We don't have a lot of room for growth. The world's water supply remains constant, but per-capita water consumption is rising twice as fast as world population. At least 300 million people now live in areas that have severe water shortages. The world's forests have shrunk from 11.4 to 7.3 square kilometers per 1,000 people since 1970. The loss is concentrated in developing countries, which are exporting forest products to meet the demand for wood and paper in the industrialized world. A 1998 U.N. report on development found that over the past 50 years, 12 percent of the planet's soil has been severely degraded. That totals up to nearly 2 billion hectares, the combined size of China and India. Water shortages, soil depletion and destruction of forests all lead to famines, instability and wars.

Fertility rates are declining, thanks to the international family planning programs. The United Nations has estimated that the percentage of married couples using contraception in developing countries has risen from 10 percent in the '60s to 55 percent last year, and the fertility rate has dropped from six births per woman to three. Family planning programs are providing contraceptive choices and are reaching many more people in rural areas. They are providing counseling and instruction, and often are the only source of women's health care.

But population is still growing by 78 million a year. A Population Reports study by the Johns Hopkins University School of Public Health in 1996 found that more than 100 million married women of reproductive age in developing countries want to avoid or postpone childbearing but are not using contraception.

The need to provide reproductive health care was a centerpiece of the U.N. International Conference on Population and Development in Cairo in 1994. Representatives of 174 countries agreed to improve reproductive health care. They agreed to contribute $17 billion each year, with donor countries providing one-third of that and developing countries providing two-thirds. Few countries have lived up to their commitment. The U.N. Population Fund estimates that failure to meet the Cairo funding goals has resulted in 42 million unintended pregnancies, 17 million induced abortions and 99,000 maternal deaths each year.

The Cairo consensus was endorsed again by these countries this year, with a call to the developing countries to take more effective steps to improve reproductive health care and to cut the unmet need for family planning in half by 2005. At the same time, they urged donor countries to reverse the trend of declining funding for reproductive health care.

That's where the United States comes in and where the world has been paying a stiff price for having a bunch of anti-abortion Republican knuckleheads running Congress. In 1985, the United States gave the U.N. Population Fund $45 million. That was cut back to $25 million and then eliminated in protest of China's one-child policy and coerced abortions. That $25 million was restored this summer by Congress, one of the few victories in recent years for family planning advocates. But it's still a far cry from $45 million 15 years ago. By contrast, Japan now contributes $59 million.

Donor countries had pledged to spend $5.7 billion a year on family planning programs. They have given $1.4 billion. Despite the funding shortfall, family planning programs have been a success in many countries. So have programs that empower girls and women to take control of their reproductive destinies and that encourage girls' education, which is directly linked to later marriage and childbirth. Iran, a Muslim theocracy, has had one of the most successful programs, offering free contraception to married couples. Contraception use has gone from 26 percent in 1979 to 75 percent today.

Family planning programs work. They reduce the number of abortions by reducing unwanted pregnancies. Hacking away at these programs is one of the most villainous legacies of the Republicans in Congress and one that has received the least amount of attention. But access to family planning programs in the most remote countries in the world will ultimately affect all of us and have a tremendous impact on our ability to shepherd the planet. All 6 billion of us are in this together, as never before.