Climate change may be making El Niño and its far-reaching weather disruptions more intense than at any time in the past 1,000 years, according to a new study.
The research, published in the journal Science on August 27, found that ocean-temperature variations associated with the El Niño–Southern Oscillation (ENSO), have been substantially greater during the past 40 years than during the pre-industrial period.
ENSO is a naturally occurring fluctuation between unusually warm conditions, known as El Niño, and unusually cool conditions, called La Niña, in the central and eastern tropical Pacific Ocean. Although it begins thousands of kilometres from Africa, the cycle alters atmospheric circulation and can shift rainfall, temperature and storm patterns worldwide.
Researchers found that eastern-Pacific ENSO temperature variability during the past four decades was 36.5 per cent greater than during the pre-industrial period between AD 1000 and 1850. It was also 16.2 per cent greater than during the period from 1850 to 1981.
The study, led by University of Michigan palaeoclimatologist Julia Cole, provides some of the strongest observational evidence yet that human-caused global warming is changing the behaviour of this natural climate cycle.
“ENSO is the leading source of year-to-year climate extremes globally,” the researchers say.
El Niño often favours increased rainfall in East Africa during the October-to-December short-rains season. Its effects can become especially powerful when it coincides with a positive Indian Ocean Dipole (IOD), another ocean pattern involving warmer-than-normal water in the western Indian Ocean.
The latest regional outlook has made the new study particularly relevant. The World Meteorological Organization says the Greater Horn of Africa is likely to experience warmer and wetter-than-usual conditions during the October to December short rains as the current El Niño strengthens.
Parts of north-eastern Kenya have a 90 per cent probability of above-normal rainfall, while sections of central Kenya and the Lake Victoria Basin could receive more than 400 millimetres during the season.
The October-to-December rains provide as much as 70 per cent of annual rainfall in some parts of Kenya, Ethiopia and Somalia, making disruption during this period especially consequential for farming and food security. WMO cautions that the forecast also points to greater risks of flooding, crop destruction, disease and infrastructure damage.
Each El Niño behaves differently, however. Its effects depend on its strength, location, duration and interaction with the Indian Ocean and other climate systems. While it is commonly associated with wetter short rains in the Horn of Africa, it can suppress rainfall across parts of Southern Africa.
Previous events have contributed to major crop losses, livestock deaths, reduced hydropower generation and rising food prices in countries already facing poverty, conflict and limited
