I've seen more than one documentary on this topic...quite a few actually.
The one outstanding work of evidence (and you don't see it often), is the collection of satellite infra red photos.
As soon as we were able to, we have been studying this Earth in every way we can. And the temperature changes are seen best in infra red.
From the time satellites began doing so, until this present day, the temperature, has risen no less than an average of 6 degrees.
Doesn't sound like a lot, but when the glaciers covered New York, 10thousand years ago, the average temp was seven degrees less than 1950.
But I suppose this type of debate will bounce back and forth, as some people contend that a sudden rise in average temp, is not unusual.
Even so, 30years of high temp can produce enough change to alter life and living for several generations.
When temperature spikes, it takes awhile for the effect to dissipate.
The Earth is not like a pot of water, once it begins to boil, can be turned down to simmer, whenever you feel like it.