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Braidwood Rounds: Local weather station records rapid rise in air temperature

Local weather recordings in Braidwood since 1986 show a steady air temperature increase that is higher than the rate often cited by national and international bodies as the global warming trend. These are solid data, compiled with the Bureau of Meteorology, as our Braidwood correspondent Jill McLeod explains.

For many years, close to home, weather details have been diligently observed and recorded by Braidwood resident Roger Hosking who sees himself as weather tragic rather than a guru. He has had an abiding interest in climate and weather since growing up in seldom-rainy western NSW.

Roger records observations of many factors and daily rainfall, wind, temperatures and evaporation are forwarded to the Bureau of Meteorology at monthly intervals. His BOM site, No. 069010, started life as a rain gauge at the Braidwood PO in 1888. The recording of maximum and minimum temperatures commenced in 1945.

According to Roger, one of the positive outcomes of the lack of development at Braidwood is that the environment for weather observations has been unchanging. A lack of heavy industry, no airport with hot jet exhausts, a plateau with exposure to wind from every direction, and a stable size without a ‘heat island’ all contribute to a stable environment over time with reliable records.

 Since 1986, temperatures rise is 0.8 degrees C per decade

 A summary of some of Roger’s Braidwood records –

Despite subdued rainfall and droughts during 2001-2010, the long-term rainfall trend shows little change over the period since 1888. Median annual rainfall is 678mm (half the years are above and half are below the median).

  • Interestingly there has not been any significant change in Braidwood’s overnight minimum temperatures. (Interesting because both the BOM and the CSIRO expected a major impact of global warming to show up in minimum temperatures.)
  • The change in maximum (air) temperatures has been another story. Measured since 1947, the rate of warming is a relatively moderate 0.02 degrees C per year. However, in the 29 years since 1986, with no change in thermometers or their exposure, the rising trend is 0.08 degrees C per year, four times as fast. This equals 0.8 degrees C per decade.

Most of Roger’s equipment and instruments currently in use were supplied by the BOM and are subject to periodic inspections by that organisation.

Federal government may not want change from business as usual, but releases projections of what awaits 

The Australian Government has issued climate change data on a new website – www.climatechangeinaustralia.gov.au. The research was funded by the Department of the Environment with co-funding by the CSIRO and the BOM.       

 The two agencies have released comprehensive projections for Australia with national and regional information on how the climate may change up to the end of 2099. Information was drawn from simulations based on up to forty global climate models.

Most of the changes observed over recent decades will continue into the future. For example:

  • Hot days will become more frequent and hotter
  • Sea level will rise, oceans will become more acidic, and snow depths will decline
  • Extreme rainfall events will become more intense
  • Winter and spring rainfall will decrease in southern Australia but will increase in Tasmania in winter
  • In the rest of Australia naturally occurring fluctuations in rainfall patterns will dominate over trends until 2030. Then climate change trends will emerge
  • Tropical cyclones may occur less often but become more intense; and
  • Southern and eastern Australia will experience harsher fire weather.

My thanks to Roger for his contribution to this column and I would also like to draw attention to Dr Maria Taylor’s recent book Global Warming and Climate Change – what Australia knew and buried.

 

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