For at least 11,000 years, the eastern Pacific has experienced a cycle of warm and cold conditions, known as El Niño and La Niña respectively. This is the El Niño-Southern Oscillation (ENSO), crucial to the climate of many regions across the world. Models of the ENSO struggle to understand what will happen to it as the climate crisis worsens, but despite the uncertainties, the consequences are bad all around.

Two studies, published in Nature Reviews Earth & Environment and Nature Climate Change, attempted to tackle the complexity that is the ENSO's variability. They found different results – in the first, the variability will increase; in the second, it will instead collapse.

Despite the apparent contradictions, they both found dramatic consequences in terms of change of weather patterns, rainfall, droughts, and temperatures across the Pacific regions and beyond.

"The latest IPCC report shows clearly that if we do not drastically curb our emissions, we will head towards temperatures that Earth has not seen in millions of years," co-author on both studies Malte Stuecker, from the University of Hawaiʻi at Mānoa, said in a statement.

"Moreover, we can now say with certainty that all of the global warming that occurred since the mid-19th century is due to human activity. While these are sobering facts, we should certainly not despair. In fact, if societies choose a pathway of large reductions in greenhouse gas emissions now, the report also shows that we will avoid the worst possible future outcomes and Earth will experience only moderate additional warming over this century that we can likely adapt to."

In the review work, the team synthesizes the results from many models that have seen an uptick of variability in the ENSO since the 1950s compared to paleoclimate data from previous centuries.

The work in Nature Climate Change is the latest and most precise model yet with a resolution of 10 kilometers (6.2 miles) in the ocean and 25 kilometers (15.5 miles) in the atmosphere. It took Aleph, one of South Korea’s fastest supercomputers over one year to complete the simulation. In that model, ENSO variability will collapse. However, similar to the other model, rainfall and droughts are going to become more extreme – and they are going to do that sooner rather than later. 

“Two generations of climate scientists have looked at this issue using climate models of varying complexity. Some models simulated weaker; others predicted larger eastern Pacific temperature swings in a future warmer climate. The jury was still out.” says Prof. Axel Timmermann, co-corresponding author and Director of the ICCP, said in a statement.

The ENSO is a crucial element of our planet’s climate. A shift in either direction will have disastrous consequences. And it is already happening.