Impacts of Sea Level Rise

I have realised that my post on dangerous sea level rise, which discusses the extent to which sea level could rise under different warming scenarios, does not address the impacts (apart from some pretty scary pictures of submerged cities) it could have on the habitability of Earth (which is, after all, the whole point of my blog). So here's a quick post to fill in that gap.

Cartoon pointing out the lack of plan to mitigate against rising sea levels

A quick Google will tell you that people are seriously concerned of the disappearance of low-lying islands due to sea level rise. A Tech Insider article, has a handy list of 11 islands that are threatened by climate change. The article uses the IPCC's estimate of an increase of 8 to 16 inches (0.2-0.4m) above 1990 levels by 2090, as well as The National Academy of Sciences predictions of sea level increase by 16 inches to 56 inches (0.4-1.4m) by 2100, depending how the Earth responds to changing climate. This list really gives a face to the populations threatened by sea level rise, such as the local population of 325,000 people of the Maldives, which is on average only 1.3m above sea level.

But it's not just the media that are concerned with vulnerable islands. Church et al. (2006) studied historic and projected sea level for tropical Pacific and Indian Ocean islands such as Tuvalu and the Maldives. They estimate that relative sea level rise at Funafuti, Tuvalu is 2 ± 1 mm per year, during 1950 to 2001, with analysis showing that the rate of sea level rise will continue to increase in the future.

Apart from sinking low-lying islands, sea level rise also impacts the contents of the oceans too. With more, and warmer, water in the ocean, ocean pH is predicted to decrease (acidify). The IPCC summarise it as follows:

"The increase in acidity will be higher in areas where eutrophication or coastal upwellings are an issue. It will have negative impacts for many calcifying organisms (high confidence). Warming and acidification will lead to coral bleaching, mortality, and decreased constructional ability (high confidence), making coral reefs the most vulnerable marine ecosystem with little scope for adaptation. Temperate seagrass and kelp ecosystems will decline with the increased frequency of heat waves and sea temperature extremes as well as through the impact of invasive subtropical species (high confidence)."

Coral reefs are indicated to be the most vulnerable marine ecosystem in the face of climate change. Hughes et al. (2003) suggest that projected increases in carbon dioxide and temperature over the next 50 years exceed the conditions under which coral reefs have flourished over the past half-million years. This implies that 2°C of warming would result in the destruction of many coral reefs. Hoegh-Guldberg et al. (2007) also agree with this prediction, using the projections that atmospheric carbon dioxide concentration will exceed 500 parts per million and global temperatures to rise by more than 2°C by 2050 to 2100. These values "significantly exceed" those of at least the past 420,000 years, during which they claim the most extant marine organisms evolved. They predict carbonate reef structures will fail to be maintained under these conditions, and reefs will lose major coral communities.

This is important is coral reefs play an integral part in marine biodiversity, fisheries, tourism, coastline protection, and many other aspects of the ocean and for people on land. Coral reefs provide habitats for 25% of all marine life, so to lose a significant amount of coral communities would likely lead to a loss of equivalent marine life too.

I hope this quick summary of impacts of sea level rise on islands and coral reefs gives a better idea as to why 2°C of warming could render many populations (of people and other organisms) without a home.