Climate change may affect the production of maize (corn) and wheat as
early as 2030 under a high greenhouse gas emissions scenario, according
toa new NASA study published in the journal,/Nature Food/
[www.nature.com]. Maize crop yields
are projected to decline 24%, while wheat could potentially see growth
of about 17%.

Using advanced climate and agricultural models, scientists found that
the change in yields is due to projected increases in temperature,
shifts in rainfall patterns, and elevated surface carbon dioxide
concentrations from human-caused greenhouse gas emissions. These changes
would make it more difficult to grow maize in the tropics, but could
expand wheat�??s growing range.

�??We did not expect to see such a fundamental shift, as compared to crop
yield projections from the previous generation of climate and crop
models conducted in 2014,�?� said lead author Jonas J?�germeyr, a crop
modeler and climate scientist at NASA�??s Goddard Institute for Space
Studies (GISS) and The Earth Institute at Columbia University in New
York City. The projected maize response was surprisingly large and
negative, he said. �??A 20% decrease from current production levels could
have severe implications worldwide.�?�

To arrive at their projections, the research team used two sets of
models. First, they usedclimate model simulations
[www.climate.gov] the
international Climate Model Intercomparison Project-Phase 6 (CMIP6
[www.wcrp-climate.org]). Each of the five
CMIP6 climate models used for this study runs its own unique response of
Earth�??s atmosphere to greenhouse gas emission scenarios through 2100.
These responses differ somewhat due to variations in their
representations of the Earth's climate system.

Then the research team used the climate model simulations as inputs for
12 state-of-the-art global crop models that are part of the Agricultural
Model Intercomparison and Improvement Project (AgMIP
[agmip.org]), an international partnership coordinated by
Columbia University. Thecrop models
[agmip.org] on a large scale how
crops grow and respond to environmental conditions such as temperature,
rainfall and atmospheric carbon dioxide, which are provided by the
climate models. Each crop species�?? behavior is based on theirreal life
biological responses
[www.nasa.gov]
in indoor and outdoor lab experiments. In the end, the team created
about 240 global climate-crop model simulations for each crop. By using
multiple climate and crop models in various combinations, the
researchers were more confident in their results.

�??What we're doing is driving crop simulations that are effectively
growing virtual crops day-by-day, powered by a supercomputer, and then
looking at the year-by-year and decade-by-decade change in each location
of the world,�?� said Alex Ruane, co-director of the GISS Climate Impacts
Group and a co-author of the study.

This study focused on climate change impacts. These models do not
address economic incentives, changing farming practices, and adaptations
such as breeding hardier crop varieties, although that is an area
ofactive research [agmip.org]. The research
team plans to look at these angles in follow-up work, since these
factors will also determine the fate of agricultural yields in the
future as people respond to climate-driven changes.

The team looked at changes to long-term average crop yields and
introduced a new estimate for when climate change impacts �??emerge�?� as a
discernable signal from the usual, historically known variability in
crop yields. Soybean and rice projections showed a decline in some
regions but at the global scale the different models still disagree on
the overall impacts from climate change. For maize and wheat, the
climate effect was much clearer, with most of the model results pointing
in the same direction.

Maize, or corn, is grown all over the world, and large quantities are
produced in countries nearer the equator. North and Central America,
West Africa, Central Asia, Brazil, and China will potentially see their
maize yields decline in the coming years and beyond as average
temperatures rise across these breadbasket regions, putting more stress
on the plants.

Wheat, which grows best in temperate climates, may see a broader area
where it can be grown as temperatures rise, including the Northern
United States and Canada, North China Plains, Central Asia, Southern
Australia, and East Africa, but these gains may level off mid-century.

Temperature is not the only factor the models consider when simulating
future crop yields. Higher levels of carbon dioxide in the atmosphere
have a positive effect on photosynthesis and water retention, increasing
crop yields, though often at a cost to nutrition. This effect happens
more so for wheat than maize, which is more accurately captured in the
current generation of models. Rising global temperatures also are linked
with changes in rainfall patterns, and the frequency and duration of
heat waves and droughts, which can affect crop health and productivity.
Higher temperatures also affect the length of growing seasons and
accelerate crop maturity.

�??You can think of plants as collecting sunlight over the course of the
growing season,�?� said Ruane. �??They're collecting that energy and then
putting it into the plant and the grain. So, if you rush through your
growth stages, by the end of the season, you just haven't collected as
much energy.�?� As a result, the plant produces less total grain than it
would with a longer development period. �??By growing faster, your yield
actually goes down.�?�

�??Even under optimistic climate change scenarios, where societies enact
ambitious efforts to limit global temperature rise, global agriculture
is facing a new climate reality,�?� J?�germeyr said. �??And with the
interconnectedness of the global food system, impacts in even one
region�??s breadbasket will be felt worldwide.�?�

/Ellen Gray/ <mailto:ellen.t.gray@nasa.gov>
/NASA�??s Earth Science News Team/


/Global Climate Change Impact on Crops Expected Within 10 Years | NASA
[www.nasa.gov]