We can only achieve climate neutrality with a fundamentally restructured energy system, the design of which takes into account the remaining quantities of permitted greenhouse gas emissions for the energy sector. This is stated in the joint ad hoc statement “Energy transition 2030: Europe’s path to climate neutrality” from the German National Academy of Sciences Leopoldina, acatech – German National Academy of Science and Engineering, and the Union of the German Academies of Sciences and Humanities. Published in 2020, the statement emphasises that while a fundamental transformation of the energy system is technologically possible, it still represents the key challenge of climate protection.

Energy conversion worldwide needs to be completely rethought so that industry and society as a whole can completely cease the use of fossil fuels. Legal interventions (requirements and bans) and effective incentives are all essential in setting the course for this transformation.

Cross-sectoral energy transition

The energy sector is responsible for approximately three quarters of global greenhouse gas emissions. Many sectors must be switched to electric as quickly as possible to limit global warming. This is why more electricity will be needed in future – from renewable energies. Developing photovoltaics and wind turbines plays an important part in this. But energy generation is not the only crucial point. The departure from coal-based energy must include all sectors, including heating and transport, and industrial processes.

A comprehensive transformation is required if net zero greenhouse gas emissions are to be achieved worldwide by 2050. The roadmap “Net Zero by 2050” published by the International Energy Agency in 2021 states that an extensive development of solar and wind energy is necessary. Photovoltaics must be expanded by an additional 630 gigawatts (billion watts) annually up until 2030; wind power by 390 gigawatts. To compare: The world’s largest solar parks in India and China are working towards approximately 55 square kilometres on each surface, or approximately 2,200 megawatts (million watts).

At the beginning of 2022, the German Federal Government announced their goal of being able to cover approximately 80 percent of gross energy requirement using renewable energies. This means that the annual addition of solar and wind turbines has to be tripled. In terms of photovoltaic plants, this addition must be increased from five to 20 gigawatts, land-based wind turbines from two to ten gigawatts, and wind turbines in the sea from less than one gigawatt to seven. This is explained in a statement published in June 2022 entitled “How can the expansion of photovoltaics and wind energy be accelerated?” (“Wie kann der Ausbau von Photovoltaik und Windenergie beschleunigt werden?”) from the ESYS (Energy Systems of The Future) academy project.

Short- and long-term storage as well as flexible power use models are required to compensate for the inconsistent availability of solar and wind energy. Alongside pumped storage plants and batteries, flexible electrolysis facilities for generating hydrogen and methane are increasingly gaining in significance.

Given its cavern and pore storage, the existing natural gas network could be used as a long-term storage space. Reserve capacity is needed to ensure supply in all weather situations and at all times of the year. Low-emission gas power plants, combined heat and power plants powered by hydrogen, natural gas or synthetic methane, and fuel cells all represent suitable reserve systems.

Carbon pricing

Scientists consider carbon pricing an effective tool for shifting the decisions of stakeholders in all sectors of the energy system away from fossil fuels and toward regenerative energy sources. This is likewise emphasised by Leopoldina in its statements on climate protection as well as its May 2022 statement in cooperation with the science academies of the G7 countries entitled “Decarbonisation: The Case for Urgent International Action.”

While there might be several approaches to implementing this economic tool in practice, the basic idea is simple. The use of fossil fuels such as coal, oil and natural gas is made more expensive by associating greenhouse gas emissions with costs. This increases the appeal of alternative energy sources and decreases the appeal of using fossil fuels.

Carbon pricing would be more effective as an incentive if it were to be supplemented with further measures, especially infrastructure investments that would provide society with more options. For example, pricing emissions in the transport sector would only convince people to convert to electromobility if a sufficiently developed charging infrastructure already existed. The strength of carbon pricing is that it creates incentives for individual action, which lead in the right direction even if stakeholders think little about whether their actions meet high moral standards.

With regard to the practical implementation of this idea there are two basic ways to put a price tag on greenhouse gases. First, CO₂ emissions can be reduced by assigning a fixed price in the form of a tax or fee. Second, maximum emission amounts could be set and then bought and sold as certificates in an emissions trading system. Such certificates would give someone the right to release a certain amount of CO₂ into the atmosphere. The permissible amount of CO₂ is defined according to the carbon budget specified in the emissions trading system. A global emissions trading system would be based on the remaining carbon budget at a given time in order to meet the Paris Agreement targets of maximum warming less than 1.5 °C or 2 °C. The smaller the budget, the more expensive the certificates would be in the emissions trade.

