Coastlines at risk: Higher waves due to climate change

28 August 2019, by Griffith University / CEN Universität Hamburg

Photo: UHH/CEN/T.Wasilewski

A team of researchers has mapped out how much waves are likely to change around the globe under climate change and found that if we can limit warming to 2 degrees, signals of wave climate change are likely to stay within the range of natural climate variability. The study was just published in Nature Climate Change. However, if we do not reduce greenhouse gas emissions drastically, nearly 50 per cent of the world’s coast is at risk of wave climate change. PhD Mikhail Dobrynin from the Centre for Earth System Research and Sustainability (CEN) at the University of Hamburg contributed to the study.

If we don’t limit climate change to 2 degrees, waves will change in either wave height, period or direction. The southern coasts of Australia are one of the areas predicted to be at risk of increasing wave heights if we don’t limit climate change to 2 degrees. The team of researchers conducted a comprehensive assessment of existing, community-driven, multi-method global wave climate projections.

Wave climate is the nature of wave characteristics and how they occur naturally in the ocean, and how they’re distributed in time and space around the world. The three main parameters used to describe wave climate are height, length and direction.

Under a high-emission scenario, lead author Joao Morim from Giffith University and his team demonstrated widespread ocean regions with robust changes in annual mean significant wave height and mean wave period of 5–15% and shifts in mean wave direction of 5–15°. The study has found that there is agreement amongst wave climate projections for approximately 50% of the world’s coastline, with ~40% revealing robust changes in at least two variables. The analysis considered numerous projections for a time slice at the end of the century (2081-2100) compared with the present-day climate to quantify the results.

 ‘A precondition for our reliable results was the coordinated production and analysis of the large amount of data we needed for this,‘ says Mikhail Dobrynin from the CEN. Within the Coordinated Ocean Wave Climate project a total of ten international research teams using different wave models agreed on an identical approach to produce results of several climate models for different climate scenarios that are directly comparable.

 ‘While we identified some differences between different studies, we found that if the 2° C Paris Agreement target is kept, signals of wave climate change are unlikely to exceed the magnitude of natural climate variability,‘ Morim said. ‘However, under a business-as-usual future climate scenario, we found agreement in the projected future changes in wave heights, lengths and/or directions along 50% of the world’s coasts. These changes varied by region, with regional differences in increase/decrease in wave height and length of up to 10 and 5% respectively, and rotation of wave direction of up to 17 degrees.‘

The authors also found that less than 5% of the global coastline is at risk of future increasing wave heights. These regions were the southern coasts of Australia, and segments of the Pacific coast of South and Central America. Regions where wave heights remain unchanged, but wave lengths or periods show projected increase will experience increased forces exerted on the coast or associated infrastructure. One way this might be felt is via waves running further up a beach, increasing wave driven flooding. Similarly, waves travelling from a slightly altered direction in projected climate scenarios (suggested to occur over 20% of global coasts) can alter longshore transport of sediment along a coast.