I remember I explained it to ND_TN before. Let me try it again in another way:
Let's assume the population has only 3 persons A, B and C for simplicity.
Person A whose weight is 120 pounds
Person B whose weight is 180 pounds
and person C whose weight is 300 pounds.
So, the average weight of this population is 200 pounds.
After one year of different life styles by each person,
A loses 10 pounds. So, A is 110 pounds
B gains 50 pounds, his weight becomes 230 pounds
C loses 10 pounds, i.e. C's weight is 290 pounds.
So, the average weight of this population, after one year, is 210 pounds, increased by 10 pounds. Can you say this population become fatter based on this increased average number 210 pounds? No, because most people of this population (A and C) actually have lost weight. This average number 210 (as well as 200 pounds a year ago) is purely an abstract construct. it has no physical meaning, because in reality neither A, B nor C has a weight of 210 pounds and a weight of 200 pounds a year ago.
July's global average temperature for same reason as the average weight of a population above is a abstract number. Using this number alone to mass is intentional misleading.