The impact of traffic and transport on the climate (enhanced
Arjen van Diepen 1522620
Demand for both freight and passenger transport continues to grow with increasing negative effects.
One of these effects is the emission of greenhouse gases by means of transport. What is the share of
transport in the process of global warming? Which modes have what kind of influence? Which
policies have been designed to deal with increased pressure on the environment? This paper deals
with the impact of traffic and transport on the climate, in particular the enhanced greenhouse effect.
First, the problem will be elaborated on including a short explanation of the mechanism and the
human influences on this. Then, effects of the transport sector on the greenhouse effect will be
elaborated, including some quantification and insight in shares of the transport sector compared to
other sectors and transport modes compared with each other. The last section deals with policy
designed to reduce (greenhouse gas) emissions from transport.
The (enhanced) greenhouse effect
The temperature on earth is for a large share depending on the presence of so called greenhouse
gases in the atmosphere. These gases partly hold the heat from the earth, the so called greenhouse
effect. The most important greenhouse gases are water vapor (H2O), carbon dioxide (CO2), methane
(CH4), ozone (O3), nitrogen dioxide (NO2) and other hydrocarbons. Those gases are natural and their
concentrations are regulated by natural processes. Without greenhouse gases, the average
temperature at sea level would have been -18 degrees Celsius, while with them it is 14 degrees.
The natural balance of greenhouse gases in the atmosphere is being disturbed by human influences.
Extra emission of greenhouse gases causes a higher concentration of these gases in the atmosphere.
This can lead to extra heating of the atmosphere and the earth surface. This is why this effect is
called the enhanced greenhouse effect. The majority observed increase of the average temperature
on earth in the last 50 years is probably caused by the increase of greenhouse gases in the
atmosphere. Of the mentioned greenhouse gases, carbon dioxide (CO2) contributes for more than
60% of the human influence on the climate. Carbon dioxide is released with the incineration of fossil
fuels (oil, gas, and coal) and deforestation. Since the start of the industrial revolution (around 1850)
the concentration of carbon dioxide in the atmosphere has grown with 38%. More than half of this
increase occurred after 1970. Besides carbon dioxide, also methane, nitrogen dioxide and other
hydrocarbons are released due to human processes and contribute to the enhanced greenhouse
When closer looking at global developments in the emission of greenhouse gases, a large increase
can be noted in the past decades. The emission of greenhouse gases (as listed in the Kyoto protocol)
grew 74% in the period 1970-2004 up to approximately 50.000 Mton CO2 equivalents (see also
Figure 1). The CO2 emissions have grown by 80% in that period, the CH4 emission by 40% and the
N2O emission by about 50%. The increase in CH4 emission can be explained by the increase in the
use of fossil fuels (+85%), especially the use of gas and waste production are large contributors.
Emissions agriculture remained more or less constant.
Figure 1: Global emission of greenhouse gases
When looking at the period 1990 – 2004, one should note that the CO2 emissions grew more than
twice as fast as in the period before 1990. This is mainly due to the increased use (+28%) of fossil
fuels, with major increases also in developing countries. The emission of N2O and CH4 increased by
10% in this period, with growth especially in Latin America, Asia and Africa. In Europe the CH4
emissions remained more or less constant, which had to do with the recovery of methane out of
waste and old coal mines. Furthermore, Fluor containing emissions like HFKs, PFKs and SF6 that also
contribute to the enhanced greenhouse effect almost doubled. When analyzing these figures though,
it should be noted that there are still many countries that do not report emissions which could lead
to inaccurate estimations and graphs.
Traffic and Transport
One of the sectors responsible for the emission of greenhouse gases is the transport sector. Besides
CO2 from the combustion of fossil fuels, the transport sector also emits other gases. Combustion
engines for example emit nitrogen oxides (NOx), carbon monoxide (CO) and unburned hydrocarbons
which are transformed in the atmosphere creating other gases such as ozone. Also, diesel engines
emit soot particles that absorb sunlight and thus have a warming effect on the climate. On the other
hand, sulfuric fuels (for example heavy oils used aboard ships) lead to sulfate particles that increase
the reflection of sunlight and thus have a cooling effect (Berntsen, 2010).
OECD (2010) elaborates on the share of transport in the emission of greenhouse gases. This share is
high on greenhouse gases in general (about 15%, see Figure 2) and especially high on the emission of
CO2 (23%). Total fossil fuel related CO2 emissions increased from 20.9 GT in 1990 to 28.8 Gt in 2007,
of which transport accounted for 4.58 (1990) and 6.63 (2007). This is an increase of approximately
45%. Global energy-related CO2 emissions could raise to over 40 Gt by 2030 and transport emissions
are estimated to make up about 9Gt of that, despite several mitigation measures that are built in the
scenario. The transport sector can be divided in several sectors, each responsible for different types
and amounts of emissions related to the enhanced greenhouse effect. Data for the sectors have been
derived from (Kunzemann, 2009).
