Update: Added note on Berkeley Earth.
Both the NASA GISTEMP and NOAA NCDC global temperature series have updated for December, confirming that the year just completed was once again the warmest on record. That’s since 1880 when those series start, but really since at least 1850 when the other instrumental series begin¹ :
Global monthly land+ocean temperatures since 1850 — instrumental estimates
Of the instrumental series, so far only those two have updated. We’re still waiting for December from HadCRUT and Cowtan & Way, and for the whole of 2014 from Berkeley Earth² (which updates very infrequently, unfortunately). Last year just barely made it to the top, by being pretty much uniformly hot throughout … excepting a slightly cooler February. This excellent monthly animation of NOAA NCDC at Bloomberg tells the story well (sample only, click for link):
©Bloomberg — click for full-res animation
That happened despite 2014 not turning out to be an El Niño year after all. El Niño years are on average about 0.05°C warmer than the overall average, and about 0.15°C warmer than La Niña years. The mechanism of El Niño brings warm Pacific Ocean deeper water to the surface off South America. It can be thought of as a kind of periodic stirring of an ocean covering half the planet, releasing a little spurt of the heat it has absorbed. (The oceans absorb over 90% of the excess heat from global warming.)
GISTEMP El Nino, La Nina and neutral years (NASA)
If you’re thinking record warm years are becoming more common, you’d be spot on. According to GISTEMP, nine of the ten warmest years on record have occurred since 2000 (though not all of those were ‘new records’ at the time). How soon until just about every new year is automatically a record? That’s fairly straightforward to estimate … I’m working on it.
Notes
1. Berkeley Earth now has a land-only extension back to 1750, but it is so uncertain as to be practically meaningless.
2. Berkeley Earth have published a note on 2014 temperatures, although they haven’t yet updated their on-line monthly data. The note confirms that 2014 was the hottest in their series too, but then obfuscates by claiming that it wasn’t really because it didn’t beat the previous hottest years (2005 and 2010) within the margins of error. That is of course strictly correct — it would be correct of GISTEMP and NOAA NCDC too — it’s just not very helpful in general discourse. No one has said that 2014 was a completely clear new high; it was just very marginally the hottest based on the best estimates. That is how meteorological ‘records’ are conventionally defined.
In a noisy upward-trending series where the half-width of the noise band exceeds the trend change per interval, a strict “outside the error bars” new record will be a rare thing indeed. Are we to ignore each new record as it occurs, just because its error bars didn’t quite jump those of the previous highest, which also didn’t quite beat the highest before that … and so on?
References
The NASA summary is here and the NOAA NCDC summary is here. For an authoritative local perspective, I recommend the CSIRO / Bureau of Meteorology’s State of Climate 2014 report.
