El Niño and La Niña Overview: The Pacific Drivers of Global Climate

El Niño and La Niña are the warm and cool phases of the El Niño-Southern Oscillation (ENSO) cycle, a recurring climate pattern involving changes in sea surface temperatures (SSTs) and atmospheric pressure across the equatorial Pacific Ocean. ENSO is the most powerful year-to-year variation on Earth’s climate system, affecting everything from tropical cyclone frequency to monsoon intensity and polar heat transport. During El Niño, the central and eastern Pacific warms above normal by 0.5°C or more, weakening the trade winds and shifting the location of deep tropical convection. La Niña produces the opposite: cooler-than-average SSTs in the same region, strengthened trade winds, and a westward shift of the warm pool. These oceanic changes trigger teleconnections that ripple through the atmosphere, altering air pressure patterns, jet stream positions, and heat and moisture fluxes all the way to the high latitudes of Antarctica. Understanding ENSO’s influence on the polar cryosphere is essential for predicting near-term variability in ice loss and for distinguishing natural fluctuations from human-driven climate change.

Mechanisms Linking ENSO to Antarctic Glacier Dynamics

The connection between tropical Pacific SST anomalies and Antarctic ice is not direct; it operates through a chain of atmospheric and oceanic processes. El Niño events typically generate a Rossby wave train—a series of high- and low-pressure systems—that propagates from the tropics into the Southern Hemisphere mid-latitudes. This wave train alters the strength and position of the Amundsen Sea Low, a semi-permanent pressure system located off West Antarctica. During El Niño, the Amundsen Sea Low often deepens and shifts eastward, drawing warm, moist air from the mid-latitudes onto the West Antarctic Ice Sheet (WAIS). This leads to increased surface melting, especially on vulnerable ice shelves such as Pine Island Glacier and Thwaites Glacier. La Niña, conversely, tends to produce a weaker or more westward Amundsen Sea Low, steering colder air masses over Antarctica and temporarily reducing melt. However, the relationship is not symmetric: the magnitude and spatial pattern of temperature anomalies differ between ENSO phases, and long-term warming trends increasingly overwhelm the cooling influence of La Niña.

Atmospheric Rivers and Extreme Precipitation

One of the most direct ways ENSO accelerates ice loss is through atmospheric rivers—narrow, high-moisture plumes that transport vast amounts of water vapor from the subtropics to the poles. During strong El Niño events, these atmospheric rivers can make landfall on the Antarctic Peninsula and West Antarctica, delivering intense snowfall and, critically, warm temperatures that cause rain-on-snow events. Rain infiltrates firn layers and releases latent heat upon refreezing, destabilizing the ice. In 2022, an atmospheric river associated with El Niño conditions triggered widespread surface melting on the Thwaites Glacier catchment, an event that would have been statistically improbable without ENSO forcing. Conversely, La Niña often suppresses atmospheric river activity over Antarctica, but the overall trend of increasing atmospheric river frequency due to warming oceans means that even La Niña years now show episodes of extreme heat and moisture transport.

Regional Impacts on Glacier Melting: West vs. East Antarctica

Antarctica is not a uniform ice sheet: the WAIS is marine-based, meaning much of its bed lies below sea level, making it vulnerable to warm ocean currents that melt ice shelves from below. The East Antarctic Ice Sheet (EAIS) is largely land-based and colder, but it contains the largest potential for sea level rise due to its sheer volume. ENSO’s influence differs markedly between these regions.

West Antarctica: The Thwaites and Pine Island Twin Dragons

The Amundsen Sea sector of West Antarctica hosts the fastest-flowing glaciers on the continent: Thwaites and Pine Island. These glaciers are already losing ice at accelerating rates, contributing roughly 10% of current global sea level rise. Satellite data from the Jet Propulsion Laboratory show that during El Niño events, warm Circumpolar Deep Water (CDW) flows onto the continental shelf more readily, melting the ice shelves from underneath. A 2023 study in Nature Geoscience found that El Niño-driven wind anomalies can push CDW into the Pine Island Bay with a lag of 6–12 months, causing up to 30% greater basal melt rates compared to neutral years. La Niña, by contrast, tends to enhance sea ice production in the region, which can insulate the ice shelves from warm water, but this effect is weakening as the overall ocean temperature rises.

