There are more than 90,000 livestock operations in Canada, which accounted for more than $17 billion in farm cash receipts in 2000 Despite the economic importance of livestock operations to Canada2，relatively few studies have examined how they could be impacted by climate change.3Temperature is generally considered to be4 the most important bioclimatic factor for livestock. Warmer temperatures are expected to present both benefits and challenges to livestock operations. Benefits would be particularly evident during winter, when5 warmer weather lowers feed requirements, increases survival of the young, and reduces energy costs. Challenges would increase during the summer, however, when heat waves can kill animals. For example, large numbers of chicken deaths are commonly reported in the United States during heat waves.6 Heat stress also adversely affects milk production, meat quality and dairy cow reproduction. In addition, warmer summer temperatures have been shown to suppress appetites in livestock and hence reduce weight gain. For example, a study conducted in Appalachia found that a increase in mean summer temperature7 caused a 10% decrease in cow, calf and dairy operations. Provided there is adequate moisture, warmer temperatures and elevated C02 concentrations are generally expected to increase growth rates in grasslands and pastures.8 It is estimated that a doubling of9 atmospheric C02 would increase grassland productivity by an average of 17% , with greater increases projected for colder regions and moisture-limited grassland systems. However, study results tend to vary greatly with location，and changes in species composition may affect the actual impacts10 on livestock grazing. For instance, studies have noted future climate changes, particularly extreme events, may promote the invasion of alien species into grasslands, which could reduce the nutritional quality of the grass. An increase in severe moisture deficits due to drought may require producers to reduce their stock of grazing cattle to preserve their land，as exemplified by the drought of 2001 when many Prairie producers had to cull their herds. For the 2002 season，it was predicted that many pastures would be unable to support any grazing, while others would be reduced to 20-30% of normal herd capacity. There is relatively little literature available on the impacts of extreme climate events on livestock. Nevertheless, storms, blizzards and droughts are an important concern for livestock operations. In addition to the direct effects on animals, storms may result in power outages that can devastate farms that are heavily dependent upon electricity for daily operations. This was exemplified by11 the 1998 ice storm in eastern Ontario and southern Quebec，when the lack of power left many dairy farms unable to use their milking machines. This threatened the health of the cows (due to potential mastitis) and caused significant revenue losses. Milk revenue was also lost through the inability to store the milk at the proper temperature.12 Furthermore, the lack of bam ventilation and heating, thereby making the electricity made it difficult to provide adequate animals more