FiveThirtyEight has a post describing the NOAA and USDA climate maps. There's differences in data sources and methodology as well as aim, but they do show the gradual movement north of climate zones.
Global warming skeptics like to challenge temperature histories, claiming scientists change the data to fit preconceived ideas. I view that as highly unlikely, but the most reliable evidence of global warming is: show me the money. When people spend their money, as in cruises through the Northwest Passage or in changing what plants they raise, that's good solid evidence.