It's the sort of anniversary you don't want to celebrate.
Early reports indicate that April was another record hot month - by some margin - making it 12 months in a row that have set new high marks for heat.
Eric Holthaus, a US-based meteorologist took to Twitter with an estimate that sea and land-surface temperatures would again top 1 degree compared with the average for 1951-80 period used by NASA.
Global heat wave continues: April record warm.
NASA GISS equiv: 1.15-1.25C (likely 1.19) abv 51-80 ave
Map @RyanMaue pic.twitter.com/KbVZ8U58Z2— Eric Holthaus (@EricHolthaus) May 2, 2016
The previous biggest anomaly for April was recorded in 2010 at 0.83 degrees, implying that last month was easily the warmest ever registered for the month.
If confirmed by major meteorological agencies within coming weeks, the April figures would continue the remarkably warm start to 2016, with each month among a handful over the most abnormally hot months in more than 130 years of global figures.
Australia is also exceptionally warm. During the first four months of 2016, average mean temperatures were 1.28 degrees above the 1961-90 period used by the Bureau of Meteorology for its benchmark.
The previous record to this point of the year was 1.16 degrees in 2005, Blair Trewin, senior bureau climatologist, told Fairfax Media.
El Nino shifts to La Nina?
The spurt in global temperatures is being driven in part by the unwinding of the giant El Nino in the Pacific.
For the past year, large regions of the central and eastern Pacific have been hotter than usual because of a stalling or reversal of trade winds - a phenomenon that has exacerbated the background warming from climate change, scientists say.
That climate pattern may now tilt the other way, towards a La Nina event, which could trigger alternative extreme weather, and break the sequence of record heat. Odds are about even in favour of a La Nina this year.
For instance, Australia had a record quiet season for tropical cyclones but may see a shift to a more active than usual storm season for the 2016-17 summer should a La Nina event bring stronger westward-blowing winds.
The unwinding of the current El Nino, though, could have a way to go as far as boosting temperatures in Australia and globally, Dr Trewin said.
"The El Nino warming influence on Australian temperatures is typically strongest in the first six months of the year - a little earlier than the global signal, which typically runs until August-September," he said.
Reef watch
To the worry of marine ecologists and tour operators, there's also little sign of an early let up for the Great Barrier Reef in terms of temperatures returning to normal.
The excessive heat over the past half year and longer has been blamed for widespread bleaching of corals, with as little as 7 per cent unaffected, according to scientists.
Bureau of Meteorology charts show that coastal regions of north Queensland will continue to be more than one degree above normal:
Hot spots
Leading climate scientists such as NASA's Gavin Schmidt have already predicted that 2016 is extremely likely to be the hottest year on record, making it three years in a row the mark has been lifted.
Among the areas of particular warmth has been the Indian Ocean, which continues to track at record heat levels, according to Ryan Maue, a scientist based in Atlanta, Georgia:
Indian Ocean is very warm. 31-31.5°C pic.twitter.com/pqzjkEqfeZ— Ryan Maue (@RyanMaue) May 2, 2016
The sub-continent is bearing the brunt of that heat over land, with daily temperatures reaching 47 degrees or warmer, and severe water restrictions in place affecting hundreds of millions of people.
Forest fires are also raging in parts of Nepal and northern India, killing dozens of people and devastating hundreds of thousands of hectares, Reuters reported on Monday.
"This year we have experienced a longer spell of dry weather and the temperatures have risen significantly, contributing to the disaster," Nepal's Forest Ministry official Krishna Prasad Acharya told Reuters.
North melts
The largest departures from the norm, though, have been occurring at the poles, especially in the north.
Parts of Greenland were 8 degrees warmer than average in April, sparking early-season melting of the giant ice sheets so rapid it prompted scientists to check their instruments weren't broken.
Unusual heat over the northern winter meant the Arctic Sea ice extent began at a record low level.
With less to start with and warmer seas, the area covered by sea ice is retreating, setting new records every day last month, according to US PhD student, Zack Labe:
Daily record low #Arctic sea ice extent records were broken every single day this April (JAXA, last non-min -> 3/29) pic.twitter.com/vywLg2s39s— Zack Labe (@ZLabe) May 2, 2016
