4 Billion Years On

The 4byo Climate Symphony

The world’s main climate drivers on one 15-year timeline, grouped by how they connect: ENSO and the Indian Ocean Dipole, the tropical Indo-Pacific pair that often work together; the PNA, ENSO’s route into North American weather; the NAO and Arctic Oscillation of the North Atlantic and Arctic; and the slow Atlantic background (AMV and AMOC) - then the heatwave and extreme-weather outcomes. Past and present with the official forecast, plus how the post-El Niño temperature floor - informally, the “ratchet” - has stepped higher after each major event, layered on the long-term warming trend. Toggle any driver in What-If mode to see how the combined picture shifts.

Latest data 7 Oct 2026 · weekly
Generating compound teleconnection briefing…
ENSO Tracker NAO Tracker

The 4byo Climate Symphony - Current State & Forecast

Click any panel to see how the drivers interact.

GLOBAL TEMPPost-El Niño Temperature Floor.
ENSO
IOD
PNA
NAO
AO
AMV
AMOC
HEATWAVE DAYS
EXTREME WEATHER EVENTS
Positive (+)Negative (-)Neutral

The drivers are not independent. They sit in three chains of influence, feeding the same outcomes. On the timeline above, each group has its own heading and linked drivers are marked as Linked.

The tropical Indo-Pacific pair

ENSO LinkedIODPNA

ENSO usually leads and the Indian Ocean feeds back. The PNA carries ENSO's signal into North America.

Sets the pattern

Where it shows

North American winters - and, through ENSO and the IOD, rain from East Africa to Australia

North Atlantic & Arctic

Polar VortexAONAO

A weak polar vortex tends to push the AO, then the NAO, negative a few weeks later.

Steers the storm track

Where it shows

Europe's and the Arctic's winters, largely apart from ENSO

Slow ocean background

AMOCAMV

Many studies find the AMOC's slow swings help set the AMV's phases - still debated.

Tilts the Atlantic for decades

Where it shows

Atlantic warmth and hurricane seasons, and Europe's long-run weather

The outcomes - all three feed these

Global temperature, heatwave days and extreme weather. ENSO gives the biggest push to global temperature from year to year - the others mostly move heat and storms around.

Observed floorNOAA floor forecastCNN floor forecastNOAA temp profileCNN temp profile

After each major El Niño, global temperatures decline during the La Niña that follows, but they rarely fully return to the pre-event baseline. Each event has left a higher temperature “floor” than the one before, producing the staircase shape shown by the gold line - though as the step-size card below shows, how big that step is varies a lot by event. The treads slope upward with the background anthropogenic warming rate (~0.027 °C/yr, derived from an OLS fit to the most recent 25 years of land+ocean data); most of each near-vertical step is that same background trend accumulating between events, with the El Niño peak as the moment it becomes visible rather than a separate cause.

+0.13 °C
1997–98 floor lift
+0.08 °C
2009–10 floor lift
+0.21 °C
2015–16 floor lift
~+0.15 °C†
2023–24 floor lift

† 2023–24 floor lift is provisional — post-event temperatures are still settling 12–24 months after the peak. These card values are approximate empirically-observed raw floor lifts (including trend); the forecast step model uses detrended coefficients derived from 24 El Niño events back to 1950 (see below).

What updates automatically: The observed temperature line, trend rate, staircase floors, step and peak coefficients, and forecast profiles are all dynamically derived each time new snapshot data arrives — no manual calibration. The ENSO forecast lines update when the NOAA and SNU CNN model outputs are refreshed.

The long-dashed staircases extend the floor into the forecast period: gold uses NOAA's official RONI outlook median peak; purple uses the SNU CNN peak (typically larger), producing a higher riser and post-event floor. Step height is estimated using a category-tiered coefficient derived from 24 historical events. The fine dotted lines (and amber shading) show the predicted month-by-month actual temperature: the ratchet floor plus ~0.19 × Niño 3.4 for the ENSO contribution, spiking above the floor during the event then settling to the new level.

Why doesn’t ENSO average out to zero on its own?

