Three Trillion Isn't As Big a Number As You'd Think...

Global warming deniers frequently claim that humans are too puny and weak to have any significant effect on the planet's climate. A recent study published in Nature sheds some light on just how much of an effect humans can have on the planet: 

There are roughly 3 trillion trees on Earth — more than seven times the number previously estimated — according to a tally by an international team of scientists. The study also finds that human activity is detrimental to tree abundance worldwide. Around 15 billion trees are cut down each year, the researchers estimate; since the onset of agriculture about 12,000 years ago, the number of trees worldwide has dropped by 46%.

“The scale of human impact is astonishing,” says Thomas Crowther, an ecologist now at the Netherlands Institute of Ecology in Wageningen who led the study while at Yale University in New Haven, Connecticut. “Obviously we expected humans would have a prominent role, but I didn’t expect that it would come out as the as the strongest control on tree density.”

Trees and other plants produce half the world's oxygen (phytoplankton in the seas produce the other half).

Now, 3 trillion sounds like a lot of trees. But there are 7 billion humans -- and counting -- on earth. That means there are only about 430 trees per person. That means that, if we were of a mind to, we could destroy every tree on earth in just a couple of years, even if we just went at them with axes and saws.

One man on a bulldozer can tear down thousands of trees in a day, and a careless smoker can burn a million trees in a day.

How any trees do we need? Estimates vary, but it seems that each human needs between 7 and 22 trees to produce the oxygen we consume. Since there other animals and insects breathe, 430 trees per person isn't a very big number. Crops do produce oxygen, but not much: trees produce far more oxygen per acre because of their vertical profile.

Will phytoplankton save the day? Maybe not. As we burn more fossil fuels, we put more CO2 in the air. A lot of that CO2 is absorbed into the ocean, forming carbonic acid. That increases the acidity of the ocean, and that may make dramatic changes in phytoplankton.

So, are we going to suffocate ourselves by burning all this oil and coal? Probably not -- but that's not the point. There are so many people on this planet that we can no longer pretend that our actions have no effect on the environment -- and the climate -- of the entire planet.

Two photographs show how pervasive humans are. Here's the earth during the day. There's no sign of humans anywhere. All you see are those big weather systems:

But here's the earth at night:

Humans cover the entire half of the United States, and our farms in the plains cover a lot of the rest. We are visible from the moon.

So when climate change deniers say that humans are too puny to affect the climate, they're flat-out lying.