Despite all the crises we currently face, the media has found space to highlight two papers published in NATURE in recent weeks that relate to the future of coastal conditions, in particular beaches.
The first paper is concerned with the future of sandy beaches under conditions of sea-level rise and other factors. It is a multi-authored paper entitled “Sandy coastlines under threat of erosion”, Vousdoukas, M.I., et al., 2020, Nature Climate Change. It looks globally at potential change to beach systems recognising that one third of the world’s coast is sandy of which a substantial proportion is in densely populated areas. Their purpose is to alert us to future shoreline dynamics dominated by sea-level rise (SLR) in most sandy beach regions and hence the need to consider “informed and effective adaptive measures”. Projections of shoreline change are derived from modelling leading to the claim that there will be “near extinction of almost half of world’s sandy beaches by the end of the century”.
This paper has received a considerable degree of critical attention from coastal beach specialists in recent weeks. Those familiar with observing beach change over time and with modelling beach dynamics are expressing strong views about the claims and methods used in the Nature paper. A response is being prepared by a group from many countries who have experience in beach studies. I will not try to pre-empt their conclusions. However, survival of beaches with SLR is a very complex issue and we await the publication of the response to the Vousdoukas et al. paper, which we will endeavour to post when available.
The second paper is not directly involved in coastal research, but indirectly it is quite significant in my view. Again a multi-authored article by Abram, N.J., et al. on “Coupling of Indo-Pacific climate variability over the last millennium”, Nature. This paper focuses on the behaviour over time of the Indian Ocean Dipole (IOD), a phenomenon only discovered in 1999. It adds to the list of those so-called atmospheric teleconnections, such as ENSO and the Pacific Decadal Oscillation, that influence our inter-annual weather. I have long been fascinated by the geomorphic implications of these teleconnections and their link to patterns of beach accretion and erosion.
A study of natural variability of IOD as outlined in this paper based on coral records has allowed the IOD signature to be defined. Of note is the frequency and intensity of positive IOD events increasing during the 20th century and may continue to intensify in a warming world. Why is this important? Positive IOD events are initiated by enhanced ocean upwelling in the eastern Indian Ocean off Indonesia. This leads to cooler ocean temperatures in the east with warmer temperatures in the western part of the Indian Ocean. While this pattern is linked to floods in east Africa, in our region it is associated with droughts and increased fire risk especially in southeast Australia. The paper points the way to improved seasonal-to-decadal forecasting of climate risks posed by IOD.
Implications for beach change under climate change need to be further explored. Drier, drought-dominated conditions prevailing in southeast Australia can be linked to beach accretion. Observations by Roger McLean, Andy Short and others including myself have generated time series of more than 40 years which provide evidence of links to decadal oscillations. The authors of this Nature paper conclude that discovery of extreme positive IOD events in the past “indicates that present-day IOD risk management needs to include the possibility of severe events beyond what is known from the instrumental record”. This interpretation must be viewed “alongside model-based evidence of an increasing occurrence of extreme positive IOD events with continued climate warming”.
It is somewhat ironic that one paper in Nature is predicting climate change will lead to loss of our beaches because of one driver (SLR), while another (IOD) points to their greater resilience due to the impact of climatic forces affecting beach survival. All this highlights complexity of beach dynamics under global warming strengthening the need to focus on regional shoreline behaviour taking into consideration a multitude of external and local factors which I alluded to in my last blog.
Words by Prof Bruce Thom. Please respect the author's thoughts and reference appropriately: (c) ACS, 2020, for correspondence about this blog post please email firstname.lastname@example.org