Justin Johnson, Ben Senauer & Ford Runge
Paper co-authors: Jonathan Foley and Stephen Polasky

Feed 9 Billion People by 2050
The Challenge:

How can we feed this many people while
minimizing environmental degradation?

Increasing yields on
existing croplands
will meet 70-80% of
future food demand.
But yield increases
are slowing.
Assume need for 25%
expansion in
cropland

Some Cropland Expansion is Necessary
• Yield increases alone are
insufficient to produce
100% more calories by
2050
• The problem:
• Cropland expansion dramatically
reduces environmental value
Source: Ray et al. 2013

For the all arable hectares on Earth, we ask:
should we cultivate this
field to grow food…
or protect it to preserve
environmental value?

Natural lands provide
Ecosystem Services
• “Natural processes that
provide economic value to
humans”
• Water purification
• Soil quality
• Pollination of crops
• Climate regulation
• From carbon storage

Identifying the optimized
trade-off globally
• We use high-resolution remote sensing
data combined with regular ground-
based surveys.
• Data divides the earth into 5x5 minute
grid-cells.
• Approximately 10x10 km at the
equator. About 10 million globally.
• To say more precisely where we should
expand agriculture

Graphical description of our method
• For each grid-cell, define the
comparative advantage of food
production relative to the loss of carbon
storage
• In this example, a higher number means the
grid-cell is relatively good at producing food
• The color corresponds to the number
.25 .5 1
.12 3 1
.12 .5 2

Calories per tons of carbon storage
0 300,000 500,000
We Apply this Approach Globally

Methodology of Crop Advantage
• We define the relative advantage of cultivation for every grid-cell as
“Crop Advantage”
• Crop Advantage = Calorie Yield / Carbon Loss
𝐶𝐴 =
𝐶𝑌
Δ𝐶
• This represents net benefit of converting land to cultivation while
taking into account marginal costs of carbon loss

Calories per Grid Cell
0 1e+11 2e+11
This defines
the numerator
in crop
advantage:
caloric yield.

This defines
the
denominator
of crop
advantage:
carbon storage
change.
Carbon Storage Loss

Calories per tons of carbon storage
0 300,000 500,000
The ratio of these defines Crop Advantage
How do we
use crop
advantage to
define the
optimal areas
to extensify?

Optimization Method

The Food-Carbon Tradeoff
• We need to increase food
production by 100% by 2050
• What about carbon?
100% more food
Current food production
Food Produced (quadrillion calories)
0 11 22

The Food-Carbon Tradeoff
• Add carbon storage on the
vertical axis
• Every point represents a
combination of carbon
storage and food production
• For example, suppose we
currently are at the indicated
point
• When we produce more
calories, we will likely lose
carbon
CarbonStored
Food Produced (quadrillion calories)
0 11 22
Situation
today
Produces enough
calories but loses
carbon storage

The Food-Carbon Tradeoff
• Our optimization approach
checks all possible choices of
where cropland can expand
• Identifies which choices
result in the least amount of
carbon loss.
• Restrict our analysis to grid-
cells between 5 & 95%
cultivated.
CarbonStored
Food Produced (quadrillion calories)
0 11 22
Potential future scenarios
Situation
today
Optimal future scenario

Define Two Scenarios
• 1.) Carbon-Selective Scenario (optimal)
• Expand cultivation on the land that minimizes carbon loss while meeting caloric
targets
• 2.) Business as Usual (BAU) Scenario
• Expand cultivation to meet caloric targets, but ignore carbon storage
• We compare these scenarios to see what we need to do differently

Present Situation
Carbon-Selective Scenario
BAU Scenario
BAU land-use
(based on existing policy,
market forces and other
drivers)
Carbon-Selective land-use
(based on same drivers)
Comparing these two scenarios
shows what we need to do

Comparison of Optimal vs. BAU Scenarios
Proportion of grid-cell preserved
-0.5 0 0.5
Green cells indicate where the optimal scenario preserves more land than BAU.
Red means the optimal solution loses carbon storage relative to BAU.

Zoomed in on the U.S. Corn Belt and S.E Asia

Crop Advantage (calories per tons carbon storage)
0 300,000 500,000
Proportion of grid-cell preserved from extensification
-0.5 0 0.5
Expand at the
edges of existing
agricultural centers
• Places like the Corn Belt & SE
Asian deltas have extremely
high crop advantage (top)
• But these areas already are
near or at maximum
cultivation
• The best remaining areas are
on the edges of the high CA
areas

Tons per grid-cell
-15,000 0 15,000
Net Carbon Storage Change.
All together,
this is 6 billion
metric tons of
carbon saved
How much carbon did we save?

Value using a Social Cost of Carbon
Climate scientists calculate that a ton of carbon storage
is worth $181 in avoided climate change damages.
Thus, we save $1.06 trillion by optimizing by 2050.

Policy Discussion
• Smartly expanding agriculture saves a very large amount of carbon.
• If we want to minimize carbon loss, we should target cropland
expansion on the edges of existing bread baskets, not in carbon-rich
areas.
• Even when considering food security, forests are almost always worth
protecting rather than cultivating, especially tropical rainforests.
• The $1.06 trillion figure likely underestimates the value dramatically
• Only one ecosystem service considered

Policy Discussion
• Optimal expansion is difficult.
• We may not get there,
• but knowing the full costs helps us know how to move toward the optimum.
• Future research will add more detail:
• More information on costs of intensification and expansion
• More ecosystem services
• More specific policies: Food-for-Nature Payments
• Currently analyzing various combinations of intensification & extensification.
• 70% increase in caloric needs; consistent with the economics literature.
• And potential policy incentives.

For Further Information
• Justin Andrew Johnson, Carlisle Ford Runge, Benjamin Senauer,
Jonathan Foley, and Stephen Polasky. 2014. “Global agriculture and
carbon trade-offs”. Proceedings of the National Academy of Sciences,
vol. 111, no. 34 (August 26): 12342-12347. (Supplemental
Information, 14 pages)