Fluctuations in global temperatures as a result of climate change have already had many observable effects on our surrounding environment. Glaciers have decreased in size, plant and animal ranges are shifting and we are experiencing more intense heat waves and more frequent and powerful storms.

Scientists have high confidence that global temperatures will continue to rise during the upcoming decades, as a result of greenhouse gasses produced by humans. The Intergovernmental Panel on Climate Change (IPCC) includes 1300 scientists from right over the globe, and they predict a temperature increase of 2.5 to 10 Fahrenheit over the next century. The extent of climate change impacts on different regions will vary over time, and will also depend on the ability of societal and environmental systems to adapt to climate change.

Climate Change and The Ocean

The ocean, coastlines and coastal communities are at the front line of climate change, as they are being disproportionately impacted by increasing carbon dioxide and greenhouse gas emissions from human activities. Predicted impacts of climate change on the ocean is also now becoming a reality. Sea ice is melting at a rapid pace, resulting in accelerated sea level rise, as well as ocean acidification and stratification as a result of more absorbed carbon in the ocean. The oceans have absorbed more than 90% of the warming caused by humans since the 1970s, and if the oceans didn’t provide that service, the atmosphere would’ve warmed by 100 degrees Fahrenheit.

Climate change is resulting in higher oceanic temperatures, which result in catastrophic coral bleaching events, the mass migration of marine species, as well as impacting the growth of fish and cephalopods. The melting of polar ice is not only impacting polar bears, penguins and walruses, but also the production of algae that depends on sea ice. When land-based polar ice melts, it results in sea-level rise. This, coupled with warmer sea water which is expanding to take up more space, is posing a threat for many human-inhabited coastal areas. Climate change also has the ability to alter ocean currents due to its impacts on ocean temperatures and wind patterns, which is impacting migratory patterns, and also in turn impacting Earth’s climate (as currents play a major role in maintaining the climate).

What About Waves?

Sea level rise and warming temperatures are not the only impacts of climate change on the ocean. A study published in Nature Climate Change has predicted that a warmer planet will also alter ocean waves along more than 50% of the world’s coastlines.

Scientists are able to study how waves have shaped our coasts, by investigating the presence of beaches, spits, lagoons and sea caves. They are then able to determine how our coast looked in the past, and also understand historic sea levels. However, this research mostly assumes that although sea levels have changed over time, wave conditions have remained the same. When considering the future of sea level rise, scientists also assume similar wave conditions.

Waves are generated by wind on the surface of the ocean. As mentioned above, climate change is altering international wind patterns, and therefore it can be assumed that wave patterns will also be influenced. Apart from the impact of wind on waves, sea level rise will also influence how waves travel from deeper to shallow water.

A study published in Science analyzed 33 years of wind and wave records using satellite measurements, and found that in the past three decades, wind speeds have increased by 1.5 meters per second, and waves have increased in height by 30 cm – a 5 % increase, over this short period of time. These changes in winds and waves were most pronounced in the Southern Ocean – and it is important to note that waves generated in the Southern Ocean are able to travel into all the other ocean basins along swells, as far north as San Francisco.

A study looking into the natural variability and warming signals in global ocean waves found that the coasts of South and Western Australia, Pacific and Caribbean Islands, East Indonesia, Japan and South Africa are already experiencing more powerful waves as a result of global warming.

The Future of Waves

Given these observed changes in historic wave conditions, scientists were eager to model future changes in atmospheric circulation and how it would alter global wave conditions.

Research teams that form part of the  Coordinated Ocean Wave Climate Project investigated a range of different global wave models in different future climate scenarios to determine how our waves may look and behave in the future. They found that if the 2oC (3.6oF) temperature increase in accordance with the Paris Agreement targets were kept, changes in wave patterns were minimal and would stay inside natural variability.

In a business-as-usual scenario where warming continues along the current trends, models indicated that there would be significant changes in wave conditions along 50% of our coasts, although the changes varied between regions. Less than 5% of the coasts are at risk of experiencing increased wave heights, however 15% of the coasts are predicted to experience decreased wave heights, which will significantly alter coastal systems.

The areas that experience waves of similar height as current conditions, may experience differences in lengths or frequencies of waves. This may result in more forceful waves hitting the coast, running up the beach and possibly resulting in flooding. It is possible that waves will also travel from altered directions, changing how sand is deposited along the coast. This will have significant impacts on coastal developments.

Although each region is expected to experience varying changes in wave patterns and force, the models predicted that 40% of the world’s coastlines are likely to experience changes in wave height, period and direction simultaneously.

Knowing exactly how coastlines will respond to future climate change is complex and will depend on an interplay of many processes all depending on different variables. To focus on only sea level rise, while overlooking the impact of waves on our coasts, is a simplification of the impacts of climate change, and can potentially be costly to human lives.