The simple and obvious way to measure global warming is to look at results from weather stations. Unfortunately results from weather stations are subject to large systematic errors: Weather stations are generally located in or near cities, and near human habitation. Cities are typically several degrees warmer than the surrounding countryside, and have been expanding.
Steve McIntyre has been examining how weather stations have been used to construct an estimate of global climate change. The examination suggests that estimates based on weather stations are unlikely to be accurate. Data has been arbitrarily include or excluded, locations have been arbitrarily classified as rural or urban, and the “adjustment” for the urban heat island effect seems likely to increase, rather than reduce the error caused by the urban heat island effect. Overall, the adjustment has resulted in an adjustment up over time rather than down over time, which would imply the absurd conclusion that weather stations are getting less urbanized.
One measure that could be very accurate is satellite measurement, for one then has a single instrument measuring the entire earth, and that instrument measures temperatures directly, and can be checked for reliability.
The satellite directly measures temperature against an absolute standard. One potentially area for creative accounting comes in the averaging to get global warming. One suspects a too clever by half averaging, similar to the too clever by half adjustment of urban sites that Steve McIntyre exposed.
The satellite directly measures the temperature of *something*, but that something is not the atmosphere at a particular height. To derive the temperature at a particular height is model dependent, depends on quantities that are not readily observable. The model can be rather too easily adjusted to give whatever results are desired. Perhaps, if we are only interested in the global anomaly, we can dispense with the model, and just look at the temperature of those wavelengths that have decent penetration to the lower atmosphere, telling us that *something* mighty big has warmed, or failed to warm, even if there is some uncertainty as to what the something we are looking at is.
To allay this suspicion, that the calculations are cooked to get a politically acceptable result, we really should have access to the raw data, and the algorithm by which it averaged.
Seems to me that if we simply took the average observed temperature at wavelengths with good penetration, that would be a good measure of global warming or cooling, and would not be vulnerable to suspicion of too clever by half corrections and adjustments.
Further, if such a simple uncomplicated average gave a result that was discordant with the adjusted data, then we could demand a plausible physical explanation of the difference.
For a long time, the advocates of anthropogenic global warming failed to explain how they derived global climate from weather station data. When this was finally revealed, it failed audit. The method was not plausible, nor were the advocates faithfully employing the method they purported to follow, but rather were arbitrarily including some data and excluding other data.
We therefore need to know how satellite temperature is used to derive global climate, and need to get access to the direct instrumental readings of temperature, in order that these also can be audited.
The satellite directly measures temperature at certain frequencies against an absolute standard. What is the simple average of the direct measurement over time at each frequency? We should be able to know.
If one wants to know the temperature at a particular location, then it is important to take account of the details of the satellite’s orbit, since it moves mighty fast, and things can potentially get complicated. If we want to know the temperature at a particular altitude, the atmosphere is not entirely transparent to heat, and we need to model the atmosphere, which we do not know how to do all that precisely. These adjustments are likely to complex and open to debate. But if one wants to know the variation in global temperature, we don’t really care about this stuff, and the raw temperature measurements should do fine.