According to reports from NOAA’s National Climate Data Center, September of 2012 tied September of 2005 for being the hottest month on record. This record also occurred during a time of massive sea ice losses in the Arctic and ENSO neutral conditions in the Pacific.
The Arctic showed record low sea ice area and extent for the month of September. These new records were hundreds of thousands of square kilometers lower than the previous records set in 2007 and 2011. Sea ice volume was 700 cubic kilometers lower than the previous record low set last year. The result is that more dark, open ocean is available to absorb the sun’s rays and less ice is available to reflect that radiation back into space.
ENSO is the periodic cycle of equatorial heating and cooling in the Pacific Ocean. Heating, or El Nino, conditions tend to warm the Earth overall. Cooling, or La Nina, conditions tend to cool the Earth overall.
On the one hand, ENSO neutral conditions would tend to keep world temperatures from the hitting new record highs. However, the massive losses of sea ice in the Arctic have caused some to speculate that enhanced heating there drove world temperatures to new records during September.
Though temperatures for the equatorial Pacific remain only slightly above average, NOAA has issued an El Nino watch giving the world a 55% chance conditions in that region will switch to warming. In the past, new records for global temperature have been set as the equatorial Pacific heats up. Now, it appears the Arctic may also play a major role in driving world temperature spikes.
What is particularly disturbing is that top ten record high temperature months are occurring during La Nina and ENSO neutral months. This would seem to indicate that the next outbreak of El Nino may result in a rather large temperature spike, potentially larger than those previously witnessed.
It is important to note that the last time September recorded a below average month was 1976. The last below average temperature for any month was during February of 1985.