Average weather or not

ONE year ago Australia had only just emerged, dripping, from its wettest two years since records began.

Back-to-back La Niña events, coupled with very warm sea surface temperatures had produced a two-year rainfall total that surpassed the old record set during 1973-74, followed closely by the big wet of the mid-fifties.

Why Lismore never flooded can only be answered by the weather gods, as the skies continued to open right through May, only becoming dry for a brief time from July through October.

Now, as we enter a new year, computer forecasts are predicting average weather until next autumn. It is the first time that the Southern Oscillation Index (SOI) has registered consistently neutral values during summer months since 2005-2006.

The Southern Oscillation Index is now in negative territory, which points to drought but the Bureau of Meteorology is quick to say that high summer is not a time for accurate SOI figures. Instead they note complex computer models forecasting neutral or average conditions for the next nine months.

Even though the Northern Rivers doesn't follow the SOI prediction as closely as areas further west, we can assume that a forecast for average conditions means just that: A bit of sun and a bit of cloud, without the extremes that we have had over the past two years.

Having said that we have experienced floods in years before when SOI values declare it to be a dry old time.

A graphic example of how our district sometimes fails to comply with the SOI trend is expressed in the rainfall data for Bangalow, where more than 737mm of rain fell in the month of October, 1972, at a time when the SOI values were 11 points in the El Nino or dry range. The same thing could be said about rainfall in Nimbin, where nearly 989mm fell in February, 1931, when SOI values were -14.9 - well into 'dry' territory.

This year coming the trend in maximum daytime temperatures will continue to climb, a product of global climate change and the Bureau of Meteorology has forecast warmer days in our region. This outlook is a result of warmer than usual waters persisting in the Indian Ocean, with warmer than normal tropical Pacific waters having less of an impact.

By the same token the number of cyclones that are predicted to spin up off our shores should be close to the average number of four, unlike two years ago when the bureau predicted a season run of between six and seven.

If these conditions persist there is the chance that cyclones may form further offshore, rather than closer to the Queensland coast, providing an excellent source of summer waves rather than the lumpy, short period junk we have experienced for the past few summers.

Having said that, sea surface temperatures off Byron Bay were 26.5 degrees on New Year's Eve and waters off Moreton Island have been consistently above 26 degrees for the past week. That is warm enough for Cyclone formation and certainly warm enough to support a cyclone tracking south from Queensland waters.

These warm waters highlight a phenomenon that is rapidly affecting the marine environment to our south and beginning in the next few months scientists will intensively monitor the warm current billowing past our shores using an array of buoys moored across the East Australian Current in a line east of Moreton island.

This rush of warmer than usual water into the Tasman, raising average sea surface temperatures buy more than 1.5 degrees since the 1960s, has created real environmental change in the marine environment south of Bass Strait. There, 34 sub-tropical species of fish from NSW and southern Queensland now reside and an invasion of warmer water sea urchins has started to crowd out endemic species and kelp beds have started to decline.

Similar hot spots have appeared in every other east coast current world wide, pointing to proof of climate change as a result of ozone depletion and contribution from greenhouse gases.

Fast Facts:

  • The national outlook averaged over January to March 2013 shows that warmer days are more likely over northern and most of eastern Australia.
  • The CSIRO and Bureau of Meteorology State of the Climate 2012 reports that:
  • Australian annual average daily mean temperatures have increased by 0.9 °C since 1910.
  • Global average mean sea level for 2011 was 210 mm above the level in 1880.
  • Sea surface temperatures have increased generally by about 0.8 °C since 1910.
  • The main cause of the observed increase in carbon dioxide concentration in the atmosphere is the combustion of fossil fuels since the industrial revolution.
  • Australian average temperatures are projected to rise by 1.0 to 5.0 °C by 2070 when compared with the climate of recent decades.
  • Climate change is continuing
  • Warming has been measured around Australia and globally during recent decades
  • 2010 Global temperatures were the warmest on record (slightly higher than 2005 and 1998)
  • Australia experienced record rainfalls and the coolest temperatures since 2001 due to a very strong La Niña event in 2010 and 2011
  • Concentrations of long-lived greenhouse gases in the atmosphere reached a new high in 2011
  • Australian temperatures are projected to increase in coming decades
  • Rising CO2 emissions from the burning of fossil fuels has affected global temperature much more than natural climate variability during the past century.

Topics:  el nino, la nina system, southern oscillation index



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