Taking planetary nutrient boundaries seriously: Can we feed
the people?
Helena Kahiluoto a,n, Miia Kuisma a, Anna Kuokkanen b, Mirja Mikkilä b, Lassi Linnanen b
a MTT Agrifood Research Finland, Lönnrotinkatu 5, FI-50100 Mikkeli, Finland
b Lappeenranta University of Technology, PO Box 20, FI-53851 Lappeenranta, Finland
a r t i c l e i n f o
Article history:
Received 11 June 2013
Accepted 8 November 2013
Keywords:
Nitrogen
Phosphorus
Reactive flows
Phosphorus reserves
Food security
Agrifood system
a b s t r a c t
Recent research suggests that anthropogenic nutrient flows may have transgressed the regulatory
capacity of the earth. Agrifood systems account for most of the flows, and the food supply is limited more
by reducing the excessive flows than by phosphorus (P) reserves or population growth. The food supply
is limited primarily by the P flow tolerated by freshwater ecosystems and next by the needed reduction
in the conversion of nitrogen (N) to reactive form in fertilizer manufacture, legume cultivation and fossil
fuel combustion. The required reduction in P and N flows would reduce the food supply to 250 and
710 kcal capita
1 d
1, respectively, in the current agrifood systems. Dietary changes, waste prevention
and nutrient recycling are parts of the necessary transformation.
& 2013 The Authors. Published by Elsevier B.V.
1. Introduction
Nutrient flows in the earth system are instrumental to food
security. Increase in the flows of nutrients is linked with climate
change and the loss of biodiversity, those being the three human-
induced shifts that have led to overstepping the ‘planetary
boundaries’ (Rockström et al., 2009a, 2009b) or ‘the upper toler-
able limits’ (Carpenter and Bennett, 2011) of the regulatory
capacity of the earth system. We cannot afford to risk the vital
processes of the earth, but can we feed the world population
within these boundaries?
The global demand for food is rapidly increasing. The world's
population has been projected to plateau at nearly ten billion people
by the middle of this century and to peak at eleven billion by the end
of the century (UN, 2011). Simultaneously, there is increasing
competition for critical resources such as land, biomass, energy and
phosphorus (P) reserves. The challenge of feeding the people is even
more striking because it must be met when the critical biophysical
boundaries for several earth system processes that determine
elementary ecosystem services have been transgressed or are on
the verge of becoming transgressed (Rockström et al., 2009a, 2009b).
Flows of reactive nitrogen (N) and P represent one such process;
excessive nutrient flows cause eutrophication and exacerbate biodi-
versity loss and N flow exacerbates climate change.
The planetary boundaries represent critical thresholds for shifts
in the major earth system processes beyond which non-linear,
abrupt environmental change may occur on a continental or
planetary scale (Rockström et al., 2009a, 2009b). Criticism has
been voiced against efforts to quantify the planetary boundaries (e.
g., Schlesinger, 2009), the deficit of excluding the social dimension
(Schmidt, 2013), the specific criteria (e.g., Samper, 2009) and the
boundaries proposed (e.g., Carpenter and Bennett, 2011). However,
‘the first guess’ (Rockström et al., 2009a) to quantify the planetary
boundaries is an important step towards operationalizing the
‘limits to growth’ (Meadows et al., 1972) and quantifying the
critical ‘thresholds’ of the earth system (Scheffer et al., 2001).
The planetary boundaries could be used to quantify the approx-
imate extent of the required transition towards sustainability. For
N, the first estimate of the extent of the conversion of N2 to the
reactive form (Nr), which the earth system can accommodate with
no major disturbance, is one quarter of the present conversion rate
(Rockström et al., 2009a, 2009b). For P, the boundary was
determined at ten times the natural background flow to avoid an
extensive anoxia at the near-bottom layers of oceans for the next
1000 years. Carpenter and Bennett (2011) showed that the
planetary boundary could be one-tenth of the previously pre-
sented boundary for P when the carrying capacity of the fresh-
water systems is taken into account. They used the criterion of
24 mg P m
3 of water, which represents the interface between
mesotrophy and eutrophy, a typical target to limit the eutrophica-
tion of lakes and reservoirs. The major threats are represented by
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/gfs
Global Food Security
2211-9124& 2013 The Authors. Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.gfs.2013.11.002
n Corresponding author. Tel.: þ358 40 5118335; fax: þ358 207 720 40.
