1. Introduction
Today, climate change is considered the most important challenge of our time. However, it is not the only challenge. Environmental change also includes issues like water scarcity and food security and thus the use of land [
1]. Sustainable transitions—for example, a shift towards low-carbon transportation—are essential to safeguard the Earth for future generations [
2]. Globally, transport accounts for 23% of CO
2 emissions, with emissions increasing with an annual growth of 2.5% between 2010 and 2015 [
3]. Transport CO
2 emissions, or carbon footprints (CFs), are high on the international policy agenda. Policy aims to decarbonize transport and decrease emissions from 7.7 Gt CO
2 per year in 2017 to 2 Gt in 2050. For example, of the nationally determined contributions to the Paris Agreement, 75% focus on the transport sector [
4]. Basically, there are four ways to decrease transport CFs: (i) decrease transport activity; (ii) improve energy efficiency of transport modes; (iii) shift to less CF intensive transport modes; (iv) use less CF intensive fuels. Although behavioral changes are needed [
5], most CF reduction scenarios focus on increasing energy efficiency and fuel shifts rather than activity reduction or modal shifts [
6]. For example, the European Union (EU) promotes the use of transport fuels from renewable sources in an attempt to decrease CFs in its member states. The directive 2009/28/EC from 2009 is forcing countries like The Netherlands to derive at least 10% of their transport fuels from renewable energy sources by 2020 [
7]. Initiatives include the blending of crude oil-based gasoline with bioethanol and the stimulation of transport modes using electricity [
8].
A lower use of transport in combination with a shift towards more efficient transport or transport modes will certainly decrease CFs. When a shift towards less CF-intensive fuels is considered, an important issue in this respect is whether a shift away from traditional fuels towards alternative fuels using new technologies will contribute to strategies to mitigate climate change without having other environmental impacts like greater land or water use. Access to materials, processes and natural resources will nearly always encounter natural limits [
2]. Hao et al. [
9], for example, have shown that hydrogen fuel cell vehicles depend on the availability of platinum, a scarce natural resource with regional supply limitations. Recently, many studies have analyzed the effects of a shift from traditional transport fuels towards less CF-intensive fuels. Fuels included in these studies are biofuels, hydrogen and also electricity, which is sometimes defined as an alternative fuel, e.g., [
10]. Biofuels derived from biomass might decrease CFs, but they have large land requirements. In the United States, for example, all the cropland used for maize and soybean is needed in order to produce only 12% of the gasoline and 6% of the total diesel demand [
11]. A study of the land and water requirements of biofuels from algae also showed the large land and water requirements [
12]. A recent study into the sustainability aspects of different generations of biofuels has shown that all generations have limitations—for example, because they do not satisfy the food–energy–water nexus [
13]. These authors have concluded that it is essential to not only take CFs into account but also to consider the scale of the economy, the availability of bioresources and planetary boundaries. Biofuels are related to a relatively large water requirement, e.g., [
14,
15,
16], showing the competition between water for food and water for energy. Mekonnen et al. [
17] confirms that water constraints currently hardly play any role in the discussion about future energy scenarios. Surprisingly, the “greenest” electricity scenario of the International Energy Agency (IEA), i.e., the scenario with a relatively small growth in electricity demand and with the largest fraction of renewables in 2035, is associated with the largest water use [
17]. When sustainable transport is promoted, not only CFs of the transport mode itself, i.e., the emissions related to transport fuel consumption, but entire production chains, from cradle to gate, need to be included in the analysis so that tradeoffs with other natural resources are also taken into account. For sustainable transport, two phases, the well-to-tank (WTT) and the tank-to-wheel (TTW) phases, need to be considered. WTT includes the production chain of a fuel and TTW the combustion of a fuel. Together, WTT and TTW are termed well-to-wheel (WTW) [
18,
19,
20,
21]. The study by Stephan and Crawford [
22], for example, included a life cycle perspective, including water requirements for infrastructure for passenger transport modes in Melbourne, Australia, showing the importance of all the actors in a supply chain.
