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LETTER
Energy and food security implications of transitioning synthetic
nitrogen fertilizers to net-zero emissions
Lorenzo Rosa1,∗and Paolo Gabrielli1,2
1Department of Global Ecology, Carnegie Institution for Science, Stanford, CA 94305, United States of America
2Institute of Energy and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland
∗Author to whom any correspondence should be addressed.
E-mail: lrosa@carnegiescience.edu
Keywords: net-zero emissions, food security, energy-food nexus, ammonia, nitrogen fertilizers, agriculture, climate solutions
Supplementary material for this article is available online
Abstract
By synthetically producing nitrogen fertilizers from ammonia (NH3), the Haber–Bosch process has
been feeding humanity for more than one hundred years. However, current NH3production relies
on fossil fuels, and is energy and carbon intensive. This commits humanity to emissions levels not
compatible with climate goals and commits agricultural production to fossil fuels dependency.
Here, we quantify food and energy implications of transitioning nitrogen fertilizers to net-zero
CO2emissions. We find that 1.07 billion people are fed from food produced from imported
nitrogen fertilizers. An additional 710 million people are fed from imported natural gas feedstocks
used for fertilizers production, meaning that 1.78 billion people per year are fed from imports of
either fertilizers or natural gas. These findings highlight the reliance of global food production on
trading and fossil fuels, hence its vulnerability to supply and energy shocks. However, alternative
routes to achieve net-zero emissions in NH3production exist, which are based on carbon capture
and storage, electrification, and biomass. These routes comply with climate targets while
mitigating the risks associated with food security. Yet, they require more land, energy, and water
than business-as-usual production, exacerbating land and water scarcity and the use of limited
natural resources. Transitioning fertilizers to net-zero emissions can contribute to climate and food
security goals, although water, land, and energy trade-offs should be considered.
1. Introduction
Global agricultural productivity relies on three key
nutrients: nitrogen, phosphorous and potassium
[1,2]. For centuries, nitrogen has been the bottle-
neck limiting global agricultural productivity [3–5].
While the raw elements to produce phosphorus and
potassium fertilizers are mined from natural deposits,
the nitrogen required to produce nitrogen fertilizers
is sourced from air [6,7]. Despite its abundance
in the Earth’s atmosphere, nitrogen is generally not
immediately available for human use, being present
in the unreactive N2form [8]. In 1908, the inven-
tion of the Haber-Bosch process to industrially pro-
duce ammonia (NH3)—a chemically reactive and
highly usable form of nitrogen—has removed lim-
itations associated with soil nutrients and dramat-
ically increased agricultural productivity [9]. Since
then, an abundant supply of nitrogen fertilizers
empowered by the Haber–Bosch process has boosted
agricultural productivity enabling the expansion of
global population [9,10].
While synthetic nitrogen fertilizers have a key
role in global food production [3,4], excess reactive
nitrogen has caused several environmental impacts,
including groundwater contamination, eutrophica-
tion of water bodies and associated biodiversity loss,
air pollution, greenhouse gas emissions, and stra-
tospheric ozone depletion [5,11–16]. Today, using
carbon-intensive energy sources such as coal or nat-
ural gas, synthetic nitrogen fertilizers production via
the Haber-Bosch process is responsible for roughly
2% of global energy consumption and directly emits
about 450 Mt CO2per year [6,17].
Current fossil-based synthetic nitrogen fertilizers
production commit humanity to emissions levels not
© 2022 The Author(s). Published by IOP Publishing Ltd
Environ. Res. Lett. 18 (2023) 014008 L Rosa and P Gabrielli
compatible with climate goals [18]. It also commits
agricultural productivity to rely on fossil fuels and
import dependencies, which can expose global food
systems to energy and supply shocks. For example,
disruptions caused by the Covid-19 pandemic and the
2022 Russia’s war in Ukraine have brought the inter-
twined nature of global energy and food supply chains
into sharp focus [19–21]. Decarbonizing the produc-
tion of synthetic nitrogen fertilizers can have the twin
benefits of reducing both the industry’s CO2emis-
sions and its reliance on fossil fuels imports, therefore
reinforcing global food security.
This study quantifies the food-energy security
implications of transitioning synthetic nitrogen fer-
tilizers to net-zero CO2emissions, via a country-
specific analysis. First, we estimate the number of
people fed from synthetic nitrogen fertilizers world-
wide. Second, we identify which countries are net-
importers and net-exporters of nitrogen fertilizers,
accounting for embedded reliance on fossil fuels
import. Third, we quantify the carbon emissions
currently associated with NH3production world-
wide; NH3is the precursor to synthetic nitrogen
fertilizers, and its current production via the con-
ventional Haber–Bosch process accounts for ∼90%
of the nitrogen fertilizer industry’s total energy
consumption [6]. Finally, we analyze three alternative
routes available to achieve net-zero-CO2-emissions
(or simply net-zero) NH3production, namely car-
bon capture and storage, electrification, and biomass
[22]. Net-zero NH3production can have unintended
environmental consequences on land use, energy, and
water consumption, further exacerbating land and
water scarcity [23–25]. Therefore, we quantify water
and land requirements for all net-zero routes and
compare them with business-as-usual production.
2. Methods
We used country-specific data of synthetic nitro-
gen fertilizers produced and used in agriculture to
quantify people fed and trade dependencies with and
without fossil fuels imports. Synthetic nitrogen fertil-
izers data are taken from the United Nation Food and
Agriculture Organization (FAO) for year 2019 [26].
This is the most up-to-date information of synthetic
nitrogen fertilizers for all countries worldwide. We
then quantified country-specific carbon emissions,
and land, water, energy required to achieve net-zero
emissions in the production of NH3—the precursor
to synthetic nitrogen fertilizers.
