Steven Howard Johnson: Let’s get our bearings on global warming

Ask a 21-year-old how much life insurance he has and you’ll likely draw a blank. His sense of caution won’t yet have been awakened.

You could say the same of John F. Kennedy Jr. on his last flight 19 years ago. He thought he would have clear skies and was wrong. He lost his bearings and crashed his plane. Everyone aboard was killed.

Global warming seems so invisible, so distant. How is anyone to get their bearings? Why not just ignore it?

Figuring it out may not be easy, but it’s not impossible.

Picture our Earth as a planet immersed in two distinct flows of energy. One we’ve experienced all our lives: the nonstop flow of energy from the sun that keeps our planet from freezing. Think of this as solar energy in.

There is a second flow we may not be conscious of: infrared energy that our Earth generates 24 hours a day from every square meter of its surface. If our eyes could see infrared light, we’d see it everywhere. Hotter areas would glow more brightly, while cooler areas would be paler, but all the Earth would be aglow.

While a portion of this infrared energy gets snagged by greenhouse gases and bounced back to the surface, most of it travels swiftly through the atmosphere and escapes into outer space. Think of this as infrared energy out.

Over long stretches of the past, greenhouse gas levels have been stable, and so has the Earth’s temperature.

But it has been a process with two settings, not just one, caused by long-acting orbital cycles. During those stretches of time when glaciers covered much of the Northern Hemisphere, atmospheric carbon dioxide partially migrated into the ocean. Then, when those glaciers disappeared, carbon dioxide was released from the ocean and migrated back into the atmosphere.

Think of this as the “warm soda pop effect.” Just as a warmer glass of soda pop won’t hold its fizz as well as a colder glass, a warmer ocean won’t hold as much carbon dioxide as a colder ocean.

These two scenarios affect infrared energy out in different ways. When atmospheric carbon dioxide levels are low, the infrared transparency of the atmosphere improves. A higher percentage of surface infrared, therefore, escapes into space.

Conversely, when atmospheric carbon dioxide levels rise, the infrared transparency of the atmosphere deteriorates. Not as much infrared from the surface will escape into space.

What really matters, though, is the total amount of infrared energy out. A cooler Earth with a more transparent atmosphere can generate just as much infrared energy out as a warmer Earth with a less transparent atmosphere.

In other words, the Earth can achieve long-term temperature stability under either scenario. The equilibrium temperature will be a little lower under the scenario with fewer greenhouse gases, a little higher under the scenario that has more.

Until 1750 or so, our ancestors were innocent bystanders — spectators perhaps but not participants. Then humans discovered fossil fuels and a new chapter opened. Atmospheric carbon dioxide is now 45 percent above the norm in the 1750s. And it’s still climbing, by more than 7 percent a decade!

A stable temperature for the Earth was nearly automatic back when the atmosphere’s store of greenhouse gases was stable. But now? With carbon dioxide levels up, rising amounts of infrared are getting bounced back to the surface and less is escaping into space. Infrared energy out can’t keep up with solar energy in. And so the Earth gets warmer. And warmer.

Post Author: c0ns_lt3th

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