The latest special report by the UN's climate change panel is being published the same week as a summit aimed at upping ambitions on tackling global warming.
A new UN report is set to issue a stark warning on the impact of climate change on oceans and frozen areas, amid a push to ratchet up efforts to tackle the crisis.
The latest in a series of special reports from the Intergovernmental Panel on Climate Change (IPCC) is being published in the same week as countries meet at the UN for a summit aimed at upping ambitions on tackling global warming.
The study, which examines the oceans, coasts and the cryosphere - or frozen areas of the world - is set to warn of huge increases in flooding damage, melting ice caps and glaciers and more ocean heatwaves that bleach and kill coral.
A draft of the report leaked to AFP suggested that if global temperatures rise to 2C above pre-industrial levels, 280 million people could be displaced by rising seas.
The final draft, being agreed by countries in Monaco, is also expected to warn of the severe impacts of melting permafrost - permanently frozen ground - releasing large amounts of greenhouse gases.
Damage to fish stocks and seafood and an increase in extreme El Ninos - a weather phenomenon in the Pacific which pushes up global temperatures and can cause an increase in wildfires - are also on the cards.
The Nature Conservancy's global reef systems lead and IPCC report contributor Dr Elizabeth McLeod said the study "reinforces the urgency of the climate crisis".
She said: "We have a clear choice: continue to imperil our most vulnerable communities and stand by as our food and water security are threatened, or take ambitious action now to boost the health of our ocean and cryosphere, and protect both people and nature."
The oceans and cryosphere provide oxygen and freshwater, regulate weather patterns and help protect from the worst impacts of climate change, she said.
"Yet, as greenhouse gas emissions rise, the ocean is taking a direct hit - from warmer ocean temperatures that cause mass bleaching and mortality of corals; to fish migrations that negatively impact our global fisheries; to melting polar ice caps contributing to rising sea levels that devastate coastal communities around the world; the time for change is here.
"What we need is the rapid deployment and scaling-up of the most effective solutions to mitigate climate change and support adaptation," she urged.
Stephen Cornelius, chief adviser on climate change for WWF-UK and head of WWF's delegation in Monaco, said it was impossible to ignore the warning signs from the planet any longer.
"No matter what any sceptic might say, the risks we face in the future are real and, if left unchecked will have disastrous consequences for millions of people and for the planet's most vulnerable ecosystems.
"Rapid and deep cuts to global greenhouse gas emissions are crucial to limit many climate risks and will also make adaptation easier and more effective."
The report is being published after world leaders gather in New York for a climate action summit convened by UN secretary-general Antonio Guterres to urge countries to up their climate efforts.
Dozens of countries are expected to commit to enhancing their climate plans by 2020, to tackle the gap between the international Paris Agreement to curb temperature rises to 1.5C or 2C above pre-industrial levels and current commitments which put the world on track for around 3C of warming.
Businesses are also delivering plans to meet the tougher 1.5C threshold, with Nestle the latest multinational company to announce a 2050 "net-zero" emissions target.
The latest report follows an assessment last year from the IPCC that found the impacts of climate change, from droughts to rising seas, will be less extreme if temperature rises are curbed at 1.5C above pre-industrial levels than if they climb to 2C.