3717111020-horizon-scanning-eng
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2 Future topics of the second horizon scanning cycle
combination with decentralised energy generation Application Consortium [QUTAC] 2021). In the future,
by private households require a sophisticated supply the solution of these problems as well as the control
and demand management (or load management). The of other complex industrial processes, e.g. fleet
balancing of supply and demand with regard to the management and route planning or manufacturing
cost or price development will therefore increasingly processes, are supposed to be found with the help
depend on the data processing capacities of the of the computing power of quantum computers.
participants (Flauger 2020). In the future, quantum Quantum computers should be able to solve these
computers will help to deal with this complexity and other optimisation problems because they can
(Khodaei 2020). This can be done by intelligent efficiently perform much more complex calculations.
algorithms that evaluate huge amounts of different
parameters simultaneously and establish the optimal In logistics, quantum computing can be used to
balance between supply and demand (Flauger 2020). calculate the fastest route for vehicles, taking into
Electric cars, for example, would thus be charged account a huge number of real-time data points about
primarily when there is a lot of electricity in the grid, traffic jams and the like (Liscouski 2021). This allows
and at the same time they would serve as buffer traffic jams to be avoided and fuel and CO2 to be
storage for days without wind (Flauger 2020). saved. The optimal management of aircraft or vehicle
fleets with little downtime or detours can also be
In the heat supply of neighbourhoods, quantum achieved through fast and complex calculations, thus
computing could lead to efficient use of heat and reducing environmental impacts in terms of energy or
thus energy and CO2 savings, as various parameters space consumption, for example for parking areas.
on weather forecasts, usage patterns and building
properties of hundreds of buildings can be calculated If manufacturing processes in industry are optimised
simultaneously and in real time, and heat energy can through quantum computing and redundant sub-
be distributed in a targeted and optimised manner processes are avoided, it can lead to energy, material
(Flauger 2020). and thus CO2 savings in the industry, i.e. to positive
effects for the environment (Quantum Technology
3. Solving optimisation problems in industry and Application Consortium [QUTAC] 2021). At the
Automotive companies such as Volkswagen are same time, optimisation of processes always harbours
faced with the challenge of optimising the efficiency the potential (or the risk) that production capacities
such as the route planning problem, whether to are increased or logistics services expanded – and
improve supplier logistics or the vehicle guidance thus environmental benefits fall victim to the
of autonomous vehicles (Quantum Technology and
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2 Future topics of the second horizon scanning cycle
rebound effect. Minimising this risk could be the task
of a forward-looking environmental policy.
Conclusion for environmental policy and research:
Quantum computing holds potential for the future.
Whether the technology can make a substantial
contribution to making the world more sustainable,
however, remains to be seen. At present, it can be
assumed that indirect energy and emission savings
(especially of CO2) can be expected. However,
the solutions discussed so far in the applications
presented are only incremental improvements. In
principle, it must be ensured that optimisations,
e.g. of processes, do not lead to rebound effects that
cancel out the environmental benefits achieved.
Direct effects of quantum computing relate primarily
to the material and power consumption of the
quantum computers themselves. This is because
quantum computers would have to be programmed,
operated and monitored by conventional computers,
thus requiring a material-intensive surrounding
infrastructure. At the same time, energy is required
for cooling and generating data (Hossenfelder 2019).
The entrepreneurial Global Future Council on
Quantum Computing concluded that significant
energy savings can be achieved because quantum
computing can solve large-scale computational
problems with a fraction of the energy consumed by
today’s supercomputers (Global Future Council on
Quantum Computing 2020).
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2 Future topics of the second horizon scanning cycle
2.2 Cryptocurrencies are gaining global acceptance as a digital currency
Trend: Many cryptocurrencies such as Bitcoin are
developing very dynamically, and more and more approved digital currencies on a global
companies as well as (digital) payment service level.
providers are accepting them as currency equivalents.
▸ From an environmental perspective,
Emerging Issues: the energy consumption of
▸ Changing relationship between environmentally traditional and currently dominant
harmful and sustainable cryptocurrencies cryptocurrencies such as Bitcoin is
▸ Stablecoins with sustainable value anchor in the particularly problematic. The mining
experimental stage of cryptocurrencies also generates
▸ Cryptocurrencies are increasingly establishing large amounts of electronic waste, for
themselves as a digital means of payment which there are hardly any established
recycling cycles. Potential for improving
the ecological footprint lies, for example,
In a nutshell: in the use of renewable energies for their
operation.
