This is Scientific American's 60 Second Science.

I'm Christopher Intagiyata.

The Manaloa Observatory sits on the side of a Hawaiian volcano,

11,000 feet above the Pacific, and for nearly 60 years an instrument there

has been sniffing the local air taking a census of carbon dioxide molecules.

In that time CO2 levels have steadily risen from about 315 parts per million to

405 and plants are enjoying the extra carbon.

It's kind of obvious that plants are going to react to the

or two in the atmosphere because it changes the environment which they're

bathed in.

Ralph Keeling, a geochemist at the Scripps Institution of Oceanography.

And it's very hard for the plants not to benefit from that by having a higher water

use efficiency, but what wasn't clear is just how much more efficient they were going to be.

So what's water use efficiency? Like us, plants need water for basic life

processes and they open tiny pores in their leaves to allow carbon dioxide in for photosynthesis. But the holes also let the precious water out. Higher water use

efficiency just means losing less water while taking in the CO2. To figure out just

how much the efficiency improves, Keeling and his team examined the ratio of CO2,

having the isotope carbon 13,

versus its lighter and much more prevalent cousin, carbon 12.

So the ratio is 0.2% lower than it was pre- industrially.

Doesn't sound like a lot, doesn't.

And yet that small change in carbon 13 versus carbon 12

...