Changing global diets is essential in curbing global warming

A new study, published today in Nature Climate Change ,
suggests that – if current trends continue – food production
alone will reach, if not exceed, the global targets for total
greenhouse gas (GHG) emissions in 2050.
The study's authors say we should all think carefully about
the food we choose and its environmental impact. A shift to
healthier diets across the world is just one of a number of
actions that need to be taken to avoid dangerous climate
change and ensure there is enough food for all.
As populations rise and global tastes shift towards meat-
heavy Western diets, increasing agricultural yields will not
meet projected food demands of what is expected to be 9.6
billion people - making it necessary to bring more land into
cultivation.
This will come at a high price, warn the authors, as the
deforestation will increase carbon emissions as well as
biodiversity loss, and increased livestock production will
raise methane levels. They argue that current food demand
trends must change through reducing waste and
encouraging balanced diets.
If we maintain 'business as usual', say the authors, then by
2050 cropland will have expanded by 42% and fertiliser use
increased sharply by 45% over 2009 levels. A further tenth
of the world's pristine tropical forests would disappear over
the next 35 years.
The study shows that increased deforestation, fertilizer use
and livestock methane emissions are likely to cause GHG
from food production to increase by almost 80%. This will
put emissions from food production alone roughly equal to
the target greenhouse gas emissions in 2050 for the entire
global economy.
The study's authors write that halving the amount of food
waste and managing demand for particularly
environmentally-damaging food products by changing
global diets should be key aims that, if achieved, might
mitigate some of the greenhouse gases causing climate
change.
"There are basic laws of biophysics that we cannot evade,"
said lead researcher Bojana Bajzelj from the University of
Cambridge's Department of Engineering, who authored the
study with colleagues from Cambridge's departments of
Geography and Plant Sciences as well as the University of
Aberdeen's Institute of Biological and Environmental
Sciences.
"The average efficiency of livestock converting plant feed to
meat is less than 3%, and as we eat more meat, more arable
cultivation is turned over to producing feedstock for animals
that provide meat for humans. The losses at each stage are
large, and as humans globally eat more and more meat,
conversion from plants to food becomes less and less
efficient, driving agricultural expansion and land cover
conversion, and releasing more greenhouse gases.
Agricultural practices are not necessarily at fault here – but
our choice of food is," said Bajzelj.
"It is imperative to find ways to achieve global food security
without expanding crop or pastureland. Food production is a
main driver of biodiversity loss and a large contributor to
climate change and pollution, so our food choices matter."
The team analysed evidence such as land use, land
suitability and agricultural biomass data to create a robust
model that compares different scenarios for 2050, including
scenarios based on maintaining current trends.
One scenario investigated by the team is on the supply side:
the closing of 'yield gaps'. Gaps between crop yields
achieved in 'best practice' farming and the actual average
yields exist all over the world, but are widest in developing
countries – particularly in Sub-Saharan Africa. The
researchers say that closing these gaps through
sustainable intensification of farming should be actively
pursued.
But even with the yield gaps closed, projected food demand
will still require additional land – so the impact on GHG
emissions and biodiversity remains. Bajzelj points out that
higher yields will also require more mineral fertiliser use
and increased water demand for irrigation.
Food waste, another scenario analysed by the team, occurs
at all stages in the food chain. In developing countries, poor
storage and transportation cause waste; in the west,
wasteful consumption is rife. "The latter is in many ways
worse because the wasted food products have already
undergone various transformations that require input of
other resources, especially energy," said Bajzelj.
Yield gap closure alone still showed a greenhouse gas
increase of just over 40% by 2050. Closing yield gaps and
halving food waste still showed a small increase of 2% in
greenhouse gas emissions. When healthy diets were added,
the model suggests that all three measures combined result
in agricultural GHG levels almost halving from their 2009
level – dropping 48%.
"Western diets are increasingly characterised by excessive
consumption of food, including that of emission-intensive
meat and dairy products. We tested a scenario where all
countries were assumed to achieve an average balanced
diet - without excessive consumption of sugars, fats, and
meat products. This significantly reduced the pressures on
the environment even further," said the team.
The 'average' balanced diet used in the study is a relatively
achievable goal for most. For example, the figures included
two 85g portions of red meat and five eggs per week, as
well as a portion of poultry a day.
"This is not a radical vegetarian argument; it is an
argument about eating meat in sensible amounts as part of
healthy, balanced diets," said Cambridge co-author Prof
Keith Richards. "Managing the demand better, for example
by focusing on health education, would bring double
benefits – maintaining healthy populations, and greatly
reducing critical pressures on the environment."
Co-author Prof Pete Smith from the University of Aberdeen
said: "unless we make some serious changes in food
consumption trends, we would have to completely de-
carbonise the energy and industry sectors to stay within
emissions budgets that avoid dangerous climate change.
That is practically impossible – so, as well as encouraging
sustainable agriculture, we need to re-think what we eat."
"Cutting food waste and moderating meat consumption in
more balanced diets, are the essential 'no-regrets' options,"
added Bajzelj.
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