Carbon pricing alone would most likely not result in the achievement of the climate targets for 2030, at least not unless the price was unrealistically high. This means that complementary measures, especially investments in infrastructure to complement the transformation of the energy system, are required. Revenue from carbon pricing can help finance such investments. This revenue, however, will also be needed to provide social compensation to the lower income-groups facing hardship during the course of the transformation. This could be generated by reducing energy prices and in the form of a “climate dividend”.

The concept of a circular economy

The pricing of CO₂ emissions would certainly help in the event that people do not change their basic attitude towards handling resources. Yet an overall rethink in terms of resource use could likewise lead to huge changes, which in combination with strict pricing and changed attitudes, presents enormous potential. The current linear economy model in which products are designed, produced, used once or only briefly and then disposed of should be increasingly replaced with a circular economy.

What many people already know from waste recycling is expanded to cover other areas. This requires products of all kinds to be made out of easily sortable and reusable materials. They must also be durable, easy to repair and suitable for intensive use. Further, reuse, redesign and recycling processes can help decrease energy and resource use and thus contribute to protecting the climate and preserving species. It is crucial that this also involves a systematic switch to a sustainable circular economy that goes beyond our current approach to waste management. It also includes policies on tax, finance and trade and must be integrated on a technical, economic, political and societal level.

Obtain climate-neutral energy

The main goal of climate neutrality can only be successfully achieved if the energy system is comprehensively restructured and consistently decarbonised, i.e. if fossil fuels are no longer used at all. According to data from the German Environment Agency, some 83 percent of greenhouse gases and air pollutant emissions in Germany in 2020 were related to energy – they arose during the conversion of energy fuels such as coal, natural gas and oil into electricity and heat.
 
Structures and facilities in the energy landscape are so durable and complex that facilities being built now can still be used in twenty or thirty years’ time. It is therefore essential that the right decisions are made as early as possible. Leaving an established path is always difficult. Yet there are only a few alternatives which could allow a successful systematic change in how energy is obtained.

Thus far, photovoltaics and wind energy are the only options that are sufficiently technologically advanced and scalable. In Germany, bioenergy, geothermics and hydropower have very limited potential for varying reasons. Scientists are also setting their hopes on “green hydrogen”, in which the energy required for water electrolysis is obtained from renewable sources. Green hydrogen will be decisive as an energy carrier when it comes to being climate neutral in cases where fossil fuels cannot be replaced with electricity. This includes, for example, steel manufacture or the chemical industry.

Safeguard carbon sinks

Limiting the release of greenhouse gases is the ultimate way to slow down climate change. However it is by no means guaranteed that this will be sufficiently successful worldwide. It is more likely that additional measures will be required with which greenhouse gases, particularly carbon dioxide, can be removed from the atmosphere. Although they are yet to be fully developed, technical processes for capturing CO₂ emissions do exist. Known as negative emissions, they remove greenhouse gas from the atmosphere and make it harmless. These options will become more relevant, especially in scenarios where humans miss the 1.5°C target or where even achieving the 2°C target becomes doubtful.

Efforts to preserve existing natural carbon sinks are among the most important measures in the fight against climate change. Soils, forests and oceans currently absorb around half of human CO₂ emissions. It is uncertain as to how long soils and forests will be able to continue doing so as their destruction and exploitation by humans is increasing. The effect may reverse as of 2050, which would mean that the forests and soils then release CO₂ instead of absorbing it, further exacerbating global warming.
 
Reforestation could work against this. Calculations show that new trees planted up until 2100 could absorb approximately a quarter of the CO₂ in the atmosphere. This would require some eight million hectares of land, corresponding to the size of Brazil.

That said, large-scale reforestation would conflict with other usage possibilities, such as for agriculture crucial to securing human nutrition. This conflict could be countered at least partially by agricultural-economic measures in which agricultural crops and (fruit)trees are planted on the same area.

There are many other reasons to make changes to agriculture. Soils used intensively for agriculture lose their ability to store CO₂ because their humus is used up more and more. When the store of CO₂ in the humus sinks, CO₂ is released. If humus stores can be increased instead, more CO₂ is bound in the long term. While building up humus is time intensive, it also helps reduce the use of synthetic fertilisers, the manufacture of which is linked to high greenhouse gas emissions.

