I have said for years that they do not have any reliable data to support any form of long term climate models. The reason is not that they fudged it. The reason is that they never had it.
70 percent of this planet is covered in water. In order to observe the temperatures over the oceans, there has to be a ship to record the measurements. The ship has to record the measurements over a period of time that will provide an accurate mean. This was never attempted. It would require ships to record the temperature over every square mile of ocean for decades.
Ships use shipping lanes for reasons to reduce distance (great circles), to avoid hazards to navigation (shoals), and to be where other ships might find them in the event of a disaster. Ships do not sail willy-nilly all over the ocean. A sailing ship transporting tea from India to England will not stop by Hawaii to see what the weather is up to. A tanker or a container ship is even less likely to leave the established lanes because it wastes fuel.
This changed in the 1960s. Ballistic missile submarines could go wherever they wanted and were encouraged to do so. This made it more difficult for the other side to find them. So the subs used circuitous routes and the surface ships had to sail around to find them. Mind that the entire fleet of US ballistic missile submarines consists of 41 boats, not all in service at the same time. The Soviets had less than that, and the British had perhaps six of them. This does not lend itself to widespread ocean exploration and monitoring.
Aside from the oceans, we do not even now monitor the temperatures in vast wilderness areas. North America has deserts and arctic tundras. Nobody goes there to record the daily temperature. Australia has the Outback, Asia has Siberia, South America has vast, nearly impassable jungles, and Africa has jungles, plains, and deserts. Perhaps 10 percent of Antarctica has been explored, and then only for very brief periods. The environment is too harsh for people and instruments.
This whole climate change scam is insulting to anyone with a rational mind.
THERE IS NO DATA TO SUPPORT GLOBAL WARMING.
As an old Boomer Quartermaster I can assure you that weather observations by a sub on patrol was limited to the observation on the rare occasions we were at periscope depth as to whether or not it was raining. At QM A school in Orlando we received training on the weather observations that surface ships make at regular intervals. The manual said that “All ships, (except submarines)”..... and I stopped paying attention after that. When we went outside for some cloud identification training, the Chief pointed to me and said, “Seaman Nigh, what kind of cloud is that?” I looked up and said, “Big, white, fluffy, might rain iffin it don’t clear up.” He looked at me, looked at my Dolphin insignia, (he had a pair just like them,) and said, “Yep, close enough.” Of course in Florida, weather observations at any given point in time have no relevance on the state of the weather in 30 minutes.