GW continues to break records, in the silence of media.

GW continues to break records, in the silence of media.

No news, no bad news, says a proverb. Since last October, 2015, the news is always the same: monthly global temperature anomaly has updated previous record of heat. At least, considering GISS database, that start from 1880. Ten consecutive months, including also the month of June 2016, in which the anomaly was equal to that of June 2015 (and higher than others). Never occurred before. With August well positioned for beating its warm record, the only hope fror avoiding a complete year of records is kept in the month of September. This when ENSO index has turned versus its negative phase, as this global SST animation shows. And this is not a good news.

Below, the update of the plots shown some months ago using linear and spiral visualization, and including the data until July. It is evident in both figures as the red line from October 2015 constitutes the upper border of the temperature ensemble.

linear_data_animation

Anomaly of monthly global mean temperatures, according with GISS database. Linear visualization.

Both visualizations show the beginning of the actual warming phase, in late 1980’s, and the violent acceleration in last nine months, much larger than those observed in previous large El Niño (positive phase of ENSO) episodes.

spiral_data_animation

Anomaly of monthly global mean temperatures, according with GISS database. Spiral viualization.

Despite these alarming data, the news about the continuous records of global temperatures does not attract public opinion too much. A research of “global warming” keywords on google trends gives a signal slowly decreasing since the peak of 2007, perhaps due to the book and movie of Al Gore “An inconvenient truth”.

trends-gw

“Global warming” key according with google trends.

Of course, soccer and olympic games, or actresses gossips, or Pokemons, are much more attractive news for common people. After all, global temperatures involve just the earth…

Annunci
Global temperature change, month by month

Global temperature change, month by month

Recently, several authors attempted to visualize the exceptionality of the global mean temperatures recorded in last months. Without pretending to be exhaustive, I would mention the very impressive spiralling of Ed Hawkins, or also the animation of monthly temperatures with annual records by Tom Randall & Blacki Migliozzi. I think that it is important to stress about the rapidity and intensity of actual global warming, underlining the word GLOBAL (eventual anomalies of few months in small areas of the planet do not have nothing to do with global warming!).

The following animation is my modest contribution. Starting dataset is still from the CRU, and in particular the dataset HadCRUT4 (filled-in by Cowtan and Way) on climexp website. Such data are already anomalies, but I have performed an additional montly detrending by substracting, month by month, the average of the period 1850-1879.

The animation updates, year by year, the coldest and warmer months.

linear

Il mese di luglio 2014 a Torino visto dalla stazione meteorologica dell’istituto di fisica

Il mese di luglio 2014 a Torino visto dalla stazione meteorologica dell’istituto di fisica

Vediamo come si colloca, dal punto di vista climatico, il mese di luglio appena trascorso esaminando i dati della stazione meteorologica ubicata sul tetto dell’istituto di fisica dell’università di Torino.

immagine della collocazione della capannina meteorologica posta sul tetto dell'istituto di fisica dell'università di Torino, contenente una parte della strumentazione.

Immagine della collocazione della capannina meteorologica posta sul tetto dell’istituto di fisica dell’università di Torino, contenente una parte della strumentazione.

Abbiamo deciso di usare un doppio riferimento climatico in questa analisi: gli ultimi dieci anni (2005-2014, periodo che chiameremo decennio recente), in cui, tra l’altro, i dati della stazione sono disponibili sul web, ed il periodo 1981-2014 (detto periodo lungo); in quest’ultimo caso, i dati relativi a temperature minime e massime, ed alla piovosità giornaliera, relativi ai periodi precedenti al 2005, sono stati presi dalla climatologia di Torino.

Nella fase finale, cercheremo di collocare i risultati all’interno degli andamenti relativi all’Europa ed all’intero planisfero.

Temperature minime: il valore medio mensile di 17,3 °C rappresenta il valore inferiore del periodo lungo; il precedente valore minimo medio si registrò nel 1993, con 17,4 °C. L’anomalia rispetto al valor medio del periodo lungo è di -2,3 °C. I 13,0 °C registrati il 9 luglio non rappresentano però il minimo assoluto, che fu invece registrato il 13 luglio 1981 con 11,0 °C, ma il terzo valor minimo.

Temperature massime: il valore medio mensile di 27,3 °C rappresenta il sestultimo valore inferiore del periodo lungo, e l’ultimo valore del decennio recente; il valore minimo delle medie si registrò nel 1981, con 26,5 °C. Tre anni fa, nel 2011, il valor medio fu simile a quello di quest’anno, con 27,5 °C. In ogni caso, l’anomalia rispetto alla media del periodo lungo è di -1,9 °C. I 32,5 °C registrati il 17 luglio, che sono il valore massimo assoluto del mese, sono molto lontani dal valore massimo assoluto di 36,9 °C del 22 luglio 2006.

