Richard Courtney's comment - Sunsettommy - 04-13-2017
Quote:Willis Eschenbach :
In your every fine article at your link you say.
Quote:The “null hypothesis” in science is the condition that would result if what you are trying to establish is not true. For example, if your hypothesis is that air pressure affects plant growth rates, the null hypothesis is that air pressure has no effect on plant growth rates. Once you have both hypotheses, then you can see which hypothesis is supported by the evidence.
In climate science, the AGW hypothesis states that human GHG emissions significantly affect the climate. As such, the null hypothesis is that human GHG emissions do not significantly affect the climate, that the climate variations are the result of natural processes. This null hypothesis is what Doctor T wants to reverse.
Actually, the scientific null hypothesis is more general than you state although the reversal desired by Trenberth does amount to what you say.
The matter has some pertinence because it is never possible to obtain evidence that something (e.g. an affect on plant growth) does not exist: it is only possible to show that available methods fail to indicate that something exists.
In all science the Null Hypothesis says it must be assumed a system has not experienced a change unless there is evidence of a change.
The Null Hypothesis is a fundamental scientific principle and forms the basis of all scientific understanding, investigation and interpretation. Indeed, it is the basic principle of experimental procedure where an input to a system is altered to discern a change: if the system is not observed to respond to the alteration then it has to be assumed the system did not respond to the alteration.
In the case of climate science there is a hypothesis that increased greenhouse gases (GHGs, notably CO2) in the air will increase global temperature. There are good reasons to suppose this hypothesis may be true, but the Null Hypothesis says it must be assumed the GHG changes have no effect unless and until increased GHGs are observed to increase global temperature. That is what the scientific method decrees. It does not matter how certain some people may be that the hypothesis is right because observation of reality (i.e. empiricism) trumps all opinions.
Please note that the Null Hypothesis is a hypothesis which exists to be refuted by empirical observation. It is a rejection of the scientific method to assert that one can “choose” any subjective Null Hypothesis one likes. There is only one Null Hypothesis: i.e. it has to be assumed a system has not changed unless it is observed that the system has changed. Hence, Trenberth’s desire to reverse the Null Hypothesis is a rejection of the scientific method.
However, deciding a method which would discern a change may require a detailed statistical specification.
In the case of global climate in the Holocene, no recent climate behaviours are observed to be unprecedented so the Null Hypothesis decrees that the climate system has not changed: i.e. there is no reason to suppose that climate changes now happening have different cause(s) to those of similar climate changes in the past.
Importantly, an effect may be real but not overcome the Null Hypothesis because it is too trivial for the effect to be observable. Human activities have some effect on global temperature for several reasons. An example of an anthropogenic effect on global temperature is the urban heat island (UHI). Cities are warmer than the land around them, so cities cause some warming. But the temperature rise from cities is too small to be detected when averaged over the entire surface of the planet, although this global warming from cities can be estimated by measuring the warming of all cities and their areas.
Clearly, the Null Hypothesis decrees that UHI is not affecting global temperature although there are good reasons to think UHI has some effect. Similarly, it is very probable that AGW from GHG emissions are too trivial to have observable effects.
Empirical evidence indicates that net feedbacks in the climate system are negative and, therefore, any effect of increased CO2 will probably be too small to discern because natural climate variability is much, much larger. This concurs with the empirically determined values of low climate sensitivity.
Empirical – n.b. not model-derived – determinations indicate climate sensitivity is less than 1.0°C for a doubling of atmospheric CO2 equivalent. This is indicated by the studies of,
Idso from surface measurements
and Lindzen & Choi from ERBE satellite data
and Gregory from balloon radiosonde data
Indeed, because climate sensitivity is observed to be less than 1.0°C for a doubling of CO2 equivalent, it is physically impossible for the man-made global warming to be large enough to be detected (just as the global warming from UHI is too small to be detected). If something exists but is too small to be detected then it only has an abstract existence; it does not have a discernible existence that has effects (observation of the effects would be its detection).
To date there are no discernible effects of AGW. Hence, the Null Hypothesis decrees that AGW does not affect global climate to a discernible degree. That is the ONLY scientific conclusion possible at present.