EnvironmentalTechnology & Robotics

Solar Geoengineering – a step too far to save the planet?

With the symptoms of Global Warming creating ever-more catastrophic weather events, Barack Obama described the 2016 Paris Climate Accord as “the best chance to save the planet”. Why? Because – among other important conclusions – the Accord detailed the emissions-reduction measures that would be necessary to limit this century’s global temperature increase to 1.5 Celsius above the levels prevalent in the years 1850-1900 (ie, pre-Industrial Revolution 2.0). In other words, it set criteria that could in effect halt and reverse much of the damage already done.

However, in 2019, the United Nations Intergovernmental Panel on Climate Change issued a grim warning that the basic presumptions of the Paris Accord might be wildly optimistic. They gave a newer version of events: one suggesting that global warming was already at an irreversible threshold of raising temperatures well in excess of 2.0 Celsius – which could, needless to say, not only drive millions of people out of previously marginal sub-desert regions, but have an unthinkable impact on the icecaps, leading to massive and unmanageable rises in sea level.

A different approach

Sceptics have long argued that few – if any – nations are capable of reversing their emissions to anything like the standards that either of these reports require. They argue that much bolder steps need to be taken if humanity wishes to develop at its present rate and not have be coerced to live in a small and super-crowded bandwidth of habitable territory. One of these solutions is Solar Geoengineering – a process that actively seeks to block the amount of the Sun’s rays that the earth receives, thereby cooling the surface of the planet. Science fiction? Not if the think-tanks of Harvard University and MIT are to be believed – they both have billion-dollar research projects defining the systems by which this could actually be achieved – along with co-venture backing from some of the world’s biggest technology titans.

As its end-game, Solar Geoengineering seeks to reflect a small fraction of sunlight back into space – or to increase the amount of solar radiation that actually escapes back into space. Either approach, the argument goes, will cool the planet. There are several proposed solar geoengineering technologies. These include marine cloud brightening, cirrus cloud thinning, space-based techniques, and stratospheric aerosol scattering, amongst others. What are these and how would they work?

  • Marine cloud brightening would attempt to brighten marine clouds to reflect more sunlight back into space.
  • Cirrus cloud thinning would attempt to reduce the thin, high-altitude cirrus clouds to emit more long-wave radiation from the earth to space.
  • Space-based technologies would attempt to reflect a small fraction of sunlight away from the earth by positioning sun shields in space.
  • Stratospheric aerosol scattering would introduce tiny reflective particles, such as sulfate aerosols or perhaps calcium carbonate, into the upper atmosphere, where they could scatter a small fraction of sunlight back into space.

Climate models have consistently shown that Solar Geoengineering, when used in moderation and combined with emissions cuts, has the potential to reduce climate changes around the globe. For example, it could reduce climate impacts such as extreme temperatures, changes in water availability, and intensity of tropical storms. So far, so good.

What about the risks?

It’s when we consider the risks that we enter the territory of the most daunting science fiction. Any benefits come with ‘novel risks’ (the term used by Harvard University scientists) and significant uncertainty. For example, while the latest science might show some benefits globally, local impacts could vary more widely. There are a lot of other scientific uncertainties that are not yet well understood, not least the enormous governance challenges – who is going to supervise all this and finance the trillion-dollar infrastructure that it would necessitate? 

What’s more, Solar Geoengineering doesn’t aim to address ocean acidification. Every year, the ocean absorbs about one-quarter of the carbon dioxide we emit into the atmosphere, changing the chemistry of the oceans and harming marine ecosystems. Given that Solar Geoengineering would not remove carbon dioxide from the atmosphere directly (because it reflects sunlight back into space), it wouldn’t do very much to address this serious problem.

That said, Solar Geoengineering could reduce rising temperatures, offsetting many of the worst impacts on the oceans. For example, by reducing sea surface temperatures, it could reduce the risk of coral bleaching events and help to maintain conditions favourable for coral reefs (as the damage to coral reefs is largely caused by rising sea surface temperatures, followed by intensifying ocean acidification). It could also reduce the amount of sea-ice loss, which could help to limit changes in ocean circulation and glacier melt. 

All these, though, are relatively small pay-backs when compared to the uncertainties that an all-out commitment to Solar Geoengineering would entail. An untried and untested science could set in motion an over-cooling, taking the earth back into an ice age within a century of the mechanisms being set up. Whatever the effects, the technologies employed might be truly irreversible and a harsh case of ‘act in haste – repent at leisure’.

The fact is that the earth doesn’t have to see Solar Geoengineering as an either-or. Rather, it can work in liaison with international efforts to cut down emissions – and constrained in this way – it may not be required to go to the more hazardous extremes of feasible science. Despite the potential appeal of a ‘sun-blocking’ solution, solar geoengineering isn’t likely to be a substitute for cutting carbon dioxide pollution. Yet it can be a powerful potential supplement.

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