by John McLean
Quadrant Online April 2, 2012
The recent climate report from the Bureau of Meteorology (BoM) and CSIRO was remarkable more for what it didn’t say than for what it did.
Like previous BoM-CSIRO climate reports it showed no evidence to support its assertions, encouraged a notion that correlation amounts to proof of cause and repeated the tired mantra of “multiple lines of evidence” without stating what these were.
This time it also failed to mention that greenhouse gas emissions have risen over the last ten years but average global temperatures have not, and that temperatures did rise during 1977-97 when emissions were lower.
Recent floods forced the report to acknowledge that the El Nino-Southern Oscillation system has a major influence on Australia’s weather but it’s curiously reluctant to fully discuss that impact.
Why was that I wonder when BoM and CSIRO scientists have written peer-reviewed papers on the subject and seemingly several web pages and documents for the BoM. The experts’ work not only describes that influence in detail but it shows good reason to attribute the findings in the climate report to the ENSO rather than human activity.
On the subject of sea level the report said:
Since 1993, the rates of sea-level rise to the north and northwest of Australia have been 7 to 11 mm per year, two to three times the global average, and rates of sea-level rise on the central east and southern coasts of the continent are mostly similar to the global average.
Almost as a footnote to the paragraph the report blandly stated
These variations are at least in part a result of natural variability of the climate system.
John Church, a CSIRO scientist, was lead author of a 2006 peer reviewed paper that tells us very clearly about this ‘natural variability’. The paper, written with two CRISO colleagues as co-authors, says:
The observed interannual sea-level variability is strongest at locations along the northwestern and western Australian coast. This variability is clearly related to El Nino–Southern Oscillation (ENSO) events … There are suggestions in both the Australian mean time-series and in a number of the individual records (e.g. Fremantle) that the rate of sea-level rise was at a minimum from the mid-1970s to the mid-1990s. This minimum occurs during the period of more frequent, persistent and intense ENSO events, as evidenced by the SOI since the mid-1970s.
The ‘natural variability’ therefore seems to be the ENSO, and the method by which the ENSO influences sea level to our north is easily explained.
Under “normal’ ENSO conditions easterly winds drive the top layer of water across the Pacific Ocean. Not only does the water warm by ten degrees or more while in transit but the western side of the Pacific can easily be a metre or two higher than the eastern side. La Nina conditions occur when the winds are even stronger and more water and heat are shifted to the west. Under El Nino conditions the winds weaken or even cease, which causes the pool of warm water to spread to the central Pacific and the ocean height to level out.
Under El Nino conditions the sea level to our north, northeast and north west will be lower than it is under La Nina conditions, but when that El Nino fades away the warm water moves back to the west. Depending on the time of the year, that warm pool might pass just north of Australia or strike the Great Barrier Reef, which incidentally is not mentioned in this latest climate report.
When the shift to La Nina is quite abrupt, as was the case in April 2010, the amount of warm water being pushed to the west and the heat in that water are considerable.
It’s no wonder that the climate report says about sea surface temperatures:
The warm sea-surface temperatures in 2010-11 were strongly influenced by La Niña. La Niña events are typically associated with warmer-than-average ocean temperatures in the Australian region.
But then it goes on to assert
Ocean temperatures around Australia were warmer during 2010-11 than for any previously identified La Niña event, likely due to the influence of the long-term warming trend of the past century.
Forget the last half of that sentence; it’s window dressing. The simple truths that the report failed to mention are that the 2010 La Nina was the strongest La Nina since 1917, lasted 10 months and came very abruptly after a sustained period when the Pacific Ocean was often in a semi-El Nino state. It’s no wonder at all that our surrounding oceans were warmer.
On the subject of rainfall the climate report says:
Australia’s rainfall is highly variable. During recent decades, there has been a general trend towards increased spring and summer monsoonal rainfall across Australia’s north, higher than normal rainfall across central parts of the continent, and decreased late autumn and winter rainfall across the south. … Recent drying trends across southern Australia in autumn and winter have been linked to circulation changes. The causes of these changes are an area of active research.
