Sea level rise is not the only consideration for the management of our coasts in the coming decades. Our research, published in Geophysical Research Letters, found it is also making waves more powerful, particularly in the Southern Hemisphere.

An energetic ocean

Since the 1970s, the ocean has absorbed more than 90% of the heat gained by the planet. This has a range of impacts, including longer and more frequent marine heatwaves, coral bleaching, and providing an energy source for more powerful storms.

Our research was focussed on how warming oceans boost wave power. We looked at wave conditions over the past 35 years and found global wave power has increased since at least the 1980s, mostly concentrated in the Southern Hemisphere, as more energy is being pumped into the oceans in the form of heat.

Why is this happening?

Ocean waves are generated by winds blowing along the ocean surface. When the ocean absorbs heat, the sea surface warms, encouraging the warm air over the top of it to rise. This helps spin up atmospheric circulation and winds, which can lead to altered global wave conditions.

Our research shows that, in some parts of the world’s oceans, wave power is increasing because of stronger wind energy and the shift of westerly winds towards the poles. This is most noticeable in the tropical regions of the Atlantic and Pacific Oceans and the subtropical regions of the Indian Ocean.

Not all changes in wave conditions are driven by ocean warming. In general, it appears changes to wave conditions towards the equator are more driven by ocean warming, whereas changes to waves towards the poles remain more impacted by natural climate variability – such as El Niño and La Niña.

Impacts at the coast.

While the response of coastlines to climate change is a complex interplay of many processes, waves remain the principal driver of change along many of the world’s open, sandy coastlines.

The impact at the coast generally depends on how much sand there is and how, exactly, wave power increases. For example, if there is an increase in wave height, this may lead to erosion. But if the waves become longer (a lengthening of the wave period), then this may have the opposite effect, by transporting sand from deeper water to help the coast keep pace with sea level rise.

Climate change impacts are already here.

It is not surprising for us to find the fingerprints of greenhouse warming in ocean waves. Our study has demonstrated that the impacts of climate change on waves is not just a thing of the future and is already occurring in large parts of the world’s oceans.

This article is an abridged version of an article in The Conversation (here). The journal article on which it is based can be accessed here.

Click here to view the pdf version of our newsletter Volume 20, Issue 2 which includes this article.