Is solar geoengineering a temporary fix?

| 5th November 2018
Mount Pinotubo
We need to consider all options if we are to keep global warming below 1.5°C - even engineering the climate.


The recent IPCC report warned us that "under emissions in line with current pledges of the Paris Agreement, global warming is expected to surpass 1.5°C ". This failure to meet the upbeat promise of COP21 is inevitable even if the pledges are supplemented with "very challenging increases in the scale and ambition of mitigation after 2030".

We're told that this increased action "would need to achieve net zero CO2 emissions in less than 15 years". What's more, even if this is achieved, "temperatures remaining below 1.5°C would depend on the geophysical response being towards the low end of the currently-estimated uncertainty range".

The message is simple: even if we make it to a net-zero economy, we have little chance of maintaining temperatures at 1.5ºC because this relies on the best and most optimistic outcomes. 

Premature techno-fixes

If things weren't looking bad enough already, we haven't even begun to see what methane will do, or to what extent the melting arctic will chip in with its feedback mechanisms. We're being told a comforting story, that we'll be fine so long as we do all we can to mitigate emissions.

Then there's the promise of technology. We can suck CO2 from the air and bury it. That's what BECCS is all about (Bio Energy with Carbon Capture and Storage): we grow a lot of trees, burn them in our power stations instead of coal, capture the CO2 that puffs out of the chimney and pump it underground.

Unfortunately, technologies such as these are not ready yet. They exist in laboratory-scale experiments.  Perhaps by 2050 we'll be doing a bit of this, but nowhere near enough to meet our net-zero commitment needed for 1.5ºC.

It looks as if we need a magic wand. Warming is accelerating, polar ice and glaciers are all melting, sea level is rising … it all looks rather bleak.

What the IPCC doesn't mention is that technologies exist, or at least they're not far away,  to directly engineer the climate. It is controversial, but maybe we can refreeze the arctic.

Solar geoengineering

This is the subject of "solar geoengineering".  Behind the scenes there are schemes afoot to cool the climate for a few decades while we work out how to reduce our dependency on carbon, and it gives us time to get the BECCS systems working.

The idea is to reflect some of the sun's energy back into space. For instance we could seed clouds and create more "whiteness", which we know is a good way to reflect the heat of the sun. There's talk of putting mirrors in space which could reflect, say, 2 percent of the sun's rays harmlessly into space (but this would be prohibitively expensive).

The most talked-about "fix" is to mimic volcanic eruptions which act to cool the planet. In 1991 Mount Pinatubo in the Philippines spewed than 10 million tonnes of sulphur dioxide high into the atmosphere where it formed tiny droplets of sulphuric acid which reflect sunlight. Pinatubo caused global cooling of about 0.4oC for about a year and then temperatures reverted to normal.

The technology to mimic volcanos is crazy but just because the IPCC isn't talking about it doesn't mean it isn't there

Even proponents are not enthusiastic about climate engineering. What if we screw it up?  The bottom line truly is that we have to stop burning fossil fuels.

Every option must be on the table

So where are we?  As I see it there are four things to do:

1.      Stop burning fossil fuels. Now.

2.      Work as hard as we can to suck CO2 out of the atmosphere.

3.      Consider solar geoengineering as a temporary fix to buy us some time.

4       Be very ready with sea defences for the inevitable climate emergency.

The IPCC is very strong on (1) and it is banking on technologies for (2). We're all anticipating (4) but why isn't anyone talking about (3)? Of course we have to cut our carbon emissions fast. At the same time we should explore as many climate engineering options as possible. All options remain on the table.

This Author 

Dr Hugh Hunt is chairman of the Cambridge Climate Lecture Series and a reader of engineering dynamics and vibration at the University of Cambridge.  He can be followed on Twitter at @HughHunt.

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