Electricity use is another option to decrease CFs because electric transport modes are more efficient than modes using traditional fuels, although consumer resistance may be important [
23]. If electricity is applied to fuel transport, it is essential to generate electricity using renewable energy sources like solar or wind energy rather than applying electricity generated using fossil fuels. In Malaysia, for example, the national electricity composition is based on 40% coal, 52% natural gas and 2% crude oil, so the introduction of electric vehicles eliminates tailpipe emissions but increases emissions related to electricity generation at the same time [
24]. This is also the case in China, where electric cars have become increasingly popular [
3,
25] but where electricity is still carbon-intensive [
26]. An important drawback of electricity generated from solar or wind is its intermittency, i.e., that there is no supply when the sun does not shine or when the wind does not blow and the other way around. Another drawback, e.g., in public transport, is the limited driving range. Electric buses, for example, already need to recharge after 200 to 250 km [
27]. Here, hydrogen as an energy carrier might be a solution. Variable renewable electricity can be used to generate hydrogen that can be stored and applied directly in the transport sector [
28], while hydrogen allows for larger traveling distances than electricity [
9,
27].
The economy of The Netherlands, one of the countries of the EU, depends on an efficient transport system, because it is the carrier of the Dutch trading system, which reflects in the slogan “Netherlands distribution nation”. Fast and reliable passenger and freight transport is vital in establishing Dutch personal visits and business relations [
29]. Therefore, mobility is essential in the Dutch economic system. At the same time, Dutch policy aims at decreasing transport CFs—for example, by encouraging consumers to buy electric cars. With transport accounting for around 27% of the total CO
2 emissions in The Netherlands, the importance of a transition in this sector is evident [
29]. Additionally, other environmental issues (land use, water use and CO
2 emissions) in the entire production chain and during the use of a fuel, from WTT and TTW, need further investigation, because trade-offs can occur if the focus is on decreasing CFs. The so-termed environmental footprint family provides a tool to assess natural resource use and emissions so that human use of these resources remains within planetary boundaries [
30]. Important footprints are the resource use footprints (e.g., blue and green water footprints and land footprints) and emission footprints (e.g., carbon footprints and grey water footprints), which can be applied from local to global levels [
30]— for example, in the transportation sector. This study aims to provide an environmental analysis of transport fuels, including the use of less CF-intensive fuels, that covers three environmental footprints—the carbon, water and land footprints—of transport in The Netherlands. It takes The Netherlands as the case study area because of the importance of transport for the country, the policy initiatives to decrease transport CFs and the availability of reliable data. In addition to investigating fuels that decrease CFs in transport, this study also includes tradeoffs among natural resources, combining carbon, land and water footprints to provide an overall analysis and, in addition, to calculate the consequences of using alternative fuels like hydrogen and electricity. The study answers the following research question: “Which fuels and technologies might be applied in alternative transport fuel scenarios and what are the consequences for the carbon, land and water footprints of the transport sector in The Netherlands compared to the reference situation in 2016?”.
This study focuses on the entire production chain, from well to tank (WTT), and the consumption, from tank to wheel (TTW), of transport fuels, and it calculates the carbon, land and water footprints of different fuel production methods for three alternative fuel supply scenarios, dominated by different fuels per scenario, using the situation in The Netherlands in 2016 as the basis for the calculations. Fuels, e.g., electricity, as an alternative fuel, can be produced in different ways, so that the results give a range of outcomes per scenario. Although the study uses The Netherlands as the case study area, it provides information that can be applied to other countries and regions as well—for example, to the other 27 EU countries that need to comply with the same directive to replace 10% of their transport fuels with renewables.
4. Results
Figure 2 shows the specific carbon footprints of fuels, including the WTT and TTW emissions (kg CO
2e/GJ).
Figure 2 shows large differences among CFs for fuel types and related primary energy sources. Hydrogen and electricity do not have TTW emissions, while liquid and gaseous fuels do. The CFs of diesel and gasoline, the traditional liquid fuels, are smaller than some of the new fuels, like hydrogen, from electrolysis using coal or natural gas, or electricity from coal. The difference in CFs between electricity from wind and hydrogen from coal, for example, is more than a factor 20. Only when renewable PESs are used are CFs small. For the biofuels, the emissions in the WTT stage are negative, because crops take up CO
2 that is released again when the fuel is combusted.
Appendix A gives the CFs per fuel type.
Figure 3 shows the specific land footprints for fuels per primary energy source (m
2/GJ) on a logarithmic scale.