2.1. Assessment of people fed from synthetic
nitrogen fertilizers
For all countries, i, we estimated the number of
people fed from synthetic nitrogen fertilizers, Pi,
by considering country-specific agricultural use of
nitrogen fertilizers, Ni(kg N), daily nitrogen intakes
in diets, µ(kg N/person), the fraction of nitrogen lost
from farm to fork, δ, and country-specific nitrogen
use efficiency, ηi(or the fraction of nitrogen lost on
the field and that is not used to produced food):
Pi=Ni
µi
δ ηi.(1)
Country-specific nitrogen fertilizers usage are
taken from the FAO database for year 2019 [26].
Country-specific daily nitrogen intakes in diets are
derived from per capita daily protein intakes as
provided by FAO for year 2019 [26] and consider-
ing that 18% of protein content is nitrogen [27].
Nitrogen is the building block of amino acids that
are required to produce proteins. The FAO database
reports country-specific annual statistics of dietary
protein consumption with a global median protein
intake of 84 g of protein per day per person; a min-
imum intake of 26 g of protein per day per person in
the Democratic Republic of Congo and a maximum
intake of 144 g of protein per day per person in Iceland
[26].
Our food systems are highly inefficient, with most
of the food being lost or wasted [28]. The share of
nitrogen lost from farm to fork is assumed to be
42.5%, an average value derived from previous global
estimates of 41% and 44% [3,29]. Such estimates
quantified production and losses from farm to fork of
digestible protein in the global food system, account-
ing for: harvesting losses, post-harvest losses, non-
food uses, processing and packaging losses, distri-
bution waste, and consumption waste [3,29]. We
acknowledge that a more appropriate analysis would
use up-to-date country-specific and crop-specific val-
ues of nitrogen lost from farm to fork. However, given
the complexity of our food systems, such data are
only partially available—see for example the analysis
of Gustavsson et al at regional level [30]—and are
affected by large uncertainties [31,32]. This high-
lights the need for more accurate data of nitrogen
wasted in food systems.
Nitrogen use efficiency represents the quantity of
applied nitrogen incorporated in crops and is assessed
as the ratio between crop nitrogen uptake and applied
nitrogen fertilizer [5,33]. It is a measure of how effi-
ciently nitrogen fertilizers are used in agriculture. The
global average nitrogen use efficiency is estimated to
be 46%, indicating substantial losses (more than half
of the total nitrogen used) of reactive nitrogen to the
environment [5]. We use country-specific and pub-
licly available nitrogen use efficiency statistics [33].
Importantly, the ongoing global increase in animal
protein intakes is leading to a decline in overall nitro-
gen use efficiency [5].
2
Environ. Res. Lett. 18 (2023) 014008 L Rosa and P Gabrielli
2.2. Self-sufficiency analyses
We analyzed country-specific trade balances to
quantify synthetic nitrogen fertilizers self-sufficiency
and determine net-importers and net-exporters. Spe-
cifically, for all countries, i, we quantify synthetic
nitrogen fertilizers produced domestically with and
without embedded natural gas imports. When not
accounting for natural gas imports, we assess the
quantity of synthetic nitrogen fertilizers imported or
exported, Di(kg N), by taking the difference between
total domestic production of synthetic nitrogen fer-
tilizer, Ti(kg N), and domestic agricultural use of
synthetic nitrogen fertilizer, Ni(kg N):
Di=Ti−Ni(2)
Direpresents the trade deficit or surplus of syn-
thetic nitrogen fertilizers in a specific country. When
Diis smaller than zero, a country is a net-importer of
synthetic nitrogen fertilizers; when Diis greater than
zero, a country is a net-exporter.
When accounting for natural gas imports, hence
for the coupling of energy and food systems, we
quantify the quantity of synthetic nitrogen fertilizers
produced domestically, Di,CH4, by taking the differ-
ence between total production of synthetic nitrogen
fertilizer made from domestic natural gas, Ti,CH4,
and agricultural use of synthetic nitrogen fertilizer,
Ni(kg N):
Di,CH4=Ti,CH4−Ni.(3)
When Di,CH4is smaller than zero, a country is a
net-importer of synthetic nitrogen fertilizers, at the
net of imported natural gas. When Di,CH4is greater
than zero, a country is a net-exporter. The discrep-
ancy between Diand Di,CH4provides a measure of
the exposure of the food system to energy trading
and potential shocks in energy supply. The total pro-
duction of synthetic nitrogen fertilizer made from
domestic natural gas, Ti,CH4, is computed by account-
ing for the fraction of nitrogen fertilizers produced
from imported natural gas:
Ti,CH4=Ti1−
Ii
Ci(4)
where Ii(m3) is the amount (volume) of imported
natural gas, and Ci(m3) is the overall natural gas con-
sumption in each country (29). To the best of our
knowledge, there are not available dataset that spe-
cify the purpose of natural gas import in each coun-
try. Therefore, we assume that the share of synthetic
nitrogen fertilizers produced from imported natural
gas is the same as the total share of imported natural
gas in each country. Data of total production of syn-
thetic nitrogen fertilizer, Ti(kg N), and agricultural
use of synthetic nitrogen fertilizer, Ni(kg N) are taken
from FAO for year 2019 [26]. The number of people
fed from imported synthetic nitrogen fertilizers with
and without natural gas imports (Diand Di,CH4) is
assessed using equation (1) and considering country-
specific daily nitrogen intakes in diets, µi(kg N/per-
son), fraction of nitrogen lost from farm to fork, δ,
and country-specific nitrogen use efficiency, ηi.
2.3. Assessment of net-zero ammonia production
Conventional production of ammonia (NH3) is car-
ried out via the Haber–Bosch process. Globally, con-
ventional Haber–Bosch processes use natural gas
(70%) and coal (26%) as feedstock, with oil and
electricity accounting for less than 4% of global
production [6]. The availability of feedstock and pro-
cess energy is a key determinant of where and how
NH3is produced. Low-cost natural gas in the United
States, Middle East, and Russia explains the promin-
ent role of these regions and their natural gas-based
plant fleets. China’s abundant coal reserves explain
its heavy reliance on the fuel, which accounts for
around 85% of its production. Here, we assume that
all countries use natural gas, except for China (mix of
85% coal and 15% natural gas), United States, South
Africa, and Indonesia (all featuring a mix of 20% coal
and 80% natural gas) [6].
