We must deal with climate realities

I have been very busy with multiple projects recently. That sounds like an excuse for reduced frequency of writing here. Because it is. These projects are entwined, encompassing net zero, overshoot, geoengineering, AI, and the technosphere. I thought I would try and see if Technosphere Earth could serve as a place where I show some of my working. I will still write standalone articles, but will also post ideas about ideas. There is so much going on, if nothing else it may help to take a beat and try and order thoughts. I hope that will be of interest to others. Let's see.

One thing to note this week is that public screenings of the National Emergency Briefing film are kicking off around the country. I attended a screening yesterday hosted by Exeter Phoenix. Tickets sold out quickly - there are plans to hold another in the city. Next month I will be in Plymouth (details TBC). If you haven't seen the film, then please do. To be honest I was steeling myself to be slightly disappointed. In the end I was completely engrossed. Congratulations to the Simon, Nick, Mike and the rest of the team. This is the sort of project that has the potential to burst out of the environmental echo chamber and produce some meaningful change.

To conclude this week I've posted a draft of an article I have been asked to write about overshoot. The brief was to consider whether returning to 1°C of warming was possible. I've tried to be as polite as possible. I've yet to talk to the editors about it. It may change - a lot. In any event, this was my first take!

A 1°C warmer world will exist only in our memories

Determining what constitutes dangerous climate change is an unavoidably subjective exercise. After decades of international negotiations, in 2015 the international community settled on “well below 2°C” as the point at which climate change must not progress. This was formalised in the Paris Agreement, adopted at COP21 on 12 December 2015. This was later refined as 1.5°C in part because of the increasing acknowledgment that while 2°C may be manageable in rich, industrialised nations, warming beyond 1.5°C would represent an existential risk to many low-lying island nations who would be underwater as a consequence of sea level rise. This issue helps highlight the large differences in vulnerabilities to climate change, as well as the vast differences when it comes to which nations are most responsible for the climate crisis.

The rapidly developing science of tipping points is refining what is considered safe, with increasing evidence that above 1°C lurk potentially rapid and irreversible changes to the Earth system that could have catastrophic consequences. Given that we are about to breach 1.5°C of warming, the only way we would be able to reduce some tipping point risks would be to reduce the amount of warming itself. The good news is that if we rapidly phased out the burning of fossil fuels at the same time as decarbonising our food systems, then the natural biogeochemical cycling processes of the Earth would remove all the extra carbon we have put into the atmosphere, and temperatures would fall. The bad news is that will take about 100,000 years.

If a week is deemed a long time in politics, then a hundred millennia is an eternity. If we hope to keep warming to anywhere around 1°C then we would need to deliberately interfere with the climate system. The term used to describe this is “geoengineering” and would be advanced via two routes. Carbon Dioxide Removal (CDR) captures a wide range of techniques that would accelerate the removal of carbon dioxide from the atmosphere. Solar Radiation Modification (SRM) covers a suite of proposals that would alter the energy balance of the Earth such that more energy leaves than enters and so warming would reduce. While some of these ideas sound like science fiction — mirrors twice the surface area of India launched into space in order to block energy from the Sun — the notion of geoengineering has become central to all climate policy that seeks to limit warming to not just 1°C but arguably any amount up to and beyond 3°C. That’s because geoengineering has become a key component of “overshoot” where warming is going to exceed safe levels with future technologies being proposed as a way to lower warming. This overshoot approach can be understood as the evolution of “net zero”.

Back in 2015, limiting warming to well below 2°C would have required a rapid phase out of fossil fuels. Given that this pace of decarbonisation would have significantly disrupted political and economic systems, researchers working on climate policies instead proposed an approach in which the pace of decarbonisation could be moderated by accompanying it with carbon capture and removal. The argument at the time was that so called “hard to decarbonise sectors” such as aviation, and steel manufacturing, would be able to continue to emit carbon dioxide as long as an equal amount of carbon dioxide could be removed from the atmosphere. If what goes down equals what goes up, then we would reach net zero in which humanity’s forcing of the climate stops. In some respects, defining exactly which sectors are hard to decarbonise is moot, because such a net zero approach depends on there being credible plans to permanently remove carbon from the atmosphere. Unfortunately, rather than pegging net zero policies to carbon removal capabilities, the effective promise of future carbon removal facilitated a “burn-now-pay-later” approach which has seen carbon dioxide emissions continue to increase over the past decade, with 2025 posting record-breaking levels.

