One
of the greatest challenges to be addressed in reducing global emissions of
GHGs, while maintaining (and increasing) energy supplies, is that of
implementing sustainable transport solutions. The issue of GHG emissions from
the transport sector was briefly addressed by this page in November (‘Costa Rica: clean power superstar?’), where it was noted that emissions from the
transport sector account for 70% of that country’s total GHG emissions.
Globally, as of 2010, the transport sector consumed 2,200 Mtoe, or around 19%
of total global energy supply (WEC, 2011). In terms of GHG emissions, as of 2013 the
transport sector was responsible for emitting 7.5 billion tonnes of CO2 in
2013, representing 23.4% of total global CO2 emissions (up from 22.7% in 2010) (IEA, 2015a).
It is therefore imperative that new low or zero-emissions means of powering the
global transport sector are found, which allow GHG emissions to be dramatically
reduced without compromising the ability of global transport systems to
efficiently and reliably conduct ever-increasing volumes of passenger traffic
and freight. The transport sector consists of four main components: rail,
shipping, road and aviation. All are currently overwhelmingly dependent on
traditional fossil-fuel propulsion methods. This post will examine each in
turn, and assess the various means of low-or-zero-emissions propulsion by which
each could most practicably be made more sustainable.
Rail
According
to the International Energy Agency (2015a), as of 2013, rail transport accounted
for just 2% of total energy used in the transport sector and only 3.5% of CO2
emissions from transport, yet provides 6.4% of global passenger transport and
8.7% of freight transport. It is widely accepted that the most effective means
of reducing GHG emissions (and increasing energy efficiency) in rail transport
is electrification, which is already a well-established means of rail
propulsion, fuelling 36.4% of global rail transport (compared to 57% fuelled by
oil products). Electric trains emit 20-35% less CO2 per passenger mile than
their diesel counterparts (DfT, 2009). This advantage will be enhanced as more
electricity is generated from renewable sources – already 8.7% of total global
rail transport is powered by renewable means (IEA, 2015a). Electrification of rail systems
coupled with increasing zero-emissions generating capacity has the potential to
practically eliminate CO2 emissions from rail transport, already highly
efficient in terms of energy consumption per passenger/freight mile, and make
rail a formidable component of future sustainable transport systems.
However,
rail electrification is a potentially demanding means of reducing GHG emissions
from transport. Installation of the necessary infrastructure requires capital
expenditure in the order of billions of pounds, which may make large-scale
electrification an impossibility in less economically prosperous jurisdictions (Keen and Phillpotts, 2010). One possible solution (employed by the UK’s Network Rail to facilitate its own
programme of electrification) is to introduce hybrid rolling stock which can
operate on diesel power until electric infrastructure is completed, and
subsequently operate as an electric locomotive. This could allow the staggered
introduction of electric infrastructure, reducing the financial burden and easing
the process.
Shipping
As
of 2013, global maritime navigation was responsible for 9.4% of total energy
consumption in the transport sector, translating into 10.2% of CO2 emissions
from transport (IEA, 2015a). According to a report by the European Commission, by 2050 CO2 emissions from global shipping are forecast to
increase by 50-250%. Numerous measures have been proposed which could
dramatically reduce emissions from global shipping by up to 75% through
operational changes and the application of existing technologies – these
measures include streamlining ships through hull coating and cleaning, recovery
of waste heat, optimisation of trim and ballast, engine tuning, autopilot
upgrades and intelligent routing based on weather conditions. By far the most
significant reduction in CO2 emissions could be achieved through simply
reducing operational speed. However, this must surely represent an unacceptable
compromise, given the crucial economic role of shipping in global freight
transport – as of 2013, 82.2% of global freight transport was conducted by sea (IEA, 2015a).
Rather than simply mitigating emissions from shipping by compromising speed,
what is arguably required is a new means of zero-emissions propulsion. Jeffs (2012) argues that nuclear power could provide an established and highly
effective means of powering ships – a great number of nuclear powered vessels
(predominantly submarines) are presently in service with the navies of several
countries, and nuclear propulsion in civilian or merchant vessels is by no
means unprecedented. Nuclear-powered ships are capable of speeds easily
equivalent to their diesel counterparts, and moreover can sail for thousands
more miles without the need to refuel. Converting existing ships to nuclear
power, and installing the necessary refuelling infrastructure in ports around
the world, would of course represent a Herculean overhaul requiring billions of
pounds of investment. Yet nuclear propulsion could represent the only means by
which global shipping may continue to expand and conduct growing volumes of
international freight while achieving the dramatic reductions in GHG emissions
which are urgently required.
