Average increase in the Sun's temperature is something that stretches over millions of years, not decades or centuries.
There's a theory that I'm looking for that I ran into some years ago about solar activity like sunspots and ionized particles or something like that affecting cloud formation on Earth which would in turn affect the amount of sunlight hitting the Earth's surface. The theory suggests the reverse has been going on therefore less cloud formation and thus more sunlight reaching the surface and therefore hotter temperatures.
Sounds real blurry the way I'm putting it, that's why I'm looking for the theory and it ain't that easy because I don't know the right words to use and the current climate fad basically shoves it into the fringes. So it isn't exactly the first thing that's going to turn up in a Google.
There are other factors as well and such as the continued reduction of forest cover and increase in open areas for farmland as well as increasingly urbanized human zones which trap more sun and thus produce more heat. Since temperature measurements tend to be near where people live for obvious reasons, the readings are going to be higher.
For example, there are temperature-related planting zones referred to in gardening. New York City should be a Zone 6, at par with much of Pennsylvania, but instead it's Zone 7 which averages 10 to 15° higher, particularly during the winter. So New York City is 10 to 15 degrees hotter than it should be just because of all the tar and concrete and reduced forest cover.
Tokyo would be very equivalent of a Zone 7 if it wasn't for the city, but being a highly urbanized area with exceedingly far less parkland than other cities might have, it's actually warm enough to grow bananas.
So those are two examples where increasing spreading and density of human habitation has caused increases in local temperatures.
I'm tired, I have a bit of a headache, and I'm not making sense.