The ocean has a significant impact on the Earth’s temperature and carbon budget. It has absorbed approximately 25% of the carbon dioxide produced by fossil fuel combustion and other human activity, as well as slowing warming by absorbing heat.

Melting ice on land, such as glaciers and ice sheets in Antarctica and Greenland, is caused by global warming, contributing water to the ocean and thereby raising sea level. The warming that has affected the atmosphere is progressively permeating the entire ocean, causing the ocean to expand and contribute to sea-level rise.

Ice and snow help to chill the climate by reflecting sunlight. Removing the ice to expose darker land or ocean diminishes cooling and so accelerates climate change. Permafrost thawing emits huge volumes of greenhouse gases, contributing to additional warming.

The ocean and cryosphere serve as habitats for ecosystems and the human population, both of which will be influenced by climate change. Aside from the many communities that rely on the water for resources such as food, over 680 million people live fewer than 10 metres above sea level, making many of them vulnerable to sea level rise. A comparable amount reside in high mountain regions where variations in snow and ice cover have an impact on their water supply.

Where we are and where we are going

The water has warmed throughout its depths and is still doing so at a rapid pace. At the surface, maritime heatwaves have more than doubled in frequency and intensity. The ocean has gotten more acidic as a result of absorbing carbon dioxide. Warming and increased acidity, as well as decreased oxygen content and changes in sea ice that floats over the polar waters, have all had an impact on marine ecosystems. All of these processes are expected to continue, leading to the shrinking of polar habitats and the movement of warm-water species into previously temperate waters. Even in a low-emissions scenario, almost all warm-water coral reefs will suffer major losses and local extinction.

Changes in ocean fish supplies and distribution are projected to result in considerable changes in fisheries and difficulties to their governance, creating nutritional hazards in some locations. There is also a possibility that some marine species will no longer be able to develop their shells as a result of acidification under a high emission scenario1.

Large amounts of heat are transported to the North Atlantic via ocean circulation, warming the United Kingdom and Europe. The circulation system known as the Atlantic Meridional Overturning Circulation (AMOC) would diminish as temperatures rise, and the effects on European climate and ecosystems, for example, are difficult to predict. The AMOC is unlikely to end before 2100, although it cannot be ruled out on longer durations if greenhouse emissions stay high.

Sea Level

Since 1902, global sea level has risen between 12 and 21 cm as a result of ocean warming and expansion, as well as melting land ice, with an increased contribution from the Greenland and Antarctic Ice Sheets in recent years. Under a low-emission scenario, sea level is anticipated to rise by 29 to 59 cm by 2100, relative to the 1986–2005 period, and by 61 to 110 cm under a high-emission scenario. Even if the climate stabilises, it is likely to rise for many more millennia after 2100 under all emission scenarios. Under a low-emissions scenario, sea level rise is expected to be 0.6 to 1.07 m by 2300. Under a high-emission scenario, sea level is expected to rise between 2.3 and 5.4 m by the 22nd century, at a rate of several millimetres each year (more than ten times the present rate).  The wide ranges of these figures reflect the lingering uncertainty in major contributing processes, such as those affecting the stability of the Greenland and Antarctic ice sheets.

The highest sea levels, those experienced during storm surges and cyclones, which have historically occurred once every century, will be reached annually in most sites by 2100. Because of the threats that sea level rise poses to populations and infrastructure, communities in low-lying coastal locations, including island atolls, will almost certainly be forced to relocate under higher sea level rise forecasts.

Cryosphere

Warming in recent decades has resulted in the loss of ice mass from mountain glaciers around the world. Warming has been exacerbated in the Arctic, where it has resulted in a 50 percent loss in June snow cover since 1967, as well as a thinning and decline in the area of Arctic sea ice to an extent likely not seen in at least 1,000 years. These impacts have resulted in:

– Changes in the distribution and seasonal activities of land-based organisms and ecosystems in polar regions and high mountain locations.

– Increased threats to food and water security in several high alpine locations and the Arctic.

– Disruption of indigenous peoples’ customary hunting and fishing activities in the Arctic; and  Increased access for ships and commercial development in the Arctic due to reduced sea ice.

If the repercussions worsen in the future, particularly under high-emission scenarios, there are concerns about:

The impact on mountain water resources as many glaciers disappear completely;  Landslides, infrastructural damage, and greenhouse gas emissions in polar and high mountain locations owing to permafrost thawing; and  Cultural, aesthetic, and economic implications of a changing Arctic.

What can be done to reduce the impacts?

The most effective strategy to avert the direst consequences is to achieve rapid and significant reductions in emissions across all industries. Even if and when emissions reach net-zero and temperatures stabilise, ice sheet losses and sea-level rise will continue, but the amount and rate of change will be significantly reduced under low-emission scenarios. Limiting the duration of any warm period would lessen the likelihood of negative consequences. Because more changes to the oceans and cryosphere are unavoidable, communities must still take steps to adapt to ocean and cryosphere change. Many of individuals who are most vulnerable to change live in low-income countries with less capability to respond.

We at Wild Harbour are dedicated to educating our customers and industry about the importance of making positive changes to reverse the current trajectory of climate change. We are pleased to be a carbon-neutral business, delivering restaurants around the UK with wild-caught fish and shellfish from the Cornish coast.