In Germany mires also play an important role in climate protection. Mires and peat-like soils only make up around seven percent of areas used for agriculture in Germany. Around 35 percent of the German agricultural sector’s total greenhouse gas emissions are caused by the CO₂ released from these extremely carbon-rich agricultural soils. Due to microorganisms breaking broken the biomass in peat, drained mires used for agricultural purposes lose more carbon dioxide in 20 years than is stored in a grassland location.

These areas need to be rewetted by raising the groundwater level to land level. This would prevent this “degassing” and restimulate the mires’ sink function. While this will also increase methane emissions, a gas certainly more harmful than carbon dioxide, this will be outweighed by the effect of saved CO₂ as the amounts are comparatively low.

Climate engineering: technology against climate change

Alongside those for reducing emissions and converting energy systems, methods and technologies for counteracting global warming exist. These can be summarised under the term “geoengineering” or “climate engineering”. They aim to purposely alter the climate system in order to mitigate the effects of climate change.

A distinction must be made between two approaches here. When it comes to Carbon Dioxide Removal (CDR), CO₂ is removed from the atmosphere or not even permitted to enter the atmosphere at all. The second approach, Solar Radiation Modification (SRM), aims to influence sun radiation and make the earth more reflective in order to compensate for the effects of greenhouse gases. Unlike CDR, SRM is not related to the cause of climate change.

In principle, technological approaches for reducing climate change are subject to Article 2 of the UN Climate Convention (UNFCCC, United Nations Framework Convention on Climate Change), which came into force in 1994. This states that a proposed technological solution must not itself represent a dangerous human intervention in the climate system. If this cannot be explicitly ruled out, Article 2 is breached and thus a central component of the Framework Convention.

Removing CO₂

There are numerous carbon dioxide removal methods. For example, biomass able to bind CO₂, such as wood or rapeseed, can be planted on large surface areas and burnt in a power plant to generate heat. The released CO₂ is captured and stored for long periods underground. This is known as Carbon Capture and Storage (CCS). The disadvantage: As with reforestation, using large areas for cultivating biomass conflicts with the use for food supply. And even if all existing agricultural land were to be used, it would still not have any significant global effect. In addition, CCS processes themselves require a lot of energy which then reduces the effectiveness of the power plants.

Other possibilities of removing carbon dioxide from the atmosphere include artificial rock weathering, in which CO₂ from the air is required, or mechanically capturing CO₂ from the air, which can also be stored underground. Since air only contains low amounts of CO₂, these plants have to filter enormous amounts of air, an expensive process which uses lots of energy. There are also concepts to fertilise the ocean with nutrients such as iron, phosphorous or nitrogen, resulting in an increased growth of algae which could bind additional CO₂ – if the additional biomass is stored in the ocean sediment.

Limit solar radiation

One of the SRM methods for limiting solar radiation on Earth is the idea to install mirrors in space close to Earth in order to reflect sunlight away from our planet. However, this would require extremely large mirror surfaces. Furthermore, the change to solar radiation would be unequally distributed, which could influence the atmospheric and oceanic circulations and thus also regional temperatures and rainfall, for example.

Another idea is to imitate the effects of volcanic eruptions by introducing aerosols that reflect sunlight to the upper layers of the atmosphere. This could, however, have undesired side effects on the climate and lead to rainfall areas being displacement, in turn altering regional water cycles. Furthermore, such a measure would have to be carried out over several decades. It would still be necessary to reduce emissions during this time as otherwise there would be an imbalance between greenhouse gas concentration and global temperature. Ending the aerosol introduction, for example due to cost reasons, would then result in extremely fast global warming to which ecosystems would barely be able to adapt.

Most climate engineering processes are therefore only more or less feasible ideas thus far. It is also unclear as to whether any of these processes are scalable on a global level. In a special report in 2018, the World Climate Council IPCC concluded that SRM is not an option for the future. CDR methods could only make a small contribution at best to limiting global warming.

At the same time, most of the scenarios in which the 1.5°C or 2°C target is achieved show that some of the released CO₂ must be removed from the atmosphere again in order to capture the leftover emissions from agriculture and industry which are difficult to avoid. It needs to be clarified which roles the various CO₂ removal methods should play in future. That said, they could nevertheless be part of a comprehensive strategy primarily focused on the reduction and elimination of fossil fuel emissions and the restructuring of the energy system – and thus tackle the cause of climate change.

Published: August 2022