E-mail address: helena.kahiluoto@mtt.fi (H. Kahiluoto).
Global Food Security 3 (2014) 16–21
Open access under CC BY license. 
Open access under CC BY license. 
an irreversible loss of biodiversity and life (cf. fish kills) in water
ecosystems as a consequence of eutrophication, and climate
change induced by nitrous oxide.
The food supply for humans depends on N and P because, with
water, they represent a universal limiting factor for biomass
production and are at the core of agricultural management.
Food and nutrient security is a critical social complement to the
ecological boundaries. Previous assessments of planetary bound-
aries for N only include the conversion of atmospheric N2 to the
reactive form (Nr) in fertilizer manufacture (Haber–Bosch process).
The previous assessments thus exclude from the calculations the
contribution made by the use of fossil energy and by cultivation-
induced biological N2 fixation to the flows of Nr, even though these
processes are conceptually included in the framework (Rockström
et al., 2009a, 2009b). An aspect not conceptually included in the
framework of planetary boundaries (Rockström et al., 2009a,
2009b; Carpenter and Bennett, 2011), that is potentially important
regarding nutrients is resource scarcity (Ragnarsdottir et al., 2011).
Resource scarcity is a factor affecting the availability of N, even
though N2 is the major component of the atmosphere; 65% of the
conversion of N2 to the reactive form vital for life relies on fossil
energy resources (Galloway et al., 2008), the 'peak oil' claimed to
be reached already (Murray and King, 2012). In contrast to the P
reserves, the use of fossil energy can be substituted for by renew-
able energy and in fertilizer manufacture by biological N2 fixation,
and does not represent a potential critical boundary in terms of
resource scarcity. Regarding P, even though it is abundant in the
earth's crust, the quality and accessibility of the reserves are
decreasing and the extraction costs increasing (Gilbert, 2009;
Sverdrup and Ragnarsdottir, 2011; Cordell and White, 2011;
Dawson and Hilton, 2011).
In this study, we complement the assessments of planetary
boundaries with the conversion of N2 to Nr in fossil fuel combus-
tion and biological fixation through the cultivation of legumes and
by the critical P reserves. We quantify the consequences of
returning to a level within the safe nutrient boundaries on the
food supply. Exploring the significance of these issues for nutrient
boundaries, we have coupled the debates on the ‘safe operating
space for humanity’ (Rockström et al., 2009a, 2009b; Carpenter
and Bennett, 2011), on P as ‘the disappearing nutrient’ (Cordell
et al., 2009; Gilbert, 2009) and on food security (Beddington, 2010;
Godfray et al., 2010; Foley et al., 2011; IAASTD, 2009; Tilman et al.,
2002), all recently raised on the world agenda. We pose the
question as to what returning to within the critical limits set by
the regulatory capacity of the earth system in terms of nutrients
would mean in quantitative terms, especially regarding food
security. Can we feed the people while ensuring the vital processes
of the earth? Specifically, these questions are raised:
1. What is the significance of the following complements to the
assessment of the planetary nutrient boundaries: fossil fuel
combustion, cultivation-induced biological N2 fixation and
scarcity of P reserves?
2. How much would the food supply be reduced by keeping
within the safe nutrient boundaries, and how would the
reduction depend on the population growth and on potential
shifts in the agrifood systems?
