El Nino sea surface temperatures in the tropical Pacific are running 3.07 degrees Celsius above the 30-year-average, tying the record intensity of 2015-2016, according to Zeke Hausfather, a climatologist at Berkeley Earth. 

"This month (September) is very likely to have the highest monthly anomalies on record, barring something quite unexpected in the coming week," Hausfather, co-author of UN climate change reports, said in an email.

Hausfather's figure, published on the Climate Brink dashboard, draws on satellite and buoy tracking from the National Oceanic and Atmospheric Administration (NOAA), which measures how far the Nino 3.4 region – a defined area of the Pacific – sits above its long-term average. 

But NOAA has shifted to a newer method, the Relative Oceanic Nino Index (RONI), which gauges the same region against warming across the whole tropical belt, and better accounts for climate change heating oceans in general.

On that metric, the numbers run lower. The current El Nino is still below the record, though expected to break it.

El Nino is the warming phase of a natural cycle in the tropical Pacific. It sets in when the east-to-west trade winds ease up, letting warm water that normally piles up in the western Pacific Ocean slide back east and rise to the surface.

When those warmer-than-average temperatures last a few months, they drive more storms and clouds over the region, with ripple effects through the global atmosphere. The upshot is hotter and drier conditions in some places, cooler and wetter in others.

Human-caused climate change can sharpen El Nino's impacts. A warmer atmosphere holds more moisture, so El Nino-linked rains can turn more extreme. It also dries out soil, deepening drought where El Nino brings it.

Scientists aren't in full agreement on whether climate change intensifies El Ninos themselves, but a recent study based on coral skeletons found "striking amplification" over the past 40 years compared with the pre-industrial period.

This El Nino is already hitting some regions hard. In Central America, animals and crops are dying from drought. Reduced water levels also disrupt the Panama Canal. Five percent of global trade passes through the waterway linking the Atlantic and Pacific. It cannot operate without the reservoir water that powers locks lifting and lowering ships at either end of their passage, and authorities have had to slash traffic.

In Indonesia, El Nino is blamed for drought that fueled wildfires across the archipelago.