Australia's first climate risk assessment will be based on a scenario well below the current trajectory of a "hellish" 3C rise in global temperatures.
The assessment has been billed a crucial part of Australia's climate change response.
It will identify and tease apart physical risks like extreme heat, with the information to inform adaptation strategies.
But there are concerns it could be outdated before it's written.
Greens Senator Larissa Waters says she can't understand why bureaucrats are working to a scenario of 1.5 to 2C of warming by 2050.
"We're not on track for that ... I wish we were," she told officials from the climate change department at a Senate estimates hearing on Monday.
She pointed to high-level warnings about accelerating climate change despite the world's Paris pact commitments to limit warming to 1.5C.
"I don't understand why you are doing a risk assessment based on a scenario that's so below what's actually going to happen," she said.
"That doesn't give you an adequate picture of risk. Isn't the whole point of doing this risk analysis to understand what the risks are?"
Officials confirmed the risk assessment would be based on two scenarios: 1.5 to 2C of warming by 2050, and 2 to 3C by 2090.
"We don't think it's unrealistic. You are expressing your take on it," Deputy Secretary Jo Evans told Senator Waters.
"We've formed the approach we've taken based on a lot of consultation ... if in the future we want to consider other ranges we'll be able to do that."
Senator Waters replied: "So you actually think that we will constrain warming to 1.5C by 2050?".
"Well that's the scenario we're working with," Ms Evans replied.
The United Nations Environment Programme has warned that under current policies the planet is on track to reach 3C of warming by the end of the century, something the UN secretary-general has called hellish.