Science - 31 January 2020

518 31 JANUARY 2020 • VOL 367 ISSUE 6477 sciencemag.org SCIENCE

PHOTO: JOERG BOETHLING/ALAMY STOCK PHOTO

Agricultural lands key to

mitigation and adaptation

In their Review “Measuring the success of
climate change adaptation and mitigation in
terrestrial ecosystems” (13 December 2019,
p. eaaw9256), M. D. Morecroft et al. ignored
the role of agricultural land. Although the
carbon density of agricultural ecosystems is
lower than for forests, the land area avail-
able (~22.2 million km^2 ) ( 1 ) and the fact that
they are actively managed make them an
important mitigation opportunity ( 1 ).
Globally, cropland soils could sequester
an additional 0.90 to 1.85 gigatons of carbon
(Gt C) per year ( 2 ), approximately equiva-
lent to the current emissions resulting from
land-use change ( 2 ). Across the European
Union, it has been estimated that agrofor-
estry could sequester 1.6 Gt C per year, or
approximately 37% of the European Un ion’s
annual emissions ( 3 ). Globally, agroforestry
accounts for ~34 Gt C ( 1 ).
Interventions such as agroforestry and
integrated soil fertility management also
deliver substantial adaptation benefits
( 4 ). Morecroft et al.’s coverage of adapta-
tion was almost entirely focused on the
co-benefits for biodiversity conserva-
tion. Livelihoods were barely mentioned.
Especially in the tropics, severe climatic
events, such as storms, droughts, and
floods, interact with poverty to cause major
humanitarian disasters [e.g., ( 5 )].
Adaptation for the world’s approximately
500 million smallholder farmers ( 6 ) means

Edited by Jennifer Sills increasing incomes, diversifying crops and
income sources, and enhancing resilience
through improved management of soils
and other natural resources. Moreover,
habitat protection and ecological resto-
ration alone will not suffice to conserve
biodiversity. It is imperative that agricul-
tural lands are managed in a way that
conserves biodiversity, through increasing
trees on farms and adopting agroecological
approaches to crop management.
Rhett D. Harrison^1 * and Anja Gassner^2

(^1) World Agroforestry, Lusaka, Zambia. (^2) Wo r l d
Agroforestry, International Rice Research Institute,
Laguna, Philippines.
*Corresponding author. Email: [email protected]
REFERENCES AND NOTES

1. R. J. Zomer et al., Sci. Rep. 6 , 29987 (2016).


2. R. J. Zomer, D. A. Bossio, R. Sommer, L. V. Verchot, Sci.
   Rep. 7 , 15554 (2017).


3. J. Aertsens, L. De Nocker, A. Gobin, Land Use Pol. 31 ,
   584 (2013).


4. A. Lavell et al., in Managing the Risks of Extreme Events
   and Disasters to Advance Climate Change Adaptation:
   Special Report of the Intergovernmental Panel on Climate
   Change (Cambridge University Press, 2012); pp. 25–64.


5. R. Maclean, “Cyclone Idai: More than 1000 feared
   dead in Mozambique” (2019); http://www.theguardian.com/
   world/2019/mar/18/cyclone-idai-death-toll-climbs-
   over-120-in-mozambique-and-zimbabwe.


6. S. K. Lowder et al., World Dev. 78 , 16 (2016).

COMPETING INTERESTS

A.G. is supported by the International Climate Initiative

(IKI) of the Federal Ministry for the Environment, Nature

Conservation and Nuclear Safety (BMU).

10.1126/science.aba6211

Response

Our Review deliberately focuses on cli-

mate change adaptation and mitigation

in natural and semi-natural ecosystems.

As Harrison and Gassner point out,

agricultural land is also critical for adapta-

tion and mitigation, and we welcome the

opportunity to broaden the discussion.

A variety of mitigation measures can be

applied in cropped systems (1–3), rang-

ing from changing management practices

within present systems, including applying

fertilizer more efficiently and increasing

soil carbon, to changing whole agricultural

systems, such as adopting agroforestry.

We agree that agricultural, nature-based

solutions can deliver a range of benefits for

adaptation and biodiversity as well as miti-

gation, food production, and livelihoods.

One of our Review’s key messages is the

importance of taking an “integrated view

of mitigation, adaptation, biodiversity, and

the needs of people.” We suggest a list of

questions to determine the suitability of

potential nature-based solutions based

on a range of criteria in which the needs

of people are integral alongside those of

biodiversity. These questions are as valid

for agro-ecosystems as they are for more

natural systems. However, the balance of pri-

orities will be different in determining what

constitutes success, with food supply and

livelihoods critical in agricultural systems.

A key challenge is to identify the most

appropriate strategies for land use and

management in different places. There is

evidence that increasing agricultural pro-

ductivity is achievable in ways that support

biodiversity as well as people ( 4 ). There

is also evidence that increasing yields in

some areas while protecting and restoring

ecosystems elsewhere provides multiple

benefits, including for climate change

mitigation ( 5 ). There is a clear case for the

LETTERS

Adaptations to

smallholder farms

can contribute to

climate resilience.

Published by AAAS