Crops All _Tai Et Al (2014)

The combination of rising temperatures and air
pollution could substantially damage crop growth in the next 40
years, according to a new paper. And if emissions stay as high as
they are now, the number of people who don’t get enough food could
grow by half by the middle of the century.

Burning question

Feeding the world’s rapidly growing population
is a serious concern.

Research shows
rising temperatures
are likely to lead to
lower crop yields. Other work suggests air pollution might reduce
the amount of food produced worldwide. But nobody has considered
both effects together, say the paper’s authors.

The two effects are closely related as warmer
temperatures increase the production of ozone in the
atmosphere, the paper explains.

new study
looks at global yields of the four
principle food crops – wheat, rice, corn and soybean – and how
they’re expected to change by 2050 under different levels of future

Together, these provide nearly
60 per cent
of all the calories consumed by
humans worldwide.

Global losses

The maps below show some of the

The top panel is an optimistic scenario in which
greenhouse gases stabilise at 630 parts per million (ppm) by 2100.
For reference, we’re at about 400 ppm now.

The team compared this with what might happen if greenhouse
gases continue to rise as rapidly as they are now. That’s the
bottom panel.


How global crop yields are expected to change between 2000
and 2050 for RCP4.5 (top) and RCP8.5 (bottom). Total annual crop
losses for each scenario compared to today are in the purple boxes
below. Source: Tai et al. (

Global food production falls by 2050 in both scenarios, as shown
in the purple boxes below each map. If emissions stay high, total
global yield falls by about 15 percent compared to today. But if
emissions are kept low, the drop is reduced to just over nine

The coloured shading shows how the total yield
for all four crops varies region to region. Red is a higher yield
than now, blue is lower.

Food security

Does this mean more people won’t get enough to

If emissions continue as they are, the drop in
crop yields will means many more people globally will be
undernourished, as the graph below shows.


The blue shading is the fraction of people in developing
countries who consume less than the minimum amount of energy
required per day. At the moment it’s about 18 per cent.

The red and blue shading together is the
fraction of undernourished people by 2050 under the high emissions
scenario. It’s about 27 per cent – about 50 per cent more than

The projections include expectations of a
per cent rise
in global population by 2050. But
they don’t take into account measures to increase resilience, such
as changing farming practices.

Are we heading for global famine?

A headline in yesterday’s
Daily Mail
suggested the new research meant
“climate change and air pollution will lead to famine by 2050”. But
Tai tells us that’s a “little bit of a stretch”.

Famine is more complex than just food shortage,
he explains:

“Famine is
an extreme form of undernutrition with significant fatalities
caused by not only crop failure but also a variety of
socio-economic factors, which our study did not examine. The
problem of undernourishment, in a more general sense, is usually
more subtle but widespread and persistent”.

Different crops, different

The scientists found not all crops are affected
in the same way. For example, corn is more susceptible to heat,
while ozone exposure is more of a problem for wheat.

How badly different countries are affected will
depend on how bad air pollution is already and which crops they
grow, the paper explains. For policymakers trying to decide how to
deal with the problem, different countries may need to try
different approaches. Tai tells us:

“Depending on the crops
of interest and where you are, you may want to focus more on air
pollution reduction or climate adaptation more.”

For example, tougher air quality regulations in
the United States could lead to a sharp decline in ozone
production, lessening the impact on crops.

“Talk to each other”

The authors are calling for greater
collaboration between agricultural planners and air quality
managers to set goals for food security and public health. Tai
tells us:

“For policymakers and
people in the field, including farmers, air pollution managers …
they do have to talk to each other … We really call for greater
collaboration between stakeholders of different interests and
fields … they cannot just be concerned about their own fields
because their objective is ultimately affected by decisions made in
other sectors.”

Scientists know cleaning up air quality will
have a significant impact on public health. This new research
suggests cutting domestic air pollution as well as curbing warming
could have big benefits for food security in some parts of the
world too.