Why net zero is not enough to avert catastrophic climate change
And what else we need to do to avert disasters
The UN says we’re on the highway to climate hell. A 40 degree heatwave bakes most of western Europe. Wildfires burn through southern Europe for the second year in a row. The western US is in its annual fire season. Rivers running dry in China and one third of Pakistan submerged under water. As you may have noticed, this isn’t a prediction of the future under climate change but a description of last summer, with even the normally mild UK hitting forty degrees. These are far from the only freak weather events to strike across the world in the last few years and a common refrain to hear now is that climate change is not a future problem but a present problem.
While this is a regular statement among environmentalists, I don’t think people have fully internalised what the consequences are. A good example of this came up in a recent article on the guardian:
Will heatwaves get worse in the future?
Yes, until the climate crisis is ended. “The current heatwave is a dangerous reminder of the accelerating impacts of global warming,” said Byrne. “With London expected to feel like Barcelona by 2050, the UK is braced for more frequent and severe heatwaves over coming years.”
This is true, but it implies that hitting net zero is the end of the climate crisis. It isn't. The problem is that once we’ve hit net zero, all that CO2 is still floating around in the atmosphere and warming the planet. The atmospheric temperature is going to stay at least 1.5 degrees, probably 2, and possibly 2.5 or 3 degrees above the pre-industrial average, for decades or centuries after we hit net zero. If we stop emitting all greenhouse gases, especially methane (which has a shorter atmospheric half life than CO2)1, we might see a decline of half a degree over the rest of the century2. In other words, if we only achieve net zero, we can expect these disastrous weather events to become a regular series of catastrophes. The only way to avoid enduring these extreme weather events for centuries is to either actively remove CO2 from the atmosphere, or geoengineering.
There are lots of places to read about carbon removal. Stripe (the payments company) have been coordinating early attempts to buy CO2 removal (here's a Volts podcast explaining it). But currently it's extremely expensive and it's not clear how cheap it will get. This causes a lot of people to be sceptical, especially given the absence of any financial incentive for anyone to do it3. Scaling it up to make a difference by mid-century seems tough because even if it's really cheap, the total cost would really add up. We could need ten gigatons a year4 and if it gets to about $100 a ton5, that’s a trillion dollars a year. Nevertheless, in the long term we will still need to do this, but there’s another option we could explore that will give us a bit more time to get the removal industry up to the scale it needs to be: geoengineering.
Geoengineering is any deliberate attempt to alter the climate (so current emissions are excluded because that's not their intent).6 The most famous method is spraying sulphur dioxide (SO2) aerosols into the stratosphere, which reflects sunlight back into space. This process is well understood as it happens naturally during volcanic eruptions, the most famous and well studied being Mount Pinatubo in the Philippines in 1991, which cooled the Earth by about half a degree. It would be surprisingly cheap to artificially mimic this: roughly $2-3 billion a year over the first 15 years. This is about the cost of Hinkley point C, which will power about 7% of the UK’s grid7. The cost would vary a bit depending on how aggressively you wanted to mitigate the increases but it’s clear that it’s affordable by the average developed nation. For comparison, the total cost of reaching net zero is likely a hundred trillion dollars.8
However, geoengineering will have consequences beyond the desired ones. In the case of SO2 emissions, the most notable is potential ozone depletion. This would obviously be bad, however there might be ways to reduce or avoid this, such as by using calcite instead of, or in addition to, SO2. Alternatively, we could build enormous numbers of mirrors to reflect the sunlight into space - this would have local benefits in terms of reducing ambient temperature and fewer atmospheric side effects9. But we won’t really know how well it works unless we try. By starting small and scaling up, we can stop if we see unbearable or unmanageable side-effects. The best method isn’t clear yet but the case for doing so - if you believe this is a crisis - is clear.
The main objection to geoengineering is moral hazard: that it will be a licence not to reduce our emissions and countries will abandon efforts to hit net zero10. That’s a legitimate worry, but I think it's now overblown and less of an issue than it would've been around ten years ago. The progress on climate over the previous decade has been better than it looks. Although emissions grew overall, they fell in the most developed countries (and no, this is not because they were outsourced) and the price of solar, wind and batteries all fell hugely - by between 60% and 90%. Lots of further reductions in emissions and renewable deployments are already locked in through legislation. Research in geoengineering isn’t going to undo any of that.
In short, fossil fuels are losing - it’s cheaper and better to be green. Electric cars are cheaper to run and more reliable than internal combustion engine cars and soon they’ll be cheaper to buy; solar and wind power are already cheaper than building new fossil fuel plants and soon they’ll be cheaper than running them; clean or lab-grown meat, eggs and dairy will be cheaper and better than industrially farmed meat, eggs and dairy.11 We’re going to hit net zero whether we deploy geoengineering or not.
