Australia's climate extremes increasing as carbon dioxide levels continue to rise, report reveals

Updated

Australia is getting wetter despite drought across much of the country, a climate report has revealed.

Key points from the report Frequency of extreme weather has increased, with more extreme heat, fewer cooler extremes

Rainfall averaged across Australia slightly increased since 1900, with largest increases in the north-west since 1970

Rainfall declined in the south-west since 1970

Extreme fire weather increased, fire season lengthened since 1970

Concentrations of greenhouse gases now at their highest levels for at least 800,000 years

The CSIRO and Bureau of Meteorology's latest State of the Climate report is a snapshot of how Australia's weather has changed over the last two years.

Average rainfall has increased in Australia since 1900, with above-average falls in Australia's north offsetting a drop in annual rainfall in the south.

The report shows south-east Australia experienced a 15 per cent decline in late autumn and early winter rainfall since the mid-1990s.

But average rainfall during the northern wet season has increased since 1970 - though this is described as the exception rather than the rule.

Since 1950, heatwaves have become longer, more intense and occur more often across much of the country.

Underpinning these extremes, according to the report, is the concentration of carbon dioxide in the atmosphere, which is likely to have reached its highest level in two million years, and in the past two years has reached some of the highest levels ever observed.

CSIRO deputy chief of marine and atmospheric research Dr Helen Cleugh said in the last two years they had observed the highest ever jump in carbon dioxide levels.

"Last year the global average over the year reached 395 parts per million, which is over 40 per cent higher than it was pre-industrial," she said.

"We take our observations of greenhouse gases in a variety of ways.

"In the near past, over the last four to five decades, we've measured the concentrations of greenhouse gases in the atmosphere using instruments and samples of air.

"To go back into the long-time records, back over hundreds of thousands if not millions of years, we use air bubbles that are trapped in ice forms and we can extract those air bubbles and analyse them for their greenhouse-gas concentration."

Air and ocean temperatures are almost a degree warmer than they were a century ago and are expected to rise further, with more extreme hot weather and fewer extremely cool days.

Most of the extreme fire weather days were in the south-east of Australia.

The report said sea levels had risen by 22.5 centimetres since 1880, the earliest year for which credible estimates are available.

CSIRO's Dr John Church said the report also found that sea levels were rising above the global average of 3.2mm a year in northern Australia.

"Three to four times above [the global average] in some locations, and that's primarily a result of natural climate variability," Dr Church said.

"This'll mean that relative sea levels are rising more rapidly in places like Darwin and that means that coastal flooding events will be increasing in frequency and intensity."

Cyclones to decrease in frequency, but increase in force

The report also projects a reduction in the frequency of tropical cyclones, but an increase in their destructive fury.

The CSIRO made it clear that more work needed to be done to confirm this, stating that it had "low confidence" in the projections.

"What that means is we still actively need to research the various factors that are going to change in the future that are going to influence the occurrence of tropical cyclones," Dr Cleugh said.

"They are one of the phenomena that are a little bit more difficult to predict into the future what their frequency and intensity might be.

"So we're still doing research to try and better quantify what that change might be."

Topics: environment, environmental-impact, climate-change, earth-sciences, australia, nt

First posted