Former Royal Dutch Shell senior executive Ian Dunlop told Macquarie Group's annual general meeting on Thursday the bank's financing activities had prioritised energy security and fossil fuel expansion at the expense of human security.
"If you keep doing things in the way we've been doing it, and they lead to the potential temperature increase that have been mentioned at two and a half, three degrees ... they're not livable worlds," Mr Dunlop said.
"These will be catastrophic, absolutely catastrophic.
"Even at two degrees, we're going to see widespread mortality, food and water shortages, conflict and economic devastation."
Mr Dunlop also chaired the Australian Coal Association in the late 1980s.
Macquarie's board has recommended shareholders reject a resolution co-filed by activist group Market Forces and super fund provider Australian Ethical asking the bank to disclose whether it is still committed to aligning its lending with the goal of net zero emissions by 2050.
Market Forces says Macquarie has become Australia's most aggressive fossil fuel financier, tripling its oil and gas financing over the past three years.
At the same time, the nation's big four retail banks have reduced their exposure to oil and gas expansion by $8 billion.
Chairman Glenn Stevens said climate change was a "wicked problem", but Macquarie could not set global policy or do things that really addressed the problem for the world.
"But we're seeking to play our part in a way that we think makes sense, is tractable, practical and is in the interests of shareholders," the former governor of the Reserve Bank of Australia said.
Another shareholder, Helen Scotts, commended Macquarie for investing in fossil fuels and said she hoped the investment bank would invest in nuclear energy next.
"I don't know of a country at the moment that relies totally on renewables for their energy," she said.
"We really need to keep going with fossil fuels to supplement the renewables until we're ready for the changeover."
Before the meeting, the Australian financial services powerhouse announced it had tapped the head of its retail bank as its next chief executive.
Macquarie Group's Greg Ward will replace 64-year-old Shemara Wikramanayake, who will retire in November after eight years as chief executive and managing director.
Mr Stevens told reporters Ms Wikramanayake had delivered sustained growth and momentum for the company during her tenure.
"She's navigated us through some very difficult times with pandemics, various other geopolitical events, and she's done that with incredible strength and grace, and with an unwavering commitment to the company and to its people and our resource and culture," he said.
Mr Ward is a 30-year veteran of Macquarie and served as its chief financial officer during the global financial crisis.
He had done an "extraordinary job" repositioning Macquarie's retail bank as a significant source of innovation and competition in the banking market during his 13 years leading the division, Mr Stevens said.
Shares in Macquarie, long referred to as the "millionaires' factory" for its high-paid executives, edged higher in early afternoon trading to $255.59 a piece, giving the group a market value of almost $98 billion.
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