When based on natural gas, the process uses
about 0.49 ton of fossil carbon (t C), or about 0.65
ton of natural gas, to produce one ton of ammonia
(t NH3); the coal-based process uses about 0.88 t C
(or about 0.62 ton of coal) to produce one t NH3[6]
(supplementary figure 2). By applying stoichiometry,
business-as-usual NH3production with natural gas
and coal emits 1.8 t CO2/t NH3and 3.2 t CO2/t NH3,
respectively (supplementary figure 2).
A stream of pure hydrogen needs to be fed into
the Haber–Bosch reaction for NH3synthesis. There-
fore, CO2is removed through primary and second-
ary steam methane reforming (SMR) and a two-stage
water-gas shift (WGS). The concentrated stream of
CO2can be used for urea-based fertilizers produc-
tion or alternatively is vented to the atmosphere con-
tributing to global warming. Similarly, the diluted
CO2in the exhaust gases from fossil fuels combustion
for energy inputs is emitted to the atmosphere. The
Haber–Bosch process is composed of two SMR react-
ors in series. The first SMR reactor is endothermic,
with the required heat being provided by external
combustion of methane fuel. The second SMR reactor
is autothermal, while the WGS reaction is exothermic,
making a significant amount of heat available for heat
integration. Such heat is typically used for producing
high-pressure steam, which is expanded in steam tur-
bines for compression purposes.
When adopting carbon capture and storage,
the concentrated CO2resulting from hydrogen
production, and the diluted CO2in the exhaust
3
Environ. Res. Lett. 18 (2023) 014008 L Rosa and P Gabrielli
gases from fossil fuel combustion are captured, trans-
ported to a suitable storage site, and permanently
sequestered [34]. Because CO2transport via pipeline
results in negligible CO2emissions, we do not con-
sider associated CO2emissions from CO2transport
and storage [35].
For the business-as-usual route, we consider an
average electricity consumption of 0.18 MWh t−1
NH3when the process uses natural gas as feedstock
(ranging from 0.08 MWh t−1NH3when the process
adopts SMR, to 0.28 MWh t−1NH3when the pro-
cess adopts auto-thermal reforming), and an average
electricity consumption of 0.91 MWh t−1NH3for the
coal-based process [6]. Such electricity consumption
is additional to the energy inputs provided by fossil
fuels and is used to run auxiliary equipment.
When implementing carbon capture and storage
to concentrated and diluted CO2streams, the elec-
tricity consumption becomes 0.35 MWh t−1NH3
(range 0.28–0.41 MWh t−1NH3) for natural gas-
based processes and 1.26 MWh t−1NH3for coal-
based processes [6]. Overall, the CO2capture pro-
cess has a capture efficiency of about 95% [6], with
5% of the emissions still escaping to the environ-
ment and being captured back with direct air cap-
ture to achieve net-zero CO2emissions. The capture
efficiency of 95% is assumed as the optimal trade-
off between higher CO2purity and higher capture
costs [6]. This efficiency value, which is higher than
typical values for post-combustion capture of about
90%, is made possible by the combination of the con-
centrated CO2resulting from hydrogen production
(higher capture efficiency) and the diluted CO2in the
exhaust gases (capture efficiency of about 90%) [6].
Various studies have assessed processes that go
beyond fossil fuels in NH3production by using
hydrogen produced from water electrolysis or
biomass [36–42]. Both the electrification and the
biomass routes still rely on the Haber–Bosch process
to produce NH3, which is either electrified or fueled
by biomass.
The electrification route relies on the use of
renewable energy to produce hydrogen and nitrogen
for NH3synthesis [38,39,41]. In this case, elec-
tricity provides all the energy requirements, repla-
cing fossil fuels as both feedstock and fuel. Hydro-
gen is produced via water electrolysis and converted
to NH3through a Haber–Bosch process like the con-
ventional one; nitrogen is produced through an air
separation unit [6]. Such a process requires 0.18 t H2
and 0.82 t N2, with an average electricity consump-
tion of 9.3 MWh t−1NH3(range 8.6–10 MWh t−1
NH3) [6,43].
Biomass-based NH3production is carried out via
a gasification process starting from dry wood chips,
here assumed to have a 43% carbon content and a
lower heating value of about 17 MJ kg−1. The process
uses about 2 ton of dry biomass and 0.37 MWh to
produce one t NH3[36,44]. This amount of biomass
is used both as a fuel, to produce the heat required
by the first reforming reactor, and as a feedstock. For
all net-zero emissions routes, schematics of processes
enabling net-zero emissions production of NH3are
shown in supplementary figure 1.
2.4. Assessment of carbon dioxide emissions
The carbon intensity of all routes is computed by con-
sidering the carbon intensity of the production pro-
cesses, as well as the carbon intensity (including the
embedded emissions) of the technologies supplying
electricity. Electricity can be supplied via: (i) electri-
city grid, with a carbon intensity varying country-
by-country (world average equal to 458 kg of CO2
equivalent per MWh of electricity) [45]; (ii) solar
photovoltaic panels, which result in a median value
of 87.5 kg CO2eq per MWh of produced electricity
(range 23–183 kg CO2eq MWh−1) [46]; (iii) wind
turbines, with a median carbon intensity of 11 kg
CO2eq MWh−1(range 8–23 kg CO2eq MWh−1)
[46]; (iv) nuclear power plants, with a median carbon
intensity of 12 kg CO2eq MWh−1(range 4–110 kg
CO2eq MWh−1) [46]. Furthermore, we consider the
lifecycle carbon emissions of the natural gas sup-
ply chain, which account for the emissions released
upon use of natural gas (both as a fuel and as a feed-
stock), as well as for natural gas leaks along the sup-
ply chain; here we assume natural gas leaks equal to
1.5% of the required amount of natural gas needed
to produce NH3under the business-as-usual and
carbon capture and storage routes. Indeed, recent
research demonstrated that natural gas leaks occur
across the entire supply chain, including production,
processing, pipeline transportation, and distribution
[47–49]. Overall, natural gas leaks rate from 0.2% to
8%, with 1.5% being a reasonable likely value [50].
