The Intergovernmental Panel on Climate Change (IPCC) Special Report on the Ocean and Cryosphere in a Changing Climate released last week highlights the urgency of prioritizing timely, ambitious and coordinated action to address unprecedented and enduring changes in the ocean and cryosphere.
The ocean and the cryosphere play a critical role for life on Earth. A total of 670 million people in high mountain regions and 680 million people in low-lying coastal zones depend directly on these systems. Four million people live permanently in the Arctic region, and small island developing states are home to 65 million people. There is overwhelming evidence that warming of the planet is resulting in profound consequences for these ecosystems and their inhabitants.
Major changes in high mountains are affecting downstream communities with increased exposure to hazards and changes in water availability, the report said. It predicted further decline of glaciers, snow, ice and permafrost, with increased hazards for people from landslides, avalanches, rockfalls and floods. Glacial retreat is altering water availability and quality downstream, with implications for communities, agriculture and hydropower.
Loss of polar ice sheets and expansion of the warmer oceans are driving sea level rise, which will continue for centuries, the report stated. Sea level rise will increase the frequency of extreme sea level events, which occur for example during high tides and intense storms, increasing risks for many low-lying coastal cities and small islands. Some island nations are likely to become uninhabitable due to climate-related ocean and cryosphere change, the report said, but habitability thresholds remain extremely difficult to assess.
The oceans have absorbed more than 90% of the excess heat in the climate system. Ocean warming reduces mixing between water layers and, as a consequence, the supply of oxygen and nutrients for marine life. Warming and changes in ocean chemistry are already disrupting species throughout the ocean food web, with impacts on marine ecosystems and people that depend on them, the report stated.
Marine heatwaves have doubled in frequency in 3 decades and increased in intensity. They are projected to further increase in frequency, duration, extent and intensity. Ocean warming and acidification, loss of oxygen and changes in nutrient supplies, are already affecting the distribution and abundance of marine life in coastal areas, in the open ocean and at the sea floor.
Shifts in the distribution of fish populations have reduced the global catch potential. In the future, some regions, notably tropical oceans, will see further decreases, but there will be increases in others, such as the Arctic. Communities that depend highly on seafood may face risks to nutritional health and food security.
The extent of Arctic sea ice is declining in every month of the year, and it is getting thinner. If global warming is stabilized at 1.5°C above pre-industrial levels, the Arctic ocean would only be ice-free in September – the month with the least ice – once in every hundred years. For global warming of 2°C, this would occur up to one year in three.
The IPCC report has projected widespread permafrost thawing in the 21st century. Even if global warming is limited to well below 2°C, around 25% of the near-surface permafrost will thaw by 2100. If greenhouse gas emissions continue to increase strongly, there is a potential that around 70% of this permafrost could be lost.
Arctic and boreal permafrost hold large amounts of organic carbon, almost twice the carbon in the atmosphere, and have the potential to significantly increase the concentration of greenhouse gases in the atmosphere if they thaw. It is unclear whether there is already a net release of carbon dioxide or methane due to the ongoing thaw of the Arctic permafrost.
In the future, increased plant growth can increase the storage of carbon in soils and offset carbon release from permafrost thaw, but not at the scale of large changes on the long term. The report also stated that wildfires are disturbing ecosystems in most tundra and boreal as well as mountain regions.
The report finds that strongly reducing greenhouse gas emissions, protecting and restoring ecosystems, and carefully managing the use of natural resources would make it possible to preserve the ocean and cryosphere as a source of opportunities that support adaptation to future changes, limit risks to livelihoods and offer multiple additional societal benefits.
Knowledge assessed in the report outlines climate-related risks and challenges that people around the world are exposed to today and that future generations will face. It presents options to adapt to changes that can no longer be avoided, manage related risks and build resilience for a sustainable future. The assessment shows that adaptation depends on the capacity of individuals and communities and the resources available to them.
The report gives evidence of the benefits of combining scientific with local and indigenous knowledge to develop suitable options to manage climate change risks and enhance resilience. This is the first IPCC report that highlights the importance of education to enhance climate change, ocean and cryosphere literacy. It comes as a timely reminder of the benefits of ambitious and effective adaptation for sustainable development and, conversely, the escalating costs and risks of delayed action.