The “State of the Climate” report from two of Australia’s lead agencies, the Bureau of Meteorology (BoM) and CSIRO, states that total rainfall has been “relatively stable” last century, but omitted their own data that clearly shows total rainfall increasing.
The fine print at the bottom of BoM graph says rainfall has increased at the “relatively stable” rate of 6.3mm per decade. On downloading the data and fitting a linear regression, the upwards slope is significantly greater than zero as follows.
Slope=0.63 S.E.=0.23 P=0.003
When autocorrelation is taken into account the values are
Slope=0.63 S.E.=0.29 P=0.014
The Chow break-test shows a significant break in 1971-72, when annual rainfall increased by 60mm. This is a 13% increase in “relatively stable” rainfall (from 432±9mm to 492±15mm per annum).
How many ways this BoM statement not match observations?
A slight increase in Australian annual mean rainfall is evident during the 20th Century although this is largely due to several wet years during the 1970s. The five year mean rainfall also shows a weak upward trend. However, the high year-to-year variability of Australian rainfall dominates any background trends.
How Much More Rain Will Global Warming Bring? This is the question asked by Frank J. Wentz. The fundamental physical relation of evaporation and temperature called the Clausius-Clapeyron relation suggests a 6% increase in evaporation per K of temperature increase, also by Wentz’s analysis. If the ocean is not to migrate into the sky, evaporation has to equal precipitation globally (although not locally) and also increase by a “relatively stable” 6% globally.
But Wentz found the climate simulation models predict an “absolutely stable” increase in precipitation of only 1-3%, although a comment on the paper says the precipitation across all models is “relatively unstable” anyway, and so can’t really be trusted.
CSIRO and BoM experts, computer simulation models, the laws of physics, and observational data — two of these belong together, two of these don’t. Can you guess which ones?