Temperature medie: con 21,9 °C il mese di luglio 2014 batte il precedente record negativo del luglio 1981, di 22,0 °C. L’anomalia rispetto alla media del periodo lungo è di -2,5 °C. Relativamente a tutti i valori termici, le anomalie superano la dispersione dei dati intorno al valor medio (deviazioni standard comprese tra 1,3 e 1,5 °C): questo significa che, se assumiamo che la distribuzione delle temperature sia normale, la probabilità di accadimento di un evento compreso tra 1 e 2 deviazioni standard sarebbe compresa tra il 3 ed il 16%.

Piovosità: sul tetto dell’istituto sono caduti 151,6 mm di pioggia, valore lievemente superiore a quello di un anno fa (149,8) e massimo assoluto del periodo lungo, ben superiore al valore medio pari a 62,0 mm (anomalia quindi di +89,6 mm, pari al 145% di pioggia in più). Anche in questo caso, l’anomalia supera la deviazione standard dei dati (41,1 mm).

Ci sono stati 14 giorni di pioggia a luglio (nuovo record: il precedente, di 13 giorni, si verificò nel 1981), molti di più rispetto ad un anno fa (8), pur avendo registrato un quantitativo di pioggia simile, che costituiscono il doppio del valor medio di luglio (7 giorni). In sei di questi giorni è stato superato il quantitativo giornaliero di 10 mm (anche questo dato rappresenta un nuovo record che aggiorna il precedente, di 5 giorni, detenuto dal luglio 2011), a fronte di una media di due giorni. Il valore massimo giornaliero è stato di 34,2 mm, lontano dal massimo assoluto di 64,4 del 1° luglio 1987.

In relazione al decennio recente, possiamo notare come soltanto in cinque giorni sia stata registrata una temperatura massima superiore a 30 °C, a fronte di una media di 14 giorni; parallelamente, la temperatura minima ha superato 23 °C soltanto in un caso, a fronte di una media di 4 casi. L’umidità relativa media è stata del 70%, superiore alla media del 62% e valore massimo del decennio recente. La pressione atmosferica media mensile è stata di 1012,7 hPa: pur non battendo il minimo di 1010,9 hPa, registrato nel 2011, rappresenta un valore inferiore alla media (1014 hPa).

In definitiva, i dati registrati presso la stazione dell’istituto di fisica delineano un mese di luglio con temperature molto inferiori non soltanto al decennio più recente, ma anche al periodo lungo preso come riferimento, in particolare per quanto riguarda le minime e le medie giornaliere. Dal punto di vista pluviometrico, l’apporto di pioggia è stato il maggiore del periodo lungo ed ha quasi uguagliato il quantitativo di un anno fa, distribuendolo però su più giorni di pioggia, il numero dei quali è stato di gran lunga superiore alla media in tutte le soglie di precipitazione, come si deduce anche dal valore elevato dell’umidità relativa media e dal valore inferiore alla norma della pressione atmosferica, nonostante le basse temperature.

Vogliamo sottolineare, in questa sede, che l’analisi si riferisce ai valori di una singola stazione, quella dell’istituto di fisica. Mentre, dal punto di vista pluviometrico, non è lecito attendersi differenze clamorose, per quanto riguarda la pioggia, in occasione di precipitazioni a carattere di rovescio o temporale, è possibile che altre stazioni, anche limitrofe, abbiano registrato quantitativi di pioggia sensibilmente differenti: come noto, infatti, la pioggia è una variabile meteorologica che risente firtemente dalla caratterizzazione geografica e orografica del territorio.

Cerchiamo, ora, di vedere come si collocano i valori termici sopra menzionati all’interno del clima a più grande scala.

La distribuzione delle anomalie delle temperature medie a livello del suolo relativa all’Europa nel mese di luglio 2014 evidenzia una grossa area, che ingloba praticamente l’intero Mediterraneo ed i paesi che si affacciano ad esso da nord (dalla penisola iberica fino al bordo occidentale della Turchia) in cui spicca un’anomalia termica negativa, con valori che, sui Pirenei e lungo la nostra penisola, sfiorano e talora eccedono i -2 °C. Al contrario, tutto il resto dell’Europa e gran parte dell’Atlantico settentrionale evidenziano anomalie positive, che culminano sulla Scandinavia settentrionale, in particolare sulla Svezia settentrionale, dove l’anomalia eccede i +6 °C.

anomalia della temperatura media superficiale rispetto al trentennio di riferimento 1981-2010. Dati NOAA/NCEP.

Anomalia della temperatura media superficiale rispetto al trentennio di riferimento 1981-2010. Dati NOAA/NCEP.

