Jennifer Marohasy

a forum for the discussion of issues concerning the natural environment

Archives for October 2008

How Melbourne’s Climate Has Changed: A reply to Dr David Jones (Part 5)

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Dr David Jones, the head of climate analysis at the Australian Bureau of Meteorology, in an opinion piece, ‘Our hot, dry future’ has argued that over the past 11 years Melbourne’s rainfall has been about 20% below the long-term average   experienced declining rainfall over the past 11 years . 

In response, Dr Jennifer Marohasy posted ‘How Melbourne’s Climate Has Changed: A reply to Dr David Jones (Part 3)’, which included a graph of high quality data of rainfall at Yan Yean, Victoria, because of its proximity to Melbourne. 

The graph is from Mr Warwick Hughes based on Bureau of Meteorology data and shows that recent rainfall decline at Yan Yean is comparable to declines during previous droughts.

I have also graphed Bureau data for some of Melbourne’s catchment areas.  While I couldn’t find a site with data extending back as far as the Yan Yean site, the Maroondah and O’Shanneyssy stations show a significant recent decline in rainfall that is greater than previous droughts in the 1896, 1925 and 1945.

Some of the Melbourne catchment areas rainfall data shows recent significant decline, but there are a number of problems with using bureau rainfall data for the Melbourne catchment.  A main problem is that the Bureau does not have rainfall data for Melbourne’s largest reservoirs, Upper Yarra and Thomson back more than 30 years.

The best publicly available data on catchment area rainfall comes from Melbourne Water. However, Melbourne Water’s publicly available data is only from 1998 to 2008.

Without long-term high quality data of catchment area rainfall for all catchment areas, it is impossible to know whether the longer-term trend shows dramatic declines at many, or just some, places in the Melbourne catchment. 

Nichole Hoskin
Blue Mountains, Australia

How Melbourne’s Climate Has Changed: A reply to Dr David Jones (Part 4)

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Dr David Jones, Head of Climate Analysis at the Australian Bureau of Meteorology, has claimed that over the past 11 years Melbourne’s rainfall has been about 20 percent below the long-term average.  

It is common to refer to “the long-term average” when discussing climate data, but if the climate along the East Coast of Australia tends to be dominated by either El Nino or La Nina conditions, how meaningful is an average? 

According to Associate Professor Stewart Franks, School of Engineering, University of Newcastle, when calculating a long-term average it is important to include an equal number of La Nina and also El Nino dominated periods.  

Professor Franks is a hydrologist with an interest in understanding the risk of flooding.    He has explained that if you take an annual maxima flood series for a northern New South Wales catchment, which is typical for the East Coast of Australia over the last 100 years, there have been two periods of El Nino conditions and a single La Nina. 

So when a long-term average is calculated from this data it probably underestimates the real risk of a big flood event.  In other words, if anything government policy and planning has underprepared us for big flood events. 

In the opinion piece by Dr Jones entitled ‘Our hot, dry future’ published by Melbourne’s The Age newspaper recently, he claimed the below average rainfall in Melbourne was due to global warming and that there was worse to come. 

But if the climate along the East Coast of Australia is a two state process dominated by El Nino or La Nina, then while Melbourne has experienced relatively dry conditions during the past 11 years, the expectation would be that at some point  we will move back into a La Nina dominated phase.    According to Professor Franks, it is probably a bit messier than that with periods that might not be dominated by either.

Nevertheless, it is reasonable to assume the longer the El Nino dominance continues, the likelier it is to end.  

So, rather than preparing for more drought as Dr Jones suggests, perhaps we should prepare for more floods?   Indeed climate always changes and floods and droughts are a natural hazard.

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For more information:

D. C Verdon & S. W. Franks, 2006.  Long-term behaviour of ENSO: Interactions with the PDO over the past 400 years inferred from paleoclimate records, Geophysical Research Letters, 33.

Part 1 of this series,
https://jennifermarohasy.com.dev.internet-thinking.com.au/blog/2008/10/how-melbourne%e2%80%99s-climate-has-changed-a-reply-to-dr-david-jones-part-2/

Part 2 of this series,
https://jennifermarohasy.com.dev.internet-thinking.com.au/blog/2008/10/how-melbourne%e2%80%99s-climate-has-changed-a-reply-to-dr-david-jones-part-1/

Part 3 of this series,
https://jennifermarohasy.com.dev.internet-thinking.com.au/blog/2008/10/how-melbourne%e2%80%99s-climate-has-changed-a-reply-to-dr-david-jones-part-3/

How Melbourne’s Climate Has Changed: A reply to Dr David Jones (Part 3)

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IN an opinion piece entitled ‘Our hot, dry future’ published by Melbourne’s The Age newspaper on October 6, 2008, Dr David Jones, head of climate analysis at the Australian Bureau of Meteorology, suggested global warming was responsible for the current long drought in Melbourne and that there was worse to come.  