For all four routes jand all countries i, the total
CO2emissions, Ci,j, are obtained as:
Ci,j=Aiϵj+αjγ(5)
where Aiis the amount of produced NH3in country
i,ϵjis the carbon intensity of the production pro-
cess of route j,αjis the specific electricity consump-
tion of route j, and γis the carbon intensity of elec-
tricity generation (which depends on the considered
generation technology among grid, solar, wind and
nuclear). The emissions resulting from NH3produc-
tion are non-zero only for the business-as-usual and
the carbon capture and storage routes (for the lat-
ter, they include the 5% fugitive emissions from the
capture process). However, for all net-zero routes the
emissions resulting from electricity production must
4
Environ. Res. Lett. 18 (2023) 014008 L Rosa and P Gabrielli
be offset via direct air capture, which also requires
energy to operate [51]. The amount of required dir-
ect air capture to achieve net-zero emissions, Di,j, is
computed as:
Di,j=Ci,j+Ci,jγλλ(6)
where λis the amount of electricity required to cap-
ture one ton of CO2via direct air capture. This is
the sum of electricity consumption and electrified
heat consumption of direct air capture. For the cal-
culations, we consider a direct air capture technology
based on solid sorbents [51]. We consider an elec-
tricity consumption of 0.35 MWh t−1CO2(which
already includes 0.1 MWh t−1CO2for CO2compres-
sion for making it ready for transport and storage)
and a heat consumption of 1.75 MWh t−1CO2[51].
Heat is required at low temperature (around 100 ◦C)
and can be supplied via heat pump (coefficient of per-
formance of 4), resulting in λ=0.79 MWh t−1CO2.
The deployment of direct air capture with CO2stor-
age can result in further environmental tradeoffs [52].
For all routes and for all countries, the total elec-
tricity consumption, Ei,j, is given by the contribution
of NH3production and the one of carbon capture via
direct air capture:
Ei,j=Aiαj+Ci,jγλ. (7)
2.5. Assessment of water and land requirements
The land use and water consumption of all routes are
computed by considering on-site electricity demand
for NH3production, hydrogen production, direct air
capture, and biomass. The calculations are based on
the data reported in supplementary table 2.
The total land use and water consumption are
computed by multiplying the total electricity produc-
tion, the amounts of required hydrogen, direct air
capture, and biomass, by the corresponding factors in
supplementary table 2. Accordingly, for all countries
and routes, the land use, Li,j, is given by:
Li,j=Ei,ja+Di,jb+Aiβjc(8)
where βjis the amount of biomass required per unit of
NH3in route j(only needed for the biomass route); a,
b, and c, are the land use intensities of electricity gen-
eration, direct air capture, and biomass, respectively.
Similarly, for all countries and routes, the total
water consumption, Wi,j, is given by:
Wi,j=Ei,jd+Di,je+Aiβjf+ηjg(9)
where ηjis the amount of hydrogen required per unit
of NH3in route j(only needed for the electrification
route); d,e,f, and gare the water consumption intens-
ities of electricity generation, direct air capture, bio-
mass, and hydrogen production, respectively.
3. Results
3.1. People fed from synthetic nitrogen fertilizers
By considering country-specific nitrogen use efficien-
cies (i.e. the fraction of nitrogen lost on the field,
which is not used to produced food) [33], nitro-
gen waste and losses in crops from farm to fork [3,
29], and country-specific per capita nitrogen intakes
[26], we quantify the number of people that consume
synthetic nitrogen fertilizers and estimate the num-
ber of people fed. Consistent with previous global
estimates around year 2000 [3,4], our updated ana-
lysis for year 2019 shows that synthetic nitrogen fer-
tilizers are used to produce half of the global pro-
tein supply, feeding 3.8 billion people worldwide
(figure 1).
According to the FAO, China is the largest con-
sumer of synthetic nitrogen fertilizers (27 Mt nitro-
gen, Mt N, per year), followed by India (19 Mt N
per year), the United States (12 Mt N per year),
Brazil (5 Mt N per year), Pakistan (4 Mt N per year),
Indonesia (3 Mt N per year), and Canada (3 Mt N
per year) [26]. Yet, by considering country-specific
nitrogen use efficiencies and nitrogen intakes in diets,
we find that India is the country producing pro-
teins that feed the largest number of people with
synthetic nitrogen fertilizers, 646 million people, fol-
lowed by China (530 million people), the United
States (480 million people), and Indonesia (225 mil-
lion people) (figure 1). These results quantify the
number of people fed by synthetic nitrogen fer-
tilizers and the reliance of global food production
on synthetic nitrogen fertilizers. Because of higher
inefficiencies in fertilizers applications and nitro-
gen intakes in diets, China—the largest consumer of
synthetic nitrogen fertilizers—can feed less people
than India—the second largest consumer of synthetic
nitrogen fertilizers. We also show that the Unites
States produces enough protein to feed 480 million
people, a number larger than its population. This is
because the Unites States are a major exporter of food
and a fraction of proteins produced from synthetic
nitrogen fertilizers within the country are interna-
tionally traded.
3.2. Synthetic nitrogen fertilizers self-sufficiency
International trade is increasingly transporting com-
modities from one country to another and exacer-
bating vulnerability to supply shocks [53]. About one
fourth of global food is traded among countries [54].
Similarly, synthetic nitrogen fertilizers are produced
and traded around the world [6]. In 2019, synthetic
nitrogen fertilizer exports equated 38% (47 Mt N per
year) of global production [26]. We analyze country-
specific trade balances to quantify synthetic nitro-
gen fertilizers self-sufficiency and determine net-
importers and net-exporters. Using country-specific
data of fertilizers production and use [26], we
5
Environ. Res. Lett. 18 (2023) 014008 L Rosa and P Gabrielli
Figure 1. Number of people fed from synthetic nitrogen fertilizers. Synthetic nitrogen fertilizers data are taken from the United
Nations food and agriculture organization (26) for year 2019, the most up-to-date year containing information of domestic usage
of synthetic nitrogen fertilizers. Globally, 107 Mt of synthetic nitrogen fertilizers were used in agriculture in 2019 [26].
calculate the net-imports and net-exports of nitrogen
fertilizers.