A livello planetario, si nota come siano presenti anomalie termiche negative su Alaska, Stati Uniti orientali, Mediterraneo, Kazakhstan, Siberia e Cina centrali (emisfero nord) e Cile, Sudafrica e Namibia, Australia nordoccidentale e Oceania, e su vaste zone dell’Antartide, compensate da valori positivi i cui massimi sono identificabili in Scandinavia e tutta L’Europa tranne le zone mediterranee, in Antartide a sud della terra del fuoco e dell’Australia, in Canada occidentale ed orientale, in Siberia orientale, India, Africa sahariana, Australia occidentale (si noti che, per esaltare le piccole differenze termiche, i colori nelle due mappe precedenti sono stati limitati all’intervallo tra -4 e +4 °C).

anomalia della temperatura media superficiale nel mondo rispetto al trentennio di riferimento 1981-2010. Dati NOAA/NCEP.

Anomalia della temperatura media superficiale nel mondo rispetto al trentennio di riferimento 1981-2010. Dati NOAA/NCEP.

Queste due mappe dimostrano come i valori termici particolarmente bassi registrati praticamente sull’intero territorio nazionale siano ascrivibili ad un pattern a scala continentale che, in questo periodo estivo, penalizza fortemente la regione mediterranea, che è una delle zone nel mondo densamente abitato che ha fatto registrare l’anomalia termica più negativa. Per inciso, si nota anche come, complessivamente, ovvero a scala globale, l’anomalia termica risulti tutt’altro che negativa.

Che cosa ha provocato questa situazione termica? Possiamo farci aiutare dalla mappa della distribuzione dell’altezza di geopotenziale a 500 hPa: esso rappresenta la quota a cui la pressione vale 500 hPa e, come valore grossolano di stima, si può approssimare al livello di 5500 m circa. Le isolinee su queste mappe rappresentano quindi una stima delle isobare ad un ipotetico livello di 5500 m. La mappa mostra, proprio sulla stessa area mediterranea in cui si è registrata l’anomalia termica negativa, un campo decisamente inferiore alla media, così come c’è un’anomalia negativa anche in corrispondenza delle isole Azzorre, zona in cui, abitualmente, d’estate è presente un’area di alta pressione ben strutturata anche in quota. Si nota, invece, un’anomalia gigantesca sulla Scandinavia.

anomalia dell'altezza di geopotenziale a 500 hPa nel mondo rispetto al trentennio di riferimento 1981-2010. Dati NOAA/NCEP.

Anomalia dell’altezza di geopotenziale a 500 hPa nel mondo rispetto al trentennio di riferimento 1981-2010. Dati NOAA/NCEP.

L’alterazione di questi sistemi barici provoca una rimodellazione di tutto il sistema di correnti a scala sinottica e addirittura planetaria, il cui effetto è l’arrivo fin sul Mediterraneo dei sistemi perturbati atlantici. Vediamo infatti la distribuzione media delle correnti in quota in questo mese di luglio, confrontandola con la media climatica.

Di norma, a luglio il ramo principale delle correnti più intense emerge dal nordamerica e si dirige, in direzione ENE, verso le isole britanniche e l’Europa centrosettentrionale, spingendo in tali zone i sistemi perturbati; l’Europa meridionale ed il Mediterraneo occidentale sono interessate solo di striscio da un ramo secondario di tali correnti, in direzione ESE.

andamento medio delle correnti a 500 hPa nel mondo riferito al trentennio di riferimento 1981-2010. Dati NOAA/NCEP.

Andamento medio delle correnti a 500 hPa nel mondo riferito al trentennio di riferimento 1981-2010. Dati NOAA/NCEP.

In questo mese di luglio, invece, il ramo principale delle correnti si è diviso in due parti al largo delle isole britanniche: il ramo più robusto ha circumnavigato la Scandinavia per poi ritornare quasi da N sul Kazakhstan , mentre l’altro ramo, anch’esso intenso, si è diretto sul Mediterraneo, attraversando la penisola iberica e rinforzandosi (probabilmente per motivi orografici) proprio sul Mediterraneo occidentale.

andamento delle correnti a 500 hPa nel mondo nel mese di luglio 2014.  Dati NOAA/NCEP.

Andamento delle correnti a 500 hPa nel mondo nel mese di luglio 2014. Dati NOAA/NCEP.

L’intero anello di flussi occidentali che, alle medie latitudini, circonda l’emisfero nord (e che può essere ascritto alle note correnti di Rossby) appare molto meno intenso e più ondulato del solito, di modo che le onde di Rossby risultano molto più ampie di quanto normalmente non succeda a luglio. Notiamo, per inciso, che anche nell’emisfero sud le correnti sull’oceano indiano risultano nettamente meno intense del solito, pur mantenendo la loro struttura e direzione.