I don’t think the article was very convincing. I am annoyed that it didn’t include any real data.  While Dr Jones claimed that “We know that over the past 11 years Melbourne’s rainfall has been about 20% below the long-term average”, he didn’t explain what period this “long-term average” covers and what is the relevance of the last 11 years given it is accepted that over this period there has been a dominance of El Nino, and therefore dry conditions.   

Key Australian Institutions have claimed for some time that we have a water crisis because of climate change. 

Indeed in 2005 CSIRO published a “Melbourne Water Climate Change Study” claiming  “…the greater Melbourne Region has had its lowest rainfall on record compared to all other periods of similar length.” 

But as blogger, Warwick Hughes, showed some time ago, the period chosen was just 92 months, from October 1996 to May 2004.

In order to put their statement in some context Mr Hughes graphed high quality rainfall data for the weather station closest to Melbourne, Yan Yean, back to January 1863 – and he has just updated the chart to the end of September 2008. 

A high quality version of this chart can be found at Mr Hughes’ website, click here.

The chart indicates that Melbourne experiences dry periods every so often and that the current drought is similar in magnitude to the droughts of 1896, 1925 and 1945.  The chart showing 145 years of data, does not support the claim, made by Dr Jones in his article in Melbourne’s The Age, that there has been recent unusual climate change in Melbourne.  Indeed periods of drought and flood are a natural hazard.

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Read Part 1 here:
https://jennifermarohasy.com.dev.internet-thinking.com.au/blog/2008/10/how-melbourne%e2%80%99s-climate-has-changed-a-reply-to-dr-david-jones-part-2/ 
Read Part 2 here:
https://jennifermarohasy.com.dev.internet-thinking.com.au/blog/2008/10/how-melbourne%e2%80%99s-climate-has-changed-a-reply-to-dr-david-jones-part-1/

Bob Carter in Brisbane Speaking on Climate Change as a Natural Hazard

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The Institute of Public Affairs holds lectures on interesting topics at the Brisbane Club.   Last night eighty guests heard Professor Bob Carter from James Cook University explain how climate always changes and why climate change is a natural hazard.   

Thanks Bob for another great presentation!

In the New Year, the Institue of Public Affairs is hoping to start a lecture series in Sydney along the lines of the Brisbane Club Lectures and Bob has agreed to give the inaugural lecture.

To be sure to be invited to these and other events become a member of the Institute of Public Affairs.

Not Enough CO2 in Fossil Fuels to Make Oceans Acidic: A Note from Professor Plimer

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In response to a question concerning the likelihood of our oceans becoming acidic from global warming Ian Plimer, University of Adelaide, has replied:

THE oceans have remained alkaline during the Phanerozoic (last 540 million years) except for a very brief and poorly understood  time 55 million years ago.

Rainwater (pH 5.6) reacts with the most common minerals on Earth (feldspars) to produce clays, this is an acid consuming reaction, alkali and alkaline earths are leached into the oceans (which is why we have saline oceans), silica is redeposited as cements in sediments, the reaction consumes acid and is accelerated by temperature (see below).

In the oceans, there is a buffering reaction between the sea floor basalts and sea water (see below). Sea water has a local and regional variation in pH  (pH 7.8 to 8.3). It should be noted that pH is a log scale and that if we are to create acid oceans, then there is not enough CO2 in fossil fuels to create oceanic acidity because most of the planet’s CO2 is locked up in rocks. 

When we run out of rocks on Earth or plate tectonics ceases, then we will have acid oceans.

In the Precambrian, it is these reactions that rapidly responded to huge changes in climate (-40 deg C to +50 deg C), large sea level changes (+ 600m to -640m) and rapid climate shifts over a few thousand years from ‘snowball’ or ‘slushball’ Earth to very hot conditions  (e.g. Neoproterozoic cap carbonates that formed in water at ~50 deg C lie directly on glacial rocks). During these times, there were rapid changes in oceanic pH and CO2 was removed from the oceans as carbonate. It is from this time onwards (750 Ma) that life started to extract huge amounts of CO2 from the oceans, life has expanded and diversified and this process continues (which is why we have low CO2 today.

The history of CO2 and temperature shows that there is no correlation.

Ask your local warmer:

1. Why was CO2 15 times higher than now in the Ordovician-Silurian glaciation?

2. Why were both methane and CO2 higher than now in the Permian glaciation?

3. Why was CO2 5 times higher than now in the Cretaceous-Jurassic glaciation? 

The process of removing CO2 from the atmosphere via the oceans has led to carbonate deposition (i.e. CO2 sequestration).

The atmosphere once had at least 25 times the current CO2 content, we are living at a time when CO2 is the lowest it has been for billions of years, we continue to remove CO2 via carbonate sedimentation from the oceans and the oceans continue to be buffered by water-rock reactions (as shown by Walker et al. 1981). 

