Science1 publisher2 min readPublished
A modeled 60% AMOC slowdown takes 19 percent off German and Ukrainian cereal yields
An ALLFED preprint ran two 100-year simulations under 2C of warming, one with the Atlantic circulation forced down and one left alone, then layered wheat, maize and rice models on top of both. It has not been peer reviewed.
The Scientist · Science desk
What happened
- Researchers modeled a roughly 60% decline in the Atlantic Meridional Overturning Circulation, forcing the slowdown over the first 50 years of one 100-year run and leaving the circulation untouched in a second.
- Three crop models covering the commonest varieties of wheat, maize and rice, layered on those simulations, put global yields for the three crops 5.3% lower by the 50-year mark.
- Germany and Ukraine lost up to 19% of their cereal yields to sudden, sharp cooling in the model, and Canada showed a 12% decline in production for the same reason.
- The study went up on the website of ALLFED, the nonprofit that produced it, on July 7, and has not been through peer review.
- Estimates put the AMOC at its weakest in more than 1,000 years, having already lost 10% to 20% of its strength to climate change.
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Why it matters
- constraint One run of one warming scenario on monthly climate fields will not carry a national planning figure; the 19% indicates direction and rough scale, and Hinge himself called the exercise a proof of concept.
- exposure The producers the model hurts most are cool-temperate ones currently planning for heat, so money spent adapting to hotter summers could land in places the circulation cools instead.
- cost Cereal importers pay in the bad years rather than the average one, and the study's price channel runs through governments holding grain back from trade.
- precedent Paul Ritchie's 2020 Exeter work on British agriculture points the same way with the same limitations, so the next round of studies is more likely to refine the size of the loss than its sign.
The second simulation is the control. Both runs carried the same 2 degrees Celsius of warming above preindustrial levels across 100 modeled years [2]. In one, the team forced the circulation down over the first 50 years. In the other, they left the circulation alone [3]. The difference between the two is the circulation's contribution inside this model, held apart from the warming. There was one run of each, on monthly climate fields, not daily. Michael Hinge, a senior economist at the nonprofit ALLFED and a co-author, said the results should be interpreted as a proof of concept [15][4].
The ratio between the two headline figures is about 3.6: the German and Ukrainian cereal loss against the global one [20]. Two separate mechanisms produce it. Across the mid-latitudes the Northern Hemisphere cools broadly, and nearer the equator the belt of clouds and rain that circles the globe shifts south [4]. In the tropics the model produced what Hinge called a "very nasty brown splodge" of reduced precipitation over India, Pakistan and big parts of China [11]. Iran, Sudan and Eritrea, already water-stressed, showed severe rainfall declines too [12].
"Scandinavia, the United Kingdom and Canada are particularly exposed," Hinge said, adding that many other vulnerable locations show up as well, some of which may be surprising even to the people living there [10].
Damage arrives before the 50-year mark where the pipeline reports. "Lots of these effects manifest earlier, so it's a moving target," Hinge said [17]. The global figure is also an average across model years, and Hinge said some years could bring cereal losses of 10% or more [13]. Ten percent is nearly twice the mean [22].
The forced decline is large against what has already been measured. Roughly 60% against the 10% to 20% of strength that estimates say the AMOC has lost works out at three to six times as much [21]. It also does not stop when the forcing peaks. "Once the damage is inflicted, it stays there," Hinge told Live Science, and in the 50 years after the peak rate of slowdown in the model the circulation weakened by a further 20% [5][6].
Hinge's worry about the human response is maladaptation. "You're preparing and setting up for much hotter temperatures or trying to develop areas for these temperatures and the trends you're seeing, and suddenly you see something different," he said. "That may cause an even larger compounding effect [on agriculture]" [18].
What to watch
- Peer review of the ALLFED paper, and whether the 5.3% global yield figure holds up in it.
- Other AMOC scenarios pushed through the same crop pipeline, which Hinge said is ready to take any scenario that can generate high-resolution climate data.
- Whether adaptation plans in Canada, the UK and Scandinavia start hedging for cooling as well as heat.