Outlook - Scenarios for the transition to a world with deliberate climate intervention?

Whether climate engineering will ever be used remains an open question. The use or non-use of a given method ultimately depends on its potential and risks. Several conceivable scenarios could lead to a future where our climate is deliberately influenced on a large scale. Some involve a gradual adoption of CDR methods. Others see future deployment as an emergency response.

Before any CDR or RM method can be deployed on a large scale, many in-depth questions would have to be answered – not only on management and control, but also on the potential, feasibility and side effects of the various methods. Answering such questions is difficult, because for many CDR and RM methods, not even geographically limited field experiments will suffice to gauge their limits and side effects prior to large-scale deployment. Knowledge deficits and uncertainties will remain as a result. Scientific analyses, based on scenarios of future developments, serve in the performance of integrated impact assessment and the identification and quantification of uncertainties.

In theory, any state could deploy climate engineering methods if it can rule out the possibility of neighbouring states being affected. This is almost impossible to determine, however, because both CDR and RM measures can have transboundary negative environmental impacts when applied on a large scale – although the effects of land-based CDR methods tend to be more regionally restricted than those of other CE methods. One consequence of cross-border effects could be political tensions. For this reason, internationally agreed rules of procedure and institutions for dispute resolution are needed before CE methods can begin to be used.

Climate engineering has repeatedly attracted heavy criticism in public debate in recent years, for example with regard to risks and side effects, sustainability and ethics. This raises the question of whether, or in what circumstances, it will ever be possible to use CDR or RM. Some experts consider it realistic for CDR methods to be introduced in a strategy of small steps. As the example of afforestation shows, there could be a seamless and fluid transition from today’s climate action and nature conservation measures to climatically significant use of CDR. It is also thought to be realistic that certain methods will have a firm place in the energy landscape of the future, alongside energy efficiency and climate action – a scenario that moves away from the black-and-white ‘CDR or no CDR’.

The examples that follow illustrate conceivable paths and scenarios for a transition to a world with deliberate climate intervention on a large scale. This is a neutral compilation and is provided for the sole purpose of outlining the range of conceivable scenarios.

1. Gradual transition from climate action to carbon removal

Various companies have long offered customers the option of offsetting their CO2 emissions from air travel or consumption. Consumers pay a certain amount per purchase or per mile flown in order, for example, to finance reforestation projects in suitable regions. The companies benefit from an image gain, which gives them a competitive advantage. Consumers, for their part, can reduce their carbon footprint without having to change their lifestyles to any great extent. As a result, in this scenario, there is an increase in locally adapted afforestation and restoration of peatlands and coastal ecosystems (such as seagrass meadows and mangrove swamps). Storage of carbon on pasture and arable land is increased by spreading biochar and adopting specific agricultural practices. This can improve soil fertility and the resilience of agricultural ecosystems. These measures are also compatible with nature conservation. But verification is needed – by measurements or computer modelling –to ensure that the net climate balance is positive. In wetland and peatland restoration, for example, the additional absorption of CO2 must not be cancelled out by increased emissions of the greenhouse gas methane.

It is true that substantial quantities of CO2 are removed from the atmosphere in this way. But the measures are not enough to limit climate change. In this scenario, demand for offsetting measures increases. The methods are then included in emissions trading schemes, which becomes economically worthwhile when the price of CO2 rises. There are proposals for finance schemes involving international offsetting mechanisms. The methods implemented reach a scale where conflicts ensue with other human objectives: conflicts over water, about land for food production, and with regard to nature conservation concerns such as avoiding biodiversity loss. Computer models also show that large-scale afforestation projects change precipitation patterns.

What began in individual states without harming the population or neighbouring states thus reaches a scale that calls for close cooperation between all parties involved, from farmers to consumers to politicians. Policymakers start to realise, albeit rather late, that there is a need for regulation and introduce control and steering mechanisms with assistance from international bodies.