The differences between the land footprints (LFs) are larger in comparison to the carbon footprints (CFs). In particular, fuels derived from agriculture have large LFs. Bioethanol from wheat, for example, requires a factor 10,000 more land per unit of energy than diesel (from crude oil). Fossil fuels have the smallest LFs, while the LFs of wind and solar energy find themselves in between the two extremes.
Appendix B gives the specific land footprints.
Figure 4 shows the specific water footprints per fuel and related primary energy source on a logarithmic scale (m
3/GJ).
WFs of biofuels have a large green component and a small grey component, while all other WFs are blue. The differences among WFs are significant. Bioethanol from rapeseed oil, for example, requires a factor 10,000 more water than diesel from crude oil. In general, WFs are the largest for fuels derived from agriculture and the smallest for electricity from wind. The figure also shows that if renewable energy is stored as hydrogen, the WF increases.
Appendix C gives the specific water footprints, including green, blue and grey WFs.
Figure 5 shows the total energy demand per scenario, in which the reference scenario’s energy demand forms the basis for the energy demand of the other three scenarios.
Figure 5 shows that transport using electricity is the most energy efficient, with a total annual energy use of 159 PJ, while the reference scenario (492 PJ), the scenario with liquid biofuels (492 PJ) and the hydrogen scenario (434 PJ) are less energy efficient. If the electricity scenario is not possible, a hybrid scenario (242 PJ) is most favorable.
Figure 6a–d shows the total annual energy demand per fuel in (PJ), the annual CF (kt CO
2e), the annual LF (m
2) and annual WF (m
3) for scenario 1 (reference scenario), with regard to the situation in The Netherlands in 2016.
Figure 6a shows that energy use for transport in The Netherlands is dominated by the use of gasoline and diesel, which also contribute the most to the carbon footprint (CF). The contribution of the other fuels is small. However,
Figure 6c,d show that the use of small amounts of bioethanol and biodiesel cause large LFs and WFs compared to gasoline and diesel.
Figure 7 shows the annual CF of the four scenarios, including the reference scenario (kt CO
2e).
The figure shows that CFs decrease compared to the situation in 2016 if the alternatives are chosen wisely. If hydrogen that is generated using fossil fuels is applied, however, the total emissions increase. Additionally, a shift towards electricity does not always decrease the emissions substantially. This is only the case when wind and solar energy are applied. In addition, the use of bioenergy decreases CFs.
Figure 8 shows the annual LF of the four scenarios for transport fuels in The Netherlands, including the reference scenario for fuel use in 2016 on a logarithmic scale (10
9 m
2).
The LF of scenario 1, the reference scenario for 2016, is relatively large when compared to the LFs of scenarios 2 and 3, which do not include any biofuels. This is caused by the use of a mixture of gasoline and ethanol, and diesel and biodiesel, in The Netherlands. All LFs in biofuel scenario 4 are large compared to the LFs of scenarios 2 and 3, because this scenario relies on crops from agriculture.
Figure 9 shows the annual total WF of the four scenarios for transport fuels in The Netherlands, including the reference scenario for fuel use in 2016, on a logarithmic scale (10
9 m
3)
Scenario 4, using crops from agriculture, has the largest WFs (mainly green), followed by scenario 1, the reference scenario, which also includes some biofuels. The scenario using hydrogen from coal, natural gas or solar photovoltaics has blue WFs which are smaller than the reference. When electricity from wind or sun is applied, WFs are smallest.
The main message of this article is the importance of combining different environmental assessments in a complex assessment. Policy aims to decrease CFs.
Figure 6 shows the present CF and the related LF and WF.
Figure 7 shows the different options for decreasing CFs, compared to the situation in 2016 (reference scenario), indicating that not all options are favorable and that the choice of PES is important.
Figure 8 and
Figure 9 show the consequences of a specific fuel choice on LFs and WFs. In order to decrease CFs, a shift towards biofuels generates large LFs and WFs. This is the case even for the reference scenario, in which a contribution of only 2.5% of the energy in the form of biofuel to the total energy use of transport generates large LFs and WFs. If a decrease in CFs is the policy’s priority, the best fuel choices, if LFs and WFs are also taken into account, are electricity from wind or sun, followed by hydrogen from wind or solar.
