Sea ice
The importance of the sea ice and its state of health
The sea ice is a floating ice sheet that forms in the polar ocean regions. The survival of, for example, polar bears depends primarily on the early formation of this icy surface, as it is here that they hunt. According to satellite observations that began in 1979, the average maximum extent of the Arctic during the months of March is decreasing decade by decade, confirming a worrying trend.
Human activity is causing the Earth's average temperature to rise, which is having a particular impact at the poles, where both sea ice and glaciers are seeing their surface area shrink year by year. Climate change is a reality and the state of the sea ice caps is one of the thermometers that warns of the seriousness of the situation and the urgency of taking measures, not only to protect ourselves, but also the biodiversity of the area.
What is sea ice
The ice shelves, present in both the Arctic and Antarctic throughout the year, are composed of frozen ocean waters over a wide but variable extent depending on the time of year. For example, during the winter months, the Arctic ice shelf increases in size until it reaches its maximum extent in March and loses ground during the following months. Its thickness ranges from one metre when it is renewed each year to four or five metres when it persists over time, which is the case in the areas closest to the poles.
The formation process is as follows: salt water freezes at a lower temperature than fresh water, specifically at -1.8 ºC, in a phenomenon known as cryoscopic descent. The sun's rays reach this area of the planet very weakened, and solidification begins at the surface because the lower part of the planet is warmer. Subsequently, small lenticular crystals of pure water are formed, which eventually coalesce to form a completely frozen sea floor.
Types of sea ice
The two major areas of sea ice are located in the Arctic and around Antarctica, at the South Pole. These ice caps exhibit opposite trends as they are situated in different hemispheres; that is to say, the northern winter coincides with the southern summer and vice versa, which means that when the Arctic ice cap is at its peak, the Antarctic ice cap shrinks considerably.
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Arctic sea ice
The Arctic sea ice is located in the Earth's northern hemisphere. It consists of sea ice that floats on the Arctic Ocean around continental landmasses such as Greenland and the coastlines of the Americas, Europe and Asia. Each year, the sea ice partially melts in the areas closest to these continents, allowing navigation through the Arctic Ocean. The extent of the sea ice changes throughout the year, reaching approximately 15 million km² in March before shrinking to around 6.5 million km² in September.
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Antarctic sea ice
Located in the Earth's southern hemisphere, the surface area of this ice floe varies even more dramatically throughout the year, at times almost disappearing. At the height of the cold season, known as the polar night, the area can reach 18.8 million km2. However, during the polar day — the next six months when the sun never sets — it can shrink to 2.6 million km2.
Sea ice, glaciers and ice shelves
Sea ice, glaciers and ice shelves are three types of ice formation that differ mainly in their origin and the environment in which they are found. Sea ice forms directly from the freezing of seawater in the polar regions. It floats on the ocean, is relatively thin and is characterised by numerous fractures. Its extent varies considerably throughout the year, expanding in winter and retreating in summer, making it a valuable indicator of climate change.
A glacier, by contrast, is a large mass of ice resting on land that forms through the accumulation and compaction of snow over many years in cold or mountainous regions. This ice does not float but rests on the ground and slowly flows downhill under the force of gravity, eroding rock and shaping the landscape. An ice shelf lies somewhere between the two: it is a floating extension of a continental ice sheet or glacier that remains attached to the ice resting on land. It forms when ice flowing from the interior of the continent reaches the coast and continues to advance over the ocean, gradually thinning with distance. Ice shelves can fracture into large blocks that become icebergs.
The importance of sea ice and their current status
Ice shelves are essential because of their ability to modulate the balance of atmospheric and oceanic heat. How do they do this? During the summer they reflect a significant part of the sun's radiation and during the winter they act as an insulator. In other words, ice shelves help keep the poles cool by limiting heat absorption. Given their importance, it is worth asking about their current situation.