East Antarctica: The Sleeping Giant Stirring

East Antarctica was long considered stable, but recent research reveals that large sectors—particularly the Wilkes Land and Totten Glacier regions—are beginning to respond to warming. ENSO teleconnections to East Antarctica are less direct, but during strong El Niño events, a wave train from the Pacific can induce anomalous high pressure over the eastern South Pacific, which then alters the zonal winds around the continent. This can bring warm, dry air to parts of East Antarctica, leading to surface melting on the ice shelves of the Ross Sea and the Amery Ice Shelf. However, the dominant forcing for East Antarctica remains ocean-driven basal melting, which is less sensitive to ENSO than to long-term changes in the Southern Ocean circulation. A 2024 analysis from the National Snow and Ice Data Center indicates that although El Niño can briefly increase mass loss from East Antarctic outlet glaciers, the contribution is dwarfed by the steady acceleration caused by anthropogenic warming.

Global mean sea level has risen by about 21 cm since 1900, with the rate accelerating from ~1.4 mm/yr in the early 20th century to over 4.5 mm/yr in the 2010s. ENSO contributes to interannual variability in this rise, but its role is complex. During El Niño years, the combination of warmer ocean temperatures causing thermal expansion and faster glacier discharge from Antarctica can elevate the global rate by 0.2–0.5 mm/yr above the trend. For example, the 2015–2016 El Niño was associated with a spike in global sea level rise of about 5 mm over the previous year, largely due to changes in water storage on land and enhanced ice loss from the Antarctic Peninsula. La Niña years, such as 2020–2021, show a temporary slowdown, but the underlying trend remains upward.

Ice Shelf Collapse and Feedback Loops

The greatest threat from ENSO-amplified melting is not the direct meltwater input but the destabilization of buttressing ice shelves. Ice shelves like Larsen C, Getz, and Dotson act as structural dams that slow the flow of grounded ice into the ocean. When warm ocean water or surface meltwater weakens them, they can fracture and collapse, as seen with Larsen B in 2002. El Niño events increase the likelihood of such collapse by promoting both basal and surface melting. The loss of an ice shelf can trigger a rapid acceleration of upstream glaciers—the Pine Island Glacier sped up by 13% within months of its ice shelf thinning in the 2017 El Niño. These feedbacks mean that the impact of a single El Niño can persist for years, as the unbuttressed glaciers continue to flow faster even after ENSO returns to neutral. The IPCC Sixth Assessment Report highlights that the WAIS could contribute up to half a meter to sea level by 2100 under high-emissions scenarios, with ENSO acting as a pacemaker for short-term fluctuations within that trajectory.

Key Factors Influencing Glacier Response to ENSO

Several interconnected factors determine how Antarctic glaciers react to a given ENSO event. Understanding these helps scientists improve seasonal-to-decadal forecasts of ice loss and sea level rise.

  • Sea surface temperature anomalies: The magnitude and spatial pattern of Pacific SST anomalies govern the strength of the Rossby wave train. El Niño events with SSTs >2°C above normal in the Nino3.4 region produce the strongest Antarctic teleconnections.
  • Atmospheric temperature variations: Surface air temperature over West Antarctica can rise by 2–4°C during strong El Niño events, pushing the 0°C isotherm inland and causing melting on ice shelves that normally remain frozen year-round.
  • Wind pattern shifts: Changes in the Amundsen Sea Low alter the direction and speed of coastal winds, which in turn modulate the inflow of warm circumpolar deep water onto the continental shelf. Easterly wind anomalies during La Niña can upwell cold water, while westerly anomalies during El Niño drive warm water onto the shelf.
  • Ocean currents: The Antarctic Circumpolar Current (ACC) and the Ross Gyre respond to ENSO with a lag of months to years. Shifts in the ACC’s frontal positions can bring warm water closer to the ice shelf fronts, accelerating basal melting.
  • Long-term climate trends: The background warming of the Southern Ocean and atmosphere amplifies ENSO’s effects. A 1°C increase in ocean temperature since the 1990s means that even neutral ENSO years now produce melting rates that would have been considered unusual during past La Niña decades.
  • Sea ice extent: La Niña typically increases sea ice around Antarctica, which can protect ice shelves from wave action and warm air. However, the dramatic decline in Antarctic sea ice since 2016—with record lows in all seasons—has weakened this protective buffer, making ice shelves more vulnerable during ENSO events.
  • Ice shelf geometry and basal channels: Ice shelves with deep basal channels (like the Dotson Ice Shelf) are more susceptible to warm water intrusion. ENSO-driven ocean currents can preferentially funnel warm water into these channels, thinning them from below at up to 10 m/yr.

