I live in Montreal. When I got married 42 years ago on Nov 10th, (A weekend), I can tell you that two days later, winter hit with a 2 foot snowfall and sub-zero weather. Winter started the 12th of November and that was the norm.
Since then, on the average, winter has been arriving one day later each year. Last week, on Dec 7th, winter arrived. Snow and cold. Today (15 Dec) is the kind of weather we usually had in November.
From my perspective, in the past 60 years, I have seen winter shortened by one month in the fall, and around 15 days in the spring.
Living in Canada, with global warming, we will be OK as the earth warms. But the mid-west USA and elsewhere will become unbearable in summer, and the USA will experience (in my view) severe water shortages.
We do have to go on the assumption that the trend is there, and to ignore it is to cause your grand-children to pay the hardship price for today's inaction.