Germany is hosting the talks and asked Bainimarama to act as president to highlight how the issue is affecting Pacific island nations on the frontline of global warming.
As incoming president of the United Nations Conference on Climate Change (COP23), Bainimarama has criss-crossed the world in recent months voicing islanders' fears.
"Rising seas, extreme weather events or changes to agriculture... threaten our way of life, and in some cases our very existence," he said.
"We who are most vulnerable must be heard."
Scientists warn some low-lying island nations risk being swamped entirely as sea levels rise.
Droughts and flooding have become commonplace across the region as the weather swings from one extreme to the other.
Farmland and sources of drinking water have been rendered useless by seawater and even graveyards have been lost to rising tides in the Marshall Islands.
Bainimarama said Fiji, an island nation of about one million people, was left reeling when Severe Tropical Cyclone Winston hit like a wrecking ball in February last year.
Packing gusts of 325 kilometres (202 miles) per hour, it was the strongest cyclone to ever make landfall in the South Pacific.
Its trail of destruction left 44 people dead, destroying 40,000 homes and wiping out a third of Fiji's economy.
Such super-cyclones used to be a once-in-a-decade occurrence, but only a year before Cyclone Pam slammed into neighbouring Vanuatu, killing at least 11 people.
Bainimarama said Fiji now had to live with the threat that such tempests could flare up "out of nowhere, at any time".
"We are facing a situation in which a single event scoring a direct hit on Fiji could wipe out years of development and set us back for decades," he said.
- 'Frighteningly real' -
He said the experiences of Fijians and people around the world meant there was no longer room to question the scientific consensus on global warming.
"This says that man-made climate change is not a hoax, it is frighteningly real," he said.
"The evidence is global -- whether it is the loss of the Arctic ice floes within four decades, the loss of cities like Miami in five decades, or in the Pacific, the loss of three entire nations over a similar period -- Kiribati, Tuvalu and the Marshall Islands."
Bainimarama said his top priority at the Bonn meeting was "to build a grand coalition of governments, civil society and the private sector" to implement the Paris Agreement on climate change.
Under the deal struck in the French capital in 2015, more than 190 countries agreed to limit global warming to "well below" 2.0 degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial levels.
Bainimarama's comments come just days after the UN's environment chief warned there is a "catastrophic" gap between national pledges to reduce greenhouse gas emissions and the actions needed to meet that target.
"One year after the Paris Agreement entered into force, we still find ourselves in a situation where we are not doing nearly enough to save hundreds of millions of people from a miserable future," said Eric Solheim.
Fiji and other island nations hope to persuade major polluters to go further and keep global warming to 1.5 degrees Celsius of pre-industrial levels.
Bainimarama described it as the greatest challenge humanity has ever faced, saying it will take a global mobilisation and commitment akin to preparing for war.
He was optimistic the United States would not carry out President Donald Trump's pledge to withdraw from the Paris Agreement, saying the evidence underpinning the deal was overwhelming.
"The issue is settled and the impacts are obvious, and humankind ignores these facts at its peril," he said.