Farming Combine

A combine runs through a barley field off Kagy Blvd. in 2011.

Plants remove carbon gases from the air, using the carbon to build stems and leaves. Now a new study indicates that wildlands remove the most carbon, providing the most promise for minimizing climate change.

In a study highlighted this month in the journal Nature Geoscience, a team of University of Montana and U.S. Geological Survey scientists presented satellite data showing that farmland and other disturbed areas process less carbon than areas where the native vegetation is undisturbed.

Lead author Bill Smith said the team compared visible and infrared satellite images of natural and agricultural areas for a snapshot of the Earth's vegetative production, which is a measure of the amount of carbon being processed.

Agricultural land tends to be planted in rows alternating with uncovered soil, and every year, most plants are removed.

So it wasn't surprising that such areas took up less carbon than wild areas with a wider variety of more plants that used more carbon throughout the year.

But how much more carbon?

The study reported that the agriculture that exists now has reduced the Earth's potential productivity by 7 percent.

That doesn't sound like much, but it's a global average, Smith said. Some forests of the planet show bigger productivity losses than others if they're mowed down.

The rainforests of the tropics are the most productive ecosystems on the planet, locking up tons of carbon.

So the productivity loss caused by tropical deforestation is double that of more temperate forests, Smith said.

Tropical deforestation is a continuing source of concern, especially after an article in the February edition of the journal Science reported that drug trafficking is leading to increased deforestation in remote regions of Central America.

Drug traffickers are slashing forests to build runways and roads to move drugs and converting forests into agribusinesses to launder drug profits.

Looking just at temperate parts of the world, variation in carbon uptake is caused mainly by differences in farm technology.

Smith said some farmland in the U.S. is almost as productive as wildlands thanks to effective use of water, fertilizer and high-tech farm equipment.

The same cannot be said about farming in less-developed parts of the world.

Across the globe, productivity is reduced in 88 percent of agricultural lands.

Smith said even in the U.S., productivity might improve if crops were better matched with the areas where they're grown, such as growing wheat in drier areas rather than water-demanding corn.

“That's one of the messages of this study – it highlights the potential benefits of improving the crops that are grown on already-existing ag land,” Smith said.

Nobel prize-winning ecologist and co-author Steve Running said he's been trying to find a way to calculate the Earth's upper limit of productivity.

Once they know the limit, scientists can calculate the amount of manmade greenhouse gases that exceed that limit and that therefore need to be eliminated in order to slow climate change.

Thanks to improved satellite technology and computer analysis, some evidence is finally available.

“No one has tried to see what the capacity of the world for bioenergy might be – it provides an upper limit on what the world could possibly produce. It sounds crazy, but you start with the assumption of ‘what would happen if we clear-cut the world every year?'” Running said.

Running said he set out to find the Earth's upper limit of productivity to counter some economists who insist that growth can continue indefinitely, whether in the form of resource extraction or land conversion to feed a growing population.

“There are obviously some limits to the planet, and in the past, we haven't been able to measure the planet well enough to have any clue to where we might be as far as consumption. But now we do,” Running said. “We think we have some evidence that we're approaching these planetary boundaries, and we'd better wake up.”