▸ With the enormous growth in
value of Bitcoin, Ethereum and Co., ▸ Cryptocurrencies can be used for
cryptocurrencies have developed in various sustainable purposes, e.g. to
recent years from an experiment in promote the development of renewable
the creation of independent, digital energies or to monitor supply chains.
alternative currencies to a speculative There are also use cases that may
object. The ongoing speculative hype require environmental regulation, such
and the media attention attached to as the use of cryptocurrencies in the
it, as well as the intensive debate on metaverse8, when trading in (virtual)
cryptocurrencies by science, business, land, real estate or works of art.
politics and investors, are driving
further technical developments, the
improvement of the eco-balance of Background:
digital currencies and the creation of Cryptocurrencies are digital asset certificates that
state legal frameworks. In the medium are stored in a decentralised database, usually a
term, this could lead to cryptocurrencies blockchain. They usually have no intrinsic value but
establishing themselves as (state-) represent a perceived value. In theory, they fulfil the
typical functions of a currency. These include the
8 The Metaverse is conceived as a virtual space in which elements of the virtual and real worlds coexist or are interconnected, and in which the people of the future can communicate
and interact with each other.
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2 Future topics of the second horizon scanning cycle
function as a medium of exchange, the function as a 378 billion US dollars (CoinMarketCap 2022; as of
unit of account and the function as a store of value. 01.10.2021).
Already today, cryptocurrencies can be used as
digital means of payment on many platforms, such as The “classic” cryptocurrencies such as Bitcoin and
the food delivery service Lieferando. Ethereum belong to the so-called non-backend
cryptocurrencies and do not have a stabilising value
Cryptocurrencies are peer-to-peer currencies. This anchor with which they are secured, for example
means that they are not issued by a central authority gold. This makes them very volatile, which is
or controlling body, such as a central bank, like state why they can only be used as a regular means of
currencies, but are “mined” decentrally – as it is payment to a limited extent. Stablecoins, which first
called in technical jargon. In the case of the first and appeared in 2014, are considered the second wave of
most widespread cryptocurrency, Bitcoin, the mining cryptocurrencies. Unlike Bitcoin and the like, these
consists of solving complex mathematical problems. are linked to a fixed asset or covered by it.
For each correct solution, a few bitcoins are paid out.
A total of approximately 21 million Bitcoins can be Emerging Issues:
mined. This limit is due to the algorithm behind the The current discourse on whether cryptocurrencies
Bitcoin and does not apply to cryptocurrencies in will become established as a global means of
general. So far, about 80% of the maximum Bitcoin payment contains various aspects of environmental
mass has been mined. In addition to access software, relevance: from the optimisation of energy-intensive
powerful hardware is a fundamental prerequisite for mining processes to leaving the experimental
mining cryptocurrencies. This is almost exclusively stage of stablecoins to a development in which
affordable by professional players whose business cryptocurrencies may become a larger part of global
model is aimed at mining cryptocurrencies. payments.
The mined Bitcoins, like all cryptocurrencies, can 1. Changed relationship between environmentally
be traded. This enables citizens, who are usually harmful and sustainable cryptocurrencies
not involved in the complex mining process, to The discourse on environmental and sustainability
access such digital currencies. In Germany, the most aspects of cryptocurrencies has long been dominated
widespread cryptocurrencies as well as crypto-ETNs9 by the bad image of Bitcoin, the dominant and
are traded via trading platforms such as eTorro10, most widespread cryptocurrency, and the high
TradeRepublic11 or Bison12. energy consumption of its hardware, which is used
for “crypto-mining”. For Bitcoin, the University
Flood of cryptocurrencies and speculative object of Cambridge publishes the “Cambridge Bitcoin
Since the introduction of the Bitcoin in 2009, Electricity Consumption Index (CBECI)”, a regularly
cryptocurrencies have undergone a very dynamic updated estimate of energy consumption, which
development in value and have become an object of is currently at around 102 terawatt hours (Twh)
speculation for many investors. Not least due to this annually (Cambridge Centre for Alternative Finance
hype, more and more cryptocurrencies are being [CCAF] 2022a; as of October 2021). This is close to
brought onto the market. The number of available the energy consumption of the Netherlands (110.7
cryptocurrencies has more than quadrupled in Twh/a) or about 75% of the global gold industry’s
the past five years. While 1,353 cryptocurrencies consumption of 131 Twh/a (Cambridge Centre
were available in December 2017, 10,894 different for Alternative Finance [CCAF] 2022b). This high
cryptocurrencies could be obtained in July 2022 energy consumption leads to enormous amounts of
(Statista GmbH 2022). The two most important and greenhouse gas emissions and thus fuels climate
widespread cryptocurrencies include the already change. In terms of life cycle assessment, the use
mentioned Bitcoin with a market capitalisation of phase, i.e. the electricity consumption for mining,
approx. 890 billion US dollars and Ethereum with plays a major role, accounting for 98% of the
9 Exchange-traded notes (ETNs) are exchange-traded bearer bonds that replicate the performance of an underlying asset on a 1:1 basis.
