Project would require twice the concrete of Hoover Dam
Concrete’s main ingredient is potent source of greenhouse gas
Concrete is a potent source of greenhouses gas, and Trump’s “great wall” will need a lot of it -- more than double the amount in Hoover Dam, according to engineers at New York University and University College London.
A 1,000-mile (1,600-kilometer) wall would require an estimated 275 million cubic feet of concrete. It would release as much as 1.9 million metric tons of carbon dioxide into the atmosphere, according to Christoph Meinrenken, an associate research scientist at Columbia University’s Earth Institute. That’s more than the annual emissions from every home in Pittsburgh.
“The carbon footprint of a wall that size would be huge,” Dan Millis, borderlands program coordinator for the Sierra Club’s Arizona chapter, said in an interview.
Trump’s executive order to build the wall comes as nations around the globe push to reduce greenhouse gases and meet goals set under the Paris Climate accord. Last year was the hottest on the record, with temperatures inching ever loser to the level scientists say would be catastrophic, according to the United Nations.
‘Not Building Walls’
The U.S. needs to invest in infrastructure and many worthwhile projects will require concrete, said Rachel Cleetus, lead economist and climate policy manager at the Union of Concerned Scientists. But those projects should be in line with the broader goal of fighting global warming.
“Let’s talk about modernizing electric grids -- not building walls,’’ Cleetus said in an interview.
Most of the carbon dioxide from concrete comes from its main ingredient: cement. The cement industry accounts for about 5 percent of global carbon dioxide emissions, according to the Earth Institute. That’s in part because it’s made by heating limestone, a process that releases carbon, and also because it requires the equivalent of about 400 pounds (181 kilograms) of coal to crank out a single ton of cement.
To be clear, these emissions figures are estimates. Trump hasn’t issued precise specifications for the wall, saying on various occasions it would cover about 1,000 miles and be anywhere from 35 feet to 50 feet tall. The estimates compiled by Bloomberg assume a steel-reinforced wall, 1,000 miles long, 35 feet tall and 18 inches thick, producing 1.2 million to 1.9 million tons of carbon dioxide.
The carbon footprint will also vary depending the quality and composition of concrete. And Trump could always skip concrete and opt for a fence, as Republican leaders have suggested.
There are also environmentally friendly options. Carbicrete, a Montreal-based clean technology company, developed a type of concrete that absorbs carbon dioxide. Using Carbicrete cinder blocks to build the wall would potentially remove 1.2 million metric tons from the atmosphere, at comparable prices, chief executive Chris Stern said in an interview.
The Sierra Club’s Millis said carbon dioxide would hardly be the wall’s only environmental impact. It would also cause flooding and cut off migratory paths for endangered jaguars, ocelots and other creatures, he said. And the barrier would do little to stop immigrants.
“People have already traveled hundreds, if not thousands, of miles by the time they get to to the border,” he said. “They are not going to look at a wall and turn around. They are going to go find a ladder or a rope.”