If there are photos and other documentation of polar ice reaching similar volume/area/mass/whatever from the 1800s or 1700s as today then that would be compelling evidence of no long term global warming. There wasn't any significant burning of fossil fuels until about the 1850s, a time when coal fired locomotives began to replace horse drawn buggies, coal fired ships were replacing sailing ships, and electric lights began to replace whale oil lamps.
I expect there's an argument that fossil fuel use was still pretty minimal up to the 1930s. World War One lead to a big change in industrialization of war, and that lead to industrialization of many other aspects of human civilization, and that industrialization tended to move from wind and hydro power to fossil fuels. With World War Two we saw another rapid shift in energy use. In the time between those two wars was when we saw hydro dam construction slow down as all the best spots for a dam were pretty much used up by then. The Dust Bowl made biomass fuels something of a scarcity, which would have lead to greater use of fossil fuels to make up for it.
I recall Neil DeGrasse Tyson talking about how there's photos of big cities in the 1920s (or something about that, I may recall the date incorrectly) being full of horses, and 10 years later they'd be full of automobiles. In ten years a horse went from being invaluable to worthless.
Where's the point at which humans were undoubtedly impacting the global temperature from the burning of fossil fuels? A wide range guess would be sometime between 1840 and 1940. So, if anyone can produce evidence of polar ice being at the same level as today at any time before this shift then that could be seen as disproving human caused global warming.
The problem is that until weather satellites were a thing sometime around 1970 we didn't have good data on polar ice. We have some proof of ships sailing through the "Northwest Passage" which can bring some doubt to human activity causing polar ice shrinking.
A quote from: https://en.wikipedia.org/wiki/...
In 1906, the Norwegian explorer Roald Amundsen was the first to complete the passage solely by ship, from Greenland to Alaska in the sloop GjÃa.[18] Since that date, several fortified ships have made the journey.
The ships were "fortified" against the ice but that doesn't make them anything like a modern icebreaker. We can certainly open paths for shipping in polar ice today with an icebreaker, and people using shipping in polar ice as evidence of thinning out polar ice does not follow. Just because we can brute force our way through the ice isn't evidence of shrinking ice area/volume/whatever, it is merely evidence that we can build big and heavy ships. Being able to take a sailboat through those waters does prove the ice was pretty thin over 100 years ago, and that the world has cooled since in spite of humans burning fossil fuels.
When anyone claims we are seeing global warming causing problems then there should be a question on when in the past the global temperature was ideal. We know the world was warmer in the past with records of vineyards and wineries in the UK, as well as paintings and firsthand accounts of a "little ice age" in the UK causing ice over rivers being thick enough that people were ice skating there and communities holding festivals of sorts on the iced over rivers.
We know the climate changes over time so a call to stop climate change appears to be an impossible task. If we assume that humans could stop climate change then there would have to be some near global agreement on where to stop that change. Do we want rivers to freeze over during winters in UK? Or should we prefer vineyards in the UK? Can't have both.
Don't anyone call me a "denier" for my statements above. I'm asking that if we are to stop climate change then we'd need to have an agreement on where to make it stop. There will be places in the world that benefit from this current global warming, how can we deal with their opposition to continued global warming? Are we to bomb their coal-fired power plants? Are people willing to wage war on these people? Maybe not a shooting war as we could create an economic war to where they starve to death for lack of trade with the outside world, or perhaps migrate to other regions as "climate refugees" that others caused them to become.