2. Material and methods
The prior assessments of the planetary nutrient boundaries
(Carpenter and Bennett, 2011; Rockström et al., 2009a, 2009b)
served as a starting point for our study. Our stepwise assessment
(Table 1) proceeded starting with the complementation of the
estimates for the current flows and planetary N boundary pre-
sented by Rockström et al. (2009a, 2009b) with cultivation-
induced biological N2 fixation and fossil fuel combustion. We
applied the assessment of Carpenter and Bennett (2011) of the
lower carrying capacity of the freshwater systems for the plane-
tary P boundary. We estimated whether the P resource scarcity
sets an additional constraint to P use. The food supply within the
nutrient boundaries was assessed based on the share of the
agrifood systems of the nutrient flows, and the additional effect
of the shifts in the agrifood systems and of the projected popula-
tion growth was estimated. The resultant N and P flows, the
nutrient boundaries and the excess flows were divided by the
global population figure for 2010, thus assuming an equal dis-
tribution across the world's population (7.0 billion)
(UN, 2011).
Table 1
The stepwise assessment of the needed reduction in current nutrient flows to return to within the planetary nutrient boundaries (Mt a
1, kg capita
1 a
1). PB¼planetary
nutrient boundaries.
Current flows PB Excess
Mt a
1 kg capita
1 a
1a Mt a
1 kg capita
1 a
1a Mt a
1 kg capita
1 a
1a
Nitrogen (N)—N2 conversion to reactive N (Nr)
Rockström et al. (2009a, 2009b)b 121 17 35 5.0 86 12
Complemented: BNF, fossil fuelsc 187 27 47 6.7 140 20
Agrifood systemsd 139 20 35 5.0 104 15
Population growthe 3.2
Phosphorus (P)—P flow to water systems
Rockström et al. (2009a, 2009b)f 10 1.5 11 1.6 
0.7 
0.1
Freshwater systemsg 9–32 1.3–4.6 1.2 0.2 7.8–31 1.1–4.4
Agrifood systemsh 7–26 1.0–3.7 1.0 0.1 6.2–25 0.9–3.5
Population growthe 0.1
a The current flows, planetary boundaries and excess flows were divided by the global population in 2010 (UN, 2011).
b Including the Haber–Bosch process only (Galloway et al., 2003, 2008).
c Including Haber–Bosch, other fossil fuel combustion and cultivation-induced biological N2 fixation (Galloway et al., 2003, 2008).
d The complemented planetary boundary allocated to agrifood systems (Galloway et al., 2003, 2004, 2008; Pimentel et al., 2008).
e Planetary boundary of agrifood systems divided by the global population in 2100 (UN, 2011).
f Taking only the marine ecosystems into account.
g Taking the vulnerability of the freshwater ecosystems into account (Carpenter and Bennett, 2011). The range of the estimates of current flows: Bennett et al. (2001),
Howarth et al. (1996), Seitzinger et al. (2010), Smil (2000).
h The complemented planetary boundary allocated to agrifood systems (Seitzinger et al., 2010).
H. Kahiluoto et al. / Global Food Security 3 (2014) 16–21 17
2.1. Complements to the assessment of the planetary nutrient
boundaries
The assessment of the Nr flow (121 Mt a
1 by Rockström et al.,
2009a, 2009b) which includes fossil fuel combustion because of
fertilizer manufacture and production of chemicals (i.e., the
Haber–Bosch process chemistry) only, was complemented with
the estimates of the Nr flow of cultivation-induced biological
N2 fixation (40 Mt a
1) and fossil fuel combustion (25 Mt a
1)
(Galloway et al., 2003, 2008). The complemented planetary
boundary was determined to be 25% of the complemented current
conversion to Nr according to the criterion of Rockström et al.
(2009a, 2009b).
The P boundary was complemented by a new conceptual
element, the effect of the scarcity of the P reserves. The potential
additional limitation resulting from the P reserves was assessed
assuming the current global average use (2.4 kg capita
1 a
1)
(Cordell et al., 2009) and the P recovery of 13% for P rock
(Cordell and White, 2011), yielding 7920 Mt P from the total
technically and economically available global P reserve (Dawson
and Hilton, 2011; Van Kauwenbergh, 2010) distributed equally
across the growing population until 2100. It was expected that a
population of 9.7 billion would be reached in 2050, rising to the
peak population of 10.9 billion by 2100 (UN, 2011).
2.2. Food supply within the planetary nutrient boundaries
The agrifood systems’ share of the nutrient flows was assessed
based on the shares managed in the agrifood systems of the total
complemented (see Section 2.1) global Nr flow (74%) (Galloway
et al., 2003, 2004, 2008; Pimentel et al., 2008) and of the total
global P flow (80%) (Seitzinger et al., 2010).
