Climate change is already causing a decline in agricultural productivity worldwide

This assessment was made by Jerry Hatfield, Director of the National Laboratory for Agriculture and the Environment at the US Department of Agriculture, in a workshop at FAPESP headquarters.

By Elton Alisson

Agência FAPESP – Climate change has altered the phases of reproduction and the development of a variety of agricultural crops, including maize, wheat and coffee. The impacts of these alterations are already reflected in the declining agricultural productivity observed in countries such as Brazil and the United States.

This assessment was made by researchers participating in the Workshop on Impacts of Global Climate Change on Agriculture and Livestock, held on May 27 in the FAPESP auditorium.

Promoted by the FAPESP Research Program on Global Climate Change, the event’s objective was to bring together researchers from Brazil and the United States to share their research and experience of the impacts of global climate change on agriculture and livestock.

“We’ve known for some time that climate change will have direct and indirect impacts on agricultural crops,” said Jerry Hatfield, Director of the National Laboratory for Agriculture and the Environment at the US Department of Agriculture (USDA). “The question is what the impact and the magnitude of these changes will be on the different agriculture-producing countries,” said the researcher during his lecture at the event.

According to Hatfield, one of the main impacts noted in the United States is the decline in the productivity of crops such as maize and wheat. The United States is the world’s biggest producer of corn and the third biggest producer of wheat. “Wheat production [in the United States] is no longer achieving large increases in harvests, such as those seen between 1960 and 1980,” he said.

One of the reasons for the decline in productivity of these and other crops worldwide, according to the researcher, is the increase in temperature during the growth and pollination phase.

Plants such as wheat, soybean, maize, rice, cotton and tomato have different ideal temperature ranges for periods of vegetation (the phases from seed germination to plant growth) and reproduction (the phases of flowering and seed formation).

Corn, for example, does not tolerate high temperatures during the reproductive phase. Soybean, however, is more heat tolerant during this stage, Hatfield explained.

Several countries have observed an increase in the number of hot days, with temperatures up to 5 °C higher than the average temperature recorded in previous years, particularly during the phase of growth and pollination.

“We observed several cases of failure in the pollination of rice, wheat and corn due to an increase in temperature during this phase. And the impact may be exacerbated if the temperature increase is accompanied by a water shortage,” he said.

According to Hatfield, the minimum nocturnal temperatures have increased more than the maximum nocturnal temperatures. This change is having an impact on plant respiration at night and is reducing plants’ capacity for photosynthesis during the day, he explained.

Studies using corn

In a study performed in Hatfield’s USDA laboratory in a rhizotron – equipment used to analyze plant roots as they grow – researchers maintained three varieties of corn in a chamber at temperatures 4 °C hotter than one kept at normal temperatures to analyze the impact of temperature on the vegetative and reproductive phases of the plant.

“We determined that the plant’s physiology is highly affected by a temperature increase, especially in the reproductive phase,” explained the researcher.

In another experiment, the researchers maintained a variety of corn cultivated in the United States in a chamber whose temperature was 3 °C above what the plant could tolerate during the growth phase, which is the phase that determines the size of the ear of corn.

The increase in temperature caused a 15-day reduction in the period over which corn kernels were formed and prevented the plant from completing this process, which was then reflected in a decline in productivity.

“We observed that if the plants were exposed to a relatively high nocturnal temperature during the period that the grains fill, this phase of development was interrupted,” said Hatfield.

“The problem is not the average temperature to which a plant in the reproductive phase is exposed, but rather the minimum temperature. We need to better understand how agricultural crops interact with climate and the environment so as to increase their resilience to higher temperatures and the frequency of extreme climate events,” he explained. 
 

Impact in Brazil

In Brazil, climate change is already modifying the geography of agricultural production, said Hilton Silveira Pinto, Director of the Center for Meteorological and Climate Research on Agriculture (CEPAGRI) at the University of Campinas (Unicamp).

Last year was the driest year since 1988, when CEPAGRI began recording climate measurements. CEPAGRI registered an average of 1.186 millimeters (mm) of rain, in contrast to the 1.425 mm observed in previous years. The most critical month of the year was December, when there was only 83 mm of rain. The average for this month is 207 mm, Silveira Pinto explained.

“The very dry year-end really hurt São Paulo’s agriculture because the planting season for farmers here is October and November,” Silveira Pinto said during his lecture.

“There should be a delay in planting some crops because there is quite a noticeable range in the rainfall patterns in areas where certain crops are planted,” he said.

According to the researcher, starting in the 2000s, there were practically no reports of frost in any region of São Paulo, indicating that the state had experienced an overall increase in temperature.

One reflection of this change is the migration of coffee production in São Paulo and Minas Gerais to higher altitudes, where temperatures are more favorable for plant flowering. The temperature is nearly 0.6 °C lower for every 100 meter increase in altitude, Silveira Pinto explained.

During the coffee plant’s flowering period, when buds become coffee beans, the plant cannot be subjected to temperatures above 32 °C. Just one afternoon at this temperature during the flowering period is enough to cause the flower to be aborted and prevent the formation of a coffee bean.

“Temperatures of over 32 °C have been recorded more frequently in the coffee-growing region of São Paulo. With global warming, the incidence of warm afternoons during the plant’s flowering period is expected to increase by 5 to 10 times,” Silveira Pinto said. “This could render coffee production at lower altitudes in São Paulo no longer feasible during the coming decades.”

“Coffee production in Brazil should migrate to the South,” he said. “In the coming years, Brazilian coffee will likely be produced in states such as Paraná and Santa Catarina.”