The IPCC scenarios don't really rely on feedback loops, because we don't know enough about them. They are rarely taken into account, while even the mildest plausible scenarios based on projected human activity project at least a 2°C change, which can't be stable. We underestimate feedback loops, and we might also get human activity wrong, but even if we don't you still get a planet that's just barely habitable.
The warming trend is not created by IPCC fudging past temperature data. This is a climate change denier talking point, but it's a lie. Land and ocean temperatures have been adjusted separately to account for the changes in the measurement methods. Localized sources were compared to their neighbours in order to be able to account for changes in the instruments, urbanization and so on. High-accuracy sensors are used to create a reference network of perfectly sited stations. Roughly half of the stations reduced the warming, half increased it. Deniers like to cherry-pick the stations to make a point. The biggest adjustment by far was because of earlier ships. They used to throw a bucket overboard, pull it up slowly and measure the temperature of the water with a thermometer, without accounting for the air temperature. Ships later switched to measuring temperatures through engine room intakes. These days we have a global network of automatic buoys. None of this increased the warming trend, the adjustments actually reduced it. Mostly only data from before 1940 had to be adjusted. Studies continue to use raw data along it's interpretations, but the necessity of an adjusted interpretation is constantly shown.
