> How do you know?
posed in ignorance (perhaps genuine ignorance, perhaps feigned) above, we (humans) have been measuring gas properties in isolation for 200 years (and more) and have been specifically measuring (and storing as bottled samples) atmospheric gas composition since the start of the Cold War.. seventy odd years or so now.
Much of our high quality environmental data comes from cold war research - ocean tempretures were first mapped at large scale by Scripps in order to use thermoclines to pinpoint submarines and other sounds in water.
In the civilian arena, Cape Grim is of interest: https://en.wikipedia.org/wiki/Cape_Grim_Air_Archive
https://researchdata.edu.au/cape-grim-air-archive/678420
This and other global references informs us about the changing atmospheric makeup and other experiments inform us about the increase in trapped heat from incoming solar radiation.
Before about 1940, the most common method for measuring sea surface temperature was to throw a bucket attached to a rope overboard from a ship, haul it back up, and read the water temperature. The method was far from perfect. Depending on the air temperature, the water temperature could change as the bucket was pulled from the water. (1)
In the late 1970s ... tracking what was happening to Earth temperatures was at a relatively primitive state. Much of the relevant weather station data had not been digitized and what had been, was not widely available. Previous estimates of temperature changes ... had focused on the northern hemisphere, but that obviously missed half the planet. (2) interactive map: (3)
There is analysis showing differences in model temperature variation models and actual data from balloons and satellites since 1979. (4)
Those are few examples how our ability to measure things changes with our developing knowledge.
Rising temperatures is not new phenomena. Greenland ice core project (5) showing that there was about 25 dramatic climate changes in history. Its called Dansgaard–Oeschger event. (6), (7) and shows that for example during Younger Dryas (8) there was dramatic temperature decline and increase in few decades.
Making predictions on data since 70's are fragile and should be constantly reanalyzed.
(1) https://climate.nasa.gov/explore/ask-nasa-climate/3071/the-r...
(2) https://data.giss.nasa.gov/gistemp/history/
(3) https://data.giss.nasa.gov/gistemp/station_data_v4_globe/
(4) https://naturalresources.house.gov/uploadedfiles/christytest...
(5) https://en.wikipedia.org/wiki/Greenland_ice_core_project
(6) https://en.wikipedia.org/wiki/Dansgaard%E2%80%93Oeschger_eve...
(7) https://www.ncei.noaa.gov/sites/default/files/2021-11/2%20He...
Yet they, in near majority, still stand behind the broad predictions of future climate change - even being aware of the work of Smale and Lorenz .. perhaps it's that 40+ year old understanding of stability, robustness, and the Dzhanibekov effect in which the broad arc of motion is entirely predictable despite wobbles on a minor axis or two.
Normalisation and may other adjustments to data sets are stock in trade operations across all the observational sciences- geophysical mineral exploration, radiometric surveying, radio astronomy, distributed signal aquisition, etc. etc. etc. You'll note for example that NASA et al are out in front about doing such things.
Predictions of trains headed for derailment based on speed, mass, and topography are not refuted by an inability to predict where the centrepiece vase in the dining car comes to rest.
From history we know, how terrified population is easier to manipulate by those who offer easy solutions.
The physics is sound. The grasp of physics many dissenters have is not.