Detectability of changes in the walker circulation in response to global warming

Pedro N. DiNezio, Gabriel A. Vecchi, Amy C. Clement

Research output: Contribution to journalArticlepeer-review

48 Scopus citations

Abstract

Changes in the gradients in sea level pressure (SLP) and sea surface temperature (SST) along the equatorial Pacific are analyzed in observations and 101 numerical experiments performed with 37 climate models participating in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). The ensemble of numerical experiments simulates changes in the earth's climate during the 2004-1870 period in response to changes in natural (solar variations and volcanoes) and anthropogenic (well-mixed greenhouse gases, ozone, direct aerosol forcing, and land use) radiative forcings. A reduction in the zonal SLP gradient is present in observational records and is the typical response of the ensemble, yet only 26 out of the 101 experiments exhibit a reduced SLP gradient within 95% statistical confidence of the observed value. The multimodel response indicates a reduction of the Walker circulation to historical forcings, albeit an order of magnitude smaller than the observed value. There are multiple nonexclusive interpretations of these results: (i) the observed trend may not be entirely forced and includes a substantial component from internal variability; (ii) there are problems with the observational record that lead to a spuriously large trend; and (iii) the strength of theWalker circulation, as measured by the zonal SLP gradient, may be less sensitive to external forcing in models than in the real climate system. Analysis of a subset of experiments suggests that greenhouse gases act to weaken the circulation, but aerosol forcing drives a strengthening of the circulation, which appears to be overestimated by the models, resulting in a muted response to the combined anthropogenic forcings.

Original languageEnglish (US)
Pages (from-to)4038-4048
Number of pages11
JournalJournal of Climate
Volume26
Issue number12
DOIs
StatePublished - Jun 2013

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Keywords

  • Atmospheric circulation
  • Climate change
  • Coupled models
  • Model comparison
  • Radiative forcing
  • Southern Oscillation

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