5. Discussion
The study assessed the carbon, land and water footprints related to policy goals to decrease CO2 emissions for different fuel options by assuming that the transport system itself does not change. Other possible options to decrease CFs, such as a decrease in transport activity, increased energy efficiency of transport modes or a shift towards less CO2 intensive ways of transport, were excluded. We only considered fuel shifts; however, we did include the related efficiency improvements by taking the tank-to-wheel efficiencies into account. For example, we included the larger efficiencies of electric vehicles compared to traditional cars using gasoline. This means that the scenario results might differ from a future situation in which other factors also play a role, such as technological developments in the automotive industry.
For the assessment of CFs, we mainly applied data from the Joint Research Centre (JRC) [
18,
19,
20,
21] that provide emission factors in the context of the EU. For the LFs and WFs of wind, solar and hydrogen, we used data that provide a general LF and WF. For biofuels, however, we used data for The Netherlands. In The Netherlands, crop yields are relatively large [
70] and, therefore, the LFs per unit of biofuel are relatively small. In addition, WFs are also relatively small for Dutch biofuels and are dominated by green WFs [
56]. This means that if the results are applied to other countries, the LFs and WFs of biofuels will probably be underestimated.
The EU policy to promote renewables for transport, such as the use of bioethanol, decreases CFs but has a large contribution to LFs and WFs. The term renewable energy is widely used, but it might be problematic in the context of sustainability [
71]. This means that there is a difference between renewable energy and sustainable energy. The choice to encourage the use of renewable fuels for transport might have significant consequences for other resources, not only for land and water but also for scarce raw materials [
9,
71]. The Dutch policy to encourage the use of electricity for transport must also be seen in a broader context. Electric cars are more efficient than their fossil fuel-based counterparts, so the total energy use will decrease. However, it is important to consider how the electricity is generated, and the impact of this on whether or not CFs decrease. If coal is used to generate electricity, emissions do not decrease. Only if large scale wind and solar energy are applied do emissions substantially decrease. However, at present, The Netherlands does not generate these large amounts of renewable energy. The renewable energy sources, wind and solar, are crucial in reducing CFs and have acceptable impacts on land and water. However, currently, a minor proportion (6.6%) of all energy in The Netherlands is renewable [
72]. The share of renewable energy must increase in order to supply enough energy for all different energy-consuming sectors. Therefore, it is likely that the use of renewable energy (solar and wind) will become susceptible to competition between different sectors, including transport.
Another issue is the variability of wind and solar energy or intermittency, requiring energy storage, e.g., in the form of hydrogen. This means that it is not possible to simply scale up renewable electricity production, even though this is theoretically the most efficient option. Here, hydrogen might be introduced, but with smaller efficiencies. However, the infrastructure does not yet exist for electric and hydrogen-based technologies, meaning that there are not yet enough wind turbines and solar panels to provide the entire transport system with sufficient energy. Moreover, electric and, to a larger extent, hydrogen vehicles have not yet penetrated the vehicle market, representing only 8% of the total vehicles [
73], a negligible percentage of all Dutch vehicles. In addition, for hydrogen, the fueling infrastructure is not abundant enough in The Netherlands. Therefore, these options can be considered long-term solutions.
This study assessed the LF; however, land could also be defined as use of space. This is especially relevant when it comes to wind turbines, which are very commonly placed in the sea as well as on land. For example, the coastal sea area of The Netherlands (the Exclusive Economic Zone) includes approximately 1400 km
2 of available space for wind turbines [
74]. The required space for the wind turbines in the electricity–wind scenario is 43.2 km
2, showing that the Dutch area of the North Sea is sufficient to supply enough electricity for the Dutch transport system. In line with results from the literature, e.g., [
17,
40,
52,
75,
76], basing the Dutch transport system on liquid biofuels is not an option, because its land and water requirements will compete excessively with our basic water and food requirements.
When WFs are put into perspective, the present transport system in The Netherlands has a green WF of 520 × 10
6 m
3 per year, a blue WF of 31 × 10
6 m
3 and a grey WF of 59 × 10
6 m
3 per year. Biofuels dominate the total WF and contribute 95%. If hydrogen is chosen as a transport fuel, generated by electrolysis from coal, the total WFs decrease to 381 × 10
6 m
3 per year, but the WF is completely blue and increases tenfold compared to the blue WF of the present transport system. Electricity from wind has the smallest blue WF, at only 2.6 × 10
6 m
3 per year. If biofuels are adopted, e.g., bioethanol from sugar beet, the WFs would increase enormously. In 2011, the green WF in The Netherlands was 17,591 × 10
6 m
3, the blue WF 2147 × 10
6 m
3 and the grey WF 4680 × 10
6 m
3 [
77]. These WFs are mainly external: 95% of the water is used outside the country [
77]. The scenario providing ethanol from sugar beet has a green WF of 10,416 and a grey WF of 2480 × 10
6 m
3 or 59% and 52% of the Dutch green and grey WFs in 2011, respectively. This would put a large amount of pressure on the WFs.