Queste mappe mostrano chiaramente come la circolazione a grande scala abbia assunto caratteristiche anomale nel passato mese di luglio, con deviazioni più vistose proprio sulla zona atlantica e dell’Europa, con conseguenti ripercussioni sui valori termici e sulla piovosità.

An epochal-symbolic threshold: the CO2 concentration at Mauna Loa has exceeded 400 ppm!

It was in the air for days, and it has also created a certain expectation, with trepidation. Similarly as when we are awaiting the outcome of a surgery for a family member. But this event has nothing to rejoice. The question is very simple. At the Mauna Loa observatory, CO2 values ​​whose average over an entire day was greater than 400 ppm were recorded. One ppm means one part per million. That is to say, on a million of air molecules, 400 are CO2. It seems a small and harmless number. But it is not, unfortunately. Because these small quantities of gas are those that regulate the greenhouse effect on our planet. The greenhouse effect on Earth is responsible for the fact that the average global temperature, instead of being equal to a chilling value of -18°C, is approximately 15°C, a value much more livable for our species. And this happens thanks to the presence of a number of components, in the terrestrial atmosphere, which leave no escape throughout the infrared radiation that the Earth emits, but retain a certain part. It is a positive effect, then. More greenhouse gases there are in the Earth-atmosphere system, the more the greenhouse effect is big. Variations are small, almost imperceptible, few tenths of a degree, but accumulated can lead to large variations.

The greenhouse effect in short.

The greenhouse effect in short.

Few words on Mauna Loa observatory. Where is it? Here, on Hawaii islands.

An image of Mauna Loa Observatory.

An image of Mauna Loa Observatory.

Erected in 1956, the first CO2 measurements date 1958, thus it is the most ancient observatory measuring CO2 on Earth. Somebody criticizes the choice of the site as nearby there is the Kilauea volcano, whose emissions may affect the measurements. However, the observatory altitude is 3397m, and its elevation and location (in the middle of the Pacific ocean, away from major air pollution sources) make this site as an ideal place to sample the atmosphere. The high elevation of the observatory keeps also far away the lower local pollutants emitted below the observatory (such as also volcanic emissions), due to fact that it is quite higher than the strong marine temperature inversion layer present for most of the time in the region. An “a posteriori” demonstration of the quality of these data is the comparison of the CO2 trend of the Mauna Loa data (1.64 ppm per year) with the global trend (1.66 ppm per year), calculated considering the average of all remote stations in the world: they are statistically indistinguishable.

Global atmospheric CO2 (NOAA) versus Mauna Loa CO2 (NOAA). Credits: Skeptical Science.

Global atmospheric CO2 (NOAA) versus Mauna Loa CO2 (NOAA). Credits: Skeptical Science.

Let’s now came back to the original point. Yesterday, daily mean CO2 concentration has exceeded 400 ppm. It did not happen for about 3 million years. That means this has never happened since man lives on Earth. 400 ppm is a symbolic epochal threshold for the humanity..

The news is not yet official but, after the graph produced by NOAA (National Oceanic Atmospheric Administration), here reported (that on the link is regularly updated), the U.S. federal agency that deals with climate, the CBS has released yesterday a service confirming the measure.

Last year daily and weekly CO2 concentrations at Mauna Loa.

Last year daily and weekly CO2 concentrations at Mauna Loa.

It must be emphasized, once again, that the carbon dioxide enters the atmosphere as a result of the human use (and abuse) of fossil fuels: oil, gas, coal, methane, etc. Since we have started to use them (which means, since the Industrial Revolution, or even better, since the invention of the Watt machine), the history and prehistory of the human race have been accompanied by a carbon dioxide concentration lower than 300 ppm.

A preserved Watt beam engine at Loughborough University. Credits: wikipedia.

A preserved Watt beam engine at Loughborough University. Credits: Ashley Dace.

Still in the middle of the eighteenth century, it was equal to 280 ppm. Then, it started its apparently unstoppable growth till the actual values of 400 ppm.

CO2 in last 1200 years. Credits: IPCC AR4.

CO2 in last 1200 years. Credits: IPCC AR4.

Carbon dioxide, as well known, is the main greenhouse gas (GG). I like the description of the greenhouse effect given in this Italian blog: GGs trap the sun’s heat in the atmosphere, as a duvet traps heat in our body when we are in our bed during the winter. If there were no greenhouse gases, it would be like to sleep without duvet. But having too abundant greenhouse gas is like sleeping with two duvets. Nightmares and sweat are guaranteed…

We said that our Earth experienced for the last time an atmospheric concentration of carbon dioxide of 400 ppm about three millions years ago, i.e. before the appearance of the so-called Homo sapiens. At that time, the temperatures were 3-4°C higher than now, and the sea level was about 25 meters higher than now.

