Dr. Ziska was the lead author on a 2011 article in the Proceedings of the National Academy of Sciences showing changes in ragweed pollen seasons by latitude in central North America since the mid-1990s. Updated data from this analysis are being used by the EPA in their ragweed pollen season climate change indicator: http://www.epa.gov/climatechange/science/indicators/society-eco/ragweed.html
Lewis H. Ziska, PhD – USDA-ARS