The quantity of food available within the planetary nutrient
boundaries was assessed based on the share of the agrifood
system of the current nutrient flows and the complemented
boundaries. The available food supply was calculated using the
current average food supply (2831 kcal capita
1 d
1 in 2009)
(FAO, 2013) and the proportion of the nutrient boundaries of the
current flows. The effect of population growth on the food supply
within the planetary nutrient boundaries until 2100 (UN, 2011)
was estimated. The nutrient boundaries of the agrifood system in
current diet were divided by the projected peak population of 10.9
billion in 2100 (UN, 2011).
The effect of the shifts in the agrifood systems was explored
using the example of a shift in consumption to a vegetarian diet,
and another example of a shift to total prevention of food waste.
The effect of a shift to a vegetarian diet was assessed based on the
omitted consumption of nutrients for production of animal pro-
teins in the current food supply (FAO, 2012) replaced by the
production of plant proteins. The effect was calculated using the
nutrient use efficiency values of various diets for N (Galloway and
Cowling, 2002; Leach et al., 2012) and P (Metson et al., 2012;
Reijnders and Soret, 2003). The effect of food waste prevention on
the food supply in terms of the nutritional value was estimated
(Kummu et al., 2012) relative to the current food supply.
3. Results
3.1. Complements to the assessment of the planetary nutrient
boundaries
The global requirement to reduce nutrient flows for returning
to within the planetary N boundary is 47 Mt a
1. Appropximately
one-third of the boundary and the excess to be avoided is because
of the complements with conversion of N2 to Nr through fossil fuel
combustion, and biological N2 fixation in agrifood systems, and
two thirds arise from Haber–Bosch process (Table 1).
If the technically and economically available global P reserve,
according to current knowledge, is equally divided among the
growing population, assuming the current use rate capita
1 a
1,
the extent of the P reserves will not limit use until 2100. With a
medium rate of projected population growth scenario, 74% of the
current exploitable reserves would remain untapped. Conse-
quently, the reserve would not restrict P use more than does the
flow-based planetary boundary (Fig. 1).
3.2. Food supply within the planetary nutrient boundaries
Agrifood systems are responsible for the major part of the
global N conversion and P flow. The critical boundary set by the
eutrophication of fragile freshwater systems for P, rather than the
boundary set by N conversion, determines food security (Fig. 1).
Fig. 1. The share of the agrifood systems (yellow) in the needed reduction (red) of the current nutrient flows to return to within the planetary boundaries (green).
PB¼planetary nutrient boundaries, Nr¼reactive nitrogen, P¼phosphorus.
H. Kahiluoto et al. / Global Food Security 3 (2014) 16–2118
Returning to within the critical boundaries would require the daily
food supply to drop below a tenth of the present supply per capita,
with current agricultural practices and diets (Fig. 2). At the
expected global peak population in 2100, a further drop of 40%
in comparison with the current population would occur within the
planetary nutrient boundaries.
Single major shifts in the food supply and demand chain or in
the diet would make a difference. The combined effect of the
avoidance of food waste and a vegetarian diet, for example, would
multiply the available calories of the P-limited diet by nearly four.
Consequently, 930 kcal capita
1 d
1 would be available if the
freshwater ecosystems are maintained at the mesotrophy–eutro-
phy interface according to the commonly applied target. If the N
boundary were taken as the limiting factor, even
1610 kcal capita
1 d
1 could be supplied through the elimination
of food waste and a shift to a vegetarian diet, with no other
changes in the agrifood systems.
