Portland’s downtown is practically ripped to shreds by an unprecedented building and redevelopment spurt. Doesn’t make for happy motorists, bicyclists or pedestrians. But navigating through the city’s maze of construction zones, as frustrating as it is, may not be the worst of it. Until this week, I thought I understood the primary sources of CO2 emissions. However, I’ve managed to overlook a big one: cement, the basic ingredient in concrete.

In my last post, I referred to a BusinessWeek’s latest cover story, “Little Green Lies.” One of the companies the magazine mentions is Lafarge, a giant cement manufacturer based in Paris. Despite praise from the World Wildlife Fund as a “climate saver,” Lafarge’s CO2 emissions have actually risen by “11% over two years,” the article states. The company alone generates more greenhouse gases than Portugal!

And today, the New York Times has a feature article, “Cement Industry Is at Center of Climate Change Debate.” According to the Times,

Cement plants account for 5 percent of global emissions of carbon dioxide, the main cause of global warming. Cement has no viable recycling potential; each new road, each new building needs new cement…Cement poses a basic problem: the chemical reaction that creates it releases large amounts of carbon dioxide. Sixty percent of emissions caused by making cement are from this chemical process alone, Mr. (Olivier) Luneau of Lafarge said. The remainder is produced from the fuels used in production, although those emissions may be mitigated with the use of greener technology. “Demand is growing so fast and continues to grow, and you can’t cap that,” Mr. Luneau said. “Our core business is cement, so there is a limit to what we can change.”

So therein lies the rub. Despite successes by cement producers to reduce the amount of CO2 emissions for each ton of cement, the worldwide demand for cement is skyrocketing. Especially in China, which “alone makes and uses 45 percent of worldwide output.”

But we can’t make China the scapegoat here. There are countless cities like Portland across the globe where cranes dot the skies and trucks form block-long queues to pour concrete for underground parking garages and condominium and office structures. Construction folks, like my brother, sing the praises of concrete for its strength and versatility in conforming to just about any desired shape. It’s a nearly perfect building material — if you overlook the CO2 part. Cement making’s contribution of 5 percent of global CO2 emissions exceeds that of the world’s airline industry.

So are there any cement alternatives? I’m no expert here, but a quick Google scan indicates alternatives are starting to emerge but their widespread adoption remains on the distant horizon. If you’re into this sort of thing, check out this piece that explores ways to reduce cement’s CO2 emissions and several cement alternatives.