Maybe you’ve heard the news: Last month, for the first time in 800,000 years, the world’s carbon dioxide level passed 400 parts per million (ppm), and stayed that way all of April. This was the milestone that we’ve been anticipating for many years.
It was just 330 ppm when the Beatles were big. Earlier, when many of us were in kindergarten, CO2 was 315 ppm. It had taken a long time to get there. Before the Industrial Revolution, and going back for almost a million years, the level was 280 ppm.
It will fall back below 400 ppm this summer, and then bust it again next spring. That’s because Earth’s Northern Hemisphere has more temperate, seasonal plant life than the Southern, and springtime growth releases a lot of carbon dioxide. Nonetheless, in two or three years, levels will stay permanently above 400 ppm as we continue upward.
Carbon dioxide makes up only 1/25th of one percent of the air. When you take a breath, you inhale 500 times more oxygen than you do carbon dioxide. So why the fuss?
We’ve all heard about greenhouse gases, and know that carbon dioxide (along with methane and water vapor) is the big player in this arena. Here’s how it works: Sunlight warms the ground during the day, and at night this energy radiates back into space in the form of infrared rays. Now, our air is about 80 percent nitrogen, 20 percent oxygen and one percent argon. Nitrogen and oxygen atoms commonly bond into twosomes, and form the molecules N2 and 02, while argon is a loner and exists as just plain A. The key point: When infrared from the ground travels up through the air, it encounters these atoms and molecules. When infrared hits any of them, it keeps going in a straight line and continues into space.
But a molecule with three or more atoms acts very differently during infrared encounters. Methane (CH4), carbon dioxide (CO2) and water vapor (H20) have between three and five atoms apiece. When infrared strikes any of them, it gets absorbed by the molecule, which then reradiates it in random directions. So instead of continuing upward into space, the infrared now goes sideways or upward or downward. The downward ones return to the ground. This explains why, on cloudy nights when there’s lots of water vapor overhead, the ground doesn’t cool as much as it does on a clear night. The more methane, water vapor or carbon dioxide is in the air, the less each night can cool down.
So greenhouse gases do their work during the night. They raise a region’s nightly low temperatures. It’s as inevitable as the sunrise. We see carbon dioxide in action on other worlds, and the effect is always to warm things up.
Unfortunately, this new milestone of hitting 400 parts per million is only a waypoint. In 25 years it will reach 450 ppm. And when today’s kindergartners are in their mid-50s, carbon dioxide will probably reach 500 ppm. Nobody knows how much warming this will produce: a lot more than now, and our planet is already changing. Opportunistic plants, insects and bacteria will find their way to new places. Fortunately for us, the northeastern US is one of the regions where the National Oceanic and Atmospheric Administration’s climate modeling computers predict continued ample rainfall and minimal consequences.
We could probably get the carbon dioxide to stop at 450 ppm or so if, right now or very soon, we dramatically alter our energy usage from fossil fuels to greater use of nuclear power, solar and wind. Unfortunately, a lot of money is being spent by the Koch brothers and various lobbyists to perpetuate fossil fuel usage. Advertising works. And the American electorate is not globally renowned for its perspicacity.
Much hangs in the balance. Time will tell how it plays out. Meanwhile, the 400-ppm milestone has finally arrived – with less media attention than that day’s celebrity gossip.
Join the family! 