10 www.etoro.com
11 www.traderepublic.com
12 https://bisonapp.com
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2 Future topics of the second horizon scanning cycle
emissions (Köhler and Pizol 2019). The level of with cleaner energy production, for example Norway,
greenhouse gas emissions results in particular from could positively influence the eco-balance of
the region in which the mining is carried out, or the cryptocurrencies. One thing is certain: in the future, a
prevailing electricity mix there. If the electricity mix shift to mining regions, where electricity is generated
is predominantly coal-based – as is the case in parts (more) cheaply and through renewable energies, can
of China, the current hotspot of Bitcoin mining - lead to a significant reduction of the CO2 footprint of
greenhouse gas emissions are high; if the electricity cryptocurrencies (Köhler and Pizol 2019). However,
is predominantly based on renewable energies, the opposite scenario, meaning a pull towards even
emissions are naturally much lower (Köhler and Pizol cheaper fossil electricity, is also possible, as miners
2019). usually follow the cheapest electricity price.
With regard to the environmental impact of Even though the production of the hardware used
cryptocurrencies, the focus has so far been on energy for mining is almost negligible in terms of the CO2
consumption. It is important to know that the life footprint (Köhler and Pizol 2019), the generation
cycle assessments available so far still have some of electronic waste at the end of the use phase is
uncertainties regarding the assumptions made, an increasing and so far often neglected problem.
which should be addressed in future research: This Approximately 272 g of electronic waste are produced
concerns, for example, the actual mining location per Bitcoin transaction. This is about 30,700 tonnes
and details of the equipment used by the miners, i.e. annually, as much as is produced in the Netherlands
the hardware (Köhler and Pizol 2019). However, there in the form of small IT and telecommunication
is no question that cryptocurrencies as a whole are devices in the same period (Haase 2021; Vries and
very energy-intensive. Stoll 2021). The electronic waste is mainly produced
because the hardware for mining, specifically the
In the third benchmark study on crypto-assets by the ASIC microchips, has to be kept up to date in order
Cambridge Center for Alternative Finance (Blandin to be able to mine profitably with it (Vries and Stoll
et al. 2020), the share of renewables used to mine 2021). The average lifespan of microchips is just over
cryptocurrencies such as Bitcoin and Ethereum is one year.
estimated at around 39%. This share could increase
due to the ban on trading cryptocurrencies in China Electronic waste is particularly environmentally
introduced in September 2021 (Root 2021). Up to relevant because of very low recycling rates at only
now, China has been the largest mining location 17.4% worldwide and the containing toxic chemicals
worldwide, so that a migration of miners to countries and heavy metals lead to pollution of air, water and
soil if not disposed of properly. Environmental policy
should therefore 1.) raise awareness of the electronic
waste problem associated with Bitcoin and 2.)
promote and control proper recycling at the local level
(Vries and Stoll 2021).
In addition to Bitcoin with the negative
environmental impacts described above, there are
more than 350 other so-called PoS cryptocurrencies
(PoS from Proof of Stake) on the market whose
environmental balance sheet is completely different
in terms of electricity consumption and electronic
waste. PoS as a consensus mechanism does not
require energy-intensive mining and therefore
saves energy compared to previously discussed
cryptocurrencies. The PoS-based currency “Nano”,
for example, consumes only a fraction – about
one ten-thousandth – of the KWh used for Bitcoin.
Moreover, PoS-based cryptocurrencies do not require
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2 Future topics of the second horizon scanning cycle
ultra-specific and short-lived hardware components – generating large amounts of e electronic waste, as is
an ordinary PC or laptop with access to the internet is the case with Bitcoin (Stamoulis 2021).
sufficient as a working tool (Vries and Stoll 2021).