Reconstruction of the atmospheric concentration of CO2 in the last 65 million years: in the distant geological past, there have been periods when this greenhouse gas was vastly more abundant than today. For example, between the Paleocene and Eocene, around 50 to 55 million of years ago, it was about 2000 ppm. But this comparison cannot reassure about the current situation. At that time, indeed, the planet was completely different, with a different geology, climate and environment, and even some prehistoric human species existed. But today we live in a world more and more overcrowded, short of natural resources and plagued by numerous criticalnesses (environmental, demographic, social, economic and alimentary) that make humanity fragile in the face of abrupt climate change. During the Pliocene (between about 3 and 5 million years ago, red line), for the last time before today, a CO2 concentrations next to 400, sometimes 500 ppm was reached. Source: alpineanalytics.

Reconstruction of the atmospheric concentration of CO2 in the last 65 million years: in the distant geological past, there have been periods when this greenhouse gas was vastly more abundant than today. For example, between the Paleocene and Eocene, around 50 to 55 million of years ago, it was about 2000 ppm. But this comparison cannot reassure about the current situation. At that time, indeed, the planet was completely different, with a different geology, climate and environment, and even some prehistoric human species existed. But today we live in a world more and more overcrowded, short of natural resources and plagued by numerous criticalnesses (environmental, demographic, social, economic and alimentary) that make humanity fragile in the face of abrupt climate change. During the Pliocene (between about 3 and 5 million years ago, red line), for the last time before today, a CO2 concentrations next to 400, sometimes 500 ppm was reached. Source: alpineanalytics.com.

Reconstruction of the atmospheric concentration of CO2 in the last 65 million years: in the distant geological past, there have been periods when this greenhouse gas was vastly more abundant than today. For example, between the Paleocene and Eocene, around 50 to 55 million of years ago, it was about 2000 ppm. But this comparison cannot reassure about the current situation. At that time, indeed, the planet was completely different, with a different geology, climate and environment, and even some prehistoric human species existed. But today we live in a world more and more overcrowded, short of natural resources and plagued by numerous criticalnesses (environmental, demographic, social, economic and alimentary) that make humanity fragile in the face of abrupt climate change. During the Pliocene (between about 3 and 5 million years ago, red line), for the last time before today, a CO2 concentrations next to 400, sometimes 500 ppm was reached. Source: alpineanalytics.

Usually, CO2 concentration shows a marked annual cycle, due to the effect of the vegetation respiration: for this reason, the cycle is much more evident in the midlatitudes of the northern hemisphere, where the vegetation covers more extensively the Earth surface. Normally, during the first half of May, the carbon dioxide reaches the “peak” year: the concentration decreases after the forests of the northern hemisphere have completed the foliation. Thus, this year the epochal peak of 400 ppm has been exceeded almost at the end of the increasing period, and soon the mean value will come back below 400 ppm. But, year after year, the peak always grows.

A rough graphic simulation carried out by myself using the monthly (monthly, not daily: this is way the value is significantly lower than 400 ppm!) data measured at Mauna Loa (I have just graphically repeated the last year trend; yes, I know, very rough, but it gives the idea) shows that we have still two years in which we could see some values with daily or monthly values lower than 400 ppm. Then, after 2016, we will enter in a new era: the above 400 ppm CO2 era.

Monthly mean carbon dioxide concentrations measured at Mauna Loa (until April 2013) and hypothized for the next three years by continuing the last year trend. It is evident as September and October 2014 risk to be the last months with a CO2 monthly mean value below 400 ppm.

Monthly mean carbon dioxide concentrations measured at Mauna Loa (until April 2013) and hypothized for the next three years by continuing the last year trend. It is evident as September and October 2014 risk to be the last months with a CO2 monthly mean value below 400 ppm.

Monthly mean carbon dioxide concentrations measured at Mauna Loa (until April 2013) and hypothized for the next three years by continuing the last year trend. It is evident as September and October 2014 risk to be the last months with a CO2 monthly mean value below 400 ppm.

If you do not trust my rough projection, you may enjoy in watching this video, that shows the time history of atmospheric carbon dioxide from 800,000 years before present until January, 2012 (and it is possible to imagine how it will continue).

By the way, the video shows that, at high latitudes, the 400 ppm threshold has already been exceeded in some months several years ago. But here we are talking about Mauna Loa, Hawaii: which is located in an equatorial area and is representative of the world mean (remember the first figure).

And, as now people “old” like me is surprised by thinking that the first year university students had never experienced a world without mobile phone (and few year later we may repeat the same discussion for smartphones, facebook, twitter, …), some years later the young generation will be born in an above-400-ppm-CO2-era.