Our analysis shows that exports of nitrogen fertil-
izers are concentrated in a few countries (figure 2(A)).
Russia is the largest net-exporter of synthetic nitrogen
fertilizers (9.2 Mt N per year), followed by China
(5.6 Mt N per year), Egypt (3 Mt N per year), Qatar
(3 Mt N per year), Saudi Arabia (2.6 Mt N per
year), the United States (1.6 Mt N per year), Oman
(1.6 Mt N per year), and Canada (1.4 Mt N per year)
(figure 2(A)).
However, some net-exporters of synthetic nitro-
gen fertilizers, such as China, the Netherlands, Ger-
many, Belgium, South Korea, Poland, and Japan are
large importers of natural gas [55], which make
these countries vulnerable to energy shocks—as high-
lighted by the current energy crisis [56,57]. To invest-
igate the interplay of food and energy supply, we
then investigate the self-sufficiency of all countries
worldwide when accounting for the share of syn-
thetic fertilizers produced from imported natural gas.
By accounting for natural gas imports [55], we find
that the number of countries that can produce syn-
thetic nitrogen fertilizers self-sufficiently decreases
(figure 2(B)). China, Germany, the Netherlands,
Finland, South Korea, Japan, Belarus, and Poland
become net-importers of synthetic nitrogen fertil-
izers (via the import of natural gas) (figure 2(B)). In
contrast, major fossil fuels producers, such as Rus-
sia, Qatar, Saudi Arabia, Egypt, Oman, and Iran
remain net-exporters of synthetic nitrogen fertilizers
(figure 2(B)).
This analysis shows which country can produce
enough fertilizers to meet domestic demand. It allows
to understand the countries’ vulnerability to food,
fertilizers, and energy supply shocks, and it highlights
the strong connection between the food and energy
systems, with a handful of countries controlling either
the food or the energy resources required to produce
fertilizers.
3.3. Food security risks from traded nitrogen
fertilizers
The reliance of synthetic nitrogen fertilizer on inter-
national trade represents a threat to global food secur-
ity and resilient food systems [53]. Food security is
achieved ‘when all people, at all times, have phys-
ical, economic and social access to sufficient, safe,
and nutritious food to meet their dietary needs and
food preferences for an active healthy life’ [58]. In
this study, we consider the nutrient security com-
ponent of food security considering a safe physical
access to proteins [59]. We quantify the number
of people fed with traded synthetic nitrogen fertil-
izers when accounting for fertilizers trade with and
without embedded natural gas imports (i.e. analysis
presented in figure 2(B)).
We find that 1.07 billion people per year are fed
from food reliant on fertilizers imports (figure 3).
However, when accounting for embedded natural gas
6
Environ. Res. Lett. 18 (2023) 014008 L Rosa and P Gabrielli
Figure 2. Global nitrogen fertilizers self-sufficiency with and without embedded fossil fuel imports. Panel (A) shows
net-importers and net-exporters of synthetic nitrogen fertilizers by simply referring to the fertilizer trading; panel (B) shows
net-importers and net-exporters of synthetic nitrogen fertilizers accounting for the share of imported natural gas used in the
production of fertilizers; panel (C) shows additional imported nitrogen fertilizers when accounting for natural gas imports
embedded in production.
imports, or the share of synthetic fertilizers produced
from imported natural gas, we find that an additional
710 million people rely on natural gas imports used
to produce synthetic nitrogen fertilizers. Globally,
1.78 billion people per year are fed from food reli-
ant on imports of either fertilizers or natural gas
(figure 3). India is the country relying the most on
nitrogen fertilizers import, with 176 million people
relying on direct import of fertilizers, and 379 mil-
lion people relying on either imported fertilizers or
imported natural gas (figure 3). China—a coun-
try self-sufficient in terms of nitrogen fertilizers—
becomes a net-importer when accounting for nat-
ural gas imports, with 151 million people being fed
from fertilizers produced from imported natural gas
(figure 3). When accounting for imports of either
fertilizers or natural gas, nitrogen fertilizers are used
to produce food that can feed 185 million people
in Brazil, 93 million people in France, 64 million
people in Ukraine, and 58 million people in Tur-
key (figure 3). Without trading of fertilizers or nat-
ural gas, food shortages will spread with devastating
impacts on millions of people.
3.4. Carbon emissions embedded in ammonia
production
Ammonia (NH3) synthesis for synthetic nitrogen fer-
tilizers production is energy and carbon intensive.
The global production of NH3is about 183 Mt per
year; ∼70% of which goes into synthetic nitrogen
7
Environ. Res. Lett. 18 (2023) 014008 L Rosa and P Gabrielli
Figure 3. Number of people fed from imported synthetic nitrogen fertilizers. The figure shows top importing countries and the
number of people that can be fed from imported synthetic nitrogen fertilizers with and without accounting for embedded natural
gas imports used for production of ammonia. Embedded natural gas imports accounts for the share of synthetic fertilizers
produced from imported natural gas in each country.
Figure 4. Country-specific emissions resulting from ammonia synthesis for synthetic nitrogen fertilizers production. The figure
shows countries emitting more than 1 Mt CO2per year to produce ammonia for synthetic nitrogen fertilizers use in domestic
agriculture.
fertilizers, whereas the remaining fraction is used
for plastics, explosive, and textile production [6].
While global greenhouse gas emissions from NH3
production are estimated to be 450 Mt CO2per year
[6], country-specific carbon emissions from synthetic
nitrogen fertilizers production have been overlooked
until recently [17]. Using country-specific data of
electricity carbon footprint and energy mix for NH3
production, accounting for natural gas leaks along the
supply chain, and modeling several processes for net-
zero NH3production, we quantify country-specific
CO2emissions resulting from the business-as-usual
production of synthetic nitrogen fertilizers.
