After the oceanic layer between 200 and 800 meters deep will go through an intense peak of heat in 2015, the situation has stabilized again. “Now we have roughly the same average temperature as 20 years ago,” says Vélez. This shows that many of the effects of climate change on the waters of the Canary Islands have been outdated since they consider that the increase in heat in the sea leads to a tropicalization of the Archipelago, which however, these data deny.
The highest temperature on the surface of island waters since 1982 was recorded in 2020
The last to relate both phenomena has been the Ministry of Ecological Transition in its report on climate change in Spain for 2021. The report indicates that between 2008 and 2011 there was an invasion of more tropical marine species as a consequence of the increase in water temperature by climate change. And it is that in recent years, and until at least 2015, the trend seemed to be that.
The Islands received in those years different organisms that tend to prefer warmer waters. Animals of all kinds then arrived, such as invertebrates, fish and even mammals, which are originally found roaming seas with an average surface water temperature of 25 degrees. As happens when an invasive species reaches a habitat that is not its own, some of them generated real havoc on the indigenous biodiversity of the Archipelago. The case of the small hedgehog Diadema africanum, whose uncontrolled growth caused the disappearance of native algae in many rocky areas until at least 2016, giving rise to what is known as blanquizales, that is, rocky bottoms devoid of algal cover. At that time, the plumed rooster (Canthidermis sufflamen), more common on the coasts of Cape Verde, settled on the islands and became so abundant in El Hierro as of 1994 that it became an economically important fishing resource.
However, as Vélez points out, all this “may be occurring due to many other oceanic processes that we do not know about.” For now, there are other alternatives that can explain the arrival of these stowaways. “These new species could also arrive on oil rigs or other ships” and the disappearance of others “may be due to variations inherent in the ecosystem.
This gap in knowledge is not surprising, since researchers estimate that only 5% of all oceans have been explored, which means that 95% of the seabed is totally unknown, as well as the situations that may arise. in each one of them. “There are few of us who are investigating changes in the sea in the Canary Islands, so it is possible that there is something that is escaping us,” insists the oceanographer, who warns that “the simplistic theory of climate change may be preventing others from being investigated lines”.
Meanwhile, the oceanic surface of the Canary Islands continues to set a record. In 2020, the highest temperature was recorded on the surface of the waters surrounding the Canary Islands since 1982. The researcher considers that the surface temperature is governed by different mechanisms than those that affect the ocean depths. To begin with, the surface is in direct contact with the atmosphere, which is undergoing major changes due to greenhouse gas emissions and global warming. Something that is corroborated with the fact that this year the concentration of carbon dioxide in the atmosphere set a new historical record: 421.21 parts per million (ppm), which is almost twice the concentration than in the pre-industrial period.
In any case, as Vélez indicates, surface warming affects “a few meters, initially directly” and is not homogeneous throughout the planet. The exception described is in the upwelling zone on the African coast, where the surface is cooling rather than warming. “It is believed that it is a consequence of changes in the wind regime and the increase in temperature on the African continent,” he asserts.
Some of the modifications that the marine ecosystem of the Islands has undergone in recent years may, therefore, have other explanations, such as being changes “inherent to the system itself” or “having been a specific exception”. The researcher reaffirms his theory with the fact that “there have been no more phenomena of exacerbated growth of microalgae” since 2017. Like this one, there are many other phenomena for which climate change has been blamed in the Canary Islands, and as Vélez points out, there are still many possibilities that coincidences also exist at sea.