There is exchange of viewpoints by Demetris Koutsoyiannis and colleagues and by Kundzewicz and colleagues. It is
Koutsoyiannis, D., A. Montanari, H. F. Lins, and T. A. Cohn 2009: Climate, hydrology and freshwater: towards an interactive incorporation of hydrological experience into climate research: DISCUSSION of “The implications of projected climate change for freshwater resources and their management”, 54(2), 394-405, doi: 10.1623/hysj.54.2.394
Their concluding remarks read
“Climate is, unquestionably, an intrinsic part of human activities, biological and environmental functioning, and natural processes. It is well understood that climate is highly dynamic, and that the perception of a static climate has always been, in fact, a misperception. Importantly, the mechanisms driving the changes in climate are poorly understood and possibly beyond our ability to model adequately. Even if they can be adequately modelled, predictability is not a foregone conclusion. A more moderate target would be to model the uncertainty of future climate, which must necessarily be very wide. This target is pragmatic and calls for the recognition of the structural character of uncertainty in climatic research. Within this perspective, the hydrological community could play a more proactive role; one that differs significantly from the current role that essentially consists of taking GCM model outputs and trying to extrapolate their consequences on hydrological processes and into the subsequent state of water resources. The study of the regulating role of water and hydrological processes in climate, the recognition of the structural character of uncertainty, the understanding and modelling of the long-term variability of climatic processes in a stochastic context, with particular emphasis on the Hurst-Kolmogorov dynamics and the behaviour of extremes, are all important topics on which the hydrological community has broad experience and could further contribute in an interactive manner with the climatological community. The search for the real causes of extant water problems is another area of needed interaction, particularly to ensure that water resources planning and management professionals maintain their primary focus on the more influential factors affecting the availability of water.”
A response to the Koutsoyiannis et al 2009 paper is given in
Kundzewicz, Z. W., L. J. Mata, N. W. Arnell, P. Döll, B. Jimenez, K. Miller, T. Oki and Z. Şen, 2009: REPLY to discussion “Climate, hydrology and freshwater: towards an interactive incorporation of hydrological experience into climate research”, 54(2), 406-415, doi: 10.1623/hysj.54.2.406
Their concluding remarks read
“Koutsoyiannis et al. (2009) claim that climate is not changing due to human activities (climate is “naturally trendy”: Cohn & Lins, 2005), and that climate models do not provide a credible basis for assessing possible future impacts. The first assertion is not supported by the evidence (as thoroughly reviewed by the IPCC (Hegerl et al., 2007b), and we have demonstrated here that the second claim is also false. Climate models are not used to make predictions, but are used to make plausible projections of possible future change. The challenge for water management is to use this information on possible futures to help make adaptation decisions.
Koutsoyiannis et al. (2009) imply that the climate system is unpredictable, and so one should not waste time on hopeless projections. However, instead of accepting this stance and giving up the very idea of predictability, one can be more constructive and look into every major change in the observed time series of global temperature and try to explain it, trying to strengthen the interpretation of the deterministic behaviour of the time series of climate variables. We will never know the future of climate because human behaviour, and therefore greenhouse gas emissions, cannot be predicted. Nevertheless, scenarios of the future which present plausible futures of climate are necessary for supporting present-day decisions with respect to mitigation of and adaptation to climate change, e.g. in the water sector.
Water resources practitioners are used to dealing with the variability of water quantity and quality parameters, and they design reservoirs, irrigation schemes, water quality control structures and operating policies with uncertainty in mind. Researchers know how to predict the variability of the quantity and quality of water resources with models that use temperature and precipitation data as basic inputs. Their first challenge is to provide practitioners with quick-and-dirty estimates of an uncertainty increase due to climate change, based on the pragmatic use of available information and models. The second challenge is to improve the models. Dialogue is taking place between climate and water scientists, and between practitioners and researchers, and should be enhanced, in order to agree on priorities: firstly with respect to determining practical design parameters with available models and information; and secondly with respect to research for improving system understanding and model performance.”
Climate Science needs more such published debates and both sets of authors should be recognized for participating. Readers of the Climate Science weblog are urged to read both contributions in order to see that there is a wider diversity of perspectives in the study of climate and its consequences than is commonly assumed.