An exceptionally strong El Niño event could drive atmospheric carbon dioxide (CO2) levels to record highs in 2027, the Met Office has warned.
This natural climate cycle amplifies human sources of emissions while simultaneously hindering the planet's capacity to absorb these greenhouse gases. Experts anticipate a historic surge in CO2, with climate forecasts predicting a rise of approximately 3.51 parts per million (ppm) next year, as recorded at the Mauna Loa Observatory in Hawaii. This projected increase rivals the record surge seen in 2024, which was exacerbated by exceptional wildfires.
If accurate, this forecast would elevate the total atmospheric CO2 concentration to a record 432.2 ppm. Such a level could make it significantly more challenging to maintain global warming below the 1.5°C threshold outlined in the Paris Agreement, potentially leading to devastating consequences.
El Niño, part of the El Niño Southern Oscillation (ENSO) cycle, occurs every two to seven years. During an El Niño phase, Pacific trade winds slow or reverse, causing warm waters to accumulate in the Equatorial Pacific. This disruption leads to severe weather events and above-average global temperatures.
Met Office scientist Emily Wright explained that while human emissions remain the primary driver of the long-term CO2 increase, El Niño events reduce the absorption capacity of plants, soils, and oceans. This is often due to hot, dry weather in tropical regions where large carbon sinks, like the Amazon Rainforest, are located. Drought, dry vegetation, and wildfires interfere with the planet's natural carbon storage capabilities.
Additionally, exceptionally hot weather increases energy demand for cooling systems, leading to higher emissions. Professor Richard Betts, Head of Climate Impacts Research at the Met Office Hadley Centre, emphasized that despite natural variability, the underlying trend of CO2 increase is driven by human activity. He stated that to align with the 1.5°C warming limit, the rate of CO2 increase must slow substantially, a goal not met by current projections.
While the immediate impact of this CO2 rise on next year's weather is not expected, the long-term implication is continued warming. Professor Betts noted that this situation means the UK will likely continue to experience more extreme weather, including droughts, floods, fires, and sea level rise, in the coming decades.
The Met Office forecast comes after data revealed that greenhouse gas emissions have reached an all-time high, with CO2 growth rates tripling since 1960. Between 2011 and 2020, CO2 growth rates accelerated from 0.8 ppm per year to 2.4 ppm per year. The period between 2024 and 2025 saw a global average CO2 concentration increase of 2.8 ppm, nearing the exceptional surge of the previous year. This brought atmospheric concentrations to 426.8 ppm by the end of 2025, representing 153 percent of pre-industrial levels. Experts warn that CO2's long atmospheric lifespan has locked in future warming, even with rapid emission reductions.
Furthermore, a new tool, the El Niño Heat Mortality Tracker, estimates that an additional 370,000 lives could be at risk globally over the next six months due to heat. Nigeria, India, and Brazil are projected to be disproportionately affected, accounting for over a third of these projected heat deaths by March. The UK has also seen an estimated 820 deaths attributed to El Niño's heat during the past summer.
The Paris Agreement, established in 2015, aims to limit the global average temperature increase to well below 2°C above pre-industrial levels and pursue efforts to limit it to 1.5°C. It calls for global emissions to peak as soon as possible, followed by rapid reductions in accordance with the best available science.