"This report addresses one of the most frequently asked questions about global warming: What will happen to weather and climate extremes?"

• Most of North America is experiencing more unusually hot days and nights and fewer unusually cold days.

The last 10 years have seen fewer severe cold waves than any other 10-year period in the historical record, which dates back to 1895.

The number of heat waves has also been increasing since 1950.

• There has been a decrease in frost days and a lengthening of the frost-free season over the past century.

• Extreme precipitation episodes (heavy downpours) have become more frequent and intense and now account for a larger percentage of total precipitation.

• Droughts are becoming more severe in some regions.

• Atlantic tropical storm and hurricane destructive potential has increased substantially since about 1970.