Our analysis shows that 310 Mt CO2per year are
emitted globally to produce synthetic nitrogen fertil-
izers (figure 4). China is responsible for the largest
CO2emissions related to the production of syn-
thetic nitrogen fertilizers (117 Mt CO2yr−1), fol-
lowed by India (45 Mt CO2 yr−1), the United States
(31 Mt CO2yr−1), Brazil (11 Mt CO2yr−1), Pakistan
(8 Mt CO2yr−1), and Indonesia (8 Mt CO2yr−1)
(figure 4).
8
Environ. Res. Lett. 18 (2023) 014008 L Rosa and P Gabrielli
Figure 5. Energy, land, and water intensity of ammonia production via net-zero routes. Uncertainty ranges are determined by
considering different life cycle values of land, water, and energy requirements (supplementary table 2). Reference values are
presented with dots and represent the central values in original sources. Note that the y-axes are in logarithmic scale with base 10;
1 kg of nitrogen is equal to 1.22 kg of ammonia.
3.5. Available routes for net-zero ammonia
production
NH3production accounts for ∼90% of the total
energy consumption and CO2emissions of the
nitrogen fertilizer industry [6]. Therefore, achieving
net-zero CO2emissions in NH3production would
represent a major step towards net-zero fertilizers.
The conventional Haber–Bosch process is a highly
integrated process that can be divided into two main
steps: (a) hydrogen production from fossil fuels,
and (b) NH3synthesis from the Haber–Bosch reac-
tion. Hydrogen and nitrogen production are energy-
intensive processes that can have different carbon
intensities depending on the energy source and
feedstock [6]. In the business-as-usual route, fossil
fuels are used as feedstock to produce hydrogen and
provide the energy required for the synthesis of NH3,
hence resulting in CO2emissions (supplementary
figure 1(A)). In most countries, hydrogen is cur-
rently manufactured through SMR of natural gas; in
China, hydrogen is produced via coal gasification [6].
Although improvements in energy efficiency and car-
bon intensity are underway and have reduced the
emission intensity of NH3production by 12% over
the last fifteen years [6], net-zero NH3production
needs to phase-out from fossil fuels.
Net-zero CO2emissions in NH3production can
be achieved in multiple ways: through the produc-
tion of hydrogen from fossil fuels integrated with
carbon capture and storage [6]; through the pro-
duction of hydrogen from electrolysis using low-
carbon electricity [60]; and through the production
of hydrogen from biomass gasification, such as wood
chips from crop and forestry residues [36]. In the
carbon capture and storage route (supplementary
figure 1(B)), NH3is still produced from fossil-fuels
via the conventional Haber–Bosch process [6]. Car-
bon dioxide emission generated during NH3synthesis
are captured, transported, and permanently stored in
suitable underground geological structures [34]. In
the electrification route, hydrogen is produced from
water electrolysis via low-carbon electricity, which
also power the Haber–Bosch process [60] (supple-
mentary figure 1(C)). In the biomass route, CO2is
captured from air via photosynthesis during biomass
growth and then emitted upon synthesis and dis-
posal of the biomass-based product, thus resulting in
net-zero CO2emissions. Biomass contains both the
carbon and hydrogen atoms, as well as the energy
required for the synthesis of NH3[44] (supplement-
ary figure 1(D)). For all routes to reach net-zero emis-
sions, residual emissions along the production chain
must be offset with negative emissions, for example
via direct air carbon capture coupled with CO2and
storage [6].
3.6. Energy-land-water implications
While all net-zero routes described above are technic-
ally feasible [6], and some allow to avoid reliance on
fossil fuels, a holistic approach is needed to quantify
their environmental feasibility and avert unintended
environmental consequences. We quantify the land,
water, and energy requirements of all net-zero routes
and compare them with a business-as-usual route to
produce NH3(See Methods section for a description
of all net-zero routes). All net-zero routes are more
land, energy, and water intensive than the business-
as-usual route (figure 5); this is the cost of achiev-
ing net-zero emissions. Overall, the biomass route is
the most water- and land-intensive route (mostly due
to the high water and land intensity for growing the
biomass feedstock), while the electrification route is
the most energy-intensive (mostly due to the amount
of electricity required to produce hydrogen via water
electrolysis) (figure 5).
Table 1reports the reference values of global
CO2emissions, energy requirements, land use and
water consumption, reiterating that achieving net-
zero emissions is possible, but requires high energy,
land, and water resources. For example, decarbon-
izing NH3production with the electrification route
will require TWh of electricity (or 5% of year 2019
global total electricity consumption), compared to
the 48 TWh currently used under a business-as-
usual production pathway (table 1). Achieving net-
zero emissions via the biomass route requires 26 mil-
lion hectares of land and 255 km3of water, about
a factor 1000 higher than the resources required by
9
Environ. Res. Lett. 18 (2023) 014008 L Rosa and P Gabrielli
Table 1. Global energy, land, and water required to achieve net-zero emissions in synthetic nitrogen fertilizers production. The table
shows reference values of global CO2emissions, electricity consumption, land use, and water consumption for all net-zero routes and
comparison against the business-as-usual production. See supplementary dataset for country-specific energy, land, and water
requirements to decarbonize domestic use of synthetic nitrogen fertilizers.
CO2emissions
(Mt CO2)
Electricity
requirements
(TWh) Land use (Mha)
Water
consumption (km3)
Business-as-usual 310 48 0.03 0.04
Carbon capture and storage 0 76 0.06 0.13
Electrification 0 1219 0.9 2.03
Biomass 0 49 26 255
the current production (table 1). Overall, achieving
net-zero emissions in NH3production is technically
possible. However, water, land, and energy trade-offs
should be thoroughly considered to ensure a sustain-
able transition to net-zero food systems.
