Pack your portfolios with agricultural plays like Mosaic (MOS) if Dr. Paul Ehrlich is just partially right about the impending collapse of the world’s food supply.

You might even throw in long positions in wheat (WEAT), corn (CORN), soybeans (SOYB), and rice.

It says a lot that when I update a sector report like this and half the companies have disappeared from takeovers (Potash and Agrium), you should take notice.

The never dull and often controversial Stanford biology professor told me he expects that global warming is leading to significant changes in world weather patterns that will cause droughts in some of the largest food-producing areas, causing massive famines. Food prices will skyrocket, and billions could die.

At greatest risk are the big rice-producing areas in South Asia which depend on glacial run off from the Himalayas. If the glaciers melt, this crucial supply of fresh water will disappear.

California faces a similar problem if the Sierra snowpack fails to show up in sufficient quantities as it has done in five of the last six years.

Rising sea levels displacing 500 million people in low-lying coastal areas is another big problem.

One of the 83-year-old professor’s early books The Population Bomb was required reading for me in college in the 1960s, and I used to drive up from Los Angeles to Palo Alto just to hear his lectures (followed by the obligatory side trip to the Haight-Ashbury).

Other big risks to the economy are the threat of a third world nuclear war caused by population pressures, and global insect plagues facilitated by a widespread growth of intercontinental transportation and globalization.

And I won’t get into the threat of a giant solar flare frying our electrical grid. That is already well covered on the Internet.

“Super consumption” in the US needs to be reined in where the population is growing the fastest. If the world adopts an American standard of living, we need four more Earths to supply the needed natural resources.

We must raise the price of all forms of carbon, preferably through taxes, but cap and trade will work too. Population control is the answer to all of these problems which is best achieved by giving women educations, jobs, and rights, has already worked well in Europe and Japan, and is now unfolding in Latin America.

All sobering food for thought. I think I’ll skip that Big Mac for lunch.