Economy worse in cold weather

Indeed.

Then in other world regions at higher altitudes / temperatures more energy required to cool the engine oil, (slightly true even in the UK hottest weather.) Then less oxygen, different lower octane / cetane fuels.

In the UK so lucky that there are ideal running conditions, never going to be more than 3,500 foot above sea level, or below sea level, 

temp seldom as low as -20*oC or above 35*oC, road surfaces as they pretty much are from North to South, Fuel the same to BS standard.

Pretty much weather that has no extremes of flooding, humidity / dryness.

If you drive a few years or decades in the UK you get to know how the seasons affect your vehicles economy & various vehicles economy, or you did until Euro 4 then Euro 5, & now Euro 6 Emission standards, that has had affects on many things.

Now more manufacturers are going from 5w 30 FS oil to recommending 0w 30 FS just because people are aware of just how weather affects things, 

as does the adding of more Bio or Ethanol to fuels.

Edited 31 October, 20178 yr by Headinawayoffski