by George Monbiot
October 16, 2012
It looks like scientists could have gotten
the impacts of climate change on
Photo Credit: Thomas Bethge/ Shutterstock.com
I believe we might have made a mistake: a mistake whose consequences, if I
am right, would be hard to overstate. I think the forecasts for world food
production could be entirely wrong.
Food prices are rising again, partly because of the damage done to crops in
the northern hemisphere by ferocious weather. In the US, Russia and Ukraine,
grain crops were clobbered by remarkable droughts. In parts of northern
Europe, such as the UK, they were were pummeled by endless rain.
Even so, this is not, as a report in the Guardian claimed last week,
the worst global harvests in years”.(1)
It’s one of the best. World grain
production last year was the highest on record; this year’s crop is just
The problem is that, thanks to the combination of,
...a new record must be set every year.
Though 2012’s is the third
biggest global harvest in history (after 2011 and 2008),(4) this is also a
year of food deficit, in which we will consume some 28 million tonnes more
grain than farmers produced.(5)
If 2013’s harvest does not establish a new
world record, the poor are in serious trouble.
So the question of how climate change might alter food production could not
be more significant.
It is also extremely hard to resolve, and relies on
such daunting instruments as,
“multinomial endogenous switching regression
The problem is that there are so many factors involved.
extra rainfall be cancelled out by extra evaporation?
Will the fertilizing
effect of carbon dioxide be more powerful than the heat damage it causes?
what extent will farmers be able to adapt?
Will new varieties of crops keep
up with the changing weather?
But, to put it very broadly, the consensus is that climate change will hurt
farmers in the tropics and help farmers in temperate countries.
paper published in 2005 concluded that if we follow the most extreme
trajectory for greenhouse gas production (the one we happen to be on at the
global warming would raise harvests in the rich nations by 3% by
the 2080s, and reduce them in the poor nations by 7%.(7)
This gives an
overall reduction in the world’s food supply (by comparison to what would
have happened without manmade climate change) of 5%.
Papers published since then support this conclusion: they foresee hard times
for farmers in Africa and South Asia,(8,9,10) but a bonanza for farmers in
the colder parts of the world,(11,12,13) whose yields will rise just as
developing countries become less able to feed themselves.
Climate change is
likely to be devastating for many of the world’s poor.
If farmers in
developing countries can’t compete, both their income and their food
security will decline, and the number of permanently malnourished people
could rise. The nations in which they live, much of whose growth was
supposed to have come from food production, will have to import more of
their food from abroad.
But in terms of gross commodity flows the models do
not predict an insuperable problem.
So here’s where the issue arises. The models used by most of these papers
forecast the effects of changes in averaged conditions. They take no account
of extreme weather events.(14,15)
Fair enough: they’re complicated enough
already. But what if changes in the size of the global harvest are
determined less by average conditions than by the extremes?
This is what happened in 2012. This is what seems likely to happen in
subsequent years. Here’s why.
A paper this year by the world’s leading
climate scientist James Hansen shows that the frequency of extremely hot
events (such as the droughts which hammered the US and Russia) has risen by
a factor of around 50 by comparison to the decades before 1980.(16)
years ago, extreme summer heat typically affected between 0.1 and 0.2% of
Today it scorches some 10%.
“We can project with a high degree of
confidence,” the paper warns, “that the area covered by extremely hot
anomalies will continue to increase during the next few decades and even
greater extremes will occur.”
Yet these extremes do not feature in the
standard models predicting changes in crop production.
If the mechanism proposed by another paper is correct, it is not just
extremes of heat that are likely to rise.(17) I’ve explained this before,
but I think it’s worth repeating. The jet stream is a current of air
travelling eastwards around the upper northern hemisphere.
It separates the
cold wet weather to the north from the warmer, drier weather to the south.
Wobbling along this ribbon are huge meanders called
Rossby waves. As the
Arctic heats up, the meanders slow down and become steeper. The weather gets
Stuck weather is another way of saying extreme weather. If the jet stream is
jammed to the north of where you are, the weather stays hot and dry, and the
temperature builds up - and up. If it’s lodged to the south of you, the rain
keeps falling, the ground becomes saturated and the rivers burst their
This summer the UK and the US seem to have found themselves on
opposite sides of stuck meanders, and harvests in both countries were
savaged by opposing extremes of weather.
This is where we stand with just 0.8 degrees of global warming and a 30%
loss of summer sea ice. Picture a world with 2, 4 or 6 degrees of warming
and a pole without ice, and you get some idea of what could be coming.
Farmers in the rich nations can adapt to a change in averaged conditions. It
is hard to see how they can adapt to extreme events, especially if those
events are different every year. Last winter, for example, I spent days
drought-proofing my apple trees, as the previous spring had been so dry that
- a few weeks after pollination - most of the fruit shriveled up and died.
This spring was so wet that the pollinators scarcely emerged at all: it was
the unfertilized blossom that withered and died. I thanked my stars that I
don’t make my living this way.
Perhaps there is no normal any more. Perhaps the smooth average warming
trends the climate models predict - simultaneously terrifying and oddly
reassuring - mask wild extremes for which no farmer can plan and to which no
farmer can respond.
Where does that leave a world which must either keep
raising production or starve?
Martin Parry, Cynthia Rosenzweig
and Matthew Livermore, 2005. Climate change, global food supply and
risk of hunger. Philosophical Transactions of the Royal Society - B, vol 360, pp 2125–2138. doi:10.1098/rstb.2005.1751
Eg Jerry Knox, Tim Hess, Andre Daccache
and Tim Wheeler, 2012. Climate change impacts on crop productivity
in Africa and South Asia. Environmental Research Letters 7. 034032.
Christoph Müller et al, 2012.
Climate change risks for African agriculture. Proceedings of the
National Academy of Sciences Early Edition.
P. Krishnan et al, 2011. High
temperature effects on rice growth, yield, and grain quality.
Advances in Agronomy. Vol 111, pp87-205.
Jan Beck, 2012. Predicting climate
change effects on agriculture from ecological niche modeling: who
profits, who loses? Climatic Change - published online.
Tom Osborne, Gillian Rose and Tim
Wheeler, 2012 (in press). Variation in the global-scale impacts of
climate change on crop productivity due to climate model uncertainty
and adaptation. Agricultural and Forest Meteorology.
Kyungsuk Cho et al, 2012. Winter wheat
yields in the UK: uncertainties in
climate and management impacts. Climate Research. Vol. 54, pp49–68.
Eg Martin Parry, Cynthia Rosenzweig and
Matthew Livermore, 2005 (as above) write: “The crop growth models
embody a number of simplifications. For example, weeds, diseases and
insect pests are assumed to be controlled, there are no problem soil
conditions (e.g. high salinity or acidity) and there are no extreme
weather events such as heavy storms.”
and Kyungsuk Cho et al, 2012 (as above)
state: “We do not include effects caused
by negative soil conditions such as salinity, acidity and
compaction, extreme weather events or pests and diseases, all of
which are likely to be directly or indirectly affected by climate
change and resulting changes in management practices.”
James Hansen, Makiko Satoa, Reto
Perception of climate change. Proceedings of the
National Academy of Sciences, published online.
Jennifer A. Francis and Stephen J.
Vavrus, 2012. Evidence linking Arctic amplification to extreme
weather in mid-latitudes. Geophysical Research Letters, Vol. 39,