Earth from orbit

Sun-reflecting chemicals could be ‘remarkably inexpensive’ way to reduce global warming

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Scientists at Harvard University have calculated the cost of spraying chemicals into the atmosphere to reduce global warming and found that it would be “remarkably inexpensive” - costing only around $2.25bn (£1.75bn) a year to cover the entire Earth.

The sun-dimming chemicals have been proposed as a hypothetical solution to global warming, although the technique is unproven thus far.

In a paper published in Environmental Research Letters, the researchers review the capabilities and costs of various lofting methods intended to deliver sulfates into the lower stratosphere.

The $2.25bn figure was calculated as an annual cost if the spraying exercise was repeated over a 15-year period.

Some researchers say the geo-engineering technique known as stratospheric aerosol injection (SAI) could limit rising temperatures that are causing climate change.

However, the Harvard team concluded that no existing aircraft has the combination of altitude and payload capabilities required for such a mission, so they proposed a new plane design that could be used.

The design, called SAI Lofter (SAIL), had its basic specifications mapped out and they even provided detailed cost estimates for its design, manufacture, and operation.

The planes would be equipped with huge hoses that could spray large quantities of sulfate particles into the upper layer of the atmosphere to act as a reflective barrier against sunlight.

Discounting other methods of deployment because of cost and feasibility, the research assumes a special aircraft can be designed to fly at an altitude of about 20km and carry a load of 25 tonnes.

After direct input from several aerospace and engine companies, the scientists said they have developed a design that could be suitable and could be ready to be deployed in 15 years, aiming to cut the rate of temperature change in half.

“We make no judgment about the desirability of SAI. We simply show that a hypothetical deployment programme commencing 15 years hence, while both highly uncertain and ambitious, would indeed be technically possible from an engineering perspective. It would also be remarkably inexpensive,” the report said.

There are risks to such unproven potential technologies. Scientists have said SAI could result in negative consequences such as causing droughts or extreme weather in other parts of the world, harm crop yields as well as potential public health and governance issues.

It also does not address the issue of rising carbon dioxide emissions, the main greenhouse gas blamed for global warming.

Commenting on the study, Phil Williamson at the University of East Anglia said: “Such scenarios are fraught with problems - and international agreement to go ahead with such action would seem near-impossible to achieve.”

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