|Which temperature measuring method most accurately measures global warming?||a) ground-based thermometers|
No, that is incorrect.
Ground-based thermometers that are situated in areas that were originally rural have been yielding increasingly higher temperatures over time due to urban encroachment. Asphalt and concrete structures replacing green leafy plants results in a warmer environment in the vicinity of temperature sensing stations, a phenomenon referred to as the "urban heat-island effect". Unfortunately, three dimensional computerized climate models are based on such questionable surface station data.
The first efforts to document the UHI effect were those of Kratzer who studied the Ruhr valley in 1932. T.J. Chandler’s studies followed and his book “The Climate of London”, was published in 1965. In the 1970s Atkinson showed how precipitation was higher in London because of the heat island effect. Climatologist Dr. Timothy Ball did UHI research in Winnipeg, Canada in 1972 and Oke did similar studies in Vancouver, and Hamilton, Canada in the 1980s.
In a November 1997 press release Vice President Gore proclaimed that 1997 was the hottest year on record. Ground-based temperature readings were the basis for this announcement. Had the data from orbiting satellites been cited the report would have been much different: no net increase in global temperatures in 1997. Orbiting satellites provide the most accurate global temperature readings - accurate to 0.1 degree C. From these readings we can determine with a high level of confidence that 1998 was the warmest year in the past few decades, not 2005, as Al Gore asserts in his error-riddled film, “An Inconvenient Truth”. Thanks to the work of Steve McIntyre we now know that NASA’s Goddard Institute for Space Studies (GISS), the official source of global temperature data got it wrong as well. After adjustments it turned out 1934 was the warmest year on record in the US and instead of 9 of the10 warmest years being in the 1990s, four of the top ten warmest years were in the 1930s.
In the past 28 years, Earth-orbiting satellites show only a 0.3 deg C rise, with temperatures currently headed down.