Archives for October 13, 2006

Why have we been in an out of drought for the last 15 years? Why has the distribution of rainfall over Australia changed? Perhaps we have a combination of natural variability combined with stratospheric ozone depletion, tropospheric greenhouse gases, and atmospheric aerosol pollution. This is the subject of a note from Luke:

“Drought seems to be with us again in Australia. It seems we’ve been lingering in and out of drought for the last 15 years. The overall continental rainfall may not have changed but the distribution of rainfall certainly has.

Let’s forget about 2030 and 2070 for a while. Let’s focus on our history and the present day.

How well do we know our climate record? Is what we are experiencing normal or are there anthropogenic influences already affecting Australian climate?

Firstly, do we have longer droughts or more frequent droughts in our historical coral core records which extends over the previous 400 years than in the 120 years or so years of rainfall records?

How well do we understand our base background variability?

Eight, multicentury, porites coral cores were used to develop a 373-year chronology by cross-dating techniques adapted from dendrochronology.

Burdekin River runoff was found to be significantly inversely related to El Nino-Southern Oscillation (ENSO) variability for much of the period from the 1650s through to 1800, suggesting that ENSO-related teleconnections were as dominant then as in recent decades.

Indeed, the extremely dry mid-1760s to mid-1780s stand out as a period of anomalously positive correlation between river runoff and the NINO3 reconstruction. Weak ENSO teleconnections are apparent from the 1800s to 1870s, when conditions were possibly similar to those reported for the 1920s–1950s.

In the 20th century issues like the Interdecadal Pacific Oscillation (IPO) have perhaps confounded our analysis. The 1950s and 1970s were much wetter. There were more La Ninas and a consistently negative IPO index.

Any trend analysis using the 1950s is likely to show a drying trend. So are our trend graphs from the Bureau reflecting the extreme deficit of our current rainfall or the very wet 1950s and 1970s. Multidecadal influences like the IPO will confound trends to come in the future (assuming the IPO does actually exist and is not an artifact!).

But questions still remain. In particular, why have we had an increase in frequency of El Nino events since 1976 – including back to back events?

Trenberth hypothesised the Pacific might be entering a more El Nino like “mean state” in a greenhouse world. But other studies have indicated that it is too hard to tell what will happen.

The increase in El Nino frequency still exists. However the most modern review articles on how El Nino responds to a greenhouse world are inconclusive – some simulations increase the frequency but most show little change.

A worrying recent paper published in Science discusses a permanent Pacific El Nino event in the Pliocene when temperatures were significantly warmer than they are today. Might a permanent El Nino be still lurking in a globally warmed world yet to be revealed by better modelling: the Pliocene Paradox (Mechanisms for a Permanent El Niño)?

Drought of course is caused by more than total rainfall alone. Evaporation rate is an influence and streamflow is subject to the pattern of rainfall (heavy or light), evaporation, and antecedent catchment conditions.

Has the pattern of rainfall changed?

Light interspersed rainfall in a dry catchment produces no runoff.

Roderick and Farquhar (2004a) reported that pan evaporation rates decreased between 1970 and 2002 at many Australian observing stations, although subsequent correction of the data for instrumental changes showed that, Australia-wide, the trends in pan evaporation were not statistically-significant (Roderick and Farquhar 2004b, Jovanovic et al, 2006).

Evaporation itself is a product of radiation, humidity, wind and temperature – not just temperature. Alice Springs having a higher evaporation overall than a warmer Darwin.

Detailed modelling of historical pan evaporation by Rayner (2006) showed that the declining pan evaporation at many sites, is related to declining windiness. Wind and/or global dimming aerosols? However in the 2002 drought Nicholls (2004) found a much greater evaporative demand. High temperatures are again being mentioned in the context of this current drought. Might our future droughts be more severe in evaporative demand?

Coastal Queensland has seen few coast crossing tropical cyclones in recent decades. They are so needed to replenish dams and major aquifers.

Has there been a fundamental shift in oceanic or atmospheric processes?

Which brings us to the present day. I think there may be multiple players afoot. Might we have a combination of natural variability, tropospheric greenhouse gases, stratospheric ozone depletion and atmospheric aerosol pollution that is already giving us climate change?

Is this implicated in our SW Western Australia and eastern Australian drying trends? And perhaps our tropical cyclone formation too?