4. Discussion
4.1. Food security implications
Feeding the growing and increasingly affluent human
population requires doubling global food produc-
tion by 2050 [61]. To meet this demand, nitrogen
fertilizers are required to increase agricultural pro-
ductivity. Currently, half of the world population is
supported by synthetic nitrogen fertilizers, produced
via the Haber–Bosch process—a carbon- and energy-
intensive process that commit global food systems
to rely on fossil fuels. This study sheds light on the
global food security implications of current fossil
fuel-based synthetic nitrogen fertilizers production,
which is exposed to supply and energy shocks. It iden-
tifies producers and consumers of synthetic fertilizers
and the associated number of people fed, when con-
sidering the interplay with energy supply. Further-
more, it presents routes to achieve net-zero emissions
in the production of fertilizers, and investigates their
potential for improving food security, as well as their
impact on land and water scarcity. These results can
inform the development and deployment of resili-
ent and sustainable strategies to achieve net-zero food
systems.
Our results quantify the reliance of the global food
system on synthetic nitrogen fertilizers and natural
gas trade. We find that 1.07 billion people per year are
fed from food reliant on fertilizers imports (figure 3).
However, when accounting for embedded natural gas
imports, or the share of synthetic fertilizers produced
from imported natural gas, we find that 1.78 billion
people per year are fed from food reliant on imports
of either fertilizers or natural gas (figure 3). Overall,
a handful of countries control the trade of synthetic
nitrogen fertilizers, either via their production capa-
city or energy (mostly natural gas) resources. These
countries are Russia, Egypt, Qatar, and Saudi Ara-
bia. Multiple countries, namely China, Germany, the
Netherlands, Finland, South Korea, Japan, Belarus,
and Poland, are net-importers of synthetic nitrogen
fertilizers via natural gas import, despite their fer-
tilizer production capacity (which could make them
net-exporters of nitrogen fertilizers if they had more
fossil fuels resources) (figure 2). This unveils complex
risks and threats to global food security, with more
than 20% of the global population being exposed to
either supply shocks via fertilizers trading or energy
shocks via embedded energy feedstock (mostly nat-
ural gas) trading.
Our results show that imports of synthetic nitro-
gen fertilizers and embedded natural gas produce
food that can feed 379 million people in India, 185
million people in Brazil, and 151 million people in
China (figure 3). While Brazil and the United States
are major food exporters and nitrogen fertilizers are
used to produce food that feed people in other coun-
tries, in India and China most of the food produced
from fertilizers is used to feed domestic population,
making domestic food production particularly reliant
on trade and energy and supply shocks.
4.2. Energy and environmental implications
Being more energy-intensive (figure 5), net-zero NH3
production will not necessarily decrease vulnerability
to energy shocks. For example, net-zero NH3produc-
tion based on the electrification route could reduce
the vulnerability to shocks on commodity markets,
at least for what pertains oil, methane, and coal, but
would be still vulnerable to electricity prices.
Transitioning fertilizer production to net-zero
CO2emissions can have the twin benefit of redu-
cing CO2emissions while enhancing food security.
Indeed, the deployment of processes to synthesize
nitrogen fertilizers from renewable energy (i.e. elec-
trification and biomass route) can reduce CO2emis-
sions while averting reliance on imports of fossil
fuels. In contrast, whereas carbon capture and stor-
age allows to achieve net-zero emissions, it does not
reduce the reliance of the food system on fossil fuels;
it still uses an average of 77 Mt of carbon from fossil
fuels per year, hence making the global food sys-
tem vulnerable to energy shocks. In addition, carbon
capture and storage would require a widely spread
infrastructure to transport [35,62] and perman-
ently store the CO2captured at the production site
[63]. Whereas recent assessments indicate that a vast
10
Environ. Res. Lett. 18 (2023) 014008 L Rosa and P Gabrielli
storage capacity might be available, i.e. between 7000
and 55 000 Gt CO2can be stored worldwide [64],
CO2storage still faces issues concerning the actual
availability, accessibility, and acceptance of storage
sites [65,66]. An alternative option to geological
CO2storage is carbon dioxide mineralization, which
consists in reacting CO2with metal cations to form
stable carbonate materials and achieve permanent
CO2sequestration [67–69]. Importantly, our assess-
ment accounts for natural gas leaks along the supply
chain, here assumed to be 1.5% of the required nat-
ural gas [50]. However, it is worth noting that nat-
ural gas leaks affect carbon emissions, hence land,
energy, and water consumption required to achieve
net-zero emissions of the carbon capture and storage
route only. Arguably, the carbon capture and storage
route would find a better use for carbon-rich chem-
ical products, such as methanol and plastics, which,
contrary to NH3, contain the carbon molecule in the
final product [22].
Contrary to carbon capture and storage, the elec-
trification and biomass routes can achieve net-zero
emissions while avoiding using fossil fuels. How-
ever, the electrification route would require twenty-
five times more energy than the business-as-usual
route. The biomass route would require one thou-
sand times more land and water than the business-
as-usual route, using 26 million hectares of land
and 255 billion cubic meter of water (table 1). To
grow this vast increase in biomass, further nitro-
gen inputs [70], and transport and processing facil-
ities would be required. In addition, both biomass
and electricity will be required to achieve net-zero
emissions in other sectors and a competition for
these limited resources could constrain their use for
NH3production [71]. To avert unintended environ-
mental consequences on natural resources and biod-
iversity and additional land, water, and fertilizers
use, biomass should be sourced sustainably from
waste biomass, forestry residues, and crop residues
[72,73].
While net-zero nitrogen production routes could
solve energy and food security issues present in
business-as-usual NH3production, these alternative
NH3production routes could create inequalities in
NH3nitrogen fertilizers production with more tech-
nically advanced economies continuing to dominate
production.
4.3. Solutions to reduce ammonia demand
By emitting 310 Mt CO2per year (figure 3), business-
as-usual NH3synthesis for synthetic nitrogen fer-
tilizers production commit humanity to emissions
levels not compatible with the net-zero targets
required to keep global warming below 1.5 ◦C [74].
