Are they significantly worse than aviation? In any case the same policy issues, of failure to price or tax CO2 emissions, are relevant.
My
last posting addressed one of the issues arising from the failure to price any
of the carbon/climate externality of aviation into the cost/price of aviation
fuel. Among other things this has, in the absence of low carbon aircraft alternatives,
encouraged a possibly unsustainable expansion of demand for travel, and distorted
the choices that travellers make between different modes of transport. In that
posting I compared the emissions impact of flying and driving for a
hypothetical choice of holidays travelling 2000 km on a round trip to the South
of France; the key measure was grams of CO2 per passenger-kilometre.
But
the issue is not confined to aviation. The same problems arise for shipping. Greenhouse
gas emissions from all forms of international transport contribute to
anthropogenic global warming, but were never covered under the Kyoto Protocol
and continue to escape effective action, in the form of a carbon tax or a
carbon price, to limit emissions and mitigate climate impacts.
So
it seems fair, in this context, to consider the impact of another alternative
type of holiday. More recently there has been much criticism of the negative
environmental impact of cruise ships. This is by no means confined to
emissions, and includes the overcrowding impact of very large cruise ships on
major tourist destinations, such as Dubrovnik or Venice. Ships also tend to use
heavy fuel oil which is particularly bad in terms of its immediate local
consequences on air quality.
But
the most serious issue for shipping is CO2 emissions, and, in terms
of comparison with other choices for personal travel, some attention has been
given to measuring these. Most published information on emissions statistics
comes from the cruise companies, and it is not always easy to draw exact comparisons
with other modes of transport. Among
other factors emissions per passenger-kilometre may be a rather poor metric since
so much depends on the length and nature of the journey and the consumption of
fuel for powering on-board services (lighting, catering, etc). And cruises will
tend intrinsically to cover shorter travel distances, so some holidays based on
short haul cruises will lead to lower emissions than some long-haul flights.
The BEIS has also put a figure
on ferry transport - 18g of CO2 per passenger kilometre for a foot
passenger, which is less than a coach, or 128g for a driver and car, which is close
to our earlier figures for a long-haul flight. But ferries ages and efficiency
will vary around the world - and a ferry won't get you to the Caribbean,
although a cruise ship or ocean liner would.
A
2010 paper[1] in
Energy Policy presented the results of research into international cruise ship
journeys to and from New Zealand. CO2 emissions from such journeys were calculated
using an activity based, or “bottom-up”, model. The estimates for individual
journeys by cruise ships to or from New Zealand in 2007 ranged between 250 and
2200 g of CO2 per passenger-kilometre (g CO2 per p-km), with
a weighted mean of 390 g CO2 per p-km.
Carnival Corporation and plc, which owns nine cruise lines, claims its 104 ships
emit an average of 251g of carbon dioxide equivalent per "available lower
berth" per kilometre. Given improvements
since 2010, this seems consistent with the earlier study which had argued that
values similar to those of economy-class air travel could be obtained. 
The
Energy Policy paper also calculated price elasticities and international cruise
journeys for transport purposes were found to have a greater relative decrease
in demand than plane journeys if the impact of carbon pricing was analysed. In
other words, putting a price on the environmental damage would be even more effective
in reducing emissions from cruise ships, reducing demand for cruises as a
preferred holiday option and incentivising cruise companies to develop cleaner
solutions.
There
is often a “shore-side” perversity as well. The absence of any penalty on
burning heavy fuel oil means that ships will also continue to pollute the local
environment in port when it would be a straightforward matter to power on-board
facilities through connection to the local electricity network, which will
often be based on a cleaner fuel mix.
Once
again the transport and travel sectors provide a textbook illustration of the
need to reflect clear externalities into the pricing of travel, so that consumers
can make choices that come closer to reflecting a balance of personal benefits
and societal damage. The evidence is that this can work both by shifting demand
to less “carbon-intensive” activity , and by reducing the environmental impact
of supply.
[1] Carbon
emissions from international cruise ship passengers' travel to and from New
Zealand. Howitt et al. Energy Policy. Volume 38, Issue 5, (May 2010)
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