By JR on Saturday, July 02, 2011
Could the findings of Zhang et al. mean that the projections of "almost all state-of-the-art climate models" are just plain wrong? They sure could...
Discussing: Zhang, D., Msadek, R., McPhaden, M.J. and Delworth, T. 2011. "Multidecadal variability of the North Brazil Current and its connection to the Atlantic meridional overturning circulation". Journal of Geophysical Research 116: 10.1029/2010JC006812.
Writing as background for their study, Zhang et al. (2011) report that "almost all state-of-the-art climate models project significant slowdown of the AMOC [Atlantic Meridional Overturning Circulation] during this century in response to the increased greenhouse gas concentrations in the atmosphere," citing the studies of Schmittner et al. (2005), Meehl et al. (2007) and Hu et al. (2009). And because the North Brazil Current (NBC) is, as they say, "primarily responsible for the AMOC upper branch return flow which crosses the tropical Atlantic (e.g., Hazeleger and Drijfhout, 2006)," they examined this projection via a new study of the NBC.
Working with historical hydrographic data they obtained from NOAA's World Ocean Database, Zhang et al. calculated the NBC geostrophic transport time series based on five decades of observations made off the coast of Brazil, while they also assessed the suggested connection between the NBC and AMOC via "a 700-year control simulation of the Geophysical Fluid Dynamics Laboratory's CM2.1 coupled climate model."
As a result of their analyses, the four researchers determined that the AMOC's "anticipated slowdown," as they describe it, "has not occurred yet, even though global temperatures have been significantly higher since the 1970s." They note, for example, that "while the AMOC might have been weakened from the 1960s to the early 1970s, it has been strengthening since then to the end of the last century," and they write that "analyses of subsurface temperature and salinity anomalies in the subtropical and subpolar north Atlantic (Zhang, 2008; Wang et al., 2010) also suggest a strengthening of the AMOC from the 1970s to 1990s." In addition, they report that their CM2.1 model results are also "in agreement with observations."
Could the findings of Zhang et al. mean that the projections of "almost all state-of-the-art climate models" are just plain wrong? They sure could, for real-world observations always win out over theoretical projections if they differ; and so far, at least, that's what the observations are doing -- they're winning.