Even the small piece of the staircase not explained by the background greenhouse-gas trend doesn’t obviously come from a single, settled cause. A few possible contributing mechanisms have been proposed in the literature - each plausible, none of them the dominant story here (that’s still the AGW trend above), and the size of any one is genuinely debated:

1. Power asymmetry (positive skewness)

Super El Niños (1997–98, 2015–16, 2023–24) have spiked global temperatures more sharply than La Niñas have cooled them. La Niña cooling has a physical floor (set by how cold deep Pacific water actually is) while El Niño has no equivalent ceiling, which could leave a small residual warming signal averaged over many cycles. [1, 2]

2. Nonlinear atmospheric rectification

The atmosphere is thought to respond nonlinearly to ocean heat: El Niño’s warm water triggers large-scale cloud and circulation changes that may not fully reverse when La Niña flips the Pacific back, potentially leaving a small fraction of the shifted heat behind - sometimes called “ENSO rectification”. [2, 3]

3. Decadal dominance cycles

ENSO appears to oscillate through multi-decadal phases where one state dominates. During the early-to-mid 20th century (~1900–1941) El Niño was more frequent and powerful than La Niña, which may have added an independent multi-decadal warming contribution on top of the greenhouse signal. [1, 2]

Is ENSO getting more extreme?

The baseline frequency of ENSO events (~every 2–7 years) has not conclusively increased, but the intensity distribution has shifted. IPCC AR6 and WMO assessments note that episodes since 1950 have been demonstrably stronger than those in 1850–1950. Climate models project the frequency of extreme El Niño and La Niña events could roughly double (from once every ~20 years to once every ~10 years) by the end of the 21st century under high-emissions scenarios. [4, 5]

A separate trend is the rise of multi-year clusters: the 2020–23 “triple-dip” La Niña is an example of consecutive cool phases that research (published in Nature) links directly to intensified El Niños; global warming may be increasing the chance of such consecutive La Niña years as a rebound response. [5]

[1] IPCC AR6 WGI Ch. 2 & 3 - ENSO observed changes; WMO State of the Global Climate 2024.

[2] Foster & Rahmstorf (2011), Environ. Res. Lett. 6 044022 - annual-mean regression 0.10 °C/°C; empirical monthly peak ~0.18 °C per RONI unit used for the dotted profiles (derived via OLS from 23 events, 1950–2024). Floor step-lift coefficient by category: moderate ~0.034 · strong ~0.058 · very strong ~0.049 per RONI unit, derived from detrended pre/post-event floor analysis across 23 El Niño events (1950–2024); Pinatubo 1991–92 cooling window excluded. RONI (Relative Oceanic Niño Index) is NOAA’s official ENSO index since Feb 2026; coefficients and the forecast peak used to scale them are both on the RONI basis, so the projected floor step is not inflated by the raw-ONI warming background. Model forecasts (raw Niño 3.4) are converted to RONI by subtracting the observed ONI−RONI gap season by season (~0.5°C cooler; Stockdale 2026, ECMWF).

[3] Rodgers et al. (2021), Nature Climate Change - nonlinear ENSO atmospheric response.

[4] Cai et al. (2014 & 2015), Nature - doubling of extreme El Niño & La Niña frequency under warming.

[5] Geng et al. (2023), Nature - increased consecutive La Niña years linked to global warming.

NOAA NCEI land+ocean monthly anomaly. SNU CNN Niño 3.4 forecast (Ham et al. 2019, Nature).

Sources: NOAA NCEI (temp) · Niño 3.4 + ONI + RONI (ENSO obs) · NOAA RONI Outlook + SNU ACE Lab CNN (ENSO forecast) · NOAA CPC (NAO, PNA, AO) · NOAA PSL (AMV) · NOAA PSL (IOD, monthly DMI) · EM-DAT (extremes)

ENSO Tracker NAO Tracker

Combined Global Footprint

Climate is ENSO, NAO, AMV and the Polar Vortex acting together.

Classic Mild & Wet El Nino Winter moderate matchHow well the live readings match a known historical pattern - not a measure of forecast skill. NAO has no clear live signal right now and is matched to the nearest pattern instead, which downgrades this by one level.