The effects of increased concentrations of greenhouse gases are not immediately evident. Until now, the planet’s average temperatures has increased only by 0.8°C with respect to before the Industrial Revolution, but already many people complain that no longer exist transition seasons and seasons are no longer those known in the past. The following video from NASA summarizes in 30 seconds how world temperatures have changed in the past 120 years.

The climate destabilization triggered by greenhouse gases that humans have released into the atmosphere also manifest in the increase of extreme weather events: heat or cold waves, drought and floods.

The cold spring in western Europe and a big portion of US, for example, is probably a side effect of the massive melting of Arctic ice which took place last summer. While talking of spring temperatures, let’s give a look on a global map. Here it is shown the map referring to the first two months of 2013 spring (we remember here that meteorologists count seasons starting from the first day of the month, so spring means March, April and May). I have decided to underline these data, as I am reading a lot of nonsense related to actual weather. The map reveals that there are some areas characterized by dark blue, which means cold. These areas (Canada, US and Europe) are densely populated by industrialized humans. There are also several areas characterized by quite large warm anomalies, but they concern some underpopulated, or not populated at all, areas of the planet. This is why we heard only about cold, and nothing about warm. We care only about what happens where we live. But climate do not make such distinctions, and from a climatological point of view, US and Antarctica are equal!

Anomaly of surface temperatures recorded during March and April, 2013, with respect to the period 1981-2010. A large cold area covers a big portion of North America and another one covers most of Europe, while central Asia, Africa, Greenland and both polar regions are experiencing unusually warm periods. Source: NCEP-NCAR.

Anomaly of surface temperatures recorded during March and April, 2013, with respect to the period 1981-2010. A large cold area covers a big portion of North America and another one covers most of Europe, while central Asia, Africa, Greenland and both polar regions are experiencing unusually warm periods. Source: NCEP-NCAR.

The temperature anomalies appear to be strongly connected with the corresponding anomalies of the geopotential pattern at 500 hPa.

Anomaly of 500 hPa geopotential height recorded during March and April, 2013, with respect to the period 1981-2010. Note the almost perfect coincidence between cold areas and areas with negative 500 hPa anomaly. Source: NCEP-NCAR.

Anomaly of 500 hPa geopotential height recorded during March and April, 2013, with respect to the period 1981-2010. Note the almost perfect coincidence between cold areas and areas with negative 500 hPa anomaly. Source: NCEP-NCAR.

A short look on the sea surface temperatures (SST) in the North Pole area reveals as there is a relevant positive anomaly of SST in the zone of the North Pole, which experienced on last September the largest ice-free extension. And it is impossible to think that these phenomena are not connected…

Anomaly of SST recorded during March and April, 2013, with respect to the period 1981-2010. Note the almost perfect coincidence between cold areas and areas with negative 500 hPa anomaly. Source: NCEP-NCAR.

Anomaly of SST recorded during March and April, 2013, with respect to the period 1981-2010. Note the almost perfect coincidence between cold areas and areas with negative 500 hPa anomaly. Source: NCEP-NCAR.

Very low minima of extratropical cyclones in North Atlantic

Meteorological forecasts for the approaching weekend (January 26-27, 2013) show the presence of a very deep sea level pressure minimum in the North Atlantic ocean, at high latitudes, located between Iceland and UK. Without pretending to be exhaustive, we will mention the minima forecasted by some of the most used models: less than 940 hPa (on 27th at 00 UTC) by ACCESS, 939 by ECMWF (on 27th at 00 UTC) and GEM (26th at 18 UTC), 932 by JMA (on 27th at 12 UTC), 930 by NOGAPS (27th at 00 UTC), less than 930 hPa (26th at 12 UTC) by GFS, and less than 928 hPa (26th at 12 UTC) by UKMO.

access ecmwf
gem jma
nogaps gfs+96
brack4

The pressure values are quite low and resemble those measured near or inside tropical cyclones. However, these storms have a different genesis and structure and are classified in the category of extratropical cyclones. A question that one might ask is whether these values can be considered unusual, or even exceptional.

In this blog, I will try to give a brief survey of world barometric pressure records, with the help of this blog of Christofer C. Burt and, for the maps, the very useful database stored in wetterzentrale.de. Most of the information and scientific results, as well as one figure reported in this blog, came from the original papers published by S.D. Burt, listed in the references.

As one can easily imagine, excluding the small scale phenomena such as tornadoes, the lowest pressures observed on the Earth have occurred during tropical cyclones.

The following table reports the absolute minima observed for each region.

tropiclowsThe second minimum in the list is questioned by the Australian Bureau of Meteorology, that places a minimum pressure for the storm at 905 hPa on the same date and location. For North Atlantic, the minimum value is 882 hPa: for sake of comparison, the lowest value observed during the track of hurricane Sandy in October 2012 was 940 hPa, and that of hurricane Katrina in August 2005 was 902 hPa.

