I've heard from people that deny anthropogenic global warming or global warming itself, that humans used to emit much more CO2 at the beginning of the industrial revolution than now, with many laws against that and etc.

Could that be true? It seems extremely unlikely to me given the world population now and then, and what it means to the demand for production and energy supply, all the changes in lifestyle and such things. Somewhat like, despite of the decrease on birth rates, the world population will continue to grow for the next decades rather than immediately stabilize or decrease.

Where could I find reliable data on this subject?

I've heard from people that deny anthropogenic global warming or global warming itself, that humans used to emit much more CO2 at the beginning of the industrial revolution than now, ...
Where could I find reliable data on this subject?Before the use of coal and petroleum, the long-term, net anthropogenic release of CO2 was essentially zero compared to nature's occasional net release. People suggesting otherwise, need to ask themselves: Where did the carbon being released come from? Burning wood has zero long-term, net release. (As is case today with alcohol from sugar cane powering cars.)

The "industrial revolution" began with water power. For example, in the textile mills of New England the factories all had small dams, many can still be seen, and a system of leather belts to distribute the power within the mill to the looms. At that time, coal was being used mainly for heating homes. In fact the first application of coal for power was at at the mines to pump water out.

The first "steam engine pump" was very inefficient. Just a chamber that could be filled with steam, valved off from the boiler, and then connected to the "suction line." As the chamber cooled, the steam condenses, an the partcial vacuum allowed the air pressure to push the water up perhaps 25 feet. (As old physics teacher I can not yet say "sucked the water up.") Several "lift stages" were some times needed as the open pit extraction gave way to true coal mines. Probably if there was only one lift stage, the "suction line" was always connected and some steam venting (bubbles coming up in the water to be pumped) indicated it was time to valve off the boiler.

Invictus is perhaps my favorite poem. In addition to many other things, it also illustrates the "inertia in language" in the line that includes "Black as the pit, from pole to pole." The true mines were still called "pits" even though they were entered by narrow shafts. I am old enough that I call my refrigerator an "ice box" still.