If only gay sex caused global warming

Although all human societies have moral rules about food and sex, none has a moral rule about atmospheric chemistry. And so we are outraged about every breach of protocol except Kyoto. Yes, global warming is bad, but it doesn't make us feel nauseated or angry or disgraced, and thus we don't feel compelled to rail against it as we do against other momentous threats to our species, such as flag burning. The fact is that if climate change were caused by gay sex, or by the practice of eating kittens, millions of protesters would be massing in the streets.

The third reason why global warming doesn't trigger our concern is that we see it as a threat to our futures -- not our afternoons. Like all animals, people are quick to respond to clear and present danger, which is why it takes us just a few milliseconds to duck when a wayward baseball comes speeding toward our eyes.

The brain is a beautifully engineered get-out-of-the-way machine that constantly scans the environment for things out of whose way it should right now get. That's what brains did for several hundred million years -- and then, just a few million years ago, the mammalian brain learned a new trick: to predict the timing and location of dangers before they actually happened.

Our ability to duck that which is not yet coming is one of the brain's most stunning innovations, and we wouldn't have dental floss or 401(k) plans without it. But this innovation is in the early stages of development. The application that allows us to respond to visible baseballs is ancient and reliable, but the add-on utility that allows us to respond to threats that loom in an unseen future is still in beta testing.

We haven't quite gotten the knack of treating the future like the present it will soon become because we've only been practicing for a few million years. If global warming took out an eye every now and then, OSHA would regulate it into nonexistence.

There is a fourth reason why we just can't seem to get worked up about global warming. The human brain is exquisitely sensitive to changes in light, sound, temperature, pressure, size, weight and just about everything else. But if the rate of change is slow enough, the change will go undetected. If the low hum of a refrigerator were to increase in pitch over the course of several weeks, the appliance could be singing soprano by the end of the month and no one would be the wiser.