State of the Climate 2016 — hotter days, warmer oceans, greater fire risk

The CSIRO and the Bureau of Meteorology (BOM) have delivered their biennial State of the Climate report, drawing on the latest climate monitoring to show how Australia’s climate is changing. And it’s sure to come as no surprise to learn that Australia’s average temperature is rising.

The report states that Australia has warmed by around 1°C since 1910, with the number of days per year over 35°C increasing in recent decades (except in parts of northern Australia). It projects that this overall warming trend will continue, with fewer cool days, more hot days and more fire weather days, especially in southern and eastern Australia.

“We’ve already seen an increase in fire weather and a longer fire season across southern and eastern Australia since the 1970s,” said BOM’s manager of climate monitoring, Dr Karl Braganza. “In these regions, the number of days with weather conducive to fire is likely to increase.

“Some of the record-breaking extreme heat we have been seeing recently will be considered normal in 30 years’ time.”

There has also been a temperature increase in the oceans around Australia, with warming now recorded at least 2000 m below the sea surface, and an increased level of acidity. Global sea level has risen over 20 cm since the late 19th century — about one-third of which is attributed to ocean warming — with further rising predicted in future.

Rainfall trends are trickier to monitor, as Australia’s rainfall is naturally variable; however, long-term changes can be observed. In the last few decades, northern wet season rainfall has been above average. During the April to October growing season, there has been an overall decline in rainfall across southern Australia. The report claims that winter rainfall across parts of southern Australia will decrease, with more time spent in drought.

CSIRO Senior Scientist and leader of the NESP Earth Systems and Climate Change Hub, Dr Helen Cleugh, said these changes are due to an increase in greenhouse gases such as carbon dioxide (CO₂) in the atmosphere, which act like a blanket by keeping heat in the Earth’s lower atmosphere.

“Before around 1750, the level of CO₂ was 278 ppm (parts per million),” said Dr Cleugh. “This year the Earth will record a global annual average of over 400 ppm — the highest level in the past two million years.”

State of the Climate 2016 — the fourth report in the series — can be viewed at http://www.bom.gov.au/state-of-the-climate/.

Image caption: Time series of anomalies in sea surface temperature and temperature over land in the Australian region. Anomalies are the departures from the 1961–1990 average climatological period. Sea surface temperature values are provided for a boxed region around Australia (4–46°S and 94–174°E). ©Bureau of Meteorology