The Trenberth article contains so many glaring errors and biased assumptions, it’s hard to know where to start.
First of all, the difference between theory and hypothesis:
The problem is not with dueling hypotheses, it is with dueling theories regarding the processes resulting in observed global warming. One theory states: Observed global warming is the result of human greenhouse gas emissions. Another theory states: Observed global warming is not caused by human greenhouse gas emissions, but is a result of natural geophysical processes.
The statement, “Global warming is the result of human greenhouse gas emissions” is not an hypothesis, it is a proposition, or at best, a simple theory. A theory is an explanation of process based on a body of observation.
Hypotheses, on the other hand, are predictive “if…then” statements used to test a small subset of a theory as an adequate explanation of observations, thus either strengthening or weakening the theory. The results of an individual hypothesis never disprove a theory. A theory can only be weakened and eventually replaced by the accumulation of a body of evidence that contradicts the theories explanation of observations, and the formulation of a new theory that provides a more adequate explanation.
We can test the theory of anthropogenic global warming with the hypothesis: If observed global warming is caused by human greenhouse gas emissions, then we should find a positive correlation between the amount and rate of greenhouse gas production and global average temperature rise. This is weak test of the theory, since, if we find such a positive correlation, we merely confirm the existing theory. No new information is gained. If we fail to find the positive causal correlation, it may be because we just have not looked hard enough yet, or haven’t looked in the right places. The truth is still out there!
The null hypothesis would be stated as: If observed global warming is caused by human greenhouse gas emissions, then we should not find a negative correlation between the amount and rate of greenhouse gas production and global average temperature rise. This is a much stronger test of the hypothesis, since it only takes one instance of negative correlation to negate the hypothesis and weaken the theory as an explanation of observations.
This is the process of Science, the Hypothetico-deductive Method of Theory Confirmation.
Secondly, Trenberth repeatedly fails to make a distinction between Global Warming and Anthropogenic Global Warming. There is no question that the average global surface temperature of the Earth has been increasing steadily over the past 20,000 years or so, else, we would still be skirting glaciers on our daily commute. The question is: What is the contribution of anthropogenic greenhouse gases to this warming, and, what effect will reduction of anthropogenic greenhouse gases have on this on-going global warming, if any?
Since we do not yet fully understand the natural geophysical processes that result in observed climate variations over geologic time periods, it is very difficult, if not impossible, for us to fully understand the contribution to global climate variation resulting from anthropogenic greenhouse gases. Wild predictions of future catastrophic weather events are simply science fiction prognostications with as much scientific validity as a Star Wars movie.
The periodic reports by the IPCC are not scientific documents, they are produced to give policy-makers estimations of the relevant probabilities of various climate scenarios, as an aid in preparation of national and international policies dealing with climate variation. These statements of probability have been inflated by the world press and by politicians anxious to make a name (and fortune) for themselves. Probability has been turned on its head into certainty and is being used by all manner of organizations and individuals to forward their individual agendae. Hyperinflated scare stories of sea level rise, catastrophic flooding, heat waves and droughts have been used to justify continued human growth and development in the face of dwindling natural resources and increasing air, water and soil pollution, all in the name of environmental justice.
At some point, increasing evidence of negative correlations between global average atmospheric CO2 concentrations and global average surface temperature will falsify the null hypothesis and greatly reduce the adequacy of the anthropogenic global warming theory as an explanation of observed global average surface temperature increase. Environmental organizations, politicians and science policy organizations will find they’ve hitched their wagons to a black hole. Their unceasing drum-beat for Anthropogenic Global Warming will ultimately discredit their otherwise worthwhile and necessary programs to reduce human pollution as a result of unrestricted human population and economic growth.