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California: Impact of increasing temperatures

28/09/2020 - François-Xavier Branthôme
"The biggest risk is for tomato production"

Devastating fires are currently raging from the Canadian border all the way down to Mexico. The US Department has downscaled its production forecasts to take account of the reduction in operations imposed by the heat waves of last spring. And just about all over the planet, industrial operators are announcing a premature end to the harvest season. So it seems almost trivial to comment, once again, on the impact of the rise in average temperatures on agricultural production in general and on processing tomatoes in particular. However, in addition to California, it is also the situation of the Spanish, Greek and Italian tomato sectors, and potentially many others, that a new study addresses and puts into perspective. According to the conclusions of scientists, the expected changes could have consequences in terms of cultivation periods but also – and even more so – in terms of geographical areas suitable for growing crops.

Research from the Lawrence Berkeley National Laboratory demonstrates how warmer temperatures are going to affect the Californian crop. The scientists describe pairing computer modeling with information about historic and ideal growing temperatures for five important Californian crops in their paper: “Projected temperature increases may require shifts in the growing season of cool-season crops and the growing locations of warm-season crops”, which appeared in the journal Science of the Total Environment. The study looked at five annual crops that are primarily produced in California. The lead author of the research paper, the biogeochemist Alison Marklein explains that four different scenarios were used to predict what temperatures would be like by mid-century.
We compared those temperature ranges with the temperatures that crops can grow at and determined when the temperatures would be appropriate for the crops for enough months in a row for the duration of that crop’s growing season,” said Marklein. 
We need reliable information about how future climate conditions will impact our crops in order for the agricultural system to develop an adequate response to ensure food security. For instance, one major challenge when considering relocating crops is that growers have specialized knowledge of their land and crops. If crops can no longer be grown in their current locations, then the farmer has to either move to a new area or grow a different crop, which presents a practical and economic burden on the farmer.” 

We found differences in how warmer temperatures will affect the cool-season crops versus the warm-season crops,” Marklein said. “For cool-season crops like broccoli and lettuce, it may be possible to extend their growing seasons. But it may become too warm to grow warm-season tomatoes where they have been historically farmed in summer, and that may require moving them to milder climates warm enough for growing tomatoes under the new climate scenarios.”
California crop production of vegetables such as broccoli and lettuce may actually benefit from warmer temperatures according to the study. Weather conditions on the Central Coast, where the majority of cultivation takes place, may accommodate a longer window of production. Warming temperatures could provide winter conditions suitable for growing the crops. “Their growing season can actually extend as the fall and spring seasons are bridged together by the winter,” Marklein noted. “So, it can be grown from the fall through the spring, which actually provides more time and more flexibility when the cool-season crops can be grown.”

Tomatoes could face some growing pains
According to the study, not all Californian crops will fare as well as the cool-season crops. Carrot and cantaloupe growing will be negatively impacted by higher temperatures to varying degrees. Of the crops that were looked at, the biggest risk created by warming temperatures is for tomato production.
The warmer temperatures in fall and spring suggest that tomatoes might benefit from a shift in growing season. But that could prove harder than it appears.
Looking at the hot-dry future climate scenario, although temperatures in fall and spring are likely to increase, so will summer temperatures. A shift in growing season isn’t a viable solution because the summer temperatures are likely to exceed the critical temperatures for tomatoes,” Marklein said. “Tomatoes need four consecutive months for their growing season, so the gap in the middle filled by summer makes this unfeasible.
We found between 34 and 87% of the land historically used for tomatoes will have temperatures appropriate for them in the future. So, that means we could lose 13% to 66% of that land. There is that really big range because there is some uncertainty in the future regarding climate change and especially human behavior and how we’re going to mitigate it.

One of the mitigation techniques Marklein is referring to is irrigation. The research was centered on air temperatures and not crop temperature, so there is an opportunity to offset some of the negative impacts of higher temperatures with appropriate irrigation. Currently a project scientist at UC Riverside, Marklein noted that the hope is to continue the research to include a broader range of crops.

The cost of taking on climate change
The situation is of sufficient concern that the governor of California “wants to increase the state’s climate change fight”, which could mean increased costs for Californians. According to California papers, when Gov. Gavin Newsom declared recently that “we have to step up our game” and accelerate California’s fight against climate change, Chris Rufer, the founder of The Morning Star Co. of Woodland, one of the world’s largest tomato processors, commented that under California’s climate-change initiative known as cap-and-trade, his company has to spend about USD 2 million a year buying carbon emission credits — the right to spew greenhouse gases at its processing plants in Williams, Los Banos and Santa Nella.

Fighting climate change costs money. Companies like Morning Star pay billions of dollars a year for emissions credits. If California raised the price of carbon credits, it would mean higher production costs — and price hikes for consumers of tomato paste, diced tomatoes and other Morning Star goods. The state could “make it so bad that we have to decrease production,” said Rufer, who once filed an unsuccessful lawsuit against the cap-and-trade program. Rufer’s reaction underscores the challenges that Newsom faces as he ramps up an array of new climate-change initiatives for California, as a rampage of wildfires never before seen in modern times overtakes the state.

 One possibility for change, Newsom suggested, could involve cap-and-trade. The eight-year-old program relies on a market mechanism to put a price on a ton of carbon emissions. Big industrial companies are required to reduce their emissions below a certain threshold — the “cap” — which declines slightly each year. If they can’t find a way to reduce emissions, they have to buy credits, either from other companies — the “trade” — or at auctions run every three months by the California Air Resources Board.

Last year alone the auctions raised more than USD 5 billion, although that figure includes money spent by companies in the Canadian province of Quebec. California spends its share of the proceeds on a variety of climate programs, but some experts believe the program could be strengthened by making fewer credits available for purchase.

At the latest state-run auction, credits sold for less than USD 17 per ton — the minimum price allowed by the state. With prices that low, the program doesn’t really discourage carbon emissions as much as it could, said Chris Busch, research director at Energy Innovation LLC, a San Francisco policy and research firm. “There’s a buildup of excess permits and that’s putting downward pressure on the price,” said Busch. “That undermines the effectiveness.”

Some complementary data
Further details and comments are available at:

Source:,,, The Sacramento Bee,
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