Stewart-rally-crowd-photoThe Census Bureau has come up with a new population clock on its website that provides access to new population estimates. The population clock shows the U.S. population currently growing by one person every 13 seconds. That is the net growth after subtracting deaths and residents moving out of the country.

How many new residents is that a year? It works out to be about 2.43 million population increase a year.

So, how much of that increase is due to immigration? The population clock shows that net immigration causes the population to grow by one person every 29 seconds. That works out to 1.09 million persons per year. And, if the rate of increase from immigration is compared to the overall increase, immigration accounts for 45 percent of the increase.

But that share is misleading. Immigration accounts or a much larger share: more than three quarters of the increase.

How is that? It is because the immigrants’ contribution to population growth also comes from the children born to them after they arrive. The immigrant population has a higher rate of births than the general population because they are more likely to be of child-bearing age and also because the immigrant population in general comes from regions where larger families are the norm.

Why should you care about the rate of population increase? There are many reasons such as traffic congestion and urban sprawl. But the most important reason is because there are finite resources that we extract from the earth. Some of those are energy resources (fossil fuels). Others are precious metals. Some are food resources, and probably the most critical are water resources that we pump out of aquifers. All of those extractions tend to be proportional to population size. So, faster growth means faster approaching scarcity. And the fact that the resources are finite means that they will not last forever.

So, what can we do conserve those resources? Besides adopting policies to conserve and recycle those finite resources, we can reduce the rate of population increase by reducing the share of that growth that comes from immigration. If immigration were scaled back from a net increase of more than a million persons a year to about a third of a million persons, the projected population increase would level off to about zero. That would be an enormous contribution to resource conservation.