Report of the Workshop on Cod and Future Climate Change (WKCFCC)
The Workshop on Cod and Future Climate Change (WKCFCC) was held on 17–20 June 2008 in Copenhagen, Denmark, at the ICES headquarters. It was sponsored by the ICES/GLOBEC Working Group on Cod and Climate Change (WGCCC) with objectives to develop scenarios for cod over the next 20–50 years given anthropogenic climate change. The idea was to take regional future climate scenarios over this same time period and using the knowledge gained by the WGCCC and other researchers on the impact of climate on cod to develop future scenarios for cod, taking into account not only the direct effects on cod but also consider the possible influence on cod of climate effects on their prey (including zooplankton), predators and competitors.
The workshop was informed of the problems with developing regional models downscaled from Global Circulation Models (GCMs). The few such models that do exist have usually not used the most recent IPCC model runs (2007) but rather are based on earlier IPCC GCMs. One regional model for the North Sea that was down‐scaled from a recent IPCC model found the GCM chosen was not doing an adequate job of reproducing the present climate for the region and thus the future scenarios are highly suspect. The conclusion of that study was that one should develop regional models by downscaling from several GCMs and that these should be chosen based on their ability to reproduce the current climate. However, many of the IPCC 2007 model results for the current climate also demonstrate large differences with observations especially on a regional basis. Also the GCMs are respectively not able to repro‐duce or not reproduced well the two major modes of variability over the last century respectively, the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO). Thus, the conclusion of the workshop is that the available global and regional climate models are not currently adequate for impact studies on the ma‐rine ecosystem. Without the development of regional climate model systems and the development of adequate downscaling strategies it was not possible to go on to im‐plement coupled biological models of lower trophic level dynamics and its consequences for cod population for the next 20–50 years. A considerable scientific effort will be required to design, initialize, run and test regional models which produce output that is relevant to impact studies. Until this is done the impact assessments will have to be based on “what if” scenarios. On an encouraging note, however, models that assimilate recent climate data (and include the decadal modes) demon‐strate useful forecasting skill, at least over periods of a few years.
Several “what if” scenarios were presented at the Workshop. Baltic Sea studies using statistical (multivariate autoregressive) models to assess the possible effects of cod under plausible climate scenarios have been carried out. These studies have also combined climate changes with different fishing mortality rates to explore the combined role of management and climate on cod. Results suggest that given even a rela‐tively weak decrease in salinity (>3 psu), which would impair recruitment of Baltic cod through increased egg and larvae mortality, only a drastic decrease in fishing mortality could avoid future stock collapses and ensure the existence of Baltic cod for future generations to come. Such models combining the effects of fishing and climate to determine the impacts on cod and other species are encouraging. The results of a non‐spatial model that includes temperature, zooplankton, prey and predators sug‐gest raising the temperature in the Barents Sea by 1–4°C will lead to increased cod growth, increase cod production and decrease maturation rates. On the other hand, cod cannibalism is expected to increase as well. In another study exploring the general effect of temperature on cod stocks, it was found that a 30% reduction in the car‐rying capacity of warm water stocks is expected with a 3°C rise in temperature. Other likely impacts on cod under future warming scenarios include a general northward shift in distribution, an increase in growth, and an increase in production in northern regions and a decline in southern regions. Fishing pressure will play an important role in determining the rates of change of the cod populations. On the other hand, fisheries management must evaluate the climate effects and models have and are con‐tinuing to being developed that allow such combined effects of climate and fishing to be addressed.
Future work should include: in the immediate future to extend the “what if” studies to develop future cod scenarios; in the longer term encourage improvements in GCMs, especially through conveying to the modellers what the needs of the impacts community are; develop regional models of future climate in those areas inhabited by cod using downscaling of results from several GCMs that are able to reasonably represent local present climate conditions; use the results of such models to force re‐gional biophysical models to develop scenarios of phytoplankton and zooplankton under future climate; apply the results of both the ocean climate and lower trophic impacts to effects on cod; to develop models that include the higher trophic levels, especially cod; and to explore the combined effects of climate and fishing in order to determine better management strategies under climate change.
Published under the auspices of the following ICES Steering Group or Committee
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