2. Carbon removal as an integral component of ambitious climate policy

In this scenario, the Parties to the Paris Climate Agreement have met their agreed 2030 CO2 emission reduction targets (nationally determined contributions, or NDCs). At the same time, a policy initiative is launched to further step up emission reductions beyond 2030 in order to achieve the long-term 2 °C target. This internationally agreed and differentiated climate policy for the period beyond 2030 also includes an increase in the price of CO2, which contributes to a drastic reduction in CO2 emissions. In addition, the electricity and heat sectors are decarbonised in a complete switch to renewable energy. Most of the transport sector now runs on electricity, eliminating large quantities of emissions from motor fuel. Energy efficiency measures are implemented. Yet it is evident that all of these measures are not enough to limit global warming to 2 °C. To stabilise the temperature, emissions of CO2 and other greenhouse gases must be reduced to zero in all countries – and for equity reasons in the richer countries first. Some emission sources nevertheless remain. For example, greenhouse gases are still released in industry and agriculture. It also becomes evident that the ambitious climate policy efforts have come too late and that the remaining budget for the 2 °C target will be exceeded before too long. Industrialised countries thus begin to build huge CCS infrastructures in order to reduce their industrial emissions and store CO2 extracted from the atmosphere by direct air capture. In this way, the remaining emissions are neutralised and the budget that has already been exceeded is also offset over time. Governments that have not been able to expand CCS infrastructure quickly enough face the challenge of importing CO2 emission allowances to offset the remaining residual emissions. When it comes to importing allowances from tropical countries, however, it must be borne in mind that large-scale afforestation and biomass cultivation require a lot of land, and that this could lead to displacement of indigenous peoples, rising food prices and impacts on both biodiversity and the water cycle. At the same time, the growing BECCS industry and the sale of emission permits could lead to increased prosperity, more jobs and improved quality of life. To create the conditions for fair and sustainable design of the policy initiatives, technology development and transfer policies are pursued. An international authority keeps inventories of greenhouse gas emissions and of the carbon savings achieved by removing carbon from the atmosphere. It also coordinates the measures implemented on a global scale.

3. Coastal countries deploying ocean-based CE

A different scenario presents itself for the adoption of climate engineering by coastal countries: As part of their climate action strategy, states use ocean-based technologies to remove carbon from their territorial waters. Initially, alkaline minerals are introduced during the construction of coastal defences. This provides practical experience with regard to weathering performance, CO2 removal potential and ecologically tolerable limits. The coastal countries obtain agreement for enhanced weathering of alkaline minerals to be recognised under the EU Emissions Trading Scheme (ETS), subject to compliance with strict water chemistry thresholds. This creates financial incentives that lead many companies to step up the development of basalt dust spreading technology. Due to strict environmental standards for basalt extraction, high transportation costs and narrow seawater chemistry thresholds, individual companies shift extraction and oceanic spreading of basalt dust to Australia. After the ETS is expanded to cover Australia, the mining industry there begins large-scale basalt extraction in order to advance CO2 removal via enhanced weathering in the ocean. After a decade, carbon removal amounting to one billion tonnes of CO2 per year is achieved in European and Australian territorial waters alone. But off the coasts of Australia, due to lax environmental standards, algae and fish die-off becomes a recurring problem. Amendments to international agreements for the protection of marine ecosystems to include the introduction of basalt dust lead to binding upper thresholds for chemical intervention in seawater worldwide.

4. Rain on demand

From about 2030, encouraged by new research findings, China, Saudi Arabia and India try out cloud modification to regulate precipitation over their territory. Many other countries are interested in the possibility of increasing agricultural productivity and creating more agreeable weather. Even if the success of the measures is disputed, demand for cloud modification rises. Companies invest in further research and development of cloud modification technology. A new industry starts to emerge, hailing a new era in agricultural production. Global distribution of clouds is now more even. And controlled precipitation is possible for all – for all who can afford it, that is.

There are also localised changes in temperatures. The basic principle seems to be working, so work starts on modifying marine stratus clouds to counteract the global rise in temperature. Warnings of possible changes in ocean currents and resulting changes in the global climate system, or of negative effects such as the absence of rain in areas where clouds are not modified, go ignored. The benefits of the new weather have most people convinced – and the cloud modifying industry assures the world that its technology has no notable side effects.

5. Increase in extreme weather events makes radiation management a must

Around the year 2030, it is becoming increasingly clear that most countries will continue to fall far short of their declared emission reduction targets. Extreme weather events such as droughts, tropical storms and floods are becoming far more frequent worldwide. In the eyes of the public, measures to reduce greenhouse gas emissions and adapt to climate change are no longer sufficient to counteract its effects. In many countries, calls are becoming louder for reflective particles to be introduced into the stratosphere because that works faster than reducing greenhouse gas emissions or using CDR. In addition to countries that are directly affected, the method is supported by countries highly vulnerable to sea-level rise or glacial melt, and also by a number of NGOs. A coalition of the willing forms to promote the use of radiation management methods, even though, right now, the long-term effects cannot be foreseen. Critics fear that once implemented, the method will push reduction of greenhouse gas emissions into the background. Its proponents thus commit to combining the deployment of RM methods with increased use of measures to reduce emissions and remove CO2. An international body is created to monitor and control the use of RM and greenhouse gas reduction. But many questions remain unanswered: Will the promises and pledges be kept? Does the new international body have sufficient authority and power to control and limit deployment? Will spreading reflective particles really result in fewer extreme events, or will there soon be calls to stop?