4. Discussion
4.1. Complements to the assessment of the planetary boundaries
The planetary boundary framework represents an ecosystems
approach to the sustainability of human activities, a functional
approach recognizing humans as an integral component in the
ecosystems (UN, 2002). It represents a system integrity approach
that is different from the dominant discourse on the sustainable
use of resources (Thompson, 2007) or on eco-efficiency (Korhonen
and Seager, 2008). The planetary boundary framework, if used for
further elaboration and empirical testing, offers a quantitative
measure of sustainability. Adopting such quantitative targets
enables a focus on the means to enhance sustainability and avoids
the dead-ends of paradigmatic conflict reflected in never-ending
debates on normative interpretations of sustainability. Further,
this resilience oriented systems integrity approach seems to – at
least in some cases – reveal more critical limits for the humanity
than the resource-oriented eco-efficiency approach alone does,
such as here shown for the major plant nutrients N and P.
N conversion in fossil fuel use and the cultivation-induced
biological N2 fixation were added to the estimate that previously
included fertilizer manufacture and other chemical production using
the Haber–Bosch process only (Rockström et al., 2009a, 2009b).
This complement had a marked effect on the estimate of the critical
planetary boundary notably increasing the estimate of the needed
reduction in the N flow. Involving eutrophication of freshwaters
within the boundary for P flows crucially increases the challenge to
achieve food security. The question of whether this involvement is
justified by a risk of continent- or planet-wide irreversible change
(Rockström et al., 2009a, 2009b) through, for example, biodiversity
loss or the effect on the oceans, deserves further elaboration.
The functional approach of the planetary boundary framework
appears to reveal the tolerable upper limits for P because the P
reserves did not further restrict P use in comparison with the
carrying capacity of the aquatic ecosystems. The ‘peak P’ (Cordell
and White, 2011), questioned also by the dynamic character of the
P reserves (e.g., Van Kauwenbergh, 2010), will not be met if the P
load to waterways is to be returned to within the tolerable limits.
The reduction in P flow necessary to save the freshwater systems
will require a transition of the nutrient economy to reduce and
completely recycle the P flows, including reuse of the sparingly
available P reserves in field soils (e.g., Kahiluoto, 2000; Sattari
et al., 2012) before P scarcity begins to restrict use.
4.2. Food supply within the planetary nutrient boundaries
The perspective of planetary boundaries highlights the critical
role of the agrifood systems in the functioning of the earth system.
The high share of the nutrient flows managed by the agrifood
systems emphasizes the pivotal effect on food security of main-
taining tolerable limits of the ecosystems. The limiting factor for
food security, if irreversible changes in freshwater systems and
Fig. 2. The food supply within the planetary nutrient boundaries (green) affected by the projected population growth and shifts in the agrifood systems (kcal capita
1 d
1).
The deficit in comparison with the current food supply is shown in red. PB¼Planetary nutrient boundaries.
H. Kahiluoto et al. / Global Food Security 3 (2014) 16–21 19
fragile seas are to be avoided, is P and not N, because of the
relatively wider gap to be bridged for P to return to the tolerable
limits. If we were not able to hinder continuous freshwater
eutrophication – which would also affect the planetary boundary
of freshwater use – the next limit for the safe food supply would
be set by N conversion. The complemented estimate for the
planetary boundary of N conversion would limit the food supply
more than the planetary boundary of the P flows to the oceans.
As shown by the translation of the nutrient boundaries into food
security in this study, an immediate return to within the planetary
nutrient boundaries would lead to widespread starvation and a
decrease in the current human population. The additional chal-
lenge represented by the expected population growth, to the
plateau population of 9.7 billion in 2050 or 10.9 billion in 2100
(UN, 2011), is of relatively minor significance.
Land resources are declining, and land is needed for biodiversity
and carbon reservoirs to mitigate biodiversity loss and climate
change. Narrowing the yield gap (Mueller et al., 2012; Lobell et al.,
2009) and increasing efficiency in livestock production (Wirsenius
et al., 2010), while not compromising the planetary nutrient bound-
aries (Tilman et al., 2011), is important, however, it has its limits.
