Emergence of Anthropogenic Trends in California Current Upwelling in the Presence of Natural Climate Variability

Presented at the 2016 CESM Workshop in Breckenridge, CO.

Transcript

1. Emergence of Anthropogenic Trends in California Current Upwelling in the Presence of Natural Climate Variability Riley X. Brady University of Colorado at Boulder Coauthors: Ryan Rykaczewski (U. South Carolina) Michael Alexander (NOAA ESRL) CESM Workshop June 23rd, 2016 Breckenridge, CO
2. A mechanism exists whereby global greenhouse warming could . . . lead to acceleration of coastal upwelling. (Bakun, 1990) Source: Rykaczewski & Checkley 2008 Ÿ Upwelling Ÿ Large Ensemble Ÿ Regions Ÿ Historical Upwelling Ÿ SNR Ÿ Deltas Ÿ Natural Variability Ÿ Summary Ÿ “. . . we still cannot attribute coastal wind intensification in EBUS to global warming because we cannot discount the role of multi-decadal climate variability in the observed trends.” Garcia-Reyes, et al. 2015 “Summertime winds near poleward boundaries of climatological upwelling zones are projected to intensify, while winds near equatorward boundaries are projected to weaken." Rykaczewski, et al. 2015
3. By holding the model and emissions scenario constant, we can attribute disparities entirely to internally-generated climate variability. Modified from Kay et al. 2015 1850 Control Member 1 Observations Members 2-35 Generated ensemble with 10-14K air temperature differences Forced with RCP8.5 emissions scenario Ÿ Upwelling Ÿ Large Ensemble Ÿ Regions Ÿ Historical Upwelling Ÿ SNR Ÿ Deltas Ÿ Natural Variability Ÿ Summary Ÿ
4. The California Current was split into three distinct regions based on coastal geography. Ÿ Upwelling Ÿ Large Ensemble Ÿ Regions Ÿ Historical Upwelling Ÿ SNR Ÿ Deltas Ÿ Natural Variability Ÿ Summary Ÿ North Central South
5. These regions display distinct seasonal cycles in both vertical velocity and alongshore wind stress. Ÿ Upwelling Ÿ Large Ensemble Ÿ Regions Ÿ Historical Upwelling Ÿ SNR Ÿ Deltas Ÿ Natural Variability Ÿ Summary Ÿ Vertical Velocity at 50m Depth (cm/s x 10-3) Area-Weighted Alongshore Wind Stress (dyne/cm2) North Central South Ensemble Historical Coastal Upwelling (1920 – 2005) Ensemble Historical Alongshore Wind Stress (1920 – 2005) Model Data Observational Data
6. Coastal Grid-Cell A Signal-to-Noise Ratio quantifies the relative strength of anthropogenic climate change. Signal (S) = ∆ Noise (N) = ∆ N = 35 1∘ 1∘ ∆$ %∆& ≡ ( ) > is considered a significant emergence of the signal. Ÿ Upwelling Ÿ Large Ensemble Ÿ Regions Ÿ Historical Upwelling Ÿ SNR Ÿ Deltas Ÿ Natural Variability Ÿ Summary Ÿ
7. Long-term changes in upwelling and wind stress vary by season and location. Ÿ Upwelling Ÿ Large Ensemble Ÿ Regions Ÿ Historical Upwelling Ÿ SNR Ÿ Deltas Ÿ Natural Variability Ÿ Summary Ÿ Forced Change in Alongshore Wind Stress (dyne/cm2) Forced Change in Vertical Velocity (cm/s x 10-3) RCP 8.5 (2041-2100 – 1941-2000) SNR >= 1 SNR >= 2
8. Ÿ Upwelling Ÿ Large Ensemble Ÿ Regions Ÿ Historical Upwelling Ÿ SNR Ÿ Deltas Ÿ Natural Variability Ÿ Summary Ÿ Change in Vertical Velocity (cm/s x 10-3) July Total Change in Vertical Velocity (2041-2100 – 1941-2000)
9. Ÿ Upwelling Ÿ Large Ensemble Ÿ Regions Ÿ Historical Upwelling Ÿ SNR Ÿ Deltas Ÿ Natural Variability Ÿ Summary Ÿ Change in Vertical Velocity (cm/s x 10-3) Ensemble Mean (Forced Signal) July Total Change in Vertical Velocity (2041-2100 – 1941-2000)
10. Ÿ Upwelling Ÿ Large Ensemble Ÿ Regions Ÿ Historical Upwelling Ÿ SNR Ÿ Deltas Ÿ Natural Variability Ÿ Summary Ÿ Change in Vertical Velocity (cm/s x 10-3) July Natural Component of Change in Vertical Velocity (2041-2100 – 1941-2000)
11. Ÿ Upwelling Ÿ Large Ensemble Ÿ Regions Ÿ Historical Upwelling Ÿ SNR Ÿ Deltas Ÿ Natural Variability Ÿ Summary Ÿ Run 5 Run 23 Total Natural Forced Change in Vertical Velocity (cm/s x 10-3)
12. Summary Spring intensification and summer weakening could be driven by different mechanisms. The sign of change in upwelling may vary meridionally and intra- annually. Natural variability can largely impact the magnitude of change in California Current Upwelling. Ÿ Upwelling Ÿ Large Ensemble Ÿ Regions Ÿ Historical Upwelling Ÿ SNR Ÿ Deltas Ÿ Natural Variability Ÿ Summary Ÿ