Interpreting Climate Model Projections to Support Marine Ecosystem Applications: The Role of Natural Climate Variability

There are three main sources of uncertainty arising from using models to project climate change.  Two of these, model bias and future anthropogenic affects including the amount of CO₂ and other greenhouse gases are released into the climate system, are generally well appreciated.  A third source is the natural variability of the climate that occurs from intrinsic interactions between the atmosphere-ocean-sea ice and land. Recent study by Wittenberg (2009) and Deser et. (2010) found that the amount of intrinsic variability, even at very long time scales, can be surprisingly large.  Here we will use ensembles of climate model simulations to examine the spread among model states for climate parameters that are relevant for some marine ecosystems such as sea surface temperatures in the regions with corals in the tropical oceans and alongshore winds in the upwelling region along the west coast of the United States.  Our main tool is a set of 40 simulations extending from the year 2000 through 2060 using the A1B scenario  (a middle of the road use of fossil fuels with CO₂ increasing to  ~700 ppm by 2100).  The natural variability will be assessed by examining the spread among ensemble members. Implications for ecosystem applications will be discussed in light of the diversity of the model response.