Even minor reductions in waste and the consumption of animal
products outweigh the land-use effect of feasible efficiency increases
in livestock production (Wirsenius et al., 2010). If the nutrient
planetary boundaries are to be taken seriously, a radical transforma-
tion of agrifood systems using a broad range of means is imperative
(see also Ragnarsdottir et al., 2011; Wirsenius et al., 2010). A
complete avoidance of food waste would hardly bridge the gap (cf.
e.g., Foley et al., 2011), whereas global transition to a vegetarian diet
could be of greater consequence. Only a combination of many shifts
in various parts of the agrifood systems could render the required
transformation. Increasing global nutrient use efficiency (Cassman
et al., 2002), implementing precision and comparative advantage,
and recycling residues are obvious mainstays. Reconsideration of the
human diet with a higher diversity of crops and crop mixtures, algae,
coarse fish, insects and cultured meat as well as food from the
wilderness could make an important contribution to nutritional
security. If these efforts were to fail, the freshwater ecosystems and
fragile estuaries and seas, and the ecosystem services they support,
would suffer most. Recycling of the aquatic biomass from the
eutrophic freshwaters to agricultural fields could be used to target
the management of the aquatic food web to retard the deterioration
of aquatic ecosystems.
The current sufficiency of the global food supply for the entire
population, if equally distributed, with 12% of the entire population
being simultaneously chronically undernourished (FAO, 2013),
underlines the importance of equity in the distribution of food and
nutrients. When returning to within the planetary boundaries, to
reduce the risk of disastrous consequences for humankind, there will
be less opportunity for variation among regions and individuals.
Policy and market frameworks are needed to implement the return
while ensuring intergenerational and global equity in access to
nutrients and food. An invaluable opportunity to initiate such a
global policy and market framework is offered by the on-going work
for the next Sustainable Development Goals, i.e., the ‘Post-2015’
dialogue, which flags the poorest and strives for synergy among the
goals (UN, 2013; Griggs et al., 2013). The proposed improvement in
‘full chain N use efficiency’ of 20% by 2020 (Sutton et al., 2013) is a
valuable step. Many more quick steps, however, have to be taken
such as revealed here by the planetary nutrient boundary framework
(cf. Erisman et al., 2008) to return to within the safe limits; the
implications of the present beyond-the-critical-thresholds-state are
not known. Acknowledging the safe limits to human-induced
changes in the earth system while striving to eradicate poverty and
hunger, means that the mistakes of the past (IAASTD, 2009) will not
be repeated and demands new means to make progress. One model
is offered by the global carbon trading framework, presuming that
the lessons learned from, e.g., transition costs and price formation are
used when defining the policy instruments to reduce and redis-
tribute nutrient use.
5. Conclusions
The planetary boundary framework enables quantification
of the sustainability target for nutrients in order to create a solid
foundation to prioritize and develop the means. The extent of the
change required to return to within the safe boundaries in nutrient
use is striking, and the agrifood systems are instrumental in the
change. Within the critical boundaries, securing access to food –
even with equal distribution for the present population – is
impossible without a radical transformation of the agrifood
systems. The additional challenge represented by the expected
population growth is relatively minor. Not increase in productivity
alone but many simultaneous shifts in the agrifood systems could
render the required transformation. Dietary changes, reduction of
losses across the food supply chain and efficient recycling can
make a substantial contribution. Because of the wide gap that
must be bridged, implementing the transformation through global
cross-sector policies and enabling market frameworks such as
global trading of nutrient quota could be a pivotal factor in
achieving food security while maintaining the vital processes of
the earth.
Assessment of planetary boundaries has operationalized the
discourse on limits to growth. A simplified assessment is justified
for feasibility, but only if no crucial biases appear: We conclude
that inclusion of freshwater eutrophication, as well as cultivation-
induced biological N2 fixation and combustion of fossil fuels is
decisive for assessing the planetary nutrient boundaries for the
food supply, whereas the inclusion of the finite P reserves is not a
critical factor. Further critical defining of the quantifications is,
however, of utmost importance. For the planetary nutrient bound-
aries to be taken seriously in setting the targets for action to
ensure a ‘safe space for humanity’, an interlinked social dimension
of food security – and the underlying precondition of equity –
should be added to the critical boundaries of the framework.
Acknowledgements
The work was conducted as part of the Transition Towards
Sustainable Nutrient Economy (NUTS) project (2650/31/2011) of
the Green Growth Program of Tekes—the Finnish Funding Agency
for Technology and Innovation.
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