What Is El Niño and How Would SRM Affect It?

Starting early in 2026, scientists began warning that a critical climate event was on the way: an El Niño, potentially among the strongest such events ever recorded. What is El Niño, why is it important, and how might SRM affect it?

The climate phenomenon is part of the El Niño–Southern Oscillation, or ENSO. This is a recurring, cyclical climate pattern in which the surface temperature of part of the central and eastern Pacific Ocean rises and falls. It has three states: El Niño, when those waters are particularly warm; La Niña, when they are cooler; and neutral, when temperatures lie between those extremes. In general, the ocean surface in this region can warm or cool by up to 3°C.

Part of an irregular cycle that can occur every two to seven years, these temperature shifts can last for several months or longer and have a significant influence on the global climate. On average, El Niño tends to raise global temperatures, while La Niña turns the global thermostat down. Historically, strong El Niño events have helped contribute to record-breaking global temperatures, for example in 2015–2016.

These El Niño events now occur in a different world than decades and centuries ago. The world has warmed around 1.4°C since the Industrial Revolution began, largely due to the burning of fossil fuels. With a warmer baseline, each El Niño now raises temperatures to higher highs than they did before. Global warming has also amplified the temperature and rainfall extremes that come with El Niño, making them stronger and more dangerous.¹

While climate models do not agree on many aspects of how ENSO might change in a warming world, they do suggest that temperatures in that part of the Pacific may become more variable, meaning that more extreme El Niño and La Niña events may become more frequent and intense.^2,3

All this spells danger for upcoming El Niño events. With a large El Niño on the way, experts think that 2027 is likely to be the warmest year on record – surpassing 2024 when 1.5°C of warming was eclipsed for the first time.

Regional climate and weather variation

There are regional impacts as well that stretch beyond temperatures. For example, during La Niña, the southern United States tends to be drier than usual, with lower-than-average temperatures across the northern part of the country; during El Niño, the opposite is true, with wetter conditions dominating in the south and warmer temperatures in the north.⁴

In Australia, El Niño can bring hotter, drier weather, increasing the risk of fires. The same is true in Southeast Asia, where strong El Niño events have been associated with prolonged dry conditions, potentially affecting agriculture in the region.⁵ El Niño also generally suppresses India’s summer monsoons,⁶ though it can actually increase extreme daily rainfall, again causing major issues for agriculture.⁷

El Niño also tends to reduce hurricane activity in the Atlantic basin, but can increase it in the Pacific; the reverse is true for La Niña, tamping down on Pacific cyclone activity while enhancing it in the Atlantic. In general, the cycle’s far-reaching and varying effects demonstrate how connected the world’s oceans, atmosphere, and overall climate really are.

SRM and ENSO

What effect would SRM have on ENSO, if it were ever deployed? The answer depends strongly on the type of SRM used.

The most commonly studied approach, stratospheric aerosol injection (SAI), would involve sending millions of tonnes of tiny reflective particles into the upper atmosphere in order to reflect a small amount of sunlight back into space. Though many questions about this remain, there is little doubt that it would have an overall cooling effect on global temperatures⁸ – that means that the warmer temperatures associated with an El Niño would likely be cooler under SAI, since the baseline would be lower.

Beyond that, modelling research has found that an SAI deployment would not have a significant impact on ENSO, though only a limited range of deployment scenarios have been explored.^9,10 The increasing frequency of El Niño and La Niña events seen due to warming might be offset slightly by SAI, but otherwise research generally suggests no clear trend.

Marine cloud brightening (MCB), however, is a different story. This idea, involving spraying tiny sea-salt particles into low-lying clouds over the oceans to make them more reflective, could potentially have a major impact on ENSO. One study found that if MCB were deployed over the subtropical eastern Pacific Ocean, it could reduce ENSO amplitude by around 60 percent.¹⁰ It would do this by drying the atmosphere over that area of the ocean and intensifying the trade winds, which would dramatically reduce the “air-sea feedback processes” that operate during ENSO and limit its magnitude. Another study (not yet peer-reviewed) showed that the location of an MCB deployment is critical in determining its impacts, with potential to create both El Niño- and La Niña-like temperature anomalies.¹¹

Further research on this idea found that it could, in theory, be used intentionally as a tool to suppress potentially dangerous El Niño events. Deploying targeted MCB over the relevant part of the Pacific when the event is building up could reduce its magnitude significantly, potentially reducing some of the associated impacts in other parts of the world.¹² This sort of seasonal intervention, however, might have some unintended consequences, including hastening and strengthening a subsequent La Niña even after the MCB deployment is stopped.

That potential, though, offers a demonstration of how the details of climate interventions – which approach, where, at what magnitude, and so on – could have widely varying impacts on the global and regional climate. The idea that it may be possible to use targeted SRM to “improve” a specific climate change impact – in this case, to reduce increasingly intense and potentially damaging El Niño events – raises many questions regarding human effects on the world and how they should be managed.