A new report by the United Nations warns that global warming is heating up the oceans to an unprecedented degree, so much so that their chemistry is being altered with profound implications for global food supply and millions of people living in coastal areas. The IPCC (Intergovernmental Panel on Climate Change) Special Report on the Ocean and Cryosphere in a Changing Climate, approved on 24 September by the 195 IPCC member governments, is further proof that global warming needs to be limited to the lowest possible level, as outlined in the 2015 Paris Agreement. This report will be a key scientific input for the climate and environment negotiations among global leaders, such as the UN Framework Convention on Climate Change Conference (COP25) in Chile in December. It was prepared by 104 authors and reviewed by editors from 36 countries.

The report reveals multiple, cascading effects on the planet and all living beings due to the rise in ocean temperatures. People in mountain regions are increasingly exposed to hazards and changes in water availability with a steady, continuing decline in glaciers, snow, ice and permafrost (cryosphere). This, in turn, will impact water availability and quality downstream. Melting glaciers will also result in a significant rise in sea levels which will increase the frequency of extreme sea-level events, such as high tides and intense storms. Increase in global temperatures means that once-in-a-century events will occur every year by mid-century in many regions. This has serious consequences for coastal cities and some island nations are likely to become uninhabitable.

Fish populations are declining in many regions as warming waters negatively impact marine ecosystems. Food supply and livelihoods face serious adjustments, as a result. Currently, fish and seafood provide about 17 per cent of the world’s animal proteins and millions of people depend on fishing economies for their livelihoods. 

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 2-4 times more heat than between 1970 and the present if global warming is limited to 2 °C, and up to 5-7 times more at higher temperatures. Even the former levels are significant enough to produce drastic changes. The ocean has taken up between 20 to 30 per cent of human-induced carbon emissions since the 1980s, causing ocean acidification.

The report found that measures such as substantially reducing greenhouse gas emissions, protecting and restoring ecosystems, and carefully managing the use of natural resources are required if the ocean is to be preserved. The survival of humans may depend on protecting the ocean. As Hoesung Lee, Chair of the IPCC, explains, ‘The open sea, the Arctic, the Antarctic and the high mountains may seem far away to many people, but we depend on them and are influenced by them directly and indirectly in many ways – for weather and climate, for food and water, for energy, trade, transport, recreation and tourism, for health and wellbeing, for culture and identity.’