Below are this years Belmopan temperatures. A 3% difference between the red and blue lines or the high and low of the summer red and winter red lines, would be almost insignificant.
We have Day and Night temperatures due to the round Earth rotating at about 25,000 mph, resulting in different parts facing the Sun over the 24 hour period.
The thick red and blue lines are the 31 day running average temperatures.
The thin red and blue lines are the actual daily temperatures. Their variations would completely mask any 3% you mention and also the Global Warming they try to tell us.
We have Summer and Winter as a result of the Earth's axis being tilted about 23° from the plain that the Earth orbits around the Sun, such that in northern Summer, more of the northern hemisphere is more direct, as in perpendicular to the Sun, and less in the Winter, since most heat on Earth comes from the Sun.
That is about 1 kW of heat per square metre if there is no cloud cover.