Here on Bitsofscience.org we hope to be your climate records reference point, so we try not to miss any of the major reports on temperature trends or Arctic melting records. That means we definitely could not ignore yesterday’s release by NOAA.

It is the peer-reviewed annual State of the Climate report (highlights PDF | full PDF) and it was ‘not just NOAA’ but 368 scientists from 45 countries – and close cooperation with the American Meteorological Society. Together they have tracked several thousands of measurements from different independent datasets of 41 climate indicators [including all-important temperature difference between troposphere and stratosphere] to not only see what happened, but also why it happened.

And there was good reason too, to take a thorough look at the science. That is because the year 2010 was a special year, for climatologists and meteorologists alike.

Hottest of hottest years

The biggest news was that on average it was exceptionally hot. All the leading temperature datasets place 2010 among – and in statistical tie with – the two or three hottest years ever recorded. And probably, judging by NASA GISS – the best-balanced of the global temperature records, 2010 was the hottest* of the hottest years.

[*) The global average temperature was in 2010 0.010 C higher than the previous hottest year, 2005. Now 2009 is third hottest and 2007 fourth – so please stop quoting the El Niño year of 1998 as hottest, although that year was indeed hot too, and statistically tied with the hot years of 2002, 2003, 2006, 2007 and 2009 – all according to the leading GISS dataset.]

ENSO important, but two-faced

It’s hard to find an explanation for the global temperature record in the El Niño/La Niña Southern Oscillation (ENSO), although that climatic oscillation did play a major role in influencing weather patterns worldwide throughout 2010, as ENSO switched from a warm El Niño in early 2010 to a powerful La Niña somewhere from July – showing little interest in the intermediate.

That La Niña [generally leading to a cool year – because a lot of cool deep ocean water is spread out over a vast area of the Pacific, interacting with the atmosphere] may have been one of the strongest ever. As soon as the ITCZ arrived it led to record-high rainfall in many parts of Australia and devastating floods in Queensland. Tropical cyclone activity was low everywhere, except in the Atlantic, where according to NOAA ‘near-record high hurricane activity’ was recorded. And no matter the strong La Niña, the world average ocean temperature in 2010 was third highest.

Based on an analysis of ocean salinity NOAA concludes the hydrological cycle was in high gear, exacerbating salinity differences, with extra fresh ocean water in high precipitation areas, and extra salty waters in high evaporation areas.

Persistent negative Arctic Oscillation

But there were other things going on. In September the Arctic reached the third-lowest ice extent. And while Europe and North America experienced [albeit at different months] a chilly 2010-2011 winter – the Arctic may have had its hottest winter so far – with all-time lowest ice extent records during several months of the ‘ice growth season’ (and indeed a ‘lowest maximum’ record in March 2011).

NOAA explains the relatively large regional temperature differences on the high latitude northern hemisphere with another important air pressure pattern, the Arctic Oscillation, which normally switches from a negative to a positive phase on a regular basis, but in 2010 remained negative for long periods on end, with a dominant high pressure system over the Arctic Ocean, leading to sinking hot air from lower latitudes over the North Pole, while relatively cold air flowed over the surface southwards, carrying cold spells over more densely populated areas of Europe and North America [large parts of Canada were north of the ‘zero anomaly line’ – Canada had the warmest year in recorded history in 2010].

More climate records

There were other climate records as well. The new NOAA analysis does not mention it, but ecologists have in 2010 reported a new coral bleaching record in the Caribbean, which is associated with exceptionally warm waters in the first half of the year. Also largely ignored is the 2010 Amazon drought record, although it may have large consequences for the Earth’s carbon cycle and climate.

NOAA does refer to the Greenland melting record of 2010 and to the new CO2 record – though it does not express that as [indeed also] record-high emissions, but as a record-high CO2 concentration rise, of 2.60 ppm.

Antarctic Oscillation

And meanwhile down south exactly the same thing happened as in the far north, although [due to the reversed situation of a central continent and surrounding seas – instead of a central ocean, surrounded by land masses] with exactly the opposite effect: the Antarctic sea ice reached its highest ever extent during the Southern Hemisphere winter.

NOAA relates this to the Southern Annular Mode, or Antarctic Oscillation, ‘an atmospheric pattern related to the strength and persistence of the storm track circling the Southern Hemisphere and the Antarctic.’ Its persistent phase allowed cold air to escape from Antarctica and circle over the surrounding coastal waters. As this process does not ‘produce cold air’ [as in winter albedo plays no role] – it is a mere redistribution, compensated by higher temperatures in central Antarctica. Based on observed behaviour of the Agulhas Current, in early 2011 [the Antarctic autumn] the southern hemisphere westerlies seem to have retreated further south again.

Climate change trend

We are saving the big conclusion of the NOAA analysis for the end though – and for that we have to get back to that one big anomaly that was not a local extreme: the world’s average temperature. That, NOAA concludes, can also be explained. The comprehensive analysis of indicators shows a continuation of the long-term trends scientists have seen over the last 50 years: it’s getting warmer each decade.

© Rolf Schuttenhelm | www.bitsofscience.org