When we move to extratropical cyclones, the situation is different. The minima are a little bit higher, but not so much as one could imagine.

For Southern hemisphere, the record belongs to a storm developed near Antarctica, with 919 hPa observed at Casey station on the Windmill Islands (just outside the Antarctic Circle) on Vincennes Bay (66°17’S 110° 31’ E) on August 8-9, 1976.

In the northern hemisphere, the most probable record of lowest pressure is held by the storm of January 10th, 1993, which showed a central pressure of 912-915 hPa between Iceland and Scotland near 62°N 15°W. The map from wetterzentrale.de, shows, at 00 UTC of January 11st, a deep minimum lower than 930 hPa, as a part of a large depression covering the whole northern Atlantic. I am remembering here that, in the site, the maps are available every 24 hours, at 00 UTC.

Rrea00119930111Also the storm occurred on December 15th-16th, 1986, deepened to at least 916 hPa south-east of Greenland, near 62°N 32°W, a value assessed by the British Meteorological Office, while the West German meteorological service proposed a pressure possibly as low as 912-913 hPa. The map below, at 00 UTC of December 15th, shows a minimum lower than 925 hPa, and a situation quite different from the previous one, in which the depression size was smaller and supposedly with most intense winds. In both cases, the evolution of the system was quite rapid: the low intensified by 25-30 hPa in only 24 hours, and filled by 25-30 hPa in a similar time.

Rrea00119861215

On December 15, 1986, the ship Uyir, sailing southeast of Greenland, recorded the value of 920.2 hPa. According with the British Met. Office, the central pressure of the storm, which was centered some distance southeast of the ship, was 916 hPa. The map below, at 00 UTC of December 15th, shows a minimum lower than 925 hPa, very close to Greenland. The almost explosive deepening of the depression was followed by a fast filling on the subsequent day.

Rrea00119861215

It is interesting also to mention some record values observed on the territory of individual nations. The Iceland one is 923.6 hPa, observed on December 2nd, 1929, at Storhofoi. The map on 3rd at 00 UTC shows a minimum of 945 hPa close to the Iceland; the depression has undergone a rapid deepening and a subsequent rapid filling.

Rrea00119291203

Other two relevant minima studied by the British weather historian Stephen Burt are:

921.1 hPa on Feb. 5, 1870 measured by the ship Neier at 49°N 26°W;

924 hPa on Feb. 4, 1824, measured at Reykjavik, Iceland (the lowest on land measured pressure in the North Atlantic). These two minima are too old in order to draw a map.

Also the value of 925.5 hPa, recorded on Dec. 4, 1929 by the SS Westpool somewhere in the Atlantic (the exact location is unknown) is noticeable: in this case, the map on 5th at 00 UTC shows a minimum of less than 940 hPa off the Ireland, with very strong winds on the Irish coasts.

Rrea00119291205In UK, the minimum value of sea level pressure recorded over the territory was 925.6 hPa, on January 26th, 1884, at Ochtertyre, Pershire. In this case, the map from wetterzentrale.de on 27th at 00 UTC reveals a minimum of 945 hPa located between England and Norway.

Rrea00118840127

For this event, a surface chart of the cyclone drawn 6 hours before (Burt, 2006) reveals the minimum of 925.6 hPa at Ochtertyre, in Scotland.

uklow

Even if not in the north Atlantic, also the most powerful storm observed in Alaska in modern history in October 25-26, 1977, at Dutch Harbor on the Aleutian Island of Unalaska, is remarkable. The minimum pressure observed was 926 hPa on the evening of October 25th. Winds gusted to 130 mph at Adak, and gusted for 12 consecutive hours exceeding 110mph. The map below reveals as, even in this case, the size of the depression, the proximity of the isobars, leaving deduce a very strong wind speed associated with the cyclone.

alaska_oct1977Worthy of mention is also the minimum recorded in Ireland, at Belfast, on December 8th, 1886: 927.2 hPa. In that occasion, the map on 7th at 00 UTC reveals a narrow depression elongated from North Pole to Mediterranean sea and centered on Scotland, already filled to less than 955 hPa.

Rrea00118861209Finally, we want to mention also the Finland record of 939.7 hPa, recorded on March 1st, 1990. The map of February 28th at 00 UTC clearly shows the minimum (lower than 950 hPa) over the southern Finland as the center of a large depression covering most of northwestern Europe. Differently on previous cases, the evolution of this minimum was slower, and the cyclone, formed on February 26th near Iceland, moved northwards, gradually filling.

Rrea00119900228This short overview of meteorological situations favourable to produce very low cyclones in the northern hemisphere can be sufficient to say that the vale predicted for the next weekend in the north Atlantic can be considered not exceptional and not unusual, even if rare. Normally these storms are confined, in both hemispheres, at latitudes not lower than 50°, with very few exceptions.

