Anthropogenic ocean warming:Anthropogenic ocean warming:

A stress on ocean ecosystemsA stress on ocean ecosystems

David W. PierceDavid W. PierceTim P. BarnettTim P. Barnett

Climate Research DivisionClimate Research DivisionScripps Institution of OceanographyScripps Institution of Oceanography

La Jolla, CALa 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]

Globally averaged ocean temperatures [0-100m]

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.