I didn't know if it was just because I now have a 2 year old, but New York summers have definitely seemed harder to deal with each year I've lived here.
Is there a commonly accepted minimum temperature difference threshold that is perceivable by humans? E.g., if summer in 2016 was hotter than 2015 by X, I will notice?
Humans are lousy at comparing temperature differences over the course of a year. What we remember are extreme events: four years ago we had deep snow all winter, last year I only had to shovel twice. Remember when we didn't turn on the A/C except for one week in August?
This is a "just noticeable difference", stacks of research on it. In some situations the JND for temperature is as small as 0.02 degC. Whereas if I sneak the room temperature up over the course of about 10 minutes you may not notice a 5 degC change. From one summer to another? I'm going to speculate that people have no idea whether it was cooler last year.
It's an average over time. People were talking about going to the local lake this weekend because the local weather service reported it was going to be the warmest ever water temperatures for this year - 0.1 degree warmer than last year.
Is there a commonly accepted minimum temperature difference threshold that is perceivable by humans? E.g., if summer in 2016 was hotter than 2015 by X, I will notice?