Projected rates of sea level rise and elevation change at cable landing stations by 2052. A: Sea level rise under SSP1–2.6 scenario. B: Sea level rise under SSP5–8.5 scenario (Clare et al, 2023).

By Rebecca Firth

Telecommunication and electrical service providers use subsea telecommunication cables to transmit data and power between landmasses separated by bodies of water. The entirety of a submarine telecommunication or power cable system is exposed to the potential hazards associated with climate change.

A subsea telecommunication cable system comprises two or more cable landing stations connected by a fiber-optic cable. The cable landing stations house equipment such as routers, switches and power feed. The fiber-optic cable may incorporate branching units that allow a cable to serve multiple landing points and repeaters that boost transmitted signals.

Subsea power cables commonly carry high-voltage direct current for long-distance transmission. Cable landing stations are located close to existing electrical substations or grid connection points to integrate power from the subsea cable efficiently into the regional or national electrical grid.

Impacts of Sea Level Rise and Storms

Sea level rise is a significant consequence of climate change, primarily driven by two factors: thermal expansion of seawater and the melting of ice sheets and glaciers. Between 2006 and 2015, the rate of global mean sea level rise was 8 mm per year, which is 2.5 times the rate for the period between 1901 and 1990 (1.4 mm per year).

Clare et al (2023) assessed the projected sea level by 2052 (over a 30-year operational life of a cable system) at cable landing stations, estimating that the rate of sea level rise is not geographically uniform. Moreover, within 100 years under the SSP1–2.6 scenario (warming to 1.5 to 2° C above pre-industrial levels), more than 50 percent of cable landfall locations are projected to experience more than 500 mm of sea level rise compared to 97 percent under the SSP5–8.5 scenario (warming exceeding 4° C above pre-industrial levels).

The majority of cable landing stations are located near tidally active regions and terminate at colocation facilities and points of presence that are designed to be weather and water resistant. However, they are not designed to be surrounded by or submerged in water. Durairajan et al (2018) investigated the impacts of sea level rise on terrestrial network infrastructure in the U.S., concluding that projected sea level rise by 2030 may immerse thousands of kilometers of terrestrial cable not designed to be submerged in water. The potential effects of tidal inundation include physical damage and corrosion, leading to signal loss. In addition, buried cables will be exposed continuously to these threats, and cables deployed over the past 20 years will be particularly vulnerable to damage due to the age of seals and cladding.

The risk of inundation increases in areas where there is a higher likelihood of storm surges. For example, in the Gulf of Mexico, it is anticipated that a 1-in-100-year storm surge may become a 1-in-30-year event by the end of the 21st century. At present, 4.1 percent of cable landing stations could be inundated by 1-in-100-year events, which increases to 7 percent by 2122 in the SSP5–8.5 scenario (Clare et al, 2023).

Hurricanes/typhoons/cyclones are also intensifying due to warmer oceans and shifting atmospheric conditions that promote wetter and more destructive storms.

In September 2017, Hurricane Irma caused widespread disruption to telecommunications services across the Caribbean and the U.S. East Coast, leaving millions cut off by inundated terrestrial cables. Subsea cables connecting Florida to the Caribbean islands were damaged, disrupting connectivity to the British Virgin Islands, the U.S. Virgin Islands and Puerto Rico. Typhoon Morakot, which struck in August 2009, caused extreme river discharge that led to significant damage to subsea cables connecting Taiwan to Guam and other parts of Asia. Subsea cables were damaged when debris-charged river waters plummeted to the seabed and down Gaoping Canyon. A second, more damaging sediment density flow arose three days later when river levels were near normal, damaging cables down to water depths beyond 4,000 m.

Projected shoreline change at beaches where climate-driven erosion is predicted to occur by 2100 under SSP5–8.5 scenario, based on median predicted values in Vousdoukas et al (2020).

Erosion

Erosion is another climate factor that puts subsea cables at risk. The severity depends upon the weather, wave climate, nearshore bathymetry, coastal topography, sediment supply, sea level rise and the presence of coastal ice.

Under the SSP5–8.5 scenario, the global median of predicted shoreline retreat is 128 m by 2100. Approximately 15 percent of the world’s sandy coastlines could experience severe (>100 m) erosion by 2050, escalating to 35 to 50 percent by 2100. Subsea cables on the continental shelf traveling to shore can be at risk where erosion exposes them to currents and waves.

For example, in 2012, Hurricane Sandy triggered considerable erosion, with numerous beaches and dunes losing up to 6 m vertical height, which permitted waves to travel further inland. Global Marine Systems conducted a site visit to Long Island, New York, one week following Hurricane Sandy making landfall. Hurricane Sandy caused severe erosion of beach sand and significantly changed the local beach profile. The lower shore dropped. At the top of the beach, near the boardwalk, the beach level was higher than normal, where sand had been driven up the beach by the large storm surge.

Two open plots of land were designated to store the sand washed inland during the hurricane, called “Mount Sandy” by the locals. The aftermath of this massive sand displacement reduced the sediment cover over subsea cables and pipes buried on the beach. Extensive beach nourishment was required, which involved the U.S. Army Corps of Engineers pumping millions of cubic yards of sand to restore the beach.

“Mount Sandy,” the pile of sand washed inland by the hurricane on Long Island in 2012. (Credit: Global Marine Systems)

Pipe exposed due to massive sand displacement on Long Island Beach during Hurricane Sandy. (Credit: Global Marine Systems)

Coastal permafrost erosion is another risk, affecting more than 30 percent of Earth’s coastlines situated in Arctic regions. Over the period of 1950 to 2000, the mean coastal permafrost change rate was -0.5 m a year across the Arctic. As permafrost thaws, the shoreline weakens and becomes less stable, leading to loss of coastline. Sea ice acts as a protective barrier, reducing the impacts of waves and storms, but as Arctic sea ice cover declines, coastal retreat is amplified. Consequently, permafrost thaw and coastal erosion may compromise the stability of subsea cables coming to land on Arctic coasts.

