The challenge of climate change

by Jay Sjerven
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The Third National Climate Assessment, issued May 6 by the U.S. Global Change Research Program, leads off with a simple assertion: “Climate change, once considered an issue for a distant future, has moved firmly into the present.”

The assessment indicated the nation and the world already were grappling with challenges presented by a changing climate and that the pace of change was expected to accelerate in the next several years, which will require the development of a panoply of mitigation and adaptation strategies in all areas and at all levels of human endeavor, including food production.

The assessment concluded that the evidence indicating the primary role human activity plays in climate change, primarily due to industrial emissions of heat-trapping gases, was incontrovertible. The task the assessment set before the nation was acting to limit the amount of change and the extent of its damaging impacts.

The assessment, developed by a team of more than 300 experts guided by a 60-member federal advisory committee operating under a congressional mandate, provided regional outlooks under scenarios where no sustained efforts to mitigate the human component in climate change are made and where serious steps to limit greenhouse gas emissions are undertaken. Agricultural producers will face increasing challenges under both scenarios.

The report acknowledged some climate changes may be beneficial to agriculture in the short run, such as longer growing seasons in some areas. But climate change overall was expected to have many more adverse effects than positive effects on agriculture.

The assessment included a chapter on agriculture containing six “key messages.”

The first message regarding agriculture was: “Climate disruptions to agricultural production have increased in the past 40 years and are projected to increase over the next 25 years. By mid-century and beyond, these impacts will be increasingly negative on most crops and livestock.”

The assessment forecast temperature increases of between 1.8°F and 5.4°F across the country by mid-century and further intensification of precipitation extremes, i.e droughts at one extreme and increased excessive rain downpours at the other. The combination was expected to adversely affect overall crop yields and farm profits.

“Temperature and precipitation changes will include an increase in both the number of consecutive dry days and the number of hot nights,” the assessment observed. “The western and southern parts of the nation show the greatest projected increases in consecutive dry days, while the number of hot nights is projected to increase throughout the United States. These increases in consecutive dry days and hot nights will have negative impacts on crop and animal production.”

The report indicated such effects already were taking place with high nighttime temperatures affecting corn yields in 2010 and 2012 across the Corn Belt.”

Selective breeding and genetic engineering for both plants and animals provides some opportunity for adapting to these climate changes, the assessment said. Greater drought tolerance already is a key goal for grain seed companies using both bioengineering and more traditional planting breeding technologies.

Perennial specialty crops face even greater challenges because new varieties commonly require 15 to 30 years to be developed, and once planted, the crops require time to reach their production potential, the assessment said.

A warmer climate may threaten perennial specialty crop production because of reduced opportunity for crops to realize their chilling requirements.

“Perennial specialty crops have a winter chilling requirement ranging from 200 to 2,000 cumulative hours,” the assessment noted. “Yields decline if the chilling requirement is not completely satisfied, because flower emergence and viability is low.”

The assessment suggested projections show the chilling requirements for fruit and nut trees in California will not be met by the middle to the end of this century.

“For most of the Northeast, a 400-hour chilling requirement for apples is projected to continue to be met during this century, but crops with prolonged chilling requirements, such as plums and cherries, could be negatively affected, particularly in southern parts of the Northeast,” the report said. “Warmer winters can lead to early bud burst or bloom of some perennial plants, resulting in frost damage when cold conditions occur in late spring, as was the case with cherries in Michigan in 2012.”

Stress will lead to lower yields

The second key message of the assessment was: “Many agricultural regions will experience declines in crop and livestock production from increased stress due to weeds, diseases, insect pests, and other climate change-induced stresses.” Warmer winters will allow more insect pests to survive to produce a greater number of generations per year, the report said. Invasive weeds such as privet and kudzu, already present in the southern states, may spread northward.

The assessment’s third message was: “Current loss and degradation of critical agricultural soil and water assets due to increasing extremes in precipitation will continue to challenge both rain-fed and irrigated agriculture unless innovative conservation methods are implemented.” The assessment continued, “Changes in production practices can have more effect than climate change on soil erosion; however, changes in climate will exacerbate the effects of management practices that do not protect the soil surface from the forces of rainfall.”

The fourth point was: “The rising incidence of weather extremes will have increasingly negative impacts on crop and livestock productivity because critical thresholds are already being exceeded.” The report cautioned, “Extreme events at vulnerable times could result in major impacts on growth or productivity, such as hot-temperature extreme weather events on corn during pollination.”

The reported added, “Recent studies suggest that increased average temperatures and drier conditions will amplify future drought severity and temperature extremes.”

Adaptation and food security

The fifth message related to agriculture’s adaptability.

“Agriculture has been able to adapt to recent changes in climate; however, increased innovation will be needed to ensure the rate of adaptation of agriculture and the associated socioeconomic system can keep pace with climate change over the next 25 years,” the report said.

“In the short term, existing and evolving adaptation strategies will provide substantial adaptive capacity, protecting domestic producers and consumers from many of the impacts of climate change, except possibly the occurrence of protracted extreme events,” the report said.

The report’s sixth key message concerned food security.

“Climate change effects on agriculture will have consequences for food security, both in the United States and globally, through changes in crop yields and food prices and effects on food processing, storage, transportation and retailing,” the report said.

The report concluded, “Adapting food systems to limit the impacts of climate extremes and changes involves strategies to maintain supply and manage demand as well as understanding how other regions of the world adapt their food systems in ways that might affect U.S. agricultural competitiveness, imports and prices. Supplies can be maintained through adaptations such as reducing waste in the food system, making food distribution systems more resilient to climate risks, protecting food quality and safety in higher temperatures, and policies to ensure food access for disadvantaged populations and during extreme events.”
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