We are in the midst of an ongoing climatic event that is affecting the weather worldwide. Is this just the beginning?
An extraordinary event in its scope has been hitting many countries around the world for the past two years. The climatic event resulted in an unprecedented drought in the western United States and eastern Africa, and intense flooding along the eastern coast of Australia. Usually such events, which received the name La Niña (La Niña, “the girl” in Spanish), last for a few months, but the current La Niña started over two years ago; According to climate scientists’ estimates, there is a 50 percent chance that it will even continue into its third year, as has happened only twice since tracking of La Niña events began in 1900.
La Niña is a worldwide climatic phenomenon that occurs once every few years and results in a temporary decrease in the surface temperature of the oceans. This exchange leads to changes in global wind regimes and regional precipitation amounts, especially in countries bordering the Pacific Ocean. La Niña is a sister to another and slightly better known climatic event known as El Niño (El Niño, “the boy” in Spanish), which causes reverse climate changes. Despite the great progress in climate research, the factors that dictate the appearance of such events are still not clear enough.
It is still too early to determine whether there is a connection between the unusual phenomenon and climate change, but researchers warn that global warming, which is expected to worsen in the future, may increase the frequency with which La Niña events strike the Earth, and the likelihood of additional La Niña events lasting for consecutive years.
One of the main effects of the La Niña phenomenon is a sharp increase in the amount of precipitation in some countries, alongside its reduction in other countries. For example, during La Niña events Southeast Asian countries experience heavier than normal rainfall and flooding, while South American countries suffer from severe droughts. The weather on the Australian continent is particularly sensitive to La Niña events: as the ocean surface temperature drops, so does the amount of precipitation along the eastern coast of the continent, creating devastating floods, similar to those that occurred earlier this year.
The factors that dictate the appearance of El Niño and La Niña events are still not clear enough. Storm in California following the El Nino phenomenon Photo: Gregory Ochocki / Science Photo Library
According to climate researchers, although the current La Niña event is unusual in its length, even if it continues into its third year, it will not exceed the natural limits of probability, and it cannot be linked to the climate change that has been giving its signals on Earth for the past decades. No unequivocal connection has yet been found between climate change and changes in the frequency and intensity of La Niña and El Niño events: various studies offer conflicting explanations. One of the reasons for the difficulty in pointing out a clear trend is the lack of a long enough measurement range. The collection of data on such events only began a little more than a century ago, and the large differences between the events, along with the long time intervals between them, make it impossible to create sufficiently reliable statistical analyses.
Ocean currents are also part of the equation
A study published this year in the journal Nature Climate Change offers another explanation for the difficulty in predicting changes in the appearance of La Niña and El Niño in a world where the climate is changing. It seems that the computational models, on which the climate studies dealing with these phenomena are based, have been built so far without taking into account the full effect of the melting of the Greenland ice cap on the pattern of ocean currents. The warming of the oceans accelerates the rate of melting of the ice cap in the Arctic, which leads to the intrusion of cold, fresh water into the North Atlantic and the slowing of ocean currents around the world.
According to the study, the slowing of the currents, which causes the accumulation of heat energy in the tropical part of the Atlantic Ocean, leads to the strengthening of the winds that blow westward along the equator to the Pacific Ocean. The strengthening of the winds pushes the upper layer of water in the Pacific Ocean to the west, causes a greater rise of cold deep water in its eastern part, and ultimately leads to a decrease in the water temperature there. Or in other words – La Niña.
If the results of this model-based study prove to be accurate, it means that global warming is likely to increase the frequency and intensity of La Niña events. So the severe weather and the devastating floods that hit Australia in the last year may herald a new lifestyle, to which the residents of the southern continent will have to adapt.