When LFs are put into perspective, the present Dutch transport system has a LF of 1267 km
2, or 3% of the surface area of The Netherlands, at 41,000 km
2 [
12]. This LF is dominated by biofuel use. The scenarios based on biofuels have LFs similar to or exceeding the Dutch surface area, indicating that it is not possible to produce all fuels in The Netherlands itself. For CFs, it does not matter whether emissions take place in The Netherlands or abroad, because emissions have a global impact. For CFs, the smallest footprints are the most favorable.
The example for The Netherlands is relevant for other EU countries too. Total transport energy use in the EU in 2030 could be around 24,000 PJ per year [
12] or fifty times the present Dutch energy use. All countries must comply with the same EU directive to replace 10% of the fuel with renewables, so wise choices must be made in order to prevent LFs or WFs becoming too large.
6. Conclusions
Traditional transport fuels, including diesel, gasoline, marine diesel oil and liquefied gasoline gas, have CFs between 74 (LPG) and 89 (diesel) kg CO2e per GJ. The CFs of bioethanol and biodiesel are smaller, at between 40 and 60 kg CO2e per GJ, and are related to energy use in the life cycle of the production of the biofuel. For electricity, emissions range between 3 (electricity from wind), 19 (solar), 116 (natural gas fired power plants) and 277 (electricity from coal fired power plants) kg CO2e per GJ. This means that if energy policy promotes electric transport, it is important to apply a primary energy source with small CFs, otherwise emissions will increase rather than decrease. This is even more relevant if hydrogen is applied. CFs range between 16 (electrolysis using electricity from wind), 32 (solar), 178 (natural gas fired power plants) and 431 (electricity from coal fired power plants) kg CO2e per GJ.
Traditional transport fuels have relatively small LFs, at 0.0011 m2 per GJ. Wind turbines and solar panels need space and have LFs of 0.1 and 0.6 m2 per GJ, respectively. The LFs of Dutch biofuels are large, between 21 (ethanol from wheat straw) and 125 (biodiesel from rapeseed) m2 per GJ. Dutch biofuels also have large WFs, between 5 (ethanol from wheat straw) and 80 (biodiesel from rapeseed) m3 per GJ. The WFs for hydrogen vary between 0.1 (electrolysis using wind energy) and 0.8 (electrolysis using electricity from a coal fired power plant) m3 per GJ. Other fuels have small WFs compared to biofuels.
The total energy demand for transport in The Netherlands in 2016, excluding air transport, was 492 PJ. If biofuels are applied, energy demand remains the same; for a hydrogen scenario, 434 PJ is needed. The electricity scenario is the most efficient with an energy demand of 159 PJ. From a sustainability point of view, the biofuel scenario is not attractive. The total energy demand remains the same, CFs only slightly decrease, and LFs and WFs increase enormously. This can already be observed in the reference scenario, where biofuels contribute only 2.5% to the total energy demand, but they dominate the LFs and WFs, with 99.9% of the total LF and 95% of the total WF. The electricity scenario has the smallest CFs, but only if wind or solar energy is applied. If electricity is generated using existing coal fired power plants, emissions do not decrease. This scenario also has the smallest LFs and WFs and is therefore the most favorable from a sustainability point of view. If storage is needed and hydrogen is applied, CFs for the most favorable PES, i.e., wind energy, double from 3055 to 7074 kg CO2e, LFs increase from 15 × 106 to 43 × 106 m2, and WFs increase from 3 × 106 to 37 × 106 m3 compared to the electricity scenario.
This case study for The Netherlands shows that the use of less CF-intensive fuels contributes to energy policy aims to decarbonize transport and to substantially decrease emissions. However, trade-offs with land and water resources might occur and these need to be included in the decision-making. Other countries could also adopt these strategies.