There’s no hint of the period of time used to determine those “recent drying trends” but a check of the BoM’s “Time series” graphs shows no particular decreasing trend in winter rainfall in southern Australia. There is however a slight autumn decrease that appears to be related to the state of the ENSO system, but it’s difficult to be sure because the data is skewed by a few years of very high rainfall, usually just after La Nina events.
Another document from the BoM’s website, says the greatest El Nino related decreases in rainfall are usually over inland eastern Australia; in some other regions, such as south-west Western Australia and coastal New South Wales, the effects of El Niño on rainfall are variable, and in western Tasmania the effects are generally weak.
A map accompanying this text shows that El Nino events typically cause reduced winter/spring rainfall most eastern Australia except the far north, which corresponds rather well to the numberless figure on page 5 of the climate report.
On the subject of land temperatures the climate report says Australia’s temperatures have risen since 1950, then goes on to say:
Australian annual-average daily maximum temperatures have increased by 0.75 °C since 1910, with most of the warming trend occurring since 1970. There has been an increase in the frequency of warm weather and decrease in the frequency of cold weather. … The number of climate reference stations recording warm (top ten per cent) night-time temperatures and the frequency with which this occurs have increased since the mid-1970s.
According to widely accepted knowledge of the ENSO and information from the BoM and CSIRO, these changes are easily explained.
La Nina conditions are typically cool and wet and with High and Low pressure cells that track slightly south across the Australian continent. In contrast, El Nino conditions are warmer and dryer and with pressure cells that track slightly north.
More cloud cover can be expected with La Nina conditions than with El Nino, and El Nino conditions will tend to drag warm air from central Australia towards the southern coastline. El Nino conditions might reduce but don’t prevent night-time cloud from forming, and if the ground surface is warm from bright sunshine and warm winds then the heat is easily trapped by nocturnal cloud and the night will be warmer than usual.
But surely this is known to Neville Nicholls, formerly of the BoM and author of numerous peer-reviewed papers on the impact of ENSO on Australia. Nicholls is by no means alone because several past and present employees have written papers on these subjects.
The two mentions of the 1970s in the discussion of land temperature, a mention of the same during the discussion of heat content of the oceans and another in the quote from Church et al draws attention to that time.
Atmospheric CO2 is known to have been increasing since 1959 and it’s physically impossible for the gas to have had no impact for over 15 years and then suddenly be activated.
A simpler and more plausible cause was the Great Pacific Climate Shift, the abrupt 1976 shift from La Nina dominated conditions to El Nino dominated conditions. The shift might not be mentioned on BoM web pages but it certainly is mentioned in IPCC Assessment Reports.
For all its talk on its web pages the BoM fails to tell us that the ENSO is not three distinct steps but a continuous range of states that span from La Nina at one end of the scale to El Nino at the other. We are also not told that the thresholds for declaring La Nina and El Nino events are arbitrary and by convention, and that conditions just short of a threshold are very similar to conditions just past the threshold. These facts are highly relevant when we look at ENSO history because the number of declared El Nino and La Nina events is not the complete story.
By drawing on the per-reviewed papers of BoM and CSIRO scientists, and the web pages of the BoM, we can put the climate report’s observations into the context of ENSO events. The recent sea level rise to our north and the rise in ocean temperatures are due to warm water flooding back to the region in 2010 when the Pacific changed from a multi-year period of semi-El Nino or very weak La Nina to a far stronger La Nina situation that repeated in 2011-12.
Further, according to documents from these two organisations the ENSO also can account for the change in rainfall patterns and the variations in minimum and maximum temperature.
With these simple explanations in mind we need to ask why these two organizations ignored their own experts and put the blame on greenhouse gases. Just what game are these two playing?