The weather is a chaotic system, and yes, this is the reason behind the difficult to predict if it will rain in 2 weeks. However, this is true when you try to see it at local level, and finding specific things (like raining in a particular area).

But if you see it at the global level, then it is more easy to predict. You for sure know what is the average temperature of your city.

Look this image:

source

This is the temperature change relative to 1850, almost two centuries ago. Look the bull market! it is pretty clear the tendency for the next decade.