Existing border fence in Imperial County | Photo: Eric White, some rights reserved Californias border with Baja California is a complex region with unique environmental issues. Our Borderlands series takes a deeper look at this region unified by shared landscapes and friendship, and divided by international politics.
Its more and more likely that Donald Trump will become the Republican Party's nominee in the Presidential election. As a result, it's time to start taking a serious look at his signature policy proposal - clamping down on immigration, primarily through building a massive wall along the U.S. border with Mexico.
That's not a straightforward task, primarily because Trump hasn't exactly been generous with the details of his signature border wall proposal. So far the wall has been vaporware, long on promises that it'll solve more problems than it creates, and short on any actual specs. When that's been mentioned to Trump, he's tended to comb over the bald lack of detail on the wall with a rhetorical wave of the hand.
Still, the wall is a keystone of Trump's campaign, and so it makes sense to examine the effect the wall would have on the borderlands' environment. And it doesn't look good, even without the wall's chief proponent offering much in the way of any actual details. We've come up with three reasons why, and will be describing them in stories this week. First up: the wall's effect on the climate.
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Here's one of the very few facts we know for sure about Trump's Wall: The United States' border with Mexico is 1,954 miles long, stretching from San Diego and Tijuana to Brownsville, Texas and Matamoros, Tamaulipas on the Gulf of Mexico. For 1,255 miles of that length, between the Gulf and El Paso/Juarez, the border follows the Rio Grande, known in Mexico as the Rio Bravo del Norte. The remaining 700 miles runs across some of the most forbidding landscape in North America, through the Chihuahuan and Sonoran deserts, until it reaches the less-inhospitable San Diego coast.
Building a wall like the one Trump vaguely describes along this length of border would be a mammoth undertaking. Just the materials going into the wall would have a huge environmental impact, especially with regard to our planet's beleaguered climate.
Why's that? Concrete. The building material of choice for modern construction projects would be just about the only practical material for a large wall along the border, especially given the remoteness of much of the border. And that's one of the few consistent details Trump has offered when asked to describe the wall: he's said the wall would be built of concrete and rebar.
Concrete has a big greenhouse gas footprint. That's due in part to the energy it takes to make cement, the ingredient that holds concrete together when it's mixed, poured, and allowed to dry. Cement is made by heating limestone and clay to 1,400 F, which takes energy, which generally comes from burning fossil fuels. Those fuels account for a bit less than half of the greenhouse gases released in cement production. The rest is released by the limestone as it's heated, as its main constituent, calcium carbonate, gives off carbon dioxide in a process called calcination.
The world uses a lot of cement, and the industry is responsible for something like five percent of total world greenhouse gas emissions.
Pouring a large concrete wall in North Carolina. The border wall has been described at twice this height. | Photo: NCDOT, some rights reserved
What does that mean for the proposed border wall's greenhouse gas footprint? It's hard to nail down precisely, both because of the palpable lack of border wall blueprints made available by the Trump campaign and because the proportion of cement in concrete will vary depending on the application.
But let's take the National Ready Mix Concrete Association's 2008 estimate of 500 pounds of CO2 released in the production of a typical cubic yard of concrete as a working figure. That's on the high end of the NRMCA's estimate range, which runs from 170 to 500 pounds of CO2 per yard of concrete. But it also excludes greenhouse gases released during activities such as shipping of materials, transportation for workers, and fuel for construction machinery.
How many cubic yards of concrete would the wall use? We've got the length, but to estimate its volume we'll need its average height and thickness. Again, Trump has been frustratingly arm-wavy on two of the wall's three dimensions. His claims about the wall's height have ranged from 30 to 65 feet, and that's not counting either foundations or the depth to which the wall would have to extend underground to deter tunneling beneath it.
Let's call it 55 feet in height, 50 above ground and five below, and ignore foundations for now. How thick would the wall be? Engineer Ali F. Rhuzkan has suggested that since concrete won't cure well in the heat and aridity of desert summers, that the wall project would likely require local casting facilities to make modular concrete panels eight inches thick, which would be stacked between pylon supports to make a wall 20 feet high. Presumably, a wall 50 feet high could be built in much the same way, though the panels might need to be a bit thicker.
Or perhaps Trump would farm out the design to a low bidder that would suggest pouring the wall in place, with the subsequent quality control issues that have dogged other Trump-branded projects in the past. Let's take the easy way out, and assume an average thickness of a foot. At 1,954 miles in length and 55 feet high, that would mean the wall contains 63,049,066 cubic yards of concrete.
Which - at 500 pounds of CO2 per cubic yard - means 14,299,304 metric tons of CO2 emit
