Three Ways to Measure Global Temperatures
The primary ways to monitor global average air temperatures are surface based thermometers (since the late 1800s), radiosondes (weather balloons, since about the 1950s), and satellites measuring microwave emissions (since 1979). Other technologies, such as GPS satellite based methods have limited record length and have not yet gained wide acceptance for accuracy.
Temperatures of the deep ocean, which I will not address in detail, have warmed by amounts so small — hundredths of a degree — that it is debatable whether they are accurate enough to be of much use. Sea surface temperatures, also indicating modest warming in recent decades, involve an entirely new set of problems, with rather sparse sampling by a mixture of bucket temperatures from many years ago, to newer ship engine intake temperatures, buoys, and since the early 1980s infrared satellite measurements.
Since 1979, it is generally accepted that the satellites and radiosondes measure 50% less of a warming trend than the surface thermometer data do, rather than 30-50% greater warming trend that theory predicts for warming aloft versus at the surface.
This is a substantial disagreement.
Why the Disagreement?
There are different possibilities for the disagreement:
1) Surface thermometer analyses are spuriously overestimating the true temperature trend
2) Satellites and radiosondes are spuriously underestimating the true temperature trend
3) All data are largely correct, and are telling us something new about how the climate system operates under long-term warming.
The satellites have the advantage of measuring virtually the whole Earth every day with the same instruments, which are then checked against each other. But since there are very small differences between the instruments, which can change slightly over time, adjustments must be made.
Thermometers have the advantage of being much greater in number, but with potentially large long-term spurious warming effects depending on how each thermometer’s local environment has changed with the addition of manmade objects and structures.
Virtually all thermometer measurements require adjustments of some sort, simply because with the exception of a few thermometer sites, there has not been a single, unaltered instrument measuring the same place for 30+ years without a change in its environment. When such rare thermometers were identified in a recent study of the U.S., it was found that by comparison the official U.S. warming trends were exaggerated by close to 60%. Thus, the current official NOAA adjustment procedures appear to force the good data to match the bad data, rather than the other way around. Whether such problem exist with other countries data remains to be seen.
The fact that the satellites and radiosondes – two very different types of measurement system — tend to agree with each other gives us somewhat more confidence in their result that warming has been much less than predicted by climate models. But even the thermometers indicate less warming than the models, just with less of a discrepancy.
And this is probably the most important issue…that no matter which temperature monitoring method we use, the climate models that global warming policies are based upon have been, on average, warming faster than all of our temperature observation systems.
I do believe “global warming” has occurred, but (1) it is weaker than expected, based upon independent satellite and weather balloon measurements; (2) it has been overestimated with poorly adjusted surface-based thermometers; (3) it has a substantial natural component; and (4) it is likely to be more beneficial to life on Earth than harmful.
– See more at: http://www.cfact.org/2016/01/26/measuring-global-temperatures-satellites-or-thermometers/?utm_source=CFACT%20Updates&utm_campaign=88ac25048b-Satellites_or_thermometers_1_26_2016&utm_medium=email&utm_term=0_a28eaedb56-88ac25048b-269738545#sthash.h8tb6mlr.dpuf