The most senior Catholic to be convicted of child sex abuse took his appeal to Australia's highest court Wednesday in potentially his last bid to clear his name.

Cardinal George Pell was sentenced a year ago to six years in prison for molesting two 13-year-old choirboys in Melbourne's St. Patrick's Cathedral while he was the city's archbishop in the late 1990s.

His lawyers argued in the High Court that an apparently truthful victim was not enough to dispel reasonable doubt about guilt. The seven judges will hear the prosecution case on Thursday on why the convictions should stand.

Pell was convicted by the unanimous verdict of a Victoria state County Court jury in December 2018 after a jury in an earlier trial was deadlocked. A Victoria Court of Appeal rejected his appeal against his convictions in a 2-1 majority decision in August last year.

Pope Francis' 78-year-old former finance minister argued before the High Court that the guilty verdicts were unreasonable and could not be supported by the whole of the evidence from more than 20 prosecution witnesses who include priests, altar servers and former choirboys.

Pell's lawyer Bret Walker told the judges that there had been a "reversal of onus" in which Pell was expected to prove the offending didn't happen instead of prosecutors proving the crimes were committed beyond reasonable doubt.

"That is a wrong question which sends the inquiry onto a terribly damaging wrong route," Walker said.

"Impossible was not something we had to prove, but if we showed it, then obviously there's a reasonable doubt," he added.

Walker said the evidence of a former choirboy, now aged in his 30s with a young family, was the only evidence that Pell had committed the crimes.

Walker said the allegations that Pell had molested the two boys in a priests' sacristy moments after a Mass could not be proved if the jury had accepted the evidence of sacristan Maxwell Potter and Monsignor Charles Portelli.

Potter had testified that the sacristy was kept locked during Masses and Portelli had given evidence that he was always with Pell while he was dressed in his archbishop's robes.

Walker said Pell did not have a five or six minute opportunity required to molest the boys in the sacristy before altar servers and clerics walked in.

"Unlike so many appalling historic sexual misconduct cases, the alleged offending had taken place in a milieu quite different from the usual secluded, secretive or completely private setting," Walker said.

Prosecutors have told the judges in written submissions that it is not their role to determine whether it was open to the jury to find the offending behavior proven beyond reasonable doubt.

Outside court, Pell supporters clashed with a man from a victims advocacy group. Michael Advocate from Victim Justice held signs saying, "Burn in hell Pell."

A group of Pell supporters tried to block Advocate from speaking to reporters, yelling for Pell to be forgiven.

The group of about 50 supporters, many holding Australian flags, sang hymns outside of the court as lawyers prepared for the case inside.

The court will effectively hear Pell's appeal in its entirety before they technically decide whether they will even hear his appeal.

They could decide he does not have permission to appeal, he has permission to appeal but the appeal is denied, or he has permission to appeal and the appeal is upheld.

The judges could also send Pell's appeal back to the Victoria Court of Appeals to be reheard by another three judges.

It is not known when the judges will deliver their rulings.

Pell is serving his sentence at the maximum-security Barwon Prison near Geelong, southwest of Melbourne. He hasn't traveled to Canberra for his appeal hearing.

One of Pell's victims died of a heroin overdoses in 2014 without telling anyone of the abuse.

The survivor went to police after attending his friend's funeral. Neither victim can be identified because the identities of sexual assault victims must be kept secret under state law.

Lisa Flynn, a lawyer for the dead choirboy's father who blames the abuse for his son drug attraction, said her client is "understandably quite anxious and unsettled" by the appeal.

"However he also remains very hopeful and also confident that the High Court will agree with the Court of Appeal majority and that the convictions against George Pell will be upheld," she added.

Climate change raised the chances of Australia's extreme fire season by at least 30%, according to a study released Wednesday by climate scientists at the World Weather Attribution group.

Scientists from Australia, Europe and North America calculated just how much human-caused global warming elevated the likelihood of Australia's record-setting fire season by comparing high-resolution computer models of the continent facing varying levels of climate change.

The scientists took into account differences in climate conditions in about 1900 compared to current conditions — tabulating both measured and observed changes in temperature, drought and fire intensity.

Last year was both the hottest and driest year on record in Australia since measurements began a century ago.

"There is evidence that Australian fire seasons have lengthened and become more intense — and extreme temperatures have played a role in this," said Sophie Lewis, a climate scientist at the University of New South Wales in Canberra, Australia, and a co-author of the study.

"Climate change is now part of Australia's landscape – extreme heat is clearly influenced by human-caused climate change, which can influence fire conditions," she said.

Australia's 2019-2020 wildfire season burned a record 19 million hectares (47 million acres), displacing thousands of people and killing at least 34. The fires also razed rare habitats and killed more than a billion animals, say researchers.

A decade ago, while scientists often discussed how climate change increased the likelihood of extreme weather patterns, researchers were still reluctant to explicitly connect any specific weather event with climate change.

Today, more precise computer models allow scientists to pinpoint the degree to which an altered climate influences the chances of individual extreme wildfires, floods, droughts and heatwaves.

Technology Review magazine – published by the Massachusetts Institute of Technology – recently named climate change attribution models as one of the "Breakthrough Technologies" of 2020.

