Harvard: Block the Sun Chemically to Curb Global Warming

Filling the lower stratosphere with sulfate could reflect sunlight – and slow down the planet’s warming. According to Harvard researchers, it costs just over $ 20 billion a year to spray the entire earth.

A dissertation published in Environmental Research Letters explores the possibilities of curbing global warming by spraying the lower stratosphere with sulfate – that is, salts of sulfuric acid.

It acts as an artificial volcanic eruption. In the event of major eruptions, the planet has been effectively cooled down, and at the largest it is presumed that the excluded sunlight has contributed to the Earth’s ice ages. The ash clouds contain, among other things, sulfur dioxide, which forms sulfate aerosols. The Harvard dissertation states that a similar effect can be achieved chemically with a so-called stratospheric aerosol injection (SAI).

And Harvard researchers have found that it is very cheap to implement. Their calculations indicate that one could spray the entire planet for as little as SEK 20.4 billion a year – a treatment that would be repeated for 15 years.

But the effort will require new aircraft that can take a large load to high altitude. The Harvard team calls its new aircraft type SAI Lofter. They should be equipped with large hoses that can spew out the volumes of sulfate particles needed to act as a reflective barrier to solar radiation.

The researchers believe that the aircraft must be able to carry 25 tonnes to 20 kilometers altitude – and it will take about a hundred to deliver the aerosol. After consulting the aerospace industry, scientists estimate that the delivery system could be ready within 15 years.

The researchers, however, do not hide the fact that their concept also entails risks, for example that the aerosols could cause drought, affect agriculture, contribute to extreme weather in other places on earth – or adversely affect our health.

We do not judge how desirable SAI could be. We simply show that a hypothetical delivery system, albeit highly uncertain and ambitious, over the course of 15 years would actually be technically feasible from an engineering perspective. It would also be surprisingly cheap, the researchers write in their dissertation.

The work has been commented on by, among others, Phil Williamson at the University of East Anglia, and he sees the solution as unlikely.

“Such scenarios are fraught with problems, and reaching an international agreement to initiate such an effort, in principle, feels like an impossible thing to achieve,” he tells Engineering and Technology.


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