In recent years, experiments have also been
If these currencies were to become established, the conducted with stablecoins with a sustainable value
problem of huge amounts of electronic waste and the anchor, which are intended to advance the energy
energy hunger of cryptocurrencies like Bitcoin would transition or democratise emissions trading. The
be largely solved (Vries and Stoll 2021). To promote SolarCoin13 is an example of this. Producers of solar
such a development, environmental policy could look energy can register on a platform and report and
into introducing a CO2 tax on cryptocurrencies. It will verify the energy they produce. For every MWh of
then become apparent whether the energy savings solar power they produce, they are credited with one
that may occur through the use of cryptocurrencies SolarCoin, which they can dispose of freely. The aim
or a blockchain in certain cross-sector fields of is to support the expansion of solar energy. Another
application make the tax acceptable for the users of experiment was the Climatecoin. The cryptocurrency,
inefficient cryptocurrency technology (Sedlmeir et al. which is currently inactive, is an experiment by
2020). the Spanish start-up climatetrade14. The aim was to
facilitate access to emissions trading on the basis of
2. Stablecoins with sustainable value anchor in the the cryptocurrency and to make emissions certificates
experimental stage easily tradable for private individuals. For this
Stablecoins are cryptocurrencies that are linked purpose, the cryptocurrency was to be backed by a
to or covered by fixed assets. They are divided into currency anchor of one tonne of CO2, which was to be
three categories: commodity-linked (for example, covered by certificate traders (Gierow 2015).
commodities as an asset like Tether Gold XAut),
fiat-linked (classic currencies like the US dollar as Even though these experiments have received a
an asset like TrueUSD) and cryptocurrency-linked certain amount of media attention with their launch,
stablecoins (cryptocurrencies as an asset like the cryptocurrencies with sustainable value anchors
Ethereum-based DAI). In the case of stablecoins, have not been able to establish themselves on a larger
a certain amount of, for example, gold, fiat or scale so far. However, this could change in the future.
cryptocurrency is physically or, in the latter case, Analogous to gold-backed cryptocurrencies, such as
digitally deposited by issuers of the coins for each Tether Gold XAut, sustainably produced or renewable
digital coin or unit of these cryptocurrencies, resources could be traded as stablecoins.
regardless of their respective category.
If stablecoins do not have a sustainable value anchor,
From an environmental point of view, the process but are tied to values that are unsustainable, such
of depositing, the so-called proof-of-reserve, is the as oil, they could – if further distributed – have a
advantage of stablecoins over PoW cryptocurrencies stabilising effect on these, combined with negative
(Proof of Work (PoW), the consensus procedure environmental effects.
used in Bitcoin mining). Energy-intensive mining
is no longer necessary, at least for commodity- and 3. Cryptocurrencies are increasingly establishing
fiat-linked cryptocurrencies. Instead, stablecoin themselves as a digital means of payment
issuers are responsible for outlining the storage of While cryptocurrencies have so far been known
the relevant currency or commodity. Tether, the in this country mainly as an object of speculation,
largest issuer of fiat-linked stablecoins by market they are already being used as a means of payment
capitalisation (Coindesk 2022), publishes data on in other parts of the world. There are also various
its own website (Tether 2022). By eliminating the developments that indicate that cryptocurrencies will
complicated and energy-intensive PoW processes, gain in importance as a means of payment globally:
commodity- and fiat-linked cryptocurrencies also do
not require any mining-specific hardware. This avoids
13 https://solarcoin.org
14 https://climatetrade.com
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2 Future topics of the second horizon scanning cycle
Already today, bills can be paid with Bitcoin on for this are the daily, sometimes very large, price
various internet platforms, for example Lieferando or fluctuations of Bitcoin, which make it a very unstable
the Microsoft Store. Organisations such as Wikipedia digital means of payment.
or Greenpeace also allow Bitcoin donations. Other
companies such as Tesla and PayPal, but also credit If more and more countries accept cryptocurrencies
card providers, have announced that they will accept as a legal means of payment, the environmental
Bitcoin as a means of payment (Bücker 2021). assessment will depend on which type of
cryptocurrencies will prevail. If Bitcoins are
Moreover, the number of stationary ATMs for used, as in Salvador, and widely accepted by the
cryptocurrencies is rising sharply. Within one year, population, the negative environmental impacts
from 1 October 2020 to 1 October 2021, the number (high energy consumption etc.) will increase. The use
of such ATMs has almost tripled worldwide: from of stablecoins with a sustainable value anchor, on the
10,791 to 28,262 (Coin ATM Radar 2022a). They are other hand, would definitely have the potential to tip
most widespread in the USA with approx. 86.5%, the scales in favour of more sustainability if used to a
followed by Europe with approx. 4.5%; in Germany, large extent.
