The signal from the ocean
The Met Office long-range system GloSea shows sea-surface temperature in the Nino3.4 region passing 3 degrees in the coming months. A typical El Niño keeps that rise between 1-2 degrees, and Adam Scaife, who heads long-range forecasting there, says he has never seen a signal this intense in the forecasts. What we have is a forecast, and it has to be read as a scenario conditional on the model's assumptions.[2]
The measured side is already visible. Mark Parrington, who tracks fire emissions for the Copernicus Atmosphere Monitoring Service, says emissions from the fires in Indonesia are comparable, for this time of year, to previous really big El Niño years. Ground-based sensors are reading smoke levels previously detected only in El Niño years, and the burning season is only starting.[1]
The layer that holds the carbon
Across much of the region, thick layers of peat have built up beneath the rainforests over millennia and store vast amounts of carbon. Clearing the forests dries that peat out and raises the chance of ignition in hot, dry conditions, and peat can burn underground, which makes it very hard to put out. That stock is why these fires reach a gigatonne scale. The scale may instead be set mainly by the severity of the drought and the extent of the burned area; either way, both explanations send you to the same quantity, how much dried peat is available.[1]
Past events show how large that scale can be. During the strong El Niño in 1997 and 1998, fires in Indonesia emitted as much as 2.5 gigatonnes of carbon dioxide, around a third of annual fossil fuel emissions at the time. In the strong El Niño of 2015 the estimate was 1.5 gigatonnes.[1]
Two numbers to watch through November
If the anomaly in the Nino3.4 region reaches the forecast level of 3 degrees in the coming months, the Copernicus seasonal fire-emission estimates for Indonesia should be expected to move toward the range of the previous strong El Niño years. This is a conditional expectation: if the ocean side falls short of the forecast, the land-side total falls with it.[2], [1]
The lever that works this season is keeping the peat wet. Because clearing forests dries the peat out, land management that holds the water level stands out as the most direct intervention limiting how much peat can burn, and what it answers to is the schools closed by smoke and the air quality in Singapore and Malaysia. According to Nick Dunstone at the Met Office, large El Niño events release more heat from the ocean to the atmosphere, which makes 2027 very likely to replace 2024 as the warmest year measured, and the carbon from peat fires is one entry in that same ledger.[1], [2]