Plibersek’s ‘determination’ alone won’t save the Great Barrier Reef – here’s what needs to happen

Keeping global heating as close to 1.5C as possible is critical for all ecosystems and societies, including the viability of Australia’s ocean jewel, the Great Barrier Reef.

The federal environment minister, Tanya Plibersek, this week launched a strong defence of the government’s climate targets after UN-backed scientists outlined the steps they said were needed to give the reef the best chance of retaining its status as a world heritage area.

“We are, as a government, absolutely determined to do our bit to keep global warming beneath 1.5C. We’ve legislated. We’ve invested,” Plibersek said.

But expert analysis shows Australia’s legislated goals for 2030 fall well short of the “clear government commitments to reduce greenhouse emissions” in line with 1.5C that the UN scientists are asking for.

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That doesn’t mean the government’s “determination” won’t improve matters – but where do things stand right now?

The chief executive of Climate Analytics a firm that that provides analysis of greenhouse gas pledges, Bill Hare, said although Australia’s new target was “a major improvement” on that of the previous Morrison government’s it was “still far from 1.5C aligned”.

The Albanese government has a target to cut emissions by 43% by 2030, based on 2005 levels. As a signatory to the UN climate convention, in 2025 the country will be expected to submit a new target for 2035 that improves on the current trajectory.

Hare said Australia’s 2030 target needed to be at least a 60% cut below 2005 levels by 2030 “and there would need to be policies that match this”.

“The government is still putting in place policies so we do not yet have the full picture – its 82% by 2030 renewables in the power sector is close to what is needed. To be 1.5C aligned coal needs to be out of the power sector by 2030 and gas by around 2035. We are a long way from that.”

The Albanese government is working on changes to the safeguard mechanism to cap and then reduce emissions from the country’s biggest polluting facilities.

Hare said there was concern those changes would not bring in the level of ambition needed “and the possible widespread use of offsets will not work to reduce emissions”.

Clear path to net zero?

When Plibersek said Australia was determined to “do our bit” she said the country already had “a clear path to net zero by 2050”.

Prof Frank Jotzo, a climate economist at Australian National University, said: “No – we don’t yet have a clear path to net zero. We don’t have a national strategy. There is an expectation that the Climate Change Authority will deliver advice on that.”

So what does keeping heating below 1.5C look like in Australia?

Analysis from Associate Prof Malte Meinshausen and colleagues at the University of Melbourne looked at the amount of global CO2 that can be released to give a 50% chance of keeping rises to 1.5C.

If Australia was allotted a 0.97% share – a generous portion, he said, given the country’s very high per capita emissions – then based on current emissions Australia would have used all its share in less than eight years.

Good news or bad news

In the Australian newspaper on the weekend, scientist Dr Peter Ridd from the right-wing Institute of Public Affairs accused the Bureau of Meteorology and CSIRO of ignoring what he claimed were the benefits of global heating in its biennial State of the Climate report.

Marine heatwaves would probably become more frequent and severe, the report said, leading to more coral bleaching on the Great Barrier Reef.

Ridd argued corals grow “about 15% faster for every degree temperature rise” and “almost all the corals on the reef also live in much warmer water near the equator”.

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Prof Ove Hoegh-Guldberg, a pioneering coral scientist at the University of Queensland, said while corals generally grow faster in warmer water, this was only true up to the average summer temperatures for a location.

“After that, they decline with further increases in temperature,” he said. “This means that temperatures above the summer maximums will cause the growth rates to decrease with further increases in temperature.”

Even though some coral species do grow both on the reef and near the equator, those animals had evolved over thousands of years to adapt to local conditions.

“That’s not the equivalent to suddenly exposing a coral to an underwater heatwave,” he said.

Temperature records

Ridd said the bureau had “adjusted all the temperature records reducing the temperatures a century ago by up to a degree”.

“Can we have any confidence they did this with a good scientific reason?” Ridd asked.

The bureau does carry out a process known as “homogenisation” on its long-term temperature dataset that corrects for known changes, such as the relocation of a thermometer or changes in vegetation around the weather station that could artificially influence readings.

Ridd doesn’t mention two major scientific reviews that found there were good scientific reasons for using this technique.

At the close of a three-year technical review, an independent forum of scientists wrote it “continues to support the bureau’s methodological approaches to homogenisation practices, and reiterates the importance of homogenisation in supporting the maintenance of a meaningful and consistent set of temperature records over time”.

Heroic guess

Ridd asked if “we should worry” about data from the bureau showing fire seasons are “now much worse than in 1950” that ignored “all the information on huge bushfires before 1950”.

“It is not like there is no data before 1950,” Ridd wrote, pointing to major fires in the 1930s and the “devastating 1851 Victorian bushfire”.

Scientists have found Australia’s fire season is getting longer and the number of days when conditions are conducive to dangerous fires has been rising.

That analysis uses a measure called the Forest Fire Danger Index that combines temperatures, wind speed, humidity and the state of the fuel.

The FFDI record starts in 1950 because there was a lack of reliable data – in particular in relation to wind speed – before then.

So what about those fires in the 1930s and 1851? Analysis published in Nature found the amount of forest burned in the Black Summer bushfires of 2019-20 was likely larger than fires in the 1930s.

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There is scant information about the size of the “devastating 1851 Victorian bushfire” and references to it suggest about 1.5m hectares of forest was burned in the state – potentially less than was burned in Victoria during the Black Summer fires.

But Prof David Bowman, a leading bushfire expert at the University of Tasmania, said claims about the size of historic fires were “heroic guesses.”

He said: “There is no question that in the time window of good records – the satellite epoch starting in the 1980s – fire impacts are worsening.”

Dr Grant Williamson, also at the University of Tasmania, says changes in the way land was managed before the 1950s makes it “impossible to disentangle” the effect of that with changes in climate.

“The trend in fire weather in more recent decades, however, is clear, whether you look at extreme events, global trends in overall fire weather or individual components of fire weather, like fuel moisture.”