A Berry Different Climate?

Global warming may impact New Jersey blueberry and cranberry crops

July 23, 2007

According to a recent report by the Union of Concerned Scientists, global warming may pose significant risks for New Jersey's cranberry and blueberry crops. While fruit harvests throughout the Northeast will be affected by rising temperatures, the report states that the cranberry crop in New Jersey is "particularly vulnerable."

Like many fruits, including apples and peaches, cranberries and blueberries have a chilling requirement, meaning that they require long periods of cool winter temperatures for optimal fruit development. Blueberries, the state fruit of New Jersey, require 31-33 days of chilling below 45 degrees while cranberries require 50-58 days. As winter temperatures warm and winter thaws become more frequent in the coming decades, these chilling requirements may not be met, thus reducing the productivity of the crops.

According to Dr. Nicholi Vorsa, the Director of the Blueberry and Cranberry Research and Extension Center at Rutgers, the response of blueberries and cranberries to global warming is highly dependent on the magnitude of the warming. "If we had a climate such as that of Florida or South Carolina," Vorsa explains, "there could be a negative impact on these crops." If our climate became more like that of Virginia, however, the impact on crops would not be as significant.

Depending on future greenhouse gas emissions scenarios, New Jersey's climate could become only slightly warmer--like that of Virginia-or could become as warm as that of South Carolina.

The UCS report, which was put together by over 60 scientists, analyzed two potential emissions scenarios, both drawn from the most recent report of the Intergovernmental Panel on Climate Change. The higher emissions scenario projects a future characterized by fossil fuel-intensive economic growth and a global population that peaks in the middle of the 21st century. Economic and population growth are similar in the lower emissions scenario; however, this scenario assumes a much more rapid shift to resource-efficient and less fossil fuel intensive industries.

If the higher emissions scenario prevails, by the middle of this century the varieties of blueberries currently grown in New Jersey would fail to meet their chilling requirements. Blueberry farmers may be able to adapt, however, by switching to varieties that were originally cultivated in more southern states.

Because of their higher chilling requirement, cranberries could be hit harder by warming winter temperatures. According to the report, cranberries will not be able to meet their chilling requirements by the middle of the century under either emissions scenario. Options for cranberry farmers are limited, as there are no known varieties with lower chilling requirements.

Keith Arnesen, an agricultural meteorologist in the Department of Environmental Sciences, notes that winter temperatures are just one of many factors that determine the health of berry crops. "In New Jersey, farmers flood the cranberry bogs each winter to protect the plants from cold temperatures," says Arnesen. Other factors that can affect crop yield include extreme hot temperatures in the summer and extreme cold temperatures in the spring.

Scientists are still trying to understand the preferred temperature range for different crops. Dr. Vorsa notes that, even though last December and January were unusually warm, blueberries met their chilling requirement earlier in the season than usual. "It kind of surprised me," he says. Vorsa hypothesizes that temperatures below freezing may not help blueberries meet their requirement. In that case, a moderate increase in temperatures might actually be beneficial to blueberry crops.

New Jersey is one of the top producers of both cranberries and blueberries. In 2005, the two crops brought in about $70 million, or 60% of the state's total fruit sales.