You can discuss what the climate is on any given day as long as your discussion of the climate in any given week/month/season gives you the pretty much the same answer. You are missing the bigger point though.
Your graph doesn't even show climate, it shows days below freezing. It doesn't show whether on average the temperatures are colder or warmer. Stats can be used to show anything. What are the temps on the days where it isn't below freezing? If those dropped from an average of 60 degrees down to 40, the number of days below freezing could go down but the average will still go down.
http://vancouver.weatherstats.ca/charts/temperature-25years.html
Using Vancouver's last 25 years, looks pretty darn flat. The average for the year got above 11 in 1992, 1995, 1998, 2003, 2010. Every 3 years for 9 years it would peak but then you went 5 years and then 7. Looks like the distance between averages above 11 degrees is spreading out so it must be getting colder. Of course you aren't going to agree with that but given the data I linked to, that is a reasonable conclusion.
It is amazing to me how many websites will give the 25 year average, the 50 year average, present their information in the way that they want you to see it but won't give the underlying data. I have gotten to a point where I don't trust anybody showing me their data points that aren't willing to show me the underlying data. Especially given the whole fiasco a couple years ago with them "massaging" the data to fix "errors" but unwilling to give the data without the fixes.
Actually, since the number of nights with temperatures below freezing is a long term pattern in weather conditions, and since climate is the prevailing weather conditions in general or over long periods of time, not just averages, it indeed shows climate. A change from a moderate to extreme climate (greater variability between highest and lowest temperature), or
visa versa, is a change in climate, even though the average may not change much at all. Furthermore, while Vancouver's average temperatures may appear relatively flat, this may be as much a product of the moderating effect the Pacific Ocean has on our climate. We may also be an area that is going to experience a cooler drier climate in the new regime. What is interesting is that in Canadian cities further inland (continental vs maritime climate) we see that the average temperature in the last five years has risen at least a degree compare to the first five years of that 25 year period:
http://ottawa.weatherstats.ca/charts/temperature-25years.htmlThis is even more pronounced in cities further north:
http://iqaluit.weatherstats.ca/charts/temperature-25years.htmlGiven that global warming (the rise in the global average temperature of the earth's atmosphere) in the last 100 years is a rise of less than a degree, these changes appear significant.