there are only approx. 57 such machines so far (Coin
ATM Radar 2022b; as of 3 October 2021). Bitcoin and The use of cryptocurrencies as a means of payment in
co. can be bought and/or sold against fiat currency at the digital space could also become more important
said machines, transactions can be processed via a in the future. The metaverse is currently being used to
bank account, but cash deposits and withdrawals are describe a development of such a virtual space. Since
also possible. autumn 2021 at the latest, this has received a great
deal of media attention due to the renaming of the
In September 2021, El Salvador in Central America Facebook group as Meta. A spread of the Metaverse
became the first country in the world to recognise could further drive the use of cryptocurrencies in
Bitcoin as an official means of payment by law, so the future, as things can be bought in this virtual
everyday purchases and taxes can be paid with space with cryptocurrencies: from virtual real estate
Bitcoins. However, this development is not viewed to virtual clothing. However, the environmental
exclusively positively. According to a survey, relevance of this new application and the use of
acceptance of the “Bitcoin law” is low; 70% of cryptocurrencies is not (yet) entirely clear.
Salvadorans reject it (Demmer 2021). One reason
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2 Future topics of the second horizon scanning cycle
Cryptocurrencies also have a lot of potential and
positive effects for the environment. Depending on
the design of the currency, they can make supply
chains more sustainable, for example, because they
enable more transparency and control. When it
comes to applications in the context of sustainability,
the potential of cryptocurrencies is far from
exhausted. Here, further research or support from
practitioners could develop new applications or
new variants for sustainable value anchors. Finally,
policymakers themselves have the opportunity
to apply cryptocurrencies and use their steering
effect for sustainability via CO2 taxation or similar
instruments, although there are no pilot projects on
this yet. Finally, it should be mentioned that with the
hype surrounding the still rather diffuse concept of
Conclusion for environmental policy and research: the metaverse, cryptocurrencies and their use could
Cryptocurrencies are on the rise and there are various potentially gain greater importance.
indications that they will become established on
a large scale despite their volatile development.
Depending on the cryptocurrency used, numerous
existing environmental impacts, especially in
relation to energy and waste issues, could increase
in the future if no countermeasures are taken.
Proof-of-work-based cryptocurrencies in particular
are problematic because of their high energy
consumption. When expanding renewable energies,
cryptocurrencies and their energy requirements –
whether high or moderate – should be taken into
account in the future.
The calculation of environmental impacts with life
cycle assessments is still incomplete in some cases
and should be researched more intensively in order to
make more precise and comprehensive data bases for
environmental impacts available.
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2 Future topics of the second horizon scanning cycle
2.3 Technological innovations on the way to climate-friendly aviation
Trend: Technological innovations, especially
sustainable fuels and propulsion concepts, can help construction forms and designs – often
to make aviation as climate-neutral as possible. in combination with new materials – are
being conceived and tested.
Emerging Issues:
▸ Sustainable drop-in fuels ▸ Various sustainable fuels and new
▸ New jet propulsion concepts propulsion concepts are being
▸ Innovative constructions and materials developed to enable custom-fit solutions
for climate-neutral flying on short-,
medium- and long-haul routes. The
In a nutshell: focus here is primarily on biofuels,
e-fuels/power-to-liquid (PtL), electric
▸ Global aviation contributes significantly flying and green hydrogen, which can
to global warming through greenhouse either be converted into electricity
gas (GHG) emissions and contrail with the help of fuel cells or burned
formation. In addition, the number of in gas turbines. Innovative forms of
flights worldwide has increased sharply construction are also being tested,
over the last 20 years – and forecasts which promise high efficiency gains.
predict a further increase by 2050.