An additional 30 Mt CO2per year are estimated to
come from NH3transport [17]. Although NH3is not
a greenhouse gas, its overuse lead microbes in the soil
to convert it into nitrous oxide, a greenhouse gas three
hundred times more powerful than carbon dioxide
and responsible for stratospheric ozone depletion
[75,76]. It is estimated that nitrogen fertilizers emit
2.3 Mt of nitrous oxide per year, equivalent to 670 Mt
CO2emissions per year [6], bringing global total
emissions (direct and indirect emissions) from syn-
thetic nitrogen fertilizers to 1010 Mt CO2per year
when accounting for emissions from NH3synthesis
for nitrogen fertilizers, or 2% of global greenhouse gas
emissions.
Economic and population growth are expected to
double global food demand by 2050 [61]. Thus, syn-
thetic nitrogen fertilizers are envisaged to continue to
be a major and growing component of agricultural
productivity in the 21st century [5,77,78]. While
the net-zero routes analyzed here can abate emissions
on the supply-side, demand-side measures can reduce
future NH3demand and significantly ease the task of
achieving net-zero emissions while considering envir-
onmental trade-offs and socio-political shocks (e.g.
related to food and energy supply) [79,80]. Encour-
aging diets with low nitrogen footprint or less meat,
reducing food losses and waste, and improving nitro-
gen use efficiencies can reduce future NH3demand
[15]. First, global average nitrogen use efficiency—
the share of applied nitrogen incorporated in food
production—is estimated to be around 46%, mean-
ing that more than half of synthetic nitrogen is dis-
persed in the environment and not used to grow
crops [5]. Precisions agriculture can increase the effi-
ciency of nitrogen fertilizers application to crops [81].
Second, nitrogen losses from farm to fork are estim-
ated to be between 41% and 44% and are mainly
due to harvesting and distribution losses, and food
waste [3,29]. Such losses can be reduced by redu-
cing food waste and improving efficiencies in food
supply chains. Third, a dietary transformation to less
nitrogen-intensive diets can reduce nitrogen demand.
While the recommended daily protein intake for a
healthy diet is estimated to be ∼50 g per person per
day (or about 9 g of nitrogen per person per day),
today the global median intake is 84 g of protein per
person per day [26]. Moderating the consumption
of animal-based food can reduce nitrogen demand
[82,83]. Importantly, while average protein intake
is above the recommended value for healthy diets,
one billion people still suffer from protein deficiency
worldwide [84], indicating inequalities in our food
systems.
Considering losses, inefficiencies, and waste [85],
it is estimated that only ∼20% of produced syn-
thetic nitrogen fertilizers feed global population [3,
5,29,33]. Therefore, ∼80% of synthetic nitrogen
fertilizers produced via the Haber–Bosch process are
lost due to inefficiencies in our food systems. We
believe that influencing consumer behavior to eat less
animal products, improving nitrogen fertilizers use
11
Environ. Res. Lett. 18 (2023) 014008 L Rosa and P Gabrielli
efficiencies, and reducing food waste and losses, is key
to achieve net-zero emissions.
Transitioning from a linear to a circular economy
that capture and recycle nitrogen from waste can
moderate use of resources and energy required to
produce synthetic nitrogen fertilizers [6]. Promoting
the use of organic fertilizers such as manure or com-
post can reduce NH3demand [86]. Animal manure
nitrogen outputs are a major source of nitrogen
recovery and recycling globally [6]. The digestate pro-
duced from anaerobic digestion of livestock manure
can be spread over croplands to recover nitrogen [32].
However, organic fertilizers are often more expensive,
slower in releasing nutrients, and are not presently
capable of supporting the demands of current or
future generations [6,9,87]. There are also prom-
ising scientific developments underway for alternative
fertilizers, but many of these approaches need further
development. Bioinformatics and plant genomics can
both reduce fertilizer usage [88]. Electrochemical syn-
thesis and plasma activated processes are other prom-
ising approaches that could be deployed as an altern-
ative to the Haber–Bosch process to produce NH3
[89–95].
5. Conclusions
Synthetic nitrogen fertilizers are envisaged to con-
tinue to be a major and growing component of agri-
cultural productivity in the 21st century. Currently,
3.8 billion people are fed from synthetic nitrogen fer-
tilizers. We find that 1.07 billion people are fed from
food produced from nitrogen fertilizers imports, and
an additional 700 million people are fed from impor-
ted fossil fuel feedstocks required for fertilizers pro-
duction. This highlights the reliance of global food
production on trading and fossil fuels, hence its vul-
nerability to supply and energy shocks. Our country-
specific analysis informs about which countries may
produce enough fertilizers to meet their domestic
demand, which country depends on international
trade of fertilizers and fossil fuels to feed their pop-
ulation, and thus which countries are more vulner-
able to food, energy, and fertilizers supply shocks.
Going beyond the status quo and investigating the
interplay between food security and climate targets,
we analyze alternative routes that are already avail-
able today to abate the carbon footprint of fertil-
izers via net-zero CO2emissions in NH3produc-
tion. These net-zero routes have the potential to align
food system with global climate targets, while increas-
ing food and nutrient security by reducing the reli-
ance of the food system on fossil fuels. However,
they will require additional land, water, and energy
than business-as-usual production. This highlights
the relevance of location-specific analyses, to determ-
ine optimal net-zero routes for producing fertilizers
based on technical, environmental, and geo-political
circumstances.
Data and materials availability
All data that support the findings of this study are
included within the article (and any supplementary
files).
Acknowledgments
This research was funded by the ClimateWorks
Foundation.
P G was partially funded by the Swiss National
Science Foundation Exchange Grant No. 214037, for
the research stay at Carnegie Institutions for Science,
Department of Global Ecology at Stanford.
Conflict of interest
The authors declare no conflict of interest.
Author contributions
L R conceived, designed, and wrote the study with
inputs from P G; L R and P G performed the analyses.
ORCID iDs
Lorenzo Rosa https://orcid.org/0000-0002-1280-
9945
Paolo Gabrielli https://orcid.org/0000-0003-3061-
4735
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