June, July, August and September were the four warmest months on record. September’s global temperature was the most anomalous warm month of any year in the ERA5 (European Centre for Medium-Range Weather Forecasts dataset) from 1940 onwards.

September was 0.93°C warmer than the 1991-2020 baseline and around 1.75°C warmer for the month of September compared to the pre-industrial reference 1850-1900 period. The 1.5 degree C threshold has already been breached for individual months this year.

“We already have seen a temporary breach, according to Copernicus data. September had an average surface temperature of 16.38°C. This was 0.5°C above the temperature of the previous warmest September, in 2020, and around 1.75°C warmer for the month of September compared to the pre-industrial reference 1850-1900 period,” said Christopher Hewitt, director of WMO Climate Services.

“But its important to keep it in perspective. The Paris Agreement sets long-term goals to guide all nations to substantially reduce global greenhouse gas emissions to limit the global temperature increase in this century to 2°C while pursuing efforts to limit the increase even further to 1.5°C, to avoid or reduce adverse impacts and related losses and damages. The fact that an individual month exceeds the 1.5°C limit does not mean that we will permanently exceed the 1.5°C level specified in the Paris Agreement which refers to long-term warming over many years,” he added.

“Preliminary records do show that we already crossed the 1.5°C for a few days this year. Global warming is at a fast rate as emissions continue unabated. Along with that, we have a mature El Nino in place, which acts as a mechanism to transfer the heat from the ocean to the atmosphere across the globe. This adds to the global average temperatures. Since the El Nino will peak in December and continue to the next year, we might see more of these record-breaking temperatures,” said Roxy Mathew Koll, climate scientist, IIT-M.

“The unprecedented temperatures for the time of year observed in September — following a record summer — have broken records by an extraordinary amount. This extreme month has pushed 2023 into the dubious honour of first place — on track to be the warmest year and around 1.4°C above pre-industrial average temperatures. Two months out from COP28 , the sense of urgency for ambitious climate action has never been more critical,” Samantha Burgess, deputy director of the Copernicus Climate Change Service said in a statement last week.

The 1.5°C warming threshold is significant because of the Paris Agreement goal to hold “the increase in the global average temperature to well below 2°C above pre-industrial levels” and pursue efforts “to limit the temperature increase to 1.5°C above pre-industrial levels”. But a temporary breach is not the same as breaching the 1.5°C climate goal because the Paris Agreement refers to long-term warming over many years.

In some ways, this was pre-ordained. A WMO report in May, led by the UK’s Met Office said there was a 66% likelihood that the annual average near-surface global temperature between 2023 and 2027 would temporarily breach the 1.5 degrees threshold in at least one year.

But the effects of the breach, largely caused by this year’s El Nino will be significant, experts warned.

“The threshold is one thing but such warming will trigger arctic ice melting in September and October which in turn will influence circulation patterns. It will be important to see how El Nino plays out. We also have a positive Indian Ocean Dipole (IOD) this year,” said R Krishnan, executive director, Centre for Climate Change Research, Indian Institute of Tropical Meteorology (IITM).

El Nino is characterised by an unusual warming of waters in the eastern equatorial Pacific, which has a high correlation with warmer summers and weaker monsoon rains in India. IOD refers to the temperature differential between the western and eastern Indian Oceans. A positive IOD has a direct correlation with a good monsoon.

“From 1850 global temperatures increased by 0.06°C per decade, and close to 1.0 degree for the last 170 years. But 1.5 degrees warming can occur temporarily in the near future and 1.5 degrees (average) warming since pre industrial around 2060 or so. Any incremental increase in global temperatures is catastrophic. IPCC said with 1.5°C warming, impacts could be contained but not with 2.0°C warming. An increase of 1°C in temperatures increases moisture content in the atmosphere by 7%. We should try to contain the further increase in global temperatures immediately,” said M Rajeevan, former secretary, ministry of earth sciences.

According to air temperature data records maintained and analysed by University of Maine’s Climate Reanalyzer, since June this year temperatures have been significantly above the long-term mean of 1979 to 2000, and possibly highest ever.

“Nobody knows when this is going to end but El Nino is still strengthening. As a result of that we expect heat to continue for the rest of 2023 with a 95% chance of this being the warmest or second warmest year on record. It’s possible that 2024 could be even warmer than 2023. We anticipate to be in this record category globally for several months to come,” Karin Gleason, Monitoring Section Chief, NOAA National Centers for Environmental Information said on September 21.

On September 10, sea ice in the Antarctic reached an annual maximum extent of 16.96 million square kilometres (6.55 million square miles), setting a record low maximum in the satellite record that began in 1979 according to NOAA.