Most recently, the decline in air traffic ▸ In order to make air traffic as climate-
caused by the Covid-19 pandemic has neutral as possible, it is not only
increased again. However, with the necessary to reduce greenhouse gas
start of the Russian war of aggression emissions from aircraft, but also to
in Ukraine, another unforeseen counteract the emergence of so-called
development has occurred that could non-CO2 climate effects, as these
lead to a decline in air traffic. In addition contribute significantly to the climate
to the flight behaviour of citizens, impact of air traffic. New fuels and
technical innovations for climate- propulsion systems can contribute
neutral aviation play a very important to this by significantly reducing
role.15 These include, in particular, emissions such as nitrogen oxides
sustainable fuels and new propulsion (NOX), water vapour, soot, aerosol and
concepts. Furthermore, innovative sulphate aerosol particles. Therefore,
15 Technical innovations are the focus of this paper. It should be noted, however, that technical innovations are only one important component among many whose application will be
necessary to significantly reduce the climate impact of air traffic. This also includes non-technical solutions such as climate-optimised flight route design and the shift of air traffic to
more climate-friendly modes of transport, as well as the exploitation of regulatory and economic instruments to reduce air traffic overall.
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2 Future topics of the second horizon scanning cycle
environmentally relevant aspects should It is true that air traffic has declined sharply
be considered in the production of fuels worldwide since the beginning of the pandemic.
and also in the design of aircraft. However, surveys and assessments by industry
experts expect a return to pre-crisis levels in the years
2023 to 2026 (Hader et al. 2021). Although there were
Background: many indications of this at the beginning of 2022,
Measured in terms of greenhouse gas emissions per the severe shortage of personnel, not only as a result
passenger-kilometre, global aviation is by far the of redundancies but also as a result of the exodus of
most greenhouse gas-intensive form of transport workers in the aviation industry, and the start of the
(Öko-Institut e. V. 2020; Statista GmbH 2022) and Russian war of aggression in Ukraine marked the
a strong driver of anthropogenic climate warming. beginning of a development whose consequences
Emissions from aviation to date currently account for aviation have been difficult to predict so far. If,
for about 3.5 % of the current anthropogenic climate regardless of these presumably short-term slumps,
impact (Lee et al. 2021). In addition to emitted CO2, an increase in global air traffic is generally assumed
which is responsible for about one third of the climate for the next decades, technical innovations will play
impact, condensation trails and the resulting contrail a very important role in making aviation climate-
cirrus as well as emissions of nitrogen oxides (NOX) neutral (Abel 2022).
and their effect on the formation of ozone or reduction
of methane are significant factors. These are called Interaction between technical and non-technical
non-CO2 effects. Other non-CO2 effects result from innovations
emissions such as nitrogen oxides, water vapour, However, it should be noted and taken into account:
soot, aerosol and sulphate aerosol particles. Emitted Technical innovations are only one important
soot particles act as “condensation nuclei” for water component among many whose application will be
droplets, which freeze into ice crystals and can thus necessary to significantly reduce the climate impact
form contrails in the sky. These man-made clouds of aviation (Bopst et al. 2019). This includes, in
have a cooling or warming effect depending on local particular, non-technical solutions such as climate-
conditions, e.g. position of the sun, ground conditions optimised flight route design as well as the shift of
and natural cloud cover. However, research shows air traffic to more climate-friendly modes of transport
that the warming effect clearly outweighs the cooling and the exploitation of regulatory and economic
effect on average (Deutsches Zentrum für Luft- und instruments to reduce air traffic overall.
Raumfahrt e. V. [DLR] 2021).
Technical improvements such as more fuel-efficient
Global increase in air traffic engines or the use of lightweight constructions – in
At the same time, the number of flights worldwide – conjunction with higher seat occupancy rates and
in the years before the Corona crisis – rose optimised flight routes – have already made air traffic
continuously and strongly. In 2019, there were more efficient. (Bullerdiek et al. 2020). However, in
approximately 47 million flights globally (Statista order to open up a real perspective for greenhouse
GmbH 2021), an increase of 26% compared to 2014. gas-neutral or even climate-neutral16 aviation,
To illustrate, of the 32.6 billion tonnes of CO2 emitted fundamental and far-reaching changes are required,
between 1940 and 2018, about half occurred in the for example through the use of sustainable fuels
past 20 years (Lee et al. 2021). Before the outbreak of and propulsion concepts, which are the focus of the
the Covid-19 pandemic, forecasts also assumed that present consideration.
an even stronger increase in the number of flights was
imminent, with very strong growth rates between the
years 2020 and 2050 (Gössling and Humpe 2020).
16 Greenhouse gas neutrality is achieved when greenhouse gas emissions are completely offset by the removal of these emissions. Climate neutrality refers to a state in which human
activities have no influence on the climate system.
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