Stratosphere Vortex coherent; downward coupling reinforces +NAO bias.

Wet / mild winterENSO droughtENSO wetIOD

Outcomes are precomputed from peer-reviewed teleconnection literature - deterministic lookup.

Sources: NOAA CPC ONI (ENSO) · NOAA CPC NAO index · NOAA PSL AMO · NOAA CPC Stratosphere Monitor (SPV).

ENSO Tracker NAO Tracker

Data Sources

How the Climate Symphony is Built

The Symphony is built from the same snapshots that drive the individual tracker pages (ENSO ↗, IOD ↗, PNA ↗, NAO ↗, Polar Vortex / AO ↗), so the timeline, the world map and the pillar pills all read from the same figures and cannot disagree.

How the Timeline is Grouped

  • The tropical Indo-Pacific pair - ENSO, then the IOD. They often work together: El Niño tends to push the IOD positive and La Niña negative, and recent research finds the IOD feeds back on ENSO too (Park et al. 2025). The hover explanations read the two together.
  • ENSO’s route into North America - the PNA. El Niño winters usually bring a positive PNA, La Niña winters more often a negative one, which is how the Pacific reaches North American weather.
  • North Atlantic & Arctic - the NAO, then the AO (the surface face of the polar vortex). These run Europe’s winters.
  • Slow ocean background - the AMV, a decades-long North Atlantic warm or cool phase, and the AMOC, the Atlantic’s overturning circulation, measured directly since 2004.
  • The outcomes - global temperature, heatwave days and extreme weather, where the drivers show up.

Observed (History) Data

  • ENSO / Niño 3.4 / ONI - NOAA Climate Prediction Center Oceanic Niño Index (3-month running mean ERSSTv5 SST anomaly, Niño 3.4 region) plus weekly OISST.v2.1. Monthly updates.
  • IOD - NOAA Physical Sciences Laboratory monthly Dipole Mode Index (HadISST1.1, 1870-present). Plotted with ENSO as the Indo-Pacific pair and read with it in the hover explanations, but not part of the compound stacking matrix below - see the IOD tracker ↗ for the fresher BOM weekly reading.
  • PNA - NOAA CPC daily & monthly Pacific-North American teleconnection index.
  • NAO - NOAA CPC daily & monthly NAO index (500 hPa EOF-based, 1950-present).
  • AO (proxy for stratospheric polar vortex state) - NOAA CPC daily & monthly Arctic Oscillation index.
  • SSW catalogue - Major Sudden Stratospheric Warming events from the Free University Berlin / NOAA SSW chronology.
  • AMV - NOAA Physical Sciences Laboratory Atlantic Multidecadal Variability (unsmoothed monthly SST anomaly, North Atlantic basin).
  • AMOC - RAPID-MOCHA-WBTS array at 26.5°N, monthly overturning since April 2004, shown as a 12-month mean. Released in batches a year or more after collection.
  • Global surface temperature - NOAA Climate at a Glance Global Land + Ocean monthly anomaly.

Forecast Data & Models

  • ENSO - official NOAA CPC ENSO consensus probability forecast, 9 overlapping 3-month seasons (DJF, JFM, FMA, ...). Updated monthly. Confidence: high.
  • ENSO (CNN) - the SNU deep-learning model (Ham et al. 2019, Nature) trained on CMIP5 climate model output and verified against observations. Predicts Niño 3.4 SST anomaly up to 18 months ahead. Shown as the purple dashed line and shading on the ENSO and post-El Niño floor panels; the purple shading fills only the gap where the CNN projects a stronger El Niño than the NOAA consensus. Confidence: high at leads up to ~6 months, moderate beyond.

ENSO is the only driver with a live, automated seasonal forecast, so it is the only one with a dashed forecast line on the timeline. The NAO, PNA, AO, IOD and AMV show observed history only. When the Combined Global Footprint steps forward a season in Forecast mode, the NAO and AO simply fade back to neutral within a few months (the atmosphere has a short memory, so there is no real skill to show), and the slow AMV keeps its current phase. Use What-If mode to explore other combinations.

