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.