Figure 2: Global greenhouse gas emissions by source (2005)
source: (OECD, 2010)
Figure 3: Global CO2 Emissions from Fuel Combustion (2005)
source: (OECD, 2010)
The total road transport sector consists of about 650 million cars, trucks and buses worldwide.
Together they produce about 75% of all greenhouse gas emissions from the transport sector. The
United States have the largest share in this, with about 30 percent of all automobiles producing
about 45% of the world’s CO2 road transport emissions. Developing countries like China, India and
Brazil are catching up fast leading to further pressure on the climate.
Means to reduce road transport emissions include the improvement of fuel consumption by vehicles.
For example in the EU, cars in 2004 emitted about 12 percent less fossil fuels than in 1995. The
European Commission has proposed legislation that reduces average emissions from new cars even
further. Inventions like Hybrid-electric engines could contribute to these goals. Another key factor is
consumer behavior. The main factor influencing this is the price of fuel. When fuel prices rose in
2008 for example, United States Citizens drove about 18 billion kilometers less.
The fleet of ships consists of about 50.000 ships around the world’s oceans and seas. Shipping is the
least carbon-intensive method of freight transport, however ships have large engines that burn great
amounts of fossil fuels. Together they account (international maritime) for about 2,0% of total
greenhouse gas emissions. Most of these emissions are from oil tankers and cargo vessels. Also in
this sector engines have improved fuel efficiency (up to 30%) but the increased pressure on timely
deliveries causes that many ships use these advances to increase speed and capacity rather than
reducing emissions. The OECD for example researched that if the speed of a ship increases by about
4 percent, CO2 emissions raise by 13%. Further growth in the maritime sector is expected, which
increases the need of new inventions to reduce greenhouse gas emissions.
Nowadays, airlines carry about 1.6 billion people and 30 million tons of freight each year. This leads
to aviation being responsible for about 12 percent of CO2 emissions of the transport sector. Air
traffic has grown widely, especially since the introduction of low-budget airlines. Since 1990, this
growth is estimated at about 90 percent. This growth figure is expected to continue which means air
traffic will double by the time of 2020. Although airplanes have (on some journeys) comparable fuel
usage per passenger kilometer, airplanes have the disadvantage that they pollute at high altitude
where emissions have more impact. Soot and water vapor have a warming effect, while nitrogen
oxides form ozone, which is a greenhouse gas. According to the UN, the warming effect of emissions
caused by aviation is twice that of carbon dioxide alone. Ways to reduce these emissions include the
development of more efficient planes and flight routes.
Rail traffic is the least flexible of the transport modes mentioned here, but also one of the most
environmental friendly. Rail traffic accounts for just about 2 percent of all transport related CO2
emissions in the EU. Even though there was growth in rail traffic in Europe, CO2 emissions decreased
by 20 percent between 1990 and 2000. New technologies and more aerodynamic trains make it
possible to reduce this number even further. Also, the possibility of using different power sources for
trains create the opportunity to lower emissions caused by rail traffic. Diesel-powered trains are still
less emitting than trucks, but power generation by nuclear plants or natural resources have even
more positive influence on emissions.
In order to reduce greenhouse gas emissions by transport, transport policy on national and
international levels has been developed. Examples include the European White paper transport
policy for the European Union and the Nationaal Verkeer en Vervoersplan (NVVP) for the
Generally, transport policy can be subdivided in two categories: supply oriented and demand
oriented. Supply oriented measures include the stimulation of new technologies and more efficient
transport networks. For example the European Union stimulates the use of bio-fuels in order to
reduce the life cycle of CO2 emissions. Also several technological inventions are being supported like
the mentioned hybrid-electric cars. Moreover, the aim is to optimize Trans European Networks
(TEN’s) in order to make transport through Europe more efficient (EC, 2001). Classical demand
oriented measures are pricing of transport use in both positive and negative ways. Think of taxing
fuel or charging toll for roads and the subsidization of public transport and other cleaner means of
transport. The EEA (2009) claims that transport policy discussions are too much focused on supply-
oriented measures and state that this should shift to demand-oriented measures. Such efforts not be
limited to the transport sector alone, but should also be directed at areas like urban development,
social policy and regional policy. This is because demand is mostly derived from changes in other
sectors of the economy. EEA’s proposal is to first understand the underlying motives of transport
demand before designing policy. Moreover, they claim that most measures are too soft (such as
providing information) and are in that sense not effective. More enhanced methods should be
explored to get to effective and efficient transport policy.
Berntsen, T. (n.d.). Retrieved June 21, 2010, from Cicero:
EC. (2001). White Paper: European transport policy for 2010: time to decide. Brussels: European
EEA. (2009). Transport at a crossroads. Luxembourg: European Environment Agency.
Kunzemann, T. (2009, September 3). Transport and Climate: On the Road to Nowhere? Retrieved
June 21, 2010, from
OECD. (2010). Reducing Transport Greenhouse gas emissions. OECD.