It鈥檚 2076 and the skies are looking decidedly milky. On windy plains and in parts of the seas that have been turned over to wind farms, a different kind of tower has been built alongside the turbines. They suck carbon dioxide out of the atmosphere. Vast parcels of land have been given over to forest. Trees are grown, harvested and burned for energy in power plants that don鈥檛 let CO2 escape to the atmosphere. Instead, emissions are captured and pumped into underground storage reservoirs. Ships dump powdered minerals into the water to soak up CO2 and reduce ocean acidification.
All these technologies are a desperate rearguard action to reverse more than two centuries of greenhouse gas emissions. But they are not entirely up to the task and, anyway, we are still emitting greenhouse gases. So, 10 to 18 kilometres up in the atmosphere, a fine spray of particles shields Earth from the sun and keeps us cool. It鈥檚 what is making the skies that little bit whiter.
Advertisement
鈥淚 think it鈥檚 very likely that in 60 years we鈥檒l be using both technologies,鈥� says John Shepherd of the University of Southampton, UK. He is referring to the two flavours of geoengineering: sucking CO2 out of the air and deploying a sunshade to bounce some of the sun鈥檚 rays back out into space.
Like many climate scientists, Shepherd thinks climate talks are going too slowly. Even if industrial emissions were to drop rapidly 鈥� a big if 鈥� some sectors pose an intractable problem. We have no real replacement for aeroplane fuel and feeding people demands intensive agriculture, which accounts for a quarter of global emissions.
That is why we will have to suck CO2 out of the air. And because that is a long way off, we will probably also have to rely on 鈥渟olar radiation management鈥�.
The most studied version is spraying fine particles of sulphate into the stratosphere, yet its consequences are still poorly understood. Computer models suggest there will be winners and losers. While a sunshade could lower global average temperatures to pre-industrial levels, there would be regional differences. Northern Europe, Canada, Siberia and the poles would remain warmer than they were, and temperatures over the oceans would be cooler.
Global warming is predicted to make wet regions wetter and dry ones drier. Models suggest a sunshade would rectify this, but, again, not in a uniform way. Tropical regions that depend on seasonal rains could suffer most, with monsoons drying up.
Shepherd fears all this will feed into international disputes. He envisages some kind of global council where governments lobby for a climate that meets their needs. Some might prefer a slightly warmer temperature, for tourism or agriculture. But nations whose coral reefs draw in visitors will probably want more CO2-sucking technologies to counter ocean acidification and bleaching.
There鈥檚 a final, bitter twist. What goes up must come down, and so a sunshade would have to be continually replenished. If something were to happen 鈥� say, a complete breakdown of some international geoengineering agreement 鈥� and we stopped spraying sulphates, the consequences would be catastrophic. Within a decade or two, temperatures would soar to where they would have been without the sunshade. Warm regions would fry, and who knows what tipping points we would fly past. The consequences are barely worth thinking about.
Read more: We鈥檝e seen the future, and it will blow your mind
New Scientist is 60 years old this week, so how will the next 60 play out? We look forward to how science and technology might upturn the world as we know it
This article appeared in print under the headline 鈥淲hat if鈥� We have to rescue the climate?鈥�
