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Traffic moves slowly along the 101 freeway through the Cahuenga Pass as new rainfall records are met Tuesday March 22, 2005 in  Los Angeles. (AP Photo/Phil McCarten)

In a world where 50 million new cars are being built each year, scientists consider what would happen to global carbon dioxide emissions if society simply stopped adding new vehicles and infrastructure. Their conclusion: The worst is yet to come.

Photograph by Phil McCarten, Associated Press

By Mason Inman

For National Geographic News

Published September 9, 2010

This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.

Imagine that tomorrow, the whole world will stop building things that burn fossil fuels—cars and planes, power plants, and housing tracts.

How much more global warming would the planet endure?

(See Related, from National Geographic Channel: "Aftermath: Population Zero" )

This might sound like an environmentalist's dream—or a CEO's nightmare—but it's a serious question addressed by a new study published in the September 10 issue of Science.

If we were to go on using the things we already have, but didn't build new things that used fossil fuel, then the planet would heat up another 0.5ºF to 1.2ºF (0.3ºC to 0.7ºC), the study estimates.

This would keep the total amount of warming, since pre-industrial times, to less than 3.6ºF (2ºC), according to the study.

This amount of warming happens to be the threshold identified by the Intergovernmental Panel on Climate Change as important for avoiding the worst impacts of climate change. A wide-ranging coalition of 47 environmental, science, and faith-based groups last year endorsed 2ºC as “a key guide post to measure our efforts to tackle global warming pollution.” And it was the magic number cited in the nonbinding agreement to limit global temperature increases signed by industrialized countries at the international climate summit last December in Copenhagen.

The new results show "we still have it in our hands" to meet this target, said Niklas Höhne, a climate policy expert at the consultancy Ecofys in Cologne, Germany, who was not involved in the new study.

The Worst is Yet to Come

So the analysis, “Future CO2 Emissions and Climate Change from Existing Energy Infrastructure” is "good news," Höhne said.

But in a world where 50 million new cars are being built each year, where China is rapidly expanding its electric power plant fleet—much of it coal-fired—and the housing bust has slowed but not stopped new real estate development, the Science paper’s underlying theme is a cautionary one.

(See Related: “China CO2 Emissions Growing Faster Than Anticipated”)

"The worst impacts are going to be from infrastructure that has yet to be built," warned study lead author Steven Davis, a climate researcher at the Carnegie Institution for Science in Stanford, California. "We should concentrate on building the right things going forward."

The results "could be misinterpreted to think that we could just wipe our hands and go home," study leader Davis warned. But, Davis added, "there are things being built every day, and no real prospect that we're going to restrict emissions from all of those things."

It's true that power plants, cars, and houses all have to be retired eventually and replaced. The researchers set out to estimate the lifetimes of today's stock of all these things, and to project roughly the amount of greenhouse gases they would emit up until time of retirement.

A Critical Decade Ahead

The researchers estimated that emissions of carbon dioxide (CO2), the main greenhouse gas, from today's stock of vehicles, buildings, and power plants would probably drop to zero by 2050.

If everything else built from now on were emissions-free—a lofty aspiration, to be sure--then the CO2 level in the atmosphere would top out about 410 parts per million (ppm), compared to the current level of about 390 ppm, the study found. While some activists argue that would still be too high, and have rallied around 350 ppm as the goal on which the world should set its sights, keeping the future growth in CO2 concentration to 410 ppm would be a “tremendous challenge,” Davis said.

"A lot of new equipment is being planned right now that will have [a] long lifetime," said Höhne of Ecofys.

If business as usual in the building of energy-consuming infrastructure continues for another decade, Höhne added, "then it will very difficult to achieve the 2ºC target without shutting down some of this equipment early."

So, Höhne argues, "the next ten years [are] very, very critical."

(See Related: “Mining the Truth on Coal Supplies”)

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