Anthropogenic ocean warming: A stress on ocean ecosystems David W. Pierce Tim P. Barnett Climate Research Division Scripps Institution of Oceanography La Jolla, CA

Why is ocean warming important? 1. That’s where most of the heat has gone 2. No urban heat island effect 3. Data is independent of surface land temperatures Levitus et al. 2004

Detection and Attribution framework Detection: –Has the ocean warmed more than you expect due to natural variability? Attribution: –Is the warming consistent with what you expect to see due to anthropogenic (human) effects? Natural variability a key factor

PDO effect on salmon

Globally averaged ocean temperatures [0-100m]

D&A successful on ocean temperatures Volume averaged ocean temperature change in the last 50 yrs is both: –Detectably different from what you expect due to natural variability –Consistent with what you expect due to anthropogenic influences Only sample the model where there has been an observation –Ocean very large, not especially well sampled, better in N. hemisphere, etc.

Vertical structure of warming (A climate model’s view of reality)

Warming preferentially at surface Increases stratification of water column Has an effect on vertical mixing of nutrients and how quickly column stratifies in spring

Nitrogen-Phytoplankton-Zooplankton model for North Pacific

Changes in Phytoplankton, 2050

Anthropogenic changes to salmon’s environment

Conclusions Ocean temperatures have warmed more than is expected due to natural variability -- detection The warming is consistent with what you expect to see due to anthropogenic forcing -- attribution Warming is stronger at surface, so increases stratification Expansion of “subtropical” type behavior, shrinking of “subpolar” type behavior; moving spring bloom regions “Land” changes affect salmon – change in timing of spring runoff and flow over time Note this is due to warming only. Changes due to net solar input and large-scale upwelling were small. Effect of increased deposition of aerosols was not examined.