From Garbage to Gold:Managing Grasslands for Climate Change Mitigation

Whendee L. SilverDepartment of Environmental Science, Policy, and Management

University of California, Berkeley

True Cost Accounting of American FoodApril 15, 2016

A large fraction of anthropogenic climate change resulting from CO2 emissions is irreversible on a multi-century to millennial time scale, except in the case of a large net removal of CO2 from the atmosphere over a sustained period. Surface temperatures will remain approximately constant at elevated levels for many centuries after a complete cessation of net anthropogenic CO2 emissions. Due to the long time scales of heat transfer from the ocean surface to depth, ocean warming will continue for centuries. Depending on the scenario, about 15 to 40% of emitted CO2 will remain in the atmosphere longer than 1,000 years.

IPCC AR 5 (2013)

A large fraction of anthropogenic climate change resulting from CO2 emissions is irreversible on a multi-century to millennial time scale, except in the case of a large net removal of CO2 from the atmosphere over a sustained period. Surface temperatures will remain approximately constant at elevated levels for many centuries after a complete cessation of net anthropogenic CO2 emissions. Due to the long time scales of heat transfer from the ocean surface to depth, ocean warming will continue for centuries. Depending on the scenario, about 15 to 40% of emitted CO2 will remain in the atmosphere longer than 1,000 years.

IPCC AR 5 (2013)

Atmosphere carbon760 Pg

Vegetation carbon610 Pg

Soil carbon2000 Pg

(or more)

Photosynthesis

Plant/tissue death

Microbe respiration

Grasses allocate a high proportion of their photosynthate belowground to roots greater soil carbon pools

Grasslands are geographically expansiveThe majority of grasslands are degraded

30% of global land surface area30% of US land area

23 million hectares in California (40-50 % of the land area)

At a rate of 0.5 Mg C ha-1 y-1

= 21 MMT CO2e/y

Units: Mg = Metric tonMMT= Million metric tons CO2e = CO2 equivalents

At a rate of 1 Mg C ha-1 y-1

= 42 MMT CO2e/y

Using half of California’s grasslands

At a rate of 0.5 Mg C ha-1 y-1

= 21 MMT CO2e y-1

Units: Mg = Metric tonMMT= Million metric tons CO2e = CO2 equivalents

Emissions data: CA GHG Inventory 2013

At a rate of 1 Mg C ha-1 y-1

= 42 MMT CO2e y-1

Using half of California’s grasslands

• Livestock (enteric fermentation) ~ 12 MMT CO2e y-1

• Commercial/residential~ 43 MMT CO2e y-1

• Electrical generation (in state) ~50 MMT CO2e y-1

Amendments of livestock manure increased soil carbon by 50 Mg C ha-1 in the top meter of soil

Not amended Amended0

100

200

300

Soil

Car

bon

(Mg

C h

a-1)

From Silver et al. In prepAnalysis of 35 fields (1050 samples) from Marin and Sonoma Counties

Agricultural Soil Man-agement

Stationary Combustion

Mobile Combustion

Manure Management

Nitric Acid Production

Wastewater Treatment

Composting

0 5 10 15 20 25 30

Enteric Fermentation

Natural Gas Systems

Landfills

Coal Mining

Manure Management

Petroleum Systems

Wastewater Treatment

Rice Cultivation

Composting

Livestock manure is a large source of greenhouse gases

x10

U.S. Methane Emissions (MMT CO2e) U.S. Nitrous Oxide Emissions (MMT CO2e)

U.S. EPA EPA 430-R-15-004 2013; Owen and Silver 2015 Global Change Biology

-1

0

1

2Grazed and manuredGrazed

Meth

ane

Nitrou

s oxid

e

Soil C

Net Bala

nce

Clim

ate

impa

ct (M

g C

O2e

ha-1

y-1)

From 2012 to 2100, manure applications creates a large net carbon source to the atmosphere (positive values)

Owen et al. 2015, Global Change Biology

Source

Sink

One time application

Did not increase field nitrous oxide and methane emissions

Created a slow release organic fertilizer

Composted organic matter has much lower emissions

2008 2009 2010 2011 20120

500

1000

1500

2000

2500

3000

3500

4000

Soil

orga

nic

carb

on (g

m-2)

A single application of compost increased both plant (forage) production and soil carbon stocks for multiple years

Abo

vegr

ound

Net

Prim

ary

Prod

uctio

n (g

m-2) control compost

1 2 3 40

250

500

750

1000

Year2009 2010 2011 2012

Ryals and Silver 2013, Ryals et al. 2015, Silver et al. in prep.

Year

9/08 9/09 9/10 9/11 Date

Chan

ge in

soil

moi

stur

e (%

)Compost-treated soils had higher soil moisture during the growing season in most plots

Ryals and Silver 2013 Ecological Applications

Model results suggest that carbon gains persist for approximately 100 years

Ryals et al. 2015 Ecological Applications

GHG MitigationGHG Emissions

Compost Manure Fertilizer-40

-30

-20

-10

0

10

20

30

Glo

bal w

arm

ing

pote

ntia

l (M

MT

CO

2e)

Net

Life cycle assessment suggests high climate change mitigation potential even at small scales

Emissions from livestock

Redrawn from DeLonge et al. 2013

Applied to 5% of CA Rangeland

Emissions from household energy use

Marin Carbon Project

Nicasio Native Grass Ranch

Support provided by:United States Department of Agriculture

United States National Science FoundationThe 11th Hour Foundation

The Marin Community FoundationThe Rathmann Family Foundation

The Lia FoundationThe Kearney Foundation for Soil Science

University of California, Berkeley

Science Action

It is critical that carbon sequestration be included in climate action planning at all levels

Agriculture is poised to contribute to climate change mitigation; this is supported by science

Soil is a resource that can facilitate both mitigation and adaptation; more research is needed in this area; we are just scratching the surface

Creative solutions may cross sectors, posing new regulatory challenges, and new opportunities

Ryals et al. 2016

Compost amendments did not significantly change plant diversity