WeatherData, by itself, does not go back far enough. I know that there is data for NYC going back to the 1860s, but it is not easily accessible. That may provide some hint of global warming, but the data That I do have shows that weather (as opposed to climate) is highly variable locally.

I hope that Wolfram's weather data will be made more comprehensive over time.

Very nice! Thank you @George for sharing. I wonder if this representation can detect even slightest trend of warming up earlier to reflect correlation with global warming?