A Shifting Fishing Industry

In Europe, as sea temperatures rise, many fish species that prefer warmer waters are migrating up to the North Sea, a trend called “tropicalization.” Species such as sea bass, red mullet and John Dory, which were once more common in southern European waters, are increasingly being found in the North Sea. These species are thriving in the warmer conditions, leading to shifts in the ecosystem and causing fishing fleets to follow.

This trend is expected worldwide and can bring fishing activities closer to where submarine cables are laid. Increased fishing in new regions can result in heightened risks of cable damage from trawling, especially in areas where deep-sea trawling or other high-risk fishing methods may not have been prevalent before. Cables in these areas become vulnerable to anchor drags, net entanglements and other gear impacts, which can sever or displace cables.

Coldwater species such as cod, haddock and plaice are struggling with rising temperatures. For example, the North Sea is warming faster than many other marine regions, and this is driving some coldwater species to deeper, cooler waters or further north toward the Arctic Circle.

Cod populations, which have been central to North Sea fisheries, are moving to cooler regions, and this shift affects their abundance and reproduction rates, making it harder for fisheries to maintain sustainable catches.

Furthermore, submarine cables in deeper waters may become more exposed to new fishing pressures, particularly from larger vessels and more intensive fishing operations, resulting in a higher likelihood of cable strikes.

New Shipping Routes

Climate change is opening up new shipping routes in the Arctic as ice melts, which has significant implications for submarine cables and global data infrastructure.

The Northern Sea Route that runs along the Russian Arctic coast is becoming more navigable as ice melts earlier and forms later in the year, providing a shorter path between Europe and Asia. The Northwest Passage traversing the Canadian Arctic archipelago is also becoming more accessible, offering another potential path between the Atlantic and Pacific Ocean. As more vessels travel through Arctic waters, there is a higher risk of cables being damaged by ship anchors or fishing activities in high latitudes. As traffic increases, the potential for accidents rises.

Monitoring the life cycle and extent of the sea ice will be necessary throughout the life of a cable system. If the present trends of decreasing sea ice persist, cables in shallow water will be increasingly prone to abrasion. Additionally, ice scouring caused by the keels on multiyear ice is a commonly cited risk to cables. Ice scour from icebergs or multiyear sea ice occurs when they ground on the seabed and gouge out the sediments. Ice gouges have been found to occur in water depths up to 70 m and can range in incision depth up to 5.5 m.

Mitigation and Adaptation

The International Cable Protection Committee (ICPC) published a recent paper on climate change stating that “the global climate has been and will likely continue warming at an unprecedented rate as a result of human-induced greenhouse gas emissions.”

The ICPC commented further at a consultative meeting of the United Nations on sea level rise and its impacts: “It is critical that sea level rise and climate change be considered in future route and landing station planning, as well as assessing the risk posed to existing systems.”

Current mitigation and adaption strategies to protect against the impacts of climate change include: increased armoring and/or cable burial protection at shore-ends where erosion is increasing; liaising with fishermen, route clearance of discarded fishing gear, and use of more resistant cable; avoiding low-lying areas for beach manholes and cable landing stations; learning local environmental conditions and historic events; and geographical information system (GIS) analysis using various geospatial data sets incorporated into desktop studies to identify optimal routes and landing points.

Projections of climate drivers known to damage cables as discussed in the ICPC paper are on the rise, implying that cables will likely be exposed to more hazardous conditions. Where achievable, resilient cable routing should avoid submarine canyons and channels subject to turbidity currents and other sediment flows.

This particularly applies in regions exposed to cyclones. Additionally, establishing redundant paths in the design of routes to allow for alternative channels if a primary cable is damaged would help to maintain connectivity and reduce potential service disruptions.

To appropriately evaluate the impact of climate-driven changes, it is critical to verify site-specific environmental conditions. In particular, coastal erosion is determined not solely by ocean and atmospheric conditions but also by local morphology, substrate, and human-built coastal structures. The rates at which erosion may occur at cable landing stations (and along their shore approaches) should be calculated to inform how erosion may change over the design life of a cable system.

Cable technology advances may be required to address Arctic-specific challenges, such as more durable, ice-resistant materials and smart cable systems that can monitor conditions and automatically report damage or interruptions.

Given shifting fishing patterns, submarine cable operators may need to adapt their protection measures. These could include increasing the burial depth of cables in regions now more exposed to fishing activity, reinforcing them with armoring in higher-risk areas, and utilizing deepwater areas with less fishing activity. As fish populations migrate, tensions could increase between the fishing industry and cable operators. Collaborative management strategies could mitigate risks, such as information sharing on cable locations and fishing routes and creating policies that balance the interests of both sectors.

Conclusion

The impacts of climate change will be diverse worldwide, and these changes are already being felt. The subsea cable industry is embracing numerous mitigation and adaptation strategies. Cable routes should be developed based on the analysis of local conditions, and both short-term events and long-term impacts should be considered.

As cable routes traverse higher latitudes, there is a risk of new hazards. Multiple geospatial data sets should be integrated, and future routing should consider oceanographic, atmospheric, and geological components on a case-by-case basis. Being mindful of the current and anticipated challenges is key for building resilient global communications and power networks.

Rebecca Firth is a route engineer and project assistant at OceanIQ.