Is geoengineering Earth’s last hope?

CORNELL (US) — If action is not taken soon, ocean acidification and greenhouse warming could reach a tipping point that will take more than 1,000 years to reverse.

Scientists warn that to avoid excessive warming, sea level rise, and extreme weather, CO2 in the atmosphere needs to be reduced to 350 parts-per-million (ppm) by the end of this century from the current level of around 390 ppm.

Charles Greene, professor of earth science at Cornell University and lead author of a new study, says time is running out, yet governments have done little to reverse rising carbon dioxide (CO2) levels.

The study, published in the September-October issue of Solutions magazine, suggests one way to reduce atmospheric CO2 is by setting up fields of air-capture devices that absorb it, similar to the carbon capture and storage technology being developed for coal plants.

The devices would use algal bioenergy as a power source to capture, extract, and pipe CO2 for storage or industrial use.

Algae provide a preferred bioenergy source relative to land plants because they are more productive, more efficient in their use of nutrients, and do not need to compete with food crops for prime agricultural land, Greene says.

The price tag for using this technology over the remainder of the century? About $85.5 trillion to remove the 855 gigatons of carbon needed to bring atmospheric CO2 down to 350 ppm.

Although $85.5 trillion seems high, it is comparable to the estimated cost of using carbon emission reduction strategies to reduce atmospheric CO2 down to a lesser goal of 450 ppm.

Corresponding to less than 1 percent of the global GDP for the rest of the century, such a cost is considered affordable compared with the alternative consequences of catastrophic climate change.

Still, it will take decades to develop air capture and algal bioenergy systems, scale up prototypes, prepare underground carbon repositories, and deploy such systems on a global scale.

“In an ideal case, we could have full deployment on a global scale by 2050,” Greene says.

To buy time, another geoengineering strategy being explored involves altering the Earth’s radiation budget by injecting sulfate aerosols into the atmosphere and blocking the sun’s rays, mimicking what happens after a volcanic eruption.

Other strategies involve injecting seawater droplets into clouds and deploying shades or mirrors in space, all to block the sun’s rays from reaching Earth’s surface.

Such solar radiation management strategies “can be done quickly, but should only be considered as a last resort to buy ourselves some time” since they simply “cover up the problem without doing anything about the CO2,” says Greene.

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