SINGAPORE - A major report released by the United Nations' Intergovernmental Panel on Climate Change (IPCC) on Wednesday (Sept 25) paints a grim picture of accelerating sea level rise, faster melting of ice caps and glaciers and low-lying cities and islands facing more extreme coastal flooding.
The panel's special report on oceans and ice-covered parts of Earth adds to a growing number of scientific warnings that mankind needs to radically cut greenhouse gas emissions and adapt to the changes already locked in.
What is the report?
The IPCC's Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) was compiled by more than 100 scientists from 36 nations based on nearly 7,000 publications with the goal of summarising the latest science for policymakers around the globe.
The cryosphere refers to the 10 per cent of Earth covered by ice, from the polar ice caps to glaciers in the Himalayas, Arctic, Andes and Alps.
The 43-page summary released on Wednesday was approved after a five-day review session in Monaco involving scientists and diplomats.
It is the third IPCC special report since last October.
The two previous reports looked at the impacts of global warming of 1.5 deg C and the need to radically overhaul the way we grow food to limit destruction of forests and to cut food waste.
What does the report say?
The report shows just how vital seas, ice caps and glaciers are to mankind and how tightly linked they are when it comes to climate change.
For example, tiny islands in the middle of the Pacific are far from the poles.
And yet accelerating ice melt, and increasingly warmer oceans - water expands as it warms - are already having drastic impacts, such as coastal erosion and salt water intrusion into freshwater ground water supplies.
The report says ice loss from Greenland and Antarctica is speeding up and is expected to accelerate from the middle of this century. Sea level will continue to rise for centuries.
Sea levels have already risen about 15cm during the 20th Century.
It could reach a further 30 to 60cm by 2100 even if greenhouse gas emissions are sharply reduced and global warming is limited to well below 2 deg C, but around 60 to 110cm if greenhouse gas emissions continue to increase strongly.
Major uncertainties, though, remain on how ice sheets will react to warming, especially in Antarctica, said Dr Valérie Masson-Delmotte, a co-chair of the IPCC's Working Group One, which looks at the physical scientific basis of the climate system and climate change.
Under the most pessimistic scenario of emissions continuing to increase through this century, sea level rise is projected to exceed rates of several centimetres per year resulting in a multi-metre rise by 2300.
Extreme sea levels and coastal hazards will be exacerbated by stronger tropical storms and more intense rainfall.
But sea level rise could be kept to 1m if deep emissions cuts are made, starting now.
The report also says high mountain glaciers in the Hindu Kush Himalaya region, which provide water for about two billion people, are melting quickly and this could accelerate, threatening drinking water supplies, agriculture and hydropower generation.
Glaciers elsewhere are melting fast as well.
Smaller glaciers found, for example, in Europe, eastern Africa, the tropical Andes and Indonesia are projected to lose more than 80 per cent of their current ice mass by 2100 under high emission scenarios.
Coral reefs are also increasingly under threat from higher sea temperatures and more acidic oceans, which damage the coral's calcium carbonate skeletons.
Marine heatwaves are projected to further increase in frequency, duration, extent and intensity.
Their frequency will be 20 times higher at 2 deg C warming, compared to pre-industrial levels. They would occur 50 times more often if emissions continue to increase strongly, a rate that would destroy most reefs.
Fisheries, already under threat from over-fishing and declining stocks, face more pressure from warmer waters and declining oxygen levels.
To date, the ocean has taken up more than 90 per cent of the excess heat in the climate system.
By 2100, the ocean will take up 2 to 4 times more heat than between 1970 and the present, if global warming is limited to 2 deg C, and up to 5 to 7 times more at higher emissions, the report says.
Ocean warming reduces mixing between water layers and, as a consequence, the supply of oxygen and nutrients for marine life.
The changes have already led to shifts in the distribution of fish populations. In future, tropical oceans could face further declines in catches, though there will be increases in other areas, such as the Arctic.
Why should we care?
The bottom line message from the IPCC and other scientific bodies is that mankind has run out of time and that climate change impacts are already being keenly felt. There is no dodging the growing climate emergency.
The world's poorest are the most vulnerable and least able to adapt but all nations, rich and poor, are at risk.
Pumping out greenhouse gas emissions at current record rates will condemn all societies to cope with more extreme weather, disruptions to food supplies, higher costs of adapting and rebuilding, destruction of nature and likely more conflict as some places become uninhabitable.
Making deep cuts and decarbonising economies by shifting away from coal, oil and gas, can lessen the risks, transform societies, cut pollution and reduce economic disruption.
What can be done?
Cutting greenhouse gas emissions is the main thing that can reduce the risks. But given a certain amount of warming is already locked in place and sea levels are rising, there a number of things that can be done to help coastal communities to adapt.
These include building dykes to hold back the sea, especially storm surges and king tides. Higher sea walls is another.
Build flood-proof homes and buildings and early-warning systems. Homes can be raised several metres to cope with storm surges and foundations strengthened. Larger buildings, such as hospitals, condominiums and office towers can be elevated, for instance, on piles.
Wetlands and coral reefs should be protected and restored where possible. Mangroves can also be replanted where practical to protect coastlines from erosion.
Populations can relocate in a managed retreat if safe, alternative localities are available. But many communities are reluctant to do this because of deep social and cultural ties to their local area.
What have been the reactions?
Scientists, including those who contributed to the report, have expressed deep concern.
"The report serves as a wake-up call to the world about the devastating consequences of failing to act to address climate change. We have no time to lose," said IPCC vice-chair Dr Mark Howden, who is also director of the Australian National University's Climate Change Institute in Canberra.
"An overarching main point that emerges from the report is that choices we make now are going to be key for the future for the ocean and cryosphere of our planet," said Professor Michael Meredith, an oceanographer and science leader at the British Antarctic Survey - Britain's national Antarctic operation.
"This is of huge importance, since the ocean and cryosphere influence global climate, sea level and ecosystems in many diverse ways, and have effects on the lives and livelihoods of everyone," Prof Meredith, a coordinating lead author of the report, told The Straits Times.
"We have never had such clear and almost real-time information on the state of climate and of the planet," said Dr Pep Canadell, executive director of the Global Carbon Project.
"There is absolutely no doubt that we are at a critical point in time of intensification of climate change impacts, and we need to begin deploying strategies for climate change adaptation."
"And above all, greenhouse gas emissions need to peak immediately and come down at a rapid pace if we are to avoid the worse impacts of climate change."
Ms Ko Barrett, IPCC Vice-Chair, told reporters in Monaco on Wednesday: "This report is unprecedented in the sense that it provides this complete picture of changes to water on the planet, from the highest mountain glaciers and polar regions to the depths of the oceans and the inter-connectedness of the way this water flows and impacts people across the world."