Corn yields and climate:
Their
h
inseparable
l futures
f
1
David Lobell
Assistant Professor
Environmental
E
m
Earth
E
System
y
m Science
and Program on Food Security and Environment
Stanford University
[email protected]
US Average Corn Yield since 1900 (Bu/Acre)
180
160
140
120
100
80
60
40
20
0
1900
2
1920
1940
1960
1980
2000
3
Main points for today
1) High corn yields have been, and will continue
to be, an essential
essent al way to llimit
m t emissions
em ss ons of
greenhouse gases
2) Maintaining high corn yields will be a lot
easier with a pro-active approach to dealing with
the challenges of climate change
4
US Average Corn Yield since 1900 (Bu/Acre)
180
160
140
120
100
80
60
40
20
0
1900
5
1920
1940
1960
1980
2000
6
Sutch 2008
Motivation
Modern agricultural is certainly a source of
greenhouse gases
Many use this to conclude that modern
agriculture is “bad” for climate, but that is a BIG
j
jump
in
i llogic
i
For the latter,, the only
y fair thing
g is to compare
p
it to specific alternatives.
7
The actual history of agriculture since 1960
Large increases in population and food production
8
The actual history of agriculture since 1960
oduction increases were mainly from yields, not expansion
The actual history of agriculture since 1960
This is especially the case for cereals
The actual history of agriculture since 1960
Associated with this intensification,
intensification there has
een a significant amount of GHG emissions
The actual history of agriculture since 1960
Associated with this intensification,
intensification there has
een a significant amount of GHG emissions
Paustian, Keith, et. al., “Agriculture’s Role in Greenhouse Gas
So what were the possible alternatives?
What would world have looked like without
agricultural advancements?
An impossible question, but can at least spell out
the implications of different assumptions
me counter-factual histories of agriculture since
1960
W = real world
W1 = no yield gain, but historical trends in population and living standards
W2 = no yield gain,
gain constant fertility rates and living standard since 1961
Cropland Expansion Causes GHG Emission
tal GHG Emission from real and alternate worlds
W = real world
W1 = no yield gain, but historical trends in population and living standards
W2 = no yield gain,
gain constant fertility rates and living standard since 1961
eal world has fewer GHG, how much was the cost
per ton CO2 avoided ?
Summary so far
Modern agricultural is likely a lot better for
climate than lower yielding alternatives
Investments in high yields have historically been
a bargain from a climate perspective
This does not say that high yields aren’t possible
with less emissions than currently
y achieved
This also doesn’t speak to any environmental
impacts other than climate.
climate
How to Continue Raising Yields?
In general, higher yields will require better
tuning cultivars and management to the specific
conditions of a given site and year.
year
A new challenge is that future conditions will
lik l differ
likely
diff from
f
past conditions
di i
iin the
h Corn
C
Belt.
B l
ow does weather affect corn yields?
We can examine what
weather changes drive
these variations
ow does weather affect corn yields?
orn yields are surprisingly sensitive to temperatures above ~86 ˚F
0 ˚C)
Comparing
p
g different years
y
Comparing
p
g different counties
ow does weather affect corn yields?
current example
How will climate change?
imate change is different than weather
weather. Most places have seen
gnificant warming already, but not all. In my opinion, skepticism
out climate change often tracks local experience with recent
eather
rend in Growing season average temperature for maize (˚C change 1980-2008)
How will climate change?
t the science is clear. All major growing regions are likely to warm.
Expected C change in average temperature relative to
Expected˚C
1960-1990 for an “A2” emissions scenario
1˚F
5˚F
9˚F
U.S. corn yields could be heavily impacted by climate
g , because current varieties are quite
q
sensitive
change,
to temperature and insensitive to CO2
Yield Impact (%) of Climate
Change without adaptation
Will private sector easily adapt?
Will private sector easily adapt?
To some extent, yes. But will it be enough to
avoid big impacts?
There are some unique effects of heat, aside
from drought, that have received much less
attention
i f
from companies
i
There is some evidence that heat sensitivity
y
actually increased with adoption of single-cross
hybrids
Thank
hank you for your attent
attention!
on!
[email protected]
Robert Byrd to Coal Constituents,
Constituents 2009:
To deny the mounting science of climate change is to stick
ur heads in the sand ... The future of coal and indeed of
ur total energy picture lies in change and innovation. In
act, the future of American industrial power and our
conomic ability
y to compete
p
globally
g
y depends
p
on our ability
y
o advance energy technology."
Borrowing” from Robert Byrd to Coal Constituents,
Borrowing
Constituents 2009:
To deny the mounting science of climate change is to stick
ur heads in the sand ... The future of crop yields and
ndeed of our total agriculture picture lies in change and
nnovation. In fact, the future of American agricultural
ower and our economic ability
y to compete
p
globally
g
y depends
p
n our ability to advance cropping technology."
Thank you for your attention!
[email protected]
Will private sector easily adapt?