Quirin Schiermeier quotes me with "You need to be very circumspect about the added value of downscaling to regional impacts," agrees Hans von Storch in this week's issue of nature. And: he cautions, "planners should handle them with kid gloves. Whenever possible, they'd rather wait with spending big money on adaptation projects until there is more certainty about the things to come." I have not spoken with Mr Schiermeier about regional modelling, at least not recently; the term "kid gloves" is unknown to me, not part of my vocabulary. I have asked him for evidence that I have said these sentences to whom.
Indeed, I have been in contact with Quirin Schiermeier earlier this year, asking for "myths" about climate change. I have offered him three cases, none of them had any reference to regional modelling. He had told me that he would use the first of my myths, but obviously he decided to use my name differently.
Here are my three myths:
Myth #1: "Climate models provide decision makers with predictions."
Here, "predictions" are understood as "probable developments", or even "most probable developments". However, the descriptions provided by climate models depend on a number of critical assumptions, first of all the amount of greenhouse gases emitted, or accumulated in the atmosphere. Thus they are conditional predictions – conditional upon social and economic developments. Most of these developments can not be predicted themselves but are described by "scenarios", so that the depictions of future climate itself are "scenarios", or is it often called, "projections".(Climate projections are distinguished from climate predictions in order to emphasize that climate projections depend upon the emission/concentration/radiative forcing scenario used, which are based on assumptions concerning, for example, future socioeconomic and technological developments that may or may not be realized. (see Baede, A. P. M. (Ed.) (n.d.). IPCC Annex I: Glossary. Retrieved February 9, 2009, from http://www.ipcc.ch/pdf/glossary/ar4-wg1.pdf)
If all scenarios point to the same change, e.g., warming, this results in an unconditional prediction. Thus, a warming and a rise in sea level is predicted, but the rate of warming or sea level are given as scenarios i.e., possible developments.
Unfortunately, according to a survey (Bray, D., and H. von Storch, 2009: 'Prediction' or 'Projection'? The nomenclature of climate science. Sci. Comm. 30, 534-543, doi:10.1177/1075547009333698), about 20% of scientists use the term "predictions" when speaking about "possible developments" (i.e., scenarios). 70% use it consistent with the IPCC terminology.
Myth #2: "In the course of man-made climate change, all extremes become worse."
Here, "become worse" means "happen more often" and/or "get more intense". The statement is false: only some extremes will become "worse", while others will become rarer or less intense. An example of the first relates to heat waves, which in the course of warming will become more frequent and more intensely. An example of the latter is cold periods, which become less frequent and less intense.
A popular argument is that mid-latitude wind storms must become "worse" because of elevated water vapour levels in the atmosphere. However, other effects influence the formation of storms such as vertical stability or horizontal temperature gradients, so that the European recovery from the little ice-age, which was associated with a warming, was not associated with a detectable intensification of storm activity in Northern Europe.
Thus, some extremes will get "worse", while others they may become "better". Sometimes, the change will vary regionally.
Myth #3: "All changes of climatic conditions are related to human causes".
This claim is usually not voiced explicitly, but implicit in numerous hints that certain events must be understood as "abnormal" and "consistent with" or even "due to man-made climate change". However, changes can be due to various causes, from natural variability, to changes in local conditions (e.g., urbanization), to changes in observational practices incl. instrumentation.
Before attributing a change to global climate change, a "detection and attribution study" is needed. Such a study determines first how unusual the change is compared to the statistics of changes under undisturbed conditions. If so, then the different possible causes are screened which provides the most consistent explanation. This is usually only possible if the developments has been homogeneously be documented by observations for several decades.