Road
In
terms of both energy consumption (74.9%) and CO2 emissions (73.5%) from global
transport, road transport is by a large majority the most significant
contributor (IEA, 2015a). The vast majority of global road transport is conducted by
light-duty vehicle (LDV) transport, which includes private cars, and is
responsible for 52% of total energy consumption from the entire transport sector (IEA, 2016a). Furthermore, ownership of private
cars is growing, especially in the industrialising/recently-industrialised
world, where growing incomes are allowing increasing numbers of people to
liberate themselves from dependence upon public transport and purchase their
own vehicles (Vasconcellos, 1997a; 1997b). By 2050, private car ownership in developing countries is
expected to increase by 430-557% compared to 2010 – a modest increase of 36-41%
is also forecast in developed countries (WEC, 2010).
It is therefore imperative that the near-total dependence of
road vehicle transport on oil-based fuels is dramatically reduced through the
large-scale employment of new emissions-free propulsion methods. The most
widely-established alternative to traditional internal combustion engine (ICE) power
is electric power. As of 2015 there are over 1.26 million electric vehicles
(EVs) in use, with global EV numbers having grown at an astonishing rate since
2005, when just hundreds of EVs existed, and even since 2014, in which time the
global EV stock has roughly doubled (IEA, 2016b). Strong international policy support
coupled with technological advances have made EVs less expensive and more
practical in terms of performance and range, although costs remain high and EVs
can still only travel a limited distance before having to charge for long
periods. One solution to this is the development of EVs in which exhausted
batteries can be swapped instantaneously for fully-charged replacements at
designated charging points along the highway, in exactly the same way as ICE
cars must stop and refuel at petrol stations (Gabay et al. 2011). A further zero-emissions option
which could complement electric vehicles are hydrogen fuel cell electric
vehicles (FCEVs), which use chemical energy stored within hydrogen fuel to
power electric motors to provide propulsion. FCEV technology is far from
well-established and there are very few FCEVs in service at present. The
technology is also currently highly expensive. Nevertheless, an advantage of
FCEVs over traditional electric vehicles is their increased range and ability
to refuel quickly, without requiring several hours of stationary charging. In
terms of performance FCEVs are essentially equivalent to ICE vehicles. Hydrogen
fuel, meanwhile, is abundant and easily accessible, and can indeed be distilled
from water, with reserves forecast to suffice for practically indefinite FCEV
operation (IEA, 2015b).
While EVs (potentially complemented by FCEVs) may represent
the long-term solution to global road transport emissions, a more immediate fix
may be available in the form of biofuel. It is estimated that by 2050, biofuels
could account for 27% of total global transport fuel, contributing to a
significant reduction in CO2 emissions (IEA, 2011). Biofuel may represent a more practical
short-to-medium-term means of reducing emissions from road transport than EV
technology – commercial deployment could be achieved with relatively little
overhaul of existing infrastructure. Existing diesel engines can even in some
cases be cheaply converted to run on bio-diesel.
Aviation
Globally, air transport is responsible for 10.3% of energy
consumption and produces 10.6% of CO2 emissions from the transport sector. As
of 2013, 11.4% of global passenger traffic was conducted by air, along with
just 0.8% of global freight (IEA, 2015a). In the UK alone, air traffic is predicted to
increase by around 150% by 2050 (Sustainable Aviation, 2016). In terms of propulsion, global aviation is
entirely dependent on traditional oil-based fuel, and barring a major
technological breakthrough is almost certain to remain so for the foreseeable
future. Reductions in CO2 emissions from aviation are consequently focused on
improving the fuel-efficiency of aircraft. It is estimated that by 2050,
aviation fuel-efficiency could be improved by around 39% from 2010 levels.
Modifications in aircraft design will improve aerodynamic performance, reducing
fuel consumption, while the use of sustainable fuels (such as biofuel) may
contribute to GHG emissions reductions. New highly-efficient engine designs
will allow performance to be maintained while reducing fuel consumption. Intelligent
management of operational procedures may also improve fuel efficiency. Further
ahead, it is even possible that hydrogen fuel cell technology may allow the
operation of zero-emissions commercial aircraft, although such developments are
in the very early stages of testing (Sustainable Aviation, 2016).
Conclusions
This has been an extremely overlong post so conclusions will be brief. In short, given the significant contribution of global transport systems to total energy consumption, profound changes to traditional propulsion methods must take place over the course of the 21st century in order to significantly reduce GHG emissions from transport. Solutions range from the radical and extremely complex (i.e. nuclear shipping) to the established and easily practicable (i.e. rail electrification). The most practicable solutions should be implemented as a matter of urgency, yet all other options must be seriously considered and innovative solutions applied in order to satisfy ever-increasing passenger and freight demand while achieving material reductions in GHG emissions over the course of the coming decades.
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