Compound Stacking Matrix

The 16-cell matrix is an evidence-based lookup keyed by the sign (+ or -) of four pillars - ENSO, the NAO, the AMV and the polar vortex. Cell narratives are synthesised from the peer-reviewed teleconnection literature and the documented impacts maintained by NOAA CPC, the Met Office and ECMWF. Each cell carries region-specific impact text for the UK / NW Europe, central + eastern Europe, North America and the ENSO-impacted Southern Hemisphere regions. Two partners are read alongside rather than as extra cells: the North America hover adds a PNA note (does the live PNA match ENSO’s usual pattern?), and the IOD adds a reinforcing or opposing note for East Africa, India / SE Asia and Australia.

The Post-El Niño Temperature Floor

The amber dashed lines on the Global Temperature panel mark the post-El Niño temperature floor: the 12-month mean global anomaly for the year starting 6 months after each major event’s ONI peak. After the 1997–98, 2009–10, 2015–16, and 2023–24 El Niño events, temperatures never returned to the pre-event baseline during the following La Niña - each event left a higher floor than the one before in absolute terms (+0.13, +0.08, +0.21, and +0.32 °C respectively), though the size of that step varies widely by event. This is our own descriptive label for the pattern, not a separate physical mechanism: it reflects primarily the underlying anthropogenic warming trend - each El Niño spike rides a rising baseline, so even the La Niña cooling that follows still lands above the pre-event level. Once that background trend is removed, some events (2009–10 in particular) show next to no additional ENSO-specific step - see the FAQ below for the detrended figures.

A secondary contribution may come from El Niño-induced feedbacks - Arctic sea-ice albedo loss, ocean heat redistribution - that are not fully reversible on multi-year timescales. With the 2026 El Niño now under way, the global temperature baseline can be expected to step higher again once it fades; the exact magnitude depends on event strength but historical analogues suggest a floor lift of roughly +0.1–+0.18 °C above the current post-2023-24 level (NOAA plume scenario ~+0.11 °C; CNN ~+0.16 °C).

Foster & Rahmstorf (2011, Environ. Res. Lett. 6 044022) provide the canonical framework for separating the ENSO signal from the underlying warming trend. Their analysis shows ENSO has a total range of ~0.39 °C on the global surface temperature record, with global warming lagging the MEI index by 2–5 months.

FAQs

Climate Symphony - Common Questions

What is the Climate Symphony?

The Climate Symphony is an interactive view of how Earth's major climate "drivers" combine to shape weather and climate. One timeline plots them in groups that tell a simple story: ENSO (El Niño / La Niña) and the Indian Ocean Dipole (IOD), the tropical Indo-Pacific pair that often work together; the PNA, ENSO’s route into North American weather; the NAO and AO, which run Europe’s winters; the AMV, a slow ocean background; and then the outcomes - global temperature, heatwave days and extreme weather. A world map and a 16-cell compound matrix (ENSO, NAO, AMV and the stratospheric polar vortex) show what the combined state means for each region now, next season, or in any What-If combination.

How do ENSO, the IOD and the PNA fit together?

Think of ENSO as the lead instrument. The Indian Ocean Dipole is its tropical partner: El Niño tends to push the IOD positive and La Niña negative, and recent research finds the IOD feeds back on ENSO too (Park, An, Park & Liu 2025, npj Climate and Atmospheric Science). When the two line up - El Niño with a positive IOD, or La Niña with a negative one - their rainfall effects on East Africa, Indonesia and Australia usually reinforce. The PNA is how ENSO reaches North America: El Niño winters usually bring a positive PNA (milder western Canada, colder US south-east), La Niña winters more often a negative one. The Symphony plots each pair next to each other and reads them together in the hover explanations.

Why look at all the climate systems together rather than one at a time?