According to the National Snow and Ice Data Center (NSIDC), affiliated with the University of Colorado Boulder, Arctic sea ice reached its lowest annual maximum since 1979 in 2025, covering 14.33 million km², reinforcing the downward trend observed over recent decades.
In addition to the overall decline in Arctic sea ice, the NSIDC researchers stress that the ice surface is becoming younger and more seasonal. In other words, it is weaker and more vulnerable to severe weather events such as those resulting from climate change. This also affects the surface of the Antarctic ice sheet, which, despite its particular idiosyncrasy — a more accentuated variability — follows a negative trend similar to that of the Arctic, in fact, in 2025, it reached 1.98 million km² at its annual minimum, one of the lowest figures recorded since 1978.
What are the consequences of sea ice loss?
The loss of Arctic sea ice has a number of knock-on effects that contribute to pollution and the degradation of ecosystems:
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Reduced albedo effect (reflection of solar radiation)
White ice reflects a large proportion of incoming solar radiation, whereas the dark ocean absorbs it. As sea ice disappears, more energy enters the climate system, warming both the water and the Arctic atmosphere. This reduction in Arctic albedo is a key factor in global warming.
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Changes in ocean currents and climate
As sea ice declines, the temperature and salinity of the ocean surface change. Extreme seasonal variations and severe weather events become more frequent.
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Impact on ice-dependent species
Many animals use sea ice as a platform for hunting, breeding or resting, including polar bears, seals, walruses and seabirds. With less ice available, they must travel further, expend more energy and endure greater stress to find food, potentially triggering changes in migration patterns and threatening species' survival.
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Changes to shipping routes and human activity
As sea ice retreats, new Arctic shipping routes become accessible, but the risks of pollution and the introduction of invasive species also increase.
SEE INFOGRAPHIC: The evolution of Artic sea ice over the last few decades
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Biodiversity on the sea ice
Global warming is one of the main drivers behind the loss of ice cover, significantly affecting the biodiversity associated with sea ice. Beyond polar bears, sea ice supports complex ecosystems. At its base are algae that grow beneath the ice and within its pores, providing food for microorganisms, krill and zooplankton and sustaining high biological productivity in these polar waters. These organisms, in turn, support fish adapted to extreme cold, seals, walruses and various whale species, as well as seabirds and, in Antarctica, penguins, which depend on sea ice for breeding and access to food.
In fact, almost a decade ago, the University of New South Wales (Australia) warned that one-third of the biodiversity found on polar seabeds was under threat as a result of climate change. Polar bears, together with seals, crustaceans such as krill and fish, form part of a food chain that could be severely disrupted if this issue is not addressed, undermining the delicate balance of sea ice ecosystems. The most dramatic example, and the one that produces the most striking images, is that of polar bears. They depend on sea ice to travel and hunt – in short, to survive – and the shrinking extent of sea ice threatens their habitat.
Iberdrola's firm commitment to mitigating global warming
The melting and fracturing of sea ice are just one consequence of a problem that has intensified over recent decades: global warming. Although its effects are unavoidable, at the Iberdrola Group we are working to minimise our greenhouse gas emissions and achieve carbon neutrality, helping to mitigate its ongoing impacts. To achieve this, we have made electrification and decarbonisation central pillars of our strategy.
However, our approach goes beyond operations and also focuses on conservation. That is why we developed our Biodiversity Plan 2030, through which we seek to contribute by reducing, restoring and offsetting impacts. The plan aims to avoid developments in areas of high ecological value, reduce pollution and restore affected habitats.
For example, at the New England Wind project, vessel management procedures and speed restrictions are implemented to protect the critically endangered North Atlantic right whale, which inhabits the area. Another important initiative is East Anglia ONE, where we supported the installation of two floating containers designed to collect plastic, as well as some of the oil, detergents and fuel floating near the port of Lowestoft, helping to reduce marine pollution.
In addition to delivering sustainable projects, we are also focused on developing innovative solutions to protect ecosystems through our PERSEO start-up programme, an open innovation initiative created to develop technologies and business models that promote sustainability at every level.