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

Car

bo

n S

tore

d

Food Produced (quadrillion calories)0 11 22

Situationtoday

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.

Car

bo

n S

tore

d

Food Produced (quadrillion calories)0 11 22

Potential future scenarios

Situationtoday

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 ScenarioBAU 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 and extensification in optimal and BAU simulations for the U.S. Corn Belt (left) and S.E. Asia (right).

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)