National weather services around the world are firming up forecasts for a La Nina to develop this fall and last through the Northern Hemisphere winter.
La Ninas in the fall-winter season tend to deliver wet weather to Australia and dry weather to the United States hard red winter wheat belt in the southern plains.
La Nina’s effect on crops in the Canadian Prairies are less pronounced, although La Nina winters here tend to be cooler than normal.
The impact on global crop yields depend on the intensity and duration of the La Nina.
On Aug. 13 the U.S. Weather Service Climate Prediction Center said there is about a 60 percent chance of a La Nina developing in the August-to-October quarter and lasting through the winter. That is up from 50 percent in its forecast earlier this summer.
Australia’s Bureau of Meteorology last week also raised its likelihood forecast to 70 percent, or roughly three times the normal likelihood of a La Nina.
La Nina and El Nino are the extreme phases of a natural multi-year climate cycle where surface water temperatures of the tropical Pacific Ocean oscillate between warm and cool periods.
La Nina is the part of the cycle where surface water temperatures in the central and eastern Pacific, off the coast of South America, are cooler than normal.
The most recent La Ninas in 2017-18 and 2016-17 were weak and had limited impact in terms of global crop production, but the strong 2010-12 event had major implications.
South American soybean production suffered strongly from dry weather and that shrunk global production of the crop in 2011-12 to about 240.8 million tonnes, down from 264.7 million in 2010-11 and 261 million in 2009-10.
It also shrunk Argentina’s corn crop that year.
And winter wheat yields in Texas, Oklahoma and Kansas all suffered in the period from a drought that gripped the southern U.S. from 2010 to 2013.
That drought, aided by the La Nina, crept up into the U.S. Midwest in 2012 slashing yields of corn and soybeans there.
These wide-spread production corn and soybean problems related to La Nina caused crop prices to jump higher.
A severe drought in 2012 in Russia also slashed wheat production, more than offsetting excellent wheat crops in 2011 and 2012 in Australia, which benefits from La Nina rain.
This series of production problems, most of them linked to the negative effects of a strong La Nina, kept prices for many crop rolling until global production came roaring back in 2013, pressuring markets lower.
There are signs that the ocean temperature shifts that are moving toward an official La Nina designation are already having an impact on Australia.
The grip of dry weather the previous two years has been broken and with much improved moisture Australian farmers have high hopes for their crops.
But in Argentina, dry weather and wide-spread frost is taking a toll on the wheat crop, as would be expected under La Nina conditions.
The trend of surface water cooling in the tropical Pacific has been going on for months, giving increased confidence that the La Nina threshold will be reached but there is no way yet to know if it will be strong.
If it turns out to be a doozie like in 2010-12, then expect big market-moving negative impacts on crops, particularly in South America and the southern U.S. and positive effects in Australia.