Global Warming and Late Spring Frosts: Bad for Apples?

Writing as background for their study, Eccel et al. (2009) note that "apple and other fruit crops are vulnerable to spring (late) frosts," and that "during the bloom stage, a single event with temperatures going a few degrees below zero is sufficient to harm flower buds or even kill them," while "light frosts result in the degradation of fruit quality." Therefore, as they continue, "projected climate warming prompts general concern that the already observed advances in the vegetative cycle will become more consistent and the flowering period will coincide with severe cold spells," which could lead to more frequent and greater negative consequences for fruit production.

To test this hypothesis, Eccel et al. applied a phenological model of apple flowering to two 40-year temperature series of two locations in an important area of apple production in Europe (Trentino, Italy) and to two statistically down-scaled simulations of 50-year climatic projections produced by the HadCM3 general circulation model that were based on emission scenarios A2 and B2 of the IPCC's Special Report on Emission Scenarios. This approach was taken because, in their opinion, "only a reliable phenological model, coupled to a downscaled climatic model, could answer the following questions." (1) "Is the risk of spring frost changing over the years?" and (2) "Is global warming likely to expose fruit trees (apples specifically) to higher levels of risk?"

In response to their first question, the four researchers report that "risk analysis confirmed a lower risk of exposure to frost at present than in the past," while with respect to their second question they say there is "probably either constant or a slightly lower risk in [the] future, especially given that physiological processes are expected to acclimate to higher temperatures."

Eccel et al.'s findings should be encouraging to fruit growers worldwide. However, they caution that "fruit growers who operate in climatic contexts similar to that of Trentino will still face frost risk for many years," and that standard frost protection techniques "will not disappear in the next few decades," as the climate gradually warms (presuming state-of-the-art climate model predictions are correct ... which they probably aren't).