I suspect there are already climate changes happening. Most land holders and water managers really want to know what’s happening in the next 5-10 years.

An area neglected perhaps in the discussion of future climate change. Might we already be in it! Is there more to come?

There are major economic, resource management, environmental and social issues at stake. And it may be already upon us.

I don’t know the answer to all these questions. But, the issues are confronting most Australians.

This is why we need a renewed effort using state-of-the-art modelling of rainfall scenarios for Australia.

Adaptation perhaps have been forced upon us now?

Some important papers on the topic well worth a read:

Interpretation of Recent Southern Hemisphere Climate Change
http://www.sciencemag.org/cgi/content/abstract/sci;296/5569/895

Simulation of Recent Southern Hemisphere Climate Change
http://www.sciencemag.org/cgi/content/abstract/302/5643/273

Can ozone depletion and global warming interact to produce rapid climate change?
http://www.pnas.org/cgi/content/abstract/97/4/1412

Investigations on SW western Australia rainfall decline
http://www.cmis.csiro.au/healthycountry/updates/sep05/story3.htm

The response of the Southern Annular Mode, the East Australian Current, and the southern mid-latitude ocean circulation to global warming
http://www.agu.org/pubs/crossref/2005…/2005GL024701.shtml

Antarctic ozone depletion causes an intensification of the Southern Ocean super-gyre circulation
http://www.agu.org/pubs/crossref/2006…/2005GL024911.shtml

Aerosols and how they can affect tropical circulation and rainfall; Observed Australian rainfall and cloudiness trends (especially the intriguing “north west Australia” pattern of long term rainfall increase)
http://web.maths.unsw.edu.au/~matthew/lr_aerosols.pdf

Reviews of evaporation.
http://www.greenhouse.crc.org.au/crc/ecarbon/publications/panevap_proceedings_050426.pdf
http://www.greenhouse2005.com/downloads/program/GH2005_Presentation_200511171050_1.ppt“

———————————-

Thanks Luke.

I have started a new category Climate (Part 2) for this post and will place all new climate related blog posts here. The original Climate and Climate Change category is starting to take too long to down load.

To what extent can technology protect communities from climate extremes through early warning and disaster response strategies and by having appropriate building plans, codes and drainage infrastructure? Here’s a comment from Paul Williams who’s been thinking about the situation in South Australia:

“Scientists such as Tim Flannery, the CSIRO, our Premier Mr Rann and the editorial staff of the Advertiser all tell us that climate change is coming, and it’s all due to human emission of greenhouse gases.

Droughts will increase and sea levels will rise. Apparently the science is settled and the evidence is incontrovertible.

The response to this coming disaster is to call for lifestyle changes to reduce greenhouse gas emissions.

The problem is that South Australia emits only 0.15% of global greenhouse emissions, and greenhouse emissions by other countries (and other Australian States), still affects the atmosphere and climate of South Australia. In other words, South Australian greenhouse emissions have no effect on global or South Australian climate, and reduction of greenhouse emissions by South Australians will not reduce the degree of climate change we must undergo.

Assuming Mr Rann is sincere in his desire to protect South Australia from the effects of climate change, it seems the only actions which will be of any practical use, as opposed to merely symbolic, will be engineering solutions.

For instance, if sea level is definitely going to rise by up to seven metres by 2100, why not begin construction of dykes to protect coastal infrastructure? After all, Holland has been doing that for hundreds of years.

Similarly, why not run computer simulations to study the effects of flooding the Lake Eyre basin with sea water? Computer models are apparently sophisticated enough to predict Australia’s rainfall and sea level changes for the next 100 years, so they should be adequate to assess any benefit from an inland sea.

If the science really is settled, then Mr Rann needs to take effective action, not simply enact legislation that plays well with the inner city environmentalists.”

It’s not just in South Australia that politicians are calling for emission reductions rather than proposing some more practical adaptive solutions.

Just yesterday Queensland Sunshine Coast independent MP, Peter Wellington, proposed a notice of motion calling on the Queensland Parliament to acknowledge climate change is a threat and take immediate action to reduce greenhouse gas emissions.

Come-on! There must be something more practical that Mr Wellington can propose for coastal Queensland assuming “the science is really settled” and we face catastrophic climate change and dramatic sea-level rise?