There’s an additional argument in favour of geoengineering that doesn’t suffer from the same issues of moral hazard, and might be the strongest argument altogether: tipping points. There are a range of events that could trigger further warming once reached, like an ice-free arctic, permafrosts melting, or glacier collapse. Hitting these would make everything worse and some of them are likely to happen given the current trajectory of emissions and temperatures. This could take us far past 2 degrees of warming.12 Considered in this way, geoengineering actually reduces the risk of further climate change by keeping the climate below the point at which tipping points occur, instead of increasing it through moral hazard and more fossil fuel consumption.
Some methods of geoengineering explicitly target these tipping points, mainly preserving glaciers and Arctic sea ice. Maintaining Arctic sea ice (proposals include scattering silica beads on the surface and pumping sea water onto the ice in winter) would keep the albedo of the north pole high and stop darker sea water absorbing more heat than the white, reflective ice. Slowing the melting of glaciers (in Greenland and Antarctica) would also keep the albedo high while delaying sea ice loss until temperatures stabilise and decline. They also pose less of a risk of unexpected changes to weather patterns than methods like sulphur dioxide.
There is an odd disconnect between the rhetoric about climate change and the realities of net zero. If you think the climate crisis is already here, then the climate crisis won't end for hundreds of years even once we hit net zero because net zero just stops things getting worse. The only way we can make things better is with carbon removal and geoengineering. They’re not alternatives to net zero, they’re complements. But we can’t afford to wait until net zero is achieved (sometime between 2030 and 205013) before we start working on them. That condemns us to another two decades of escalating climate disasters and increases the risk of hitting tipping points that make things truly awful. We should instead start work on them now, so we can use geoengineering to keep temperatures low - and preserve glaciers, Arctic sea ice and permafrost - while we begin drawing down CO2 from the atmosphere.
The argument that geoengineering and CO2 removal will create moral hazard and lead to more consumption of fossil fuels doesn't take into account the progress that is already locked in, or that elevated temperatures are a crisis we need to deal with now, or the fact that tipping points are a problem we can't otherwise solve. Nor is either likely to be ready at the required scale to meaningfully disincentivise efforts to hit net zero. There are some risks to both, but there are huge consequences to not doing it too. All the storms, heatwaves, wildfires, floods, droughts that we’ve endured this past decade will carry on for centuries. Given that they will only get worse as net zero remains at least a decade or two away, a refusal to explore geoengineering and CO2 removal is a commitment to their continuation.
Methane might actually be sticking around for longer due to wildfires
See this article for more detail
There are frequent arguments about the unfairness of climate change: how the developed world is responsible for a larger share of emissions, how the burdens are going to fall more heavily on less-developed countries, and the extent to which developed countries should compensate the rest of the world for it. One good form this could take is CO2 removal.
We currently emit about 34 gigatons a year.
Which is an optimistic assessment based on what we need, not what the tech will necessarily provide.
I actually think this is bad because the intent kind of doesn't matter and I think it biases the case against geoengineering. It's not messing with a pristine environment, the environment is already messed up. It's asking whether if you deliberately mess it up further in a very specific way, is that on net less bad than the mess you have already made unintentionally.
You’d get about twice as much power from solar (in the UK you’d probably get a little less because it’s much less sunny than Georgia).
Global GDP is $84 trillion to put this number in perspective. It’s not quite as crazy as it sounds. McKinsey estimate about $250 trillion. I’m not sure how or if these numbers account for the counterfactual i.e. if you didn’t spend money on renewables, you would still need to invest lots in developing new gas and oil exploration. So the incremental cost of net zero would be lower, leaving aside the many positive benefits in air quality or whatever.
Painting roofs white works in a similar way but would only make a small difference to global temperatures - the main benefit would be reducing the urban heat island effect.
People do also object to further meddling on general principles, and potentialy unintended consequences. But the one I hear most often is this.
The amount of land we’ll be able to free up from agriculture if / when we switch to lab-grown meat will be very helpful for creating lots of carbon sinks: livestock rearing currently takes up about 40% of all habitable land. This is the only way other than active removal that we’ll make a dent in the 400+ ppm any time soon.
Two degrees is the average and some places have already warmed more than that. Unfortunately for at least three of the tipping points, that includes the arctic.
I think we’ll get there sooner than 2050 because the trend lines (the prices of rewnewables and the technological development of zero carbon alternatives to industrial processess e.g. green hydrogen ) are all going in the right direction. Low carbon electricity is going to spread faster than people think and transform currently carbon intensive industries into low carbon ones. We won't hit it by 2030 - which is annoying because we probably could have got close if we'd tried harder - but 2040 is achievable with the right policies, and 2050 will happen even if lots of governments are terrible.