Climate scientists now know that geo-engineering – in principle at least – would halt global warming and keep the world at the temperatures it will reach by 2020.

It is simple: inject millions of tons of sulphate aerosols into the stratosphere at carefully chosen locations, and keep on doing so for as long as humans continue to burn fossil fuels and release greenhouse gases into the atmosphere.

The desired effect: global temperatures will be contained because the pollutants in the upper atmosphere will dim the sun’s light and counteract the greenhouse effect of all the carbon dioxide pumped from power stations, vehicle exhausts, factory chimneys and burning forests.

It won’t be the perfect answer. The oceans will go on becoming more acidic, and the skies will become subtly darker. Rainfall patterns could be affected. Repairs to the ozone layer – an invisible shield against dangerous ultraviolet radiation – would be slowed.

“For decision makers to accurately weigh the pros and cons of geo-engineering against those of human-caused climate change, they need more information. Our goal is to better understand what geo-engineering can do  and what it cannot”

The volumes of sulphate aerosols that would need to be flown to stratospheric heights and released each year would continue to grow as humans went on burning ever more fossil fuels.

The technical and energy demands of such an operation would be colossal. There could be serious geopolitical problems about the impacts and responsibility for such decisions. But, at least in principle, researchers now believe geo-engineering could be made to work.

“For decision makers to accurately weigh the pros and cons of geo-engineering against those of human-caused climate change, they need more information,” said Ben Kravitz, of the Pacific Northwest National Laboratory, and one of a consortium which has published a succession of five studies in the Journal of Geophysical Research – Atmospheres. “Our goal is to better understand what geo-engineering can do  and what it cannot.”

Unkept promises

Climate scientists have repeatedly investigated the so-called techno-fix. By burning maybe 50 million years of fossil fuel deposits in just two centuries, humans have raised global temperatures and inadvertently engineered climate change.

So perhaps science and technology could come to the rescue, and deliberately engineer the climate to a new kind of stability. The consensus is that the ideal solution would be to stop burning fossil fuels and to start restoring the planet’s forests, the great absorbers of atmospheric carbon. But despite promises by the world’s nations in Paris in 2015, global temperatures continue to rise.

Geo-engineering is an idea that won’t go away. Research teams have repeatedly examined ideas for countering global warming, instead of reducing the cause, and found them wanting: such action world ultimately fail, or it would make the world’s problems worse, or at best it would take the heat out of the hurricane season.

But scientists from the US National Centre for Atmospheric Research, along with other US institutions and international colleagues, chose a different approach: what could geo-engineering achieve?

Natural model

Famously, an eruption of Mt Pinatubo in the Philippines in 1991 cooled the planet by dumping 20 million tons of sulphur dioxide in the stratosphere. The researchers used computer simulations to test the effect of what might be called artificial eruptions: how would stratospheric winds spread these sulphate aerosols, and how would this diffuse global dust cloud cool the planet, and for how long, and to what extent?

They played with the idea of injecting sulphates at 14 different sites at seven latitudes and two altitudes, to find that the idea worked best if injections happened at 30 degrees latitude, north and south. They experimented with varying levels of sulphur dioxide: up to 12 million metric tons at a time.

They found out how to contain overall global temperature rise to the predicted 2020 average: some regions however became – in their computer models – hotter or cooler than the citizens might appreciate.

But the challenge of keeping the world cool became more and more demanding. By the end of the century, if humans went on burning fossil fuels in the notorious business-as-usual scenario, their model demanded the equivalent of almost five Mt Pinatubo eruptions a year.  The research goes on.

Deployment delay

The Carnegie Climate Geoengineering Governance Initiative aims to encourage the development of governance for research on climate geo-engineering that is balanced between enabling and regulatory aspects.

One of its priorities is to put solar geo-engineering deployment on hold until the risks and potential benefits are better known and governance frameworks are agreed.

”We are still a long way from understanding all the interactions in the climate system that could be triggered by geo-engineering, which means we don’t yet understand the full range of possible side effects,” said scientist Simone Tilmes, of the National Centre for Atmospheric Research.

“But climate change also poses risks. Continuing research into geo-engineering is critical to assess benefits and side effects and to inform decision makers and society.”

Source: Climate News Network, Tim Radford