October 2021

Water and climate: Wounded water

According to certain theories, the water on Earth is stardust, a sub-product of their formation. It is also the origin of life on Earth, the breeding ground whence all living beings originate: most contain between 60 and 70% water, reaching 80 or 90% in some aquatic organisms. Human beings gestate inside a bag of liquid which breaks at birth.

Current human civilisations originated between three rivers: the Tigris, the Euphrates and the Nile formed the «Fertile crescent», the birthplace of Neolithic culture. Human life, and that of all other living beings, depends on cyclic processes to do with water: sea currents, atmospheric circulation, seasonal changes and climate stability in each part of the globe.

Over 70% of the Earth’s surface is covered by water, but the masses of water are not uniform: concentrations of salt and differences in temperature cause horizontal and vertical shifts, creating currents which drag millions of miniscule organisms along with them. Nearly a quarter of living beings is aquatic and makes up the base of the trophic chain, conditioning the migration of many animal species which search out seasonal food booms.

Regular movements of water cause temperature changes on dry land and changes to the distribution of the current climate of our planet. In addition, its movement to the deep carries dissolved oxygen to the organisms in the abyss. Interrupting this «conveyor belt» would have extremely serious effects on life on planet Earth.

Not all the water on Earth is liquid: glaciers, the arctic ice floe and the polar caps store a huge amount of fresh water which, should it melt, would change the salinity and temperature of the oceans and cause a rise in sea level. In addition, there are quantities of water trapped beneath the frozen periglacial ground known as «permafrost», which also contain important amounts of organic carbon but, especially, carbon dioxide (CO2) and methane.

Both CO2 and methane are greenhouse gases, that is, their function is to regulate temperature so that it is appropriate for life to continue. But an increase in these gases leads to a rise in temperature of exponential proportions: the higher the temperature the greater the discharge of methane, in this case also from the ocean bed due to the warming of the intermediate water.

According to different research, the levels of CO2 in the atmosphere have increased by nearly 38 per cent since 1750 due particularly to the burning of fossil fuels and deforestation, and a large amount of the CO2 produced by human activity cannot be absorbed by vegetation or the water of the oceans.

The most reliable studies foresee greater warming of the Earth because of increases in CO2 and methane in the atmosphere, particularly in northern latitudes, where almost a million kmwould lose their ice cover resulting in a rise in sea level of about one metre during the 21st century. The effects of climate change at all levels —economic, migration, food production, etc.— would be catastrophic.

We are aware of the importance of green areas for their ability to take in CO2 and emit the oxygen which is essential for life. There is less awareness of other green areas which can absorb CO2 in much greater quantities and which are being destroyed at a rapid rate but unknown to the inhabitants of the planet, except for those directly affected or for the scientists who have been warning about this process for years. 

The coasts and coastal waters of part of the Earth are home to some unique biotopes: mangrove swamps and seagrasses. The former occupies the intertidal area of parts of the tropical and subtropical coasts and are different species of trees and bushes, sometimes more than 14, which are resistant to saltwater. Their importance is huge: on the one hand, they are highly productive systems as they are a haven for many species of birds, amphibians, reptiles and fish, both in adult life and in their younger, vulnerable stages. Under their shelter, humans have created traditional exploitations using their high productivity. On the other hand, the mangroves prevent coastal erosion and form a system of shock absorption against waves from tsunamis to other similar catastrophes. Thirdly, mangroves can trap pollutants and purify the water, converting greenhouse gases such as nitrous oxide into nitrogen. Finally, the mangrove swamps provide for human populations who make sustainable use of their resources; this is particularly important where these coastal forests border arid inland areas which are not productive.

Unfortunately, the mangrove swamps have suffered a progressive loss of surface, over 20% since 1980, for several reasons: the installation of aquaculture industries —sometimes illegally— the building of tourist resorts, pollution by petrol and salt production. Indirectly, the disappearance of the mangrove swamp favours the destruction of coastal coral reefs as it allows pollutants and sediments to reach the sea.

A group of plant species that live on the sandy seabed of the coast are known as «underwater grasslands». These are land plants that colonized the sea as they evolved, and they, therefore, need sunlight for photosynthesis. Like other land plants, they reproduce via their flowers and also produce fruit: all the species have long, ribbon-shaped leaves over a metre long, which reminds you of a meadow on land.

The most common on the Mediterranean coast is Posidonia, which covers around 1,600 kmof the continental shelf. This plant roots into the sandy bottom and form a horizontal shoot or rhizome, which advances long distances producing branches. On the island of Formentera (Balearic Islands, Spain) Posidonias have been found whose roots were over a kilometre long; it is estimated that they may have formed over 30,000 years ago.

It is estimated that over half the underwater grasslands have disappeared, around 30,000 km2, and the source of the problem is human activity, mainly contamination from coastal urbanisation and the spread of algae due to nitrogen and phosphorus from the residual waters of crops. Another common cause in some areas is the anchoring of leisure craft which uproots the plants.

The importance of underwater grasslands is similar to that of mangrove swamps: they act as protection for hundreds of species of fish, crustaceans and molluscs, particularly when they are young. Some very rare species which are in danger of extinction such as pen shells (Pinna nobilis) only live among the shoots of Posidonia. In some areas, the plant itself provides food for mammals like the dugong and certain birds like geese. On the other hand, the seagrasses also offer protection from coastal erosion, boost sedimentation and stabilize the seabed. In some tourist areas where seagrass was removed to improve the appearance of the seabed, the beach gradually disappeared.

The rate of loss of mangrove swamps and underwater seagrass remains at around 2 to 3% a year, greater than that for tropical forests. These biotopes are very important. It has been shown that one hectare of seagrass can capture more CO2 than 17 hectares of tropical forest and that the seabed can accumulate huge amounts of carbon: in a bay in Cadaqués (Girona, Spain) deposits up to 11 metres thick have been discovered, which accumulated over 10,000 years.


Juan Varela Simó is a biologist and naturalist painter. He has worked in research applied to Conservation and is the Spanish representative of the Artist for Nature Foundation. In 2001 was awarded by the Spanish Ministry of Environment and in 2015 by the Fundación BBVA. By Varela Simó, also on the VMHE Extensive shepherding, traditional exploitations  and Oak groves, horse rearing and the sustainable use of resources