Observed Events: Case Studies of ENSO-Driven Melt

Examining specific ENSO episodes illustrates the real-world consequences for Antarctic glaciers. The 1982–1983 El Niño, one of the strongest of the 20th century, caused a ~30% increase in the flow speed of Pine Island Glacier, an effect that persisted for nearly three years after the event ended. Satellite radar interferometry from the European Space Agency’s ERS missions showed that the acceleration was driven by thinning of the ice shelf due to warm ocean water. The 1997–1998 El Niño similarly triggered widespread surface melt on the Larsen C Ice Shelf, leading to the formation of the large crack that eventually calved the A-68 iceberg in 2017.

In contrast, the 2010–2011 La Niña produced colder-than-average conditions over West Antarctica, reducing melt rates temporarily. However, this respite was short-lived: the following years saw record-breaking temperatures as the background warming trend reasserted itself. The 2015–2016 El Niño coincided with the largest surface melt event ever recorded on the Ross Ice Shelf, with meltwater ponds covering an area the size of Germany. That same event contributed to the calving of the massive A-68 iceberg from the Larsen C ice shelf the following year. A 2022 study using NASA’s ICESat-2 laser altimeter found that the thinning rate of Thwaites Glacier doubled during the 2015–2016 El Niño compared to the neutral period that preceded it.

Future Projections: ENSO in a Warming World

Climate models disagree on how ENSO itself will change with global warming: some project an increase in extreme El Niño events, while others suggest a shift toward more frequent central-Pacific (Modoki) El Niños. Regardless of the exact pattern, almost all models agree that the impacts of ENSO on Antarctic ice will intensify because of the warmer background state. A 1.5°C warming of the atmosphere increases the moisture-holding capacity by about 7%, meaning future El Niño events will deliver more heat and rain to the ice shelves. Furthermore, the ocean heat content in the Amundsen Sea is projected to rise by 0.5–1°C by mid-century, making it easier for even moderate El Niño events to trigger vigorous basal melting.

Scientists are also concerned about the possibility of tipping points, where marine ice sheet instability becomes irreversible. ENSO could act as the trigger that pushes a glacier past its stability threshold. The Thwaites Glacier, for instance, is already experiencing grounding line retreat at rates of up to 1 km/yr, and a strong El Niño in the 2030s could accelerate this process beyond the point of no return. The NASA Operation IceBridge and the International Thwaites Glacier Collaboration are actively monitoring these risks, but the time scales of ice sheet response mean that decisions to reduce emissions today will determine how much ENSO-driven melt we face in the 22nd century.

Conclusion: The Need for Continuous Observation and Modeling

El Niño and La Niña are natural climate variations, but their impact on Antarctica is being amplified by human-caused warming. Glaciologists and climate scientists are working to improve the representation of ENSO teleconnections in Earth system models, as current models struggle to capture the observed frequency of extreme melt events on the WAIS. Satellite missions like ICESat-2, CryoSat-2, and the upcoming NASA-ISRO SAR Mission (NISAR) will provide the high-resolution data needed to track changes in glacier elevation and grounding line position year by year. For policymakers, the message is clear: even if ENSO cycles continue as in the past, their destructive potential on the ice sheets will grow. Reducing greenhouse gas emissions remains the only way to slow the underlying warming that makes every El Niño a more dangerous event for Antarctica’s glaciers and the world’s coastlines.