"It's one thing to paint a broad statistical picture of how climate change is loading the dice for extreme weather events. But it's quite another to really dig into the climate data and specific numbers around an individual disaster, like the Australian wildfires," said Kim Cobb, a climate scientist at the Georgia Institute of Technology in Atlanta, who was not involved in the study.

"Reducing emissions remains the most important way to limit our climate risks," she said.

Higher than average ocean temperatures have put Australia's iconic Great Barrier Reef on the brink of a severe coral bleaching event, the Australian Institute of Marine Science (AIMS) has warned on Tuesday.

Recording an increase of 1.0 to 2.5 degrees centigrade in recent weeks, AIMS Oceanographer Craig Steinberg said the World Heritage Listed Area is now facing an enormous threat.

"Our knowledge and long-term understanding of northern Australian waters tell us warming oceans place enormous pressure on the reef's ecology," he explained.

"If heatwave conditions persist or worsen, we can expect corals to exhibit stress and experience some level of regional bleaching."

Causing the corals to expel algae from their tissue and turn white, the process can then lead to stagnant growth rates, decreased reproductive capacity, increased susceptibility to diseases and a declines in genetic and species diversity.

Using satellites, weather stations and even an in-water autonomous robot to monitor ocean temperatures in real time, there is also a network of 170 electronic temperature loggers which have been deployed across the 350,000 square km reef.

"We have re-deployed an Integrated Marine Observing System (IMOS) underwater glider to areas of concern in the waters north-east of Townsville," Steinberg said.

"With its on-board sensors, the glider provides our scientists with information about ocean properties at different depths of the water column including temperature and light, to help explain any observed levels of coral bleaching."

"Knowing how deep the warm surface layer is, can help determine the depth corals are likely to experience heat stress."

Describing the situation as being "on a knife's edge," AIMS Chief Executive Officer Dr. Paul Hardisty said the underlying trend of ocean warming means the chance of coral bleaching events has greatly increased over recent years.

"The next major El Niño event, which typically results in warmer sea temperatures on the reef at this critical time of year, poses a real risk for the reef. We need to be prepared as oceans continue to warm," he said.

"The scale and severity of the bleaching damage in 2016 and 2017 highlighted the critical threat warming ocean temperatures pose to coral reefs."

Typically taking around a decade for corals to recover from a bleaching event, Hardisty said without a reduction of global temperatures, the health of the reef is expected to continue to decline.

"If we want to safeguard coral reefs for the future, we also need to begin developing options for intervening on the Great Barrier Reef to help it cope better with climate change, in conjunction with reducing global greenhouse gas emissions," he said.

Around 70,000 people packed out Australia's ANZ stadium on Sunday, to show their support for communities that have been devastated by the country's recent bushfire crisis.

Selling out in just 24 hours after tickets went on sale, the Fire Fight Australia concert was headlined by international rock giant Queen and featured an array of local and international artists including 5 Seconds of Summer, Alice Cooper, Amy Shark, Grinspoon, Jessica Mauboy, Ronan Keaing and Michael Bublé.

Thanking Australia's professional and volunteer firefighters, comedian Celeste Barber who hosted the event said, "you will never know how grateful we are."

"Our volunteers across this entire country, they are the ones who saved us," Barber told the crowd.

"They are the ones who cancel holidays to stay here and look after us, and I will speak now very confidently on behalf of a nation when I say to those volunteers, thank you."

Raising over 9 million Australian dollars (6 million U.S. dollars) for people in need, Barber said, "As Aussies, we band together because we have to look after each other."

With a brother-in-law currently serving as a volunteer firefighter in Queensland State, Irish pop star Ronan Keating told the 7 Network it was one show he just had to be a part of.

"I wanted people in Australia to know that we heard you, and that you weren't alone," he said.

"That was really important to me, that I could be here and perform or do whatever just to stand in solidarity."

Donations from the mammoth 10-hour gig will now go to Red Cross disaster relief and recovery fund, rural and regional fire services and animal welfare group, the RSPCA.

A man in Australia is lucky to be alive on Tuesday, after spending the night clinging to a tree in floodwaters.

Battered by a low pressure system bringing record rainfall and damaging winds, several drought-affected, bone-dry rivers near the township of Bega in New South Wales (NSW) State were instantly turned into roaring rapids in a matter of hours.

Walking near the Brogo River at around 6:00 p.m. local time on Monday, the man was quickly swept away by the rising floodwaters.

Desperately trying to stay afloat, he grabbed onto a tree where he stayed until 4:00 a.m. this morning, until a local resident spotted the man and called for help.

"He wasn't in great condition when we pulled him out," local State Emergency Service Commander Michelle De Frisbom told the Australian Broadcasting Corporation.

"He was suffering the effect of hypothermia ... even though it wasn't that cold."

"He had been in the water for quite a number of hours ... he is one very lucky man."

Able to be helped from the water by boat, the man was just one of around 260 flood rescues that have taken place on Australia’s east coast over the past few days.

Forecasters predict more severe weather could strike later in the week, putting more pressure on emergency services.