Because no single driver acts in isolation. A +NAO winter feels very different depending on whether ENSO is in El Niño or La Niña, whether the AMV ocean background is warm or cool, and whether the stratospheric polar vortex is strong or disrupted. The four pillars stack into 16 possible sign combinations and each combination has a documented signature in the historical record. Two partners are read alongside: the IOD (with ENSO) and the PNA (ENSO's route into North America). Looking at one pillar at a time hides the most important question: what is the combined state right now, and what is it expected to be next season?

What does the compound stacking matrix show?

The matrix is a 16-cell lookup keyed by the sign (+ or -) of each pillar - ENSO, NAO, AMV and SPV. Each cell carries an evidence-based narrative for what that combined state means for the UK and northwest Europe, central and eastern Europe, North America, and the ENSO-impacted Southern Hemisphere regions (Australia, India / SE Asia, South America, Southern Africa, East Africa). The system selects the cell that matches the live observed state, the forecast state for any upcoming CPC season, or any combination you build in What-If mode. The North America text adds a note on whether the live PNA matches ENSO's usual pattern, and the IOD adds a reinforcing or opposing note for East Africa, India / SE Asia and Australia - neither changes which of the 16 cells is selected.

Where does the forecast come from?

ENSO is the only driver with a live, automated seasonal forecast - the official NOAA CPC consensus probabilities, plus the SNU deep-learning model (Ham et al. 2019, Nature) - so it is the only one with a dashed forecast line on the timeline. The IOD, PNA, NAO, AO and AMV show observed history only. When the compound matrix and map step forward through the next CPC seasons in Forecast mode, ENSO follows the NOAA forecast, the NAO and polar vortex fade back to neutral within a few months (the atmosphere has a short memory, so there is little real skill to show), and the slow AMV keeps its current phase. Each pillar carries a confidence flag (high / moderate / low / normal).

Why does the NAO look neutral a few months ahead?

Because that is the honest answer at seasonal lead. The atmospheric drivers (NAO, PNA, AO) have very little predictive skill beyond a few weeks, so the Symphony lets them fade back to neutral rather than showing a confident +NAO or -NAO signal months out. Operational seasonal NAO forecasts (Met Office GloSea, ECMWF SEAS5) do have modest skill in some winters - see the NAO tracker for the current outlook.

What is the difference between Now, Forecast and What-If modes?

Now: the live observed state of all four pillars from the latest snapshot of each index. Forecast: step through the next ~12 months of CPC seasons; the matrix and the world map update to show the dominant fused stack for each season. What-If: toggle any pillar to any sign you want and see which historical analogue (and which combined regional impacts) you have just constructed - useful for asking questions like "what would a +NAO winter look like if AMV were cool?"

What is the AMV and why does it matter?

AMV stands for Atlantic Multidecadal Variability - the slow basin-wide warm/cool background phase of the North Atlantic sea surface temperatures, with a typical period of 60-80 years. A warm AMV tilts the NAO negative on average, boosts Atlantic hurricane activity and nudges Northern Hemisphere temperatures up; a cool AMV does the opposite. AMV phase is one of the main reasons certain decades feel persistently stormier or drier than others, even when ENSO is neutral.

Where does the AMOC fit in?

The AMOC (Atlantic Meridional Overturning Circulation) is the slow ocean circulation that carries warm water north through the Atlantic and cold water back south at depth. It sits on the timeline beside the AMV, as the RAPID array's 12-month mean at 26.5°N compared with its 2004-2024 average. Many studies link the AMV's decades-long swings to changes in the heat the AMOC carries north, though how much is still debated - the atmosphere and air pollution play a part too. The arrays release data a year or more late, so the AMOC panel stops at the latest release. The AMOC page covers the measurements, how the circulation works and the debate over a slowdown.

What is the stratospheric polar vortex (SPV) and how is it linked to weather?

The SPV is the ring of fast westerly winds that circle the North Pole each winter in the stratosphere (~30 km up). When it is strong, midlatitude weather tends to stay zonal and mild (+NAO bias). When it weakens or is disrupted (a sudden stratospheric warming, or SSW), the signal couples downward over 2-4 weeks and pushes the surface into a -NAO regime - cold spells across northern Europe and the eastern US. The Symphony page uses the AO (Arctic Oscillation) as an observational proxy for the SPV state.

