They say that everyone who finally gets it about climate change has an "Oh, shit" moment--an instant when the full scientific implications become clear and they suddenly realize what a horrifically dangerous situation humanity has created for itself. Listening to the speeches, groundbreaking in their way, that President Obama and Chinese President Hu Jintao delivered September 22 at the UN Summit on Climate Change, I was reminded of my most recent "Oh, shit" moment.

Food production will have to increase by 70% over the next 40 years to feed the world's growing population, the United Nations food agency predicts. The Food and Agricultural Organisation says if more land is not used for food production now, 370 million people could be facing famine by 2050. The world population is expected to increase from the current 6.7 billion to 9.1 billion by mid-century. Climate change, involving floods and droughts, will affect food production.

Beware of the blob—this time, it's for real. As sea temperatures have risen in recent decades, enormous sheets of a mucus-like material have begun forming more often, oozing into new regions, and lasting longer, a new Mediterranean Sea study says (sea "mucus" blob pictures). And the blobs may be more than just unpleasant. Up to 124 miles (200 kilometers) long, the mucilages appear naturally, usually near Mediterranean coasts in summer.

“In early 2008, Saudi Arabia announced that, after being self-sufficient in wheat for over 20 years, the non-replenishable aquifer it had been pumping for irrigation was largely depleted,” writes Lester R. Brown in his new book, Plan B 4.0: Mobilizing to Save Civilization (W.W. Norton & Company). “In response, officials said they would reduce their wheat harvest by one eighth each year until production would cease entirely in 2016.