Today, annual carbon dioxide equivalent emissions stand at approximately 42 billion tonnes a year. Carbon dioxide removal capacity is estimated at just over 2 billion tonnes a year with over 99% of this being deemed “nature based” in that the carbon is removed largely via reforestation and afforestation. The fundamental limitation with such approaches is that while the carbon has been removed from the atmosphere, it has not been removed from the biosphere. Trees die and when they decay the carbon they removed during their growth is respired back into the air. Tree mortality in certain regions is forecast to increase as a consequence of hotter and drier conditions driven by climate change. There have already been instances of large wildfires releasing carbon from forests that were being used to offset carbon emissions. For it to play a useful role, CDR has to permanently store captured carbon by converting the gas into minerals. This is promised to be achieved via “engineered removals” such as Direct Air Capture which strips carbon dioxide out of the air using chemical sorbents, and then stores the carbon dioxide within the crust, such as depleted oil and gas fields. There the gas will slowly form carbonaceous rocks and so will reside essentially forever. This not only solves the permanence problem but also the land use problem, because while hundreds of millions of hectares could be required for nature based CDR, the footprint of DAC is orders of magnitude smaller. Unfortunately its energy footprint is potentially vast.

Atmospheric carbon dioxide concentrations are measured in parts per million. Removing this very dilute gas from the air, compressing, and then storing it underground is essentially reducing the entropy that was increased when the highly carbon dense fossil fuels were burnt in the first place. This means there are unavoidable thermodynamic limits on how efficient this enterprise could be. Issues of efficiency could be dealt with by significantly increasing available energy. However, scaling up current DAC technologies to gigaton scale could require a substantial fraction of global electricity generation; generation that is urgently needed to decarbonise transport and other sectors. What this means is that CDR has currently very little role in limiting warming to 1°C. It is here that Solar Radiation Modification is offered as a potential climate saviour technology. SRM could be progressed in two ways: first, by decreasing the total amount of shortwave radiation entering the Earth from the Sun; second, by increasing the total amount of longwave radiation that leaves the Earth out into space. The majority of current SRM research and funding focuses on the first route, with Sulphate Aerosol Injection (SAI) generating most interest.

Volcanoes are natural sources of aerosols. Large eruptions can inject millions of tons of dust and sulphate compounds high into the atmosphere, where they will reside for around a year before being precipitated out. The eruption of Mount Pinatubo in 1991 is often cited as the inspiration for SRM research because its sulphurous ejecta dropped the global average temperature by around 0.5°C for nearly two years. However, the first proposals for SAI to be deployed in order to offset human-caused warming can be traced back to the 1970s. In that respect it is not a new idea. What is relatively recent is the increase in arguments that it should not only be researched, but actively deployed. If one considers warming beyond 1.5°C to represent unacceptable risks, and if CDR remains very limited, and if emissions continue to rise, then the only option would be to deploy SAI as this is currently the best researched SRM technology. It is hard to say what exactly SAI’s readiness level is. In principle, all the technologies exist in that a fleet of several hundred wide-bodied jets could be repurposed into sulphur tankers that could deliver the required dose at sufficient altitude to have an almost immediate cooling effect.

This would not come without risks. Tens of thousands of people may die from air pollution each year as a result of injecting several million tons of sulphurous compounds into the atmosphere. While this is significant, most SAI research is motivated to try to understand the global and regional climatic consequences. For example, there are reasons to conclude that injection in high latitudes has the potential to disrupt regional climate dynamics in lower latitudes. This could include the movement in space and time of vital seasonal rains. Research indicates that the South East Asian monsoon could be delayed, or its intensity significantly reduced. This opens up the potential for further climate inequities not to mention a significant complication of climate change diplomacy. Thus far the international community has struggled to decide how the existing carbon budget for 1.5°C of warming should be best allocated. How it is to manage individual nation states deploying SAI at a time of increasing climate related loss and damage, forced migration, and economic impacts have yet to be seriously considered.

What this means is that prospects of returning warming to 1°C anytime this century must be currently assessed as being extremely small. Therefore, the most robust and just response to the climate change challenge is to fundamentally rethink climate policy so that it can do the job of producing a rapid fossil fuel phase out. Crucially, it will also need to consider how best to respond to existing climate impacts while preparing communities for the likely serious deterioration of environmental conditions for the rest of this century and beyond.

This is a frightening prospect. It’s understandable that some may wish to take refuge in the promise of future technological solutions. But this moment demands a sober appraisal of the science and technologies available today. The amount of warming humans have produced since the industrial revolution is a surprisingly simple sum of cumulative emissions. What this means is that past actions have fixed our present climate. The amount of future warming is still very much up to us.