Climate change has increased pollen counts and the length of the pollen season, trends that are expected to continue through mid-century.
Spring is arriving earlier across the U.S. by an average of three days.
For the first time in 20 years, the U.S. is on track to set more record lows than record highs in 2013.
This season was the least active since 1982 and the sixth-quietest since 1950.
Foliage color and timing has been starting later, on average, in a warming world.
As the graphic shows, people cause most wildfires. But lightning-ignited fires burn by far the most territory.
Record highs have outpaced record lows by a bigger margin each decade since the 1960s.
The highlights of NOAA's 2013 Spring climate summary.