B. Reported Global Temperature Anomaly (change) was 0.79 degrees C between 1860 and 2019.
HadCRUT4 reported global temperature anomalies from 1850 to 2019 as approximately 0.79°C. HadCRUT4 is run by the Met Office Hadley Centre UK Met Office. They are the official keeper of the data and analysis. The graph below shows the changes in the near surface land air temperature and surface ocean temperature.
The HadCRUT4 is based on CRUTEM4 for the surface air temperature over land and HadSST3 for the surface temperature of the ocean (not marine air). It is believed that they use surface AIR temperature over the land as a proxy for the land skin temperature. They use surface OCEAN temperature directly without going through a proxy.
Why Do They Measure Surface Temperatures Only?
Quorvita believes that they measure surface temperatures so they can compare Earth’s surface temperature to other Planets where they only have estimated surface temperatures from space observations. In addition, they can compare it to black body temperatures. A black body assumes a perfect absorber, no atmosphere, non-rotating body, and thermal equilibrium. Quorvita believes that such is useful even though a black body is a theoretical situation that does not exist in nature because it is being used as a reference standard. Hence, there is a useful reason for selecting the surface temperature in the black body standard.
Is the use of Surface Air Temperature a good Proxy for Surface Land Temperature?
The average surface land temperature is affected by differing shapes, colors, compositions, biological activities etc., all which affect the temperature. Mutiibwa D. et al (2015) Land Surface Temperature and Surface Air Temperature in Complex Terrain, IEEE Journal, Vol 8, No. 10 pgs. 4762-4774]. Using a surface air temperature as a proxy for the land temperature is rough at best and far more variable than the actual land temperature. This is also true for changes in the temperature or anomaly. For example, the temperature measured a few inches down from the land surface has a very small temperature deviation over time. The reason that surface air temperatures are used is likely due to economics. Air temperature measurement stations have been around for hundreds of years and provide a means for historical comparisons. It is also economically cheaper to use existing stations rather than building millions of ground measurement stations. If air temperature measurements are to be used, then there should be a discount or comparison factor applied. That is, variations in surface air temperature should be compared to variations in actual land temperatures at the same location for a statistically significant number of places, altitudes, day-night, seasons, terrains, and weather conditions. Some studies show that air temperatures and land temperatures are strongly related at night but vary considerably with altitude as well as year, seasons, wind speeds, cloud cover, etc. [Kawashima S, et. al. (2000) Relations between Surface Temperature and Air Temperature on a Local Scale during Winter Nights, Journal of Applied Meteorology Vol 39, 1570-1578]. Mutiibwa D. et al (2015) cited above showed significant deviations with land-air temperature relationships depending upon the terrain. Standard deviations of 6.8°C for daytime measurements to -3.15°C for night time measurements, 4.85°C for winter measurements to 6.34°C for summer measurements were observed. These studies indicated that surface air temperatures are only rough proxies for land temperatures.
As such, a need exists for a statistically relevant comparison ratio study to support the use of surface air temperatures as a proxy for land temperatures and to determine what an appropriate discount or comparison factor would be. Without such a study renders the surface air temperature measurements as a very rough proxy for the surface land temperature. global temperature anomalies from 1850 to 2019 as approximately 0.79°C.
As such, the HadCRUT4 global temperature anomalies from 1850 to 2019 as being approximately 0.79°C is questionable with respect to the land temperature component.