Geoscience Reference
In-Depth Information
The following discussion with the IPCC's Chris Field ('one of two lead authors') was
broadcast by the Australian Broadcasting Commission:
CHRIS FIELD: Year-on-year, yields have increased by something like two per cent. But they've been increasing by less
than that recently, and based on a number of very careful, thorough statistical analyses, researchers are now able to see
that for at least two of the world's major food crops, wheat and maize, the increases in yields year-on-year have slowed,
partly as a consequence of climate change.
So the drag, the anchoring effect of climate change in making it more and more difficult to increase yields is something
we're seeing at the global basis. I'm sure there are some places where there are still yield increases, but there are
other places that are offsetting those where yields are decreasing. This idea that we're seeing slower-than-expected yield
increases is emerging at the global scale.
SARAH FERGUSON: But we're not just talking about—this isn't any longer about modelling; this is about
already-observable facts?
CHRIS FIELD: Absolutely. That's one of the really different things about this report than what the IPCC has said in the
past. The impacts of changes that have already occurred are widespread and consequential.
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At least with respect to wheat, this is a highly contested view. Exhaustive research by
Wilcox and Makowski has found that although higher temperatures mean reduced yields,
'the effects of high CO
2
concentrations (>640 ppm) outweighed the effects of increasing
temperature (up to 2 degrees Celsius) and moderate declines in precipitation (up to 20
percent), leading to increasing yields.'
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Globally, yields of the major crops have increased at the same rate for decades with no
signsofafall-off.Figure2belowillustratesglobalandAustralianwheattrends(Australian
yields declined for a number of country-specific reasons).
These and other doubtful measurements of human induced climate driven change by
the IPCC indicate that its estimate of slender economic loss from climate change is an
exaggeration.