How often is the data updated?

All observed pillars are refreshed monthly (and most also have daily updates). The CPC ENSO probability forecast updates monthly. The fused forecast-stack JSON is rebuilt whenever any underlying pillar snapshot changes, so the chart, the map and the pillar pills always carry the same numbers. The AMOC panel updates whenever the RAPID array releases new data, usually a year or more after it is collected.

Is the Indian Ocean Dipole (IOD) part of the Climate Symphony?

Yes - it is plotted right after ENSO as the tropical Indo-Pacific pair, and the hover explanations read the two together (for example, El Niño with a positive IOD usually means a drier Indonesia and Australia and a wetter East Africa). It is not one of the four pillars in the 16-cell compound matrix: on the map it adds a reinforcing or opposing note for East Africa, India / SE Asia and Australia, and you can toggle it in What-If mode, but it never changes which cell is selected. Making it a fifth pillar would double the matrix to 32 hand-written cells, most resting on interaction research that does not yet exist. The IOD tracker at /climate/iod has the live BOM weekly reading, its impacts and full history.

Which climate drivers matter where I live?

Every country and region page on 4billionyearson.org has a Climate Drivers section that answers this from data, not guesswork. For each place we measure how much of its seasonal temperature and rainfall swings line up with ENSO, the NAO, the AO, the PNA and the IOD since 1950 (with the long-term trend removed, and ENSO's share taken out before scoring the others), and show only the drivers with a measurable effect - with the season it matters most and the current state of each. For example, the UK's winters follow the NAO, Kenya's short rains follow the IOD, and Canada's late winters follow the PNA.

Why call it the Climate Symphony?

Because no single driver tells the whole story. Each pillar is one instrument; the weather we experience is the chord they play together. The Symphony page is the score - the live arrangement and the forecast for the next few months - so you can see the whole orchestra at once instead of listening to one violin in isolation.

Why do global temperatures stay high after an El Niño ends?

After each major El Niño event, global temperatures decline during the La Niña that follows - but they usually don't return to the pre-El Niño baseline. Each event has left a higher temperature "floor" than the one before, producing what we call the "staircase" (or informally, "ratchet") pattern in the global temperature record - our own descriptive label for the pattern, not a separate physical mechanism. The main reason is simply the underlying anthropogenic warming trend: each El Niño spike rides a rising baseline, so even the La Niña cooling that follows still lands above the pre-event level - the same reason any hot year sits above the equivalent year a decade earlier. Measured against RONI (the Relative Oceanic Niño Index - NOAA CPC's primary ENSO index since Feb 2026, which isolates the ENSO signal from background tropical warming) to see what, if anything, is left over once that background trend is removed, the 1997-98, 2009-10, 2015-16, and 2023-24 events lifted the post-event floor by +0.17, essentially flat (-0.04), +0.12, and +0.25 °C respectively. In other words: one of these four "steps" (2009-10) isn't really a step once the trend is stripped out, which is a reminder that this is a loose, event-by-event pattern rather than a fixed-size mechanism that fires every time. A secondary, less certain contribution may come from feedbacks such as Arctic sea-ice albedo loss or ocean heat redistribution, which some research suggests could make part of a step only partially reversible on multi-year timescales - see the Symphony page's "Why doesn't ENSO average out to zero on its own?" panel for the (debated) candidate mechanisms. The gold staircase line on the Global Temperature chart shows these post-event floors: the treads slope gently upward with the background warming trend (~0.027 °C/yr, derived from a 25-year OLS fit to land+ocean data), and the near-vertical steps mark where each El Niño event's floor became visible. All staircase parameters - trend rate, step coefficients, and forecast profiles - are dynamically derived from 23 historical El Niño events back to 1950, classified by RONI (Van Oldenborgh et al. 2021, ERL 16 044003; L'Heureux et al. 2024, J. Climate 37(4)). As of autumn 2026, a new El Niño is under way; the forecast step is roughly +0.11 to +0.16 °C above the post-2023-24 level, depending on peak intensity (NOAA plume vs CNN model).