Well, maybe the car is the most important (in terms of impact), but air conditioning comes close, and for much more subtle reasons.
You may have noticed that July is a little slow where you are. Same here. Web traffic goes down, productivity goes down, people work less, move slower, the whole bit. In Europe, I’ve heard, entire countries shut down in August.
There’s a reason that New York City isn’t in Belize.
For centuries, modern man in the Northern Hemisphere has adapted to a "don’t work so hard it’s hot" mindset. In places where it’s hot all the time, this is a huge hit on the economy, as you can imagine.
So what’s the big deal with air conditioning?
Well, in addition to leveling off the year (you can work just as comfortably in July in New York as you can in November now), air conditioning levels off the world. Air conditioning permits knowledge workers to thrive in India or Cancun. Air conditioning creates year-round demand for all sorts of items that would have been seasonal otherwise (from nice restaurants to shoes…)
And air conditioning has plenty of unintended (side) effects. As the less-industrialized world realizes that air conditioning pays for itself with huge increases in productivity, they buy more (air conditioning has only been popular worldwide for forty years… it’s still catching on). As people buy more, they use more energy, create more greenhouse gases, make the world hotter. Price of energy goes up… etc.
And as a marketer, air conditioning changes your world. You grew up not needing to worry about Ecuador, because it wasn’t a competitor and it wasn’t a market. Now it’s both.
Something to think about when it’s 90 degrees outside.