@Ionus,
No. I didn't assume anything. It's called statistics.
But let's examine your claim.
You claim that min/max can't be used to show a trend. Let's look at your assumptions.
Data using the average of the minimum and maximum daily temperature is showing a trend upward.
That means one of 3 things is happening.
Both the minimum and maximum are increasing over time.
The minimum is increasing while the maximum is staying the same
The maximum is increasing while the minimum is staying the same.
In all 3 of those instances we would be seeing an increase in the amount of heat during the day.
But wait. You are arguing that the increase in heat is illusory and there is some magical way that heat works differently the rest of the day today than it did 100 years ago. We'll ignore the fact that there is no evidence to support your assumption and assume you are correct.
In order for the max/min average to show an increase but there is no increase in daily temperature then there clearly has to be a change in how our days warm and cool. Let's look at the ways that can happen. The sun's output can change. The amount of sunlight reaching the surface has changed by some process such as increased/reduced cloud. The way the heat is radiated has changed in the last 100 years.
We have to eliminate the radiation theory because you are already discounting that one. CO2 increases temperature by decreasing the rate of radiation.
The sun's output has not been shown to have increased.
That leaves us with some process that is now somehow increasing/decreasing the amount of sunlight at certain parts of the day to increase the average since we are only using the maximum and minimum.
What process could be blocking the sunlight or increasing it? We know there isn't a giant magnifying glass flying around the earth increasing the sunlight. That means it has to be something in the atmosphere doing what you are claiming. It can be a chemical such as CO2 or it can be what we would call weather.
That leads us to the conclusion that either there is a chemical compound changing the way heat is trapped in the earth that somehow only works during part of the day. Not likely, but if you know of some such chemical compound please let us know. The other option is that what we know as weather is changing over time. When weather changes over time it is called climate change.
So your argument leads us to the conclusion that climate change must be occurring for your argument that the average if minimum and maximum temperature can't show the trend correctly.