Consensus Not: New paper finds 'no model consensus' on precipitation projections

A paper published today in the Journal of Geophysical Research illustrates the 'travesty' of relying on climate computer model projections, finding 19 different models had 'no model consensus' and a 'large spread' 'with both large positive and negative anomalies' in projections of future Australian tropical climate. Furthermore, the authors conclude that since model projections are all over the map, that indicates there is "large internal or natural variability in tropical Australian precipitation relative to the climate change signal" [of alleged AGW].

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, D10103, 16 PP., 2012
doi:10.1029/2011JD017365

Behind uncertainties in projections of Australian tropical climate: Analysis of 19 CMIP3 models

Key Points

• There is a large spread in model CMIP3 simulations of precipitation change
• Zonal winds changes indicate intensification of austral summer low level winds
• Regime-sorting techniques provide insight into uncertainty of precip projections

A. F. Moise

Centre for Australian Weather and Climate Research, Bureau of Meteorology, Melbourne, Victoria, Australia

R. A. Colman

Centre for Australian Weather and Climate Research, Bureau of Meteorology, Melbourne, Victoria, Australia

J. R. Brown

Centre for Australian Weather and Climate Research, Bureau of Meteorology, Melbourne, Victoria, Australia

A systematic study is undertaken for projected changes in tropical Australian climate in 19 CMIP3 Coupled Models for the A2 scenario over the 21st century. While equatorial regions to the north of Australia are projected to have increased precipitation during austral summer (December to February) by the end of the 21st century, there is no significant change over northern Australia based on the model ensemble mean. There is a large spread in model simulations of precipitation change, with both large positive and negative anomalies. The ensemble mean change in the seasonal cycle of precipitation over tropical Australia is small, with precipitation increase during March and April, suggesting a prolonged Australian wet season. There is no model consensus on how interannual variability of tropical Australian precipitation will change in future climate, although more models simulate increased variability than decreased. Correlations between full wet season (October to April) precipitation and austral spring (September to November) NINO3.4 sea surface temperature anomalies show a slight weakening. The spread in projected precipitation seasonal cycle changes between simulations from the same model is larger than the inter-model range, indicating that there is large internal or natural variability in tropical Australian precipitation relative to the climate change signal. Zonal wind changes indicate an intensification of austral summer low level westerlies although combined with a weakening of upper easterlies. Low level westerlies also persist for longer, consistent with a delay in the monsoon retreat. All models simulate an increase in the land-ocean temperature contrast in austral summer, with a significant correlation between changes in land-ocean temperature contrast in the pre-monsoon (austral spring) and summer precipitation changes. Analysis of precipitation changes using regime-sorting techniques shows offsetting tendencies from thermodynamic changes associated with enhanced atmospheric moisture and dynamic changes associated with a weakened atmospheric circulation.