Conventionally, discussion on prospective impacts of climate change have almost exclusively focused on terrestrial aspects, with the ocean frequently getting the cold shoulder despite its seminal role in regulating our climate.
It is, in fact, widely recognised that the ocean absorbs a staggering 90 per cent of the surplus heat generated through human-driven climate change as well as 25 per cent of the surplus greenhouse emissions belched out by man.
The ocean acts as a proxy conveyor belt, shuttling heat from the tropics towards the poles, distributing it evenly around the globe and thereby mitigating any thermal extremes. This makes it a pivotal partner to the atmosphere in regulating the world’s climate. The climate-ocean nexus has in fact emerged as a compelling concept in international fora, where the ocean is a staple at any high-level discussion on the ocean.
The ocean bears a disproportionate part of the brunt of climate change. The surplus atmospheric heat it absorbs translates into a similar warming pattern for our seas, with the Mediterranean and other regional seas warming up at a faster pace than the global ocean – a factor that must form a big part of our local discussion on climate change.
Locally, surface waters have repeatedly gone beyond the 30-degree Centigrade mark over the course of previous summers. This was unheard of just five to 10 years ago. The surface warm water layer sits atop the colder water layer below, like strata in a cake, so that vertical mixing and the flushing of deeper water layers with atmospheric oxygen is depressed.
The higher sea temperatures also promote the spread of diseases within marine organisms through the proliferation of parasites and opportunistic species such as marine fungi, bacteria and viruses. While some species can escape the anomalous warming of surface waters and the consequences this brings along by seeking deeper waters, other species fixed to the seabed cannot and this can result in mass mortality of species.
The anomalous warming of our seas also favours the establishment of non-indigenous species (the so-called ‘alien species’) within our waters, given that these mainly originate in tropical areas such as the Indian and Pacific oceans, as well as a higher frequency of jellyfish blooms, which can thrive in low oxygen waters.
Most alien species retain ‘a low profile’ but a few exhibit a boom-and-bust cycle, displacing indigenous species through their large populations, leading to significant environmental and socio-economic impacts. The Mediterranean is a hotspot for marine species invasions, with a number of them wreaking havoc in the areas closest to the Suez Canal.
But climate change impacts on our seas are not restricted to the warming-up phenomenon. The dissolution of greater volumes of atmospheric carbon dioxide (the most voluminous of greenhouse gases) within the ocean promotes its acidification through the formation of a weak acid – carbonic acid – which graces our carbonated drinks.
The scale of the problem has only been unveiled by scientists during the last 15 to 20 years. Ocean acidification has been labelled the ‘evil twin’ of climate change, leading to a reduced reproductive success by all those marine species secreting a calcium carbonate skeleton or shell, including crustaceans (lobsters, crabs), molluscs (snails) and echinoderms (sea urchins, starfish).
The latter phenomenon will invariably impact global fisheries since most of the affected species support the predators we consume.
The future is definitely not looking that rosy for the big blue, our faithful partner in combatting climate change.