"In many ways, this letter is the product of despair as scientists witnessed the deadly fire season unfold," Australian National University climate scientist Professor Nerilie Abram explained.
"Scientists have been warning policymakers for decades that climate change would worsen Australia's fire risk, and yet those warnings have been ignored."
With a litany of heat records tumbling across Australia in 2019 and early into 2020, the letter warns that heat waves on land and in the oceans are becoming longer, hotter and more frequent, reports Xinhua news agency.
Expecting to see regular 50-degree-Celsius days in Sydney and Melbourne by 2040, the experts said increased wildfire risk was just one part of a deadly equation.
Other impacts could see Australia's iconic Great Barrier Reef under threat along with a multitude of marine species and land animals.
"Scientists by nature tend to be conservative. Perhaps that explains why many of the projected climate impacts made in the peer-reviewed literature seem to be occurring earlier than forecast," University of New South Wales Canberra fire researcher Professor Jason Sharples said.
"It's important to remember that what we are seeing now are the dangerous and costly impacts of just one degree Celsius of global warming."
"Yet while our climate changes rapidly, Australia's climate change policies stand still and the world is on track for three degree Celsius or more of warming by the end of this century."
University of New South Wales climate scientist Professor Katrin Meissner said "the thick, choking smoke haze of this summer is nothing compared to the policy smokescreen that continues in Australia".
"We need a clear, non-partisan path to reduce Australia's total greenhouse gas emissions in line with what the scientific evidence demands, and the commitment from our leaders to push for meaningful global action to combat climate change," she said, adding: "Not tomorrow, but right now."
( With inputs from IANS )