It is easy to scoff when experts’ predictions fail. But suppose these experts also identified important problems that we have not yet solved – should we still scoff? The writings of biologist Paul Ehrlich provide a fascinating illustration.

Ehrlich believed that the “cancer” of rapid population growth threatened all humanity. In his 1968 book, The Population Bomb, he raised the possibility that mankind might “breed itself into oblivion.” Moreover, predicting that “in the 1970s the world will undergo famines – hundreds of millions of people are going to starve to death,” he claimed that “nothing can prevent a substantial increase in the world death rate.” Many other scientists and political leaders endorsed such predictions.

These predictions all proved faulty. Humanity has not bred itself into oblivion; instead, birthrates have fallen in every part of the world. Even in the region with the world’s highest birthrate, sub-Saharan Africa, the rate fell from 48 per thousand people in 1965 to 41 in 2005. Rather than the “substantial increases” in the world’s death rate that Ehrlich predicted, we have witnessed declining death rates.

The world’s population growth rate is actually lower than it was in the 1960s. Indeed, in Japan and several European countries population is either declining or would be declining if immigration were not providing a boost. The population decreases are due partly to rapidly declining birthrates.

Famines have become less, rather than more, devastating. Food supplies have increased much more rapidly than numbers of people. Since 1961, world population has grown 112 percent, while production of food grains has risen 164 percent through advances in agricultural technology, including the introduction of better farm equipment, increased use of fertilizers, and development of more productive seed varieties. Remarkably, meat production has grown almost 700 percent.

Because food production has risen so rapidly, world food prices in real terms are no higher than they were in the 1960s.

Yet, despite Ehrlich’s mistaken predictions, we should not dismiss his views wholesale. His analysis identified real dangers, which we still face. These dangers deserve our close attention.

First, it is unclear whether food production can continue to keep pace with population. While the population growth rate is slowing, world population continues to rise: the United Nations expects an increase from 6.5 billion in 2005 to about 9.2 billion in 2050.

Ehrlich noted that as the earth’s population grows, we will need greater and greater quantities of food. Farmers will cultivate land higher up on mountainsides, he said, and will intensify their farming of land already in use. This may cause additional soil erosion and diminished soil fertility, degrading our natural environment.

True, diminished soil fertility may not result in lower food production: new advances in agricultural technology may boost future farm output, despite lower soil fertility. Still, the pace of advance in agricultural technology may slacken. And of course the fact that food production recently has grown more rapidly than population does not prove that it will in the future.

If the world’s living standards continue to improve, people will demand higher quality food, intensifying the pressure on agricultural resources. Boosting meat production, for example, requires much greater production of food grains for animals – it takes 8 pounds of food grains to produce a pound of beef. Rapidly rising grain output will further damage soil fertility.

Greater numbers of people will cause other types of environmental damage. Additional people create additional demand for electricity and for motorized transportation of all sorts, leading in turn to greater consumption of coal, oil and other fossil fuels. The resulting rise in carbon dioxide emissions will add to global warming. Greater populations also will likely cause further destruction of forests, diminishing their ability to absorb carbon dioxide.

Still, the growth in sheer numbers of people is a small part of humans’ overall impact on global warming. Highly developed countries emit huge quantities of carbon dioxide per person. U.S. carbon dioxide emissions per person are 25 times greater than Nigeria’s, so it would require 25 additional Nigerians to do as much carbon dioxide damage as one additional American. While Ehrlich did insist that highly developed countries should decrease their carbon dioxide emissions per person, he over-emphasized the pollution caused by sheer additional numbers of people.

The growth in the world’s population has implications for Maine. Suppose that further soil erosion does great harm to world food production, causing mass starvation. Americans – including Mainers – almost surely would respond by sending food abroad. Further, rapid global warming will affect people everywhere: If ocean levels rise in the Netherlands and Bangladesh, flooding millions out of their homes, they also will rise in Portland Harbor and Penobscot Bay.

Ehrlich and others cried “wolf” in the 1960s, and there was no wolf. So it would be perfectly fair for us to scoff at their alarmist predictions. Still, these people did identify some real dangers of rapid population growth -greater risk of future mass starvation and more rapid environmental degradation. These dangers are still very much with us.

Edwin Dean, an economist and seasonal resident of Vinalhaven, writes monthly about economic issues.