“How do you make a flexible pipe that can carry 6,000 bar of pressure that sways in the wind of the jet stream and guarantee that it will last?” asks Justin McClellan, an engineer with Aurora Flight Sciences, which builds advanced aerospace vehicles for scientific and military applications. “A typical oil and gas rig might see 2,000 bar of pressure, and that is with a roughly quarter-inch-thick steel pipe. Solving the one-kilometer problem is probably not very hard, but when you add up all the requirements for a 20-kilometer pipe, this starts to look pretty unrealistic.”
Hunt acknowledges that multiple challenges put the project “on the edge of what is possible,” but he says that all engineering issues can be overcome within five years. Full-scale deployment could be achieved for approximately 5 billion pounds per year, he maintains.
David Keith, a professor of applied physics at Harvard University’s School of Engineering and Applied Sciences and professor of public policy at Harvard’s Kennedy School, is not impressed. He says the cost of a solution is not an issue, since the costs of climate change are so high. “The impacts of climate change are on the order of a trillion dollars a year, as are the costs of cutting emissions,” Keith says. But he says research should focus on developing the most effective and lowest-risk option for injecting sulfate particles into the atmosphere. Dispersing them by airplane allows for greater and more even distribution of particles, he says, thereby reducing the odds that they will clump together and fall back toward Earth.
“I think SPICE will be the most visible geoengineering project to date, and it may polarize public opinion. But in regards to scientific or engineering interest, I don’t see much,” Keith says.