Interview for MIT Technology Review
The intervention may break down methane, mimicking a phenomenon that could have amplified ice ages. But scientists say far more basic research still needs to be done.
Methane is relatively dilute in the atmosphere, at about 1.9 parts per million versus around 416 parts per million for carbon dioxide. There are techniques that may allow researchers to assess the impact of iron particles on atmospheric methane at small scales. But it could be challenging to reliably measure the effect of large-scale releases. 

Even a particle plume that spans some tens of cubic kilometers “might appear as one pixel in a satellite map,” says Matthew Johnson, a professor of atmospheric chemistry at the University of Copenhagen who is involved in the Spark Climate-backed research effort. “It would be difficult to see a signal, much less to accurately quantify it.”

That, in turn, could present an obstacle to verifying how much methane such an intervention removed, which would be key to the credibility of any methane removal credits analogous to the sort used in carbon dioxide markets.

Societal permission
The University of Copenhagen’s Johnson says that researchers can learn a lot more about the potential and risks of this approach without adding iron particles into the atmosphere through field experiments. Among other things, he said that researchers can sample and study the ample iron already in the air, as a result of natural sources like deserts and human activities such as shipping, heavy industry, and agriculture.

“Understanding these systems, already occurring in the atmosphere today, is the best way to move [iron salt aerosol] research forward,” he wrote in an email.

In fact, that work has already begun. In October, crews aboard several commercial ships streaming across the Atlantic began a yearlong effort to collect ocean air, using handheld glass flasks connected to pumps that suck down samples. They drop off crates filled with the flasks when the ships reach port, and the samples ultimately make their way to labs in the Netherlands for analysis as part of the research collaboration.