The literature on this subject is large yet the warmers chose to ignore this literature. 

These feldspar and silicate buffering reactions are well understood, there is a huge amount of thermodynamic data on these reactions and they just happened to be omitted from argument by the warmers.

When ocean pH changes, the carbon species responds and in more acid oceans CO2 as a dissolved gas becomes more abundant.

Royer, D. L., Berner, R. A. and Park, J. 2007: Climate sensitivity constrained by CO2 concentrations over the past 420 million years. Nature 446: 530-532.
Bice, K. L., Huber, B. T. and Norris, R. D. 2003: Extreme polar warmth during the Cretaceous greenhouse? Paradox of Turonian ∂18O record at Deep Sea Drilling Project Site 511. Palaeoceanography 18:1-11.
Veizer, J., Godderis, Y. and Francois, L. M. 2000: Evidence for decoupling of atmospheric CO2 and global climate during the Phanerozoic eon. Nature 408: 698-701.
Donnadieu, Y., Pierehumbert, R., Jacob, R. and Fluteau, F. 2006: Cretaceous climate decoupled from CO2 evolution. Earth and Planetary Science Letters 248: 426-437.
Hay, W. W., Wold, C. N., Soeding, E. and Floegel, S. 2001: Evolution of sediment fluxes and ocean salinity. In: Geologic modeling and simulation: sedimentary systems (Eds Merriam, D. F. and Davis, J. C.), Kluwer, 163-167.
Knauth, L. P. 2005: Temperature and salinity history of the Precambrian ocean: implications for the course of microbial evolution. Palaeogeography, Palaeoclimatology, Palaeoecology 219: 53-69.
Rogers, J. J. W. 1996: A history of the continents in the past three billion years. Journal of Geology 104: 91-107.
Velbel, M. A. 1993: Temperature dependence of silicate weathering in nature: How strong a negative feedback on long-term accumulation of atmospheric CO2 and global greenhouse warming? Geology 21:1059-1061
Kump, L. R., Brantley, S. L. and Arthur, M. A. 2000: Chemical weathering, atmospheric CO2 and climate. Annual Review of Earth and Planetary Sciences 28: 611-667.
Gaillardet, J., Dupré, B., Louvat, P. and Allègre, C. J. 1999:  Global silicate weathering and CO2 consumption rates deduced from the chemistry of large rivers. Chemical Geology 159: 3-30.
Berner, R. A., Lasagna, A. C. and Garrels, R. M. 1983: The carbonate-silicate geochemical cycle and its effect on atmospheric carbon dioxide over the past 100 million years. American Journal of Science 283: 641-683.
Raymo, M. E. and Ruddiman, W. F. 1992: Tectonic forcing of late Cenozoic climate. Nature 359: 117-122.
Walker, J. C. B., Hays, P. B. and Kasting, J. F. 1981: A negative feedback mechanism for the long term stabilization of the Earth’s surface temperature. Journal of Geophysical Research 86: 9776-9782.
Berner, R. A. 1980: Global CO2 degassing and the carbon cycle: comment on ‘Cretaceous ocean crust at DSDP sites 417 and 418: carbon uptake from weathering vs loss by magmatic activity.” Geochimica et Cosmochimica Acta 54: 2889.
Schwartzman, D. W. and Volk, T. 1989: Biotic enhancement of weathering and the habitability of Earth. Nature 311: 45-47.
Berner, R. A. 1980: Global CO2 degassing and the carbon cycle: comment on ‘Cretaceous ocean crust at DSDP sites 417 and 418: carbon uptake from weathering vs loss by magmatic activity.” Geochimica et Cosmochimica Acta 54: 2889.
                                                                         CO2 + H2O = H2CO3
                                                                                H2CO3 = H+ + HCO3-
                  2Ca2+ + 2HCO3- + KAl2AlSi3O10(OH)2 + 4H2O = 3Al3+ + K+ + 6SiO2 + 12H2O
                                                      2KAlSi3O8 + 2H+ + H2O = Al2Si2O5(OH)4 + 2K+ + 4SiO2
                                                    2NaAlSi3O8 + 2H+ + H2O = Al2Si2O5(OH)4 + 2K+ + 4SiO2
                                                    CaAl2Si2O8 + 2H+ + H2O = Al2Si2O5(OH)4 + Ca2+
                               KAl2AlSi3O10(OH)2 + 3Si(OH)4 + 10H+ = 3Al3+ + K+ + 6SiO2 + 12H2O
                                                                     CO2 + CaSiO3 = CaCO3 + SiO2
                                                                     CO2 + FeSiO3 = FeCO3 + SiO2
                                                                     CO2 + MgSiO3 = MgCO3 + SiO2

In the oceans, CO2 exists as dissolved gas (1%), HCO3- (93%) and CO32- (8%)