The range of pressures predicted by the different models for the storm of the January 26-27 weekend is of about 12 hPa (according with the forecasts available at 10 p.m. of January 22nd, the minimum will range between 928 and 940 hPa), and is in agreement with the standard deviation of 15 hPa of the ensemble prediction of ECMWF model (see figure below).

Rees962To get a more quantitative picture, it is possible to use the data founded by Von Ahn et al. in this study of 2005, that will be shorthly summarized here. The authors examined all extratropical or mid-latitude storm systems showing a wind speed larger than the value defined as “hurricane force” (HF, equal to or larger than 64 kts). They used near-surface winds from the National Aeronautics and Space Administration (NASA) QuikSCAT scatterometer. In this way, they observed, from October 2001 to April 2004, a total of 120 HF cyclones. The distribution in terms of minimum pressure was the one reported in the figure below.

cyclone2The authors, examining the evolution of these cyclones, have noticed that, for most cyclones, HF conditions were observed to occur at or near the time of minimum central pressure (the mature phase of the cyclone), lasting on average less than 24 hours, a relatively short-life compared to the average life span of 5 days for ocean storms. The typical evolution of an ocean storm follows the scheme depicted by Shapiro and Keyser (1990) and well summarized in the paper of Von Ahn et al., that I summarizes here. The cyclone begins as an open frontal wave with a warm front and cold front (I). As the cyclone intensifies, also the frontal wave amplifies. The cold front pushes eastward (South of the low) and the temperature gradient tightens to the West of the low center (II). The front associated with this tightening temperature gradient west of the low is referred to as the bent back front or occluded front. The wave continues to amplify (III) and the bent back (occluded) front and associated temperature gradient swings eastward to the southwest of the low center. The strongest temperature gradient in phase III is associated with the continuous warm to bent back front and not in association with the cold front to the south. Phase III is referred to as the frontal T-bone. Phase IV shows the mature cyclone or warm core frontal seclusion. At this point, the very strong temperature gradient (or front) has encircled the surface low center. A shallow pocket of relatively warm air has migrated to the low center and become cut off or secluded (thus the term warm seclusion). Within the warm seclusion the air is very unstable and convection may occur. An arc of very strong temperature gradient surrounds this pocket of warmer air with cold air found to the exterior of this temperature gradient. A very strong pressure gradient exists on the cold side of the temperature gradient (south of the low). It is in this area of strong pressure gradient that HF conditions are often observed.

cyclone3_smUsing the winds derived by QuikSCAT images to create composites of the maximum winds for 17 open ocean HF cyclones (11 in the North Pacific and 6 in the North Atlantic) near maturity or close to minimum central pressure, Von Ahn et al. have determined where HF conditions occur most frequently, deriving a conceptual model of cyclone development shown in the figure below. According with this model, the area of HF winds recorded by QuikSCAT, indicated in the figure with red hatching, is located from southeast to nearly west of the low center during the mature phase of an ocean cyclone. Figure 5 illustrates where to anticipate HF winds in a mature cyclone.

cyclone5_smIt is needless to say that, despite the short duration of HF conditions, HF cyclones can indeed be very dangerous, especially if the area of strongest winds will impact on land area. A well know example is the sequence of storms that hit France and central Europe during the Christmas holidays of 1999, at unusually low latitudes.

In the case of landfall, contrary to what happens for tropical cyclones, in which the “engine” is constituted by the presence of water vapor, the system does not dissipate too much during the landfall, but follows its natural dynamics.

Aknowledgements

Thanks to:

Cristopher Burt for his two posts on weatherunderground;

Stephen Burt for list of North Atlantic pressure records and the list of his papers;

Steve Gregory for the map of the Alaskan storm of 1977 and related information.

References

Burt, Christopher C. (2011) Weather extremes. Super Extra-tropical Storms; Alaska and Extra-tropical Record Low Barometric Pressures, available on http://www.wunderground.com/blog/weatherhistorian/comment.html?entrynum=49

Burt, Christopher C. (2011) Weather extremes. World and U.S. Lowest Barometric Pressure Records, available on http://www.wunderground.com/blog/weatherhistorian/comment.html?entrynum=50

Burt, Stephen D. (1983) New UK 20th Century low pressure extreme. Weather, 38, pp. 209-13

~ (1985) Remarkable pressure fall at Valentia, 17 October 1984. Weather, 40, pp. 48-51

~ (1987) A new North Atlantic low pressure record. Weather, 42, pp. 53-56

~ (1987) A new North Atlantic low pressure record. The Marine Observer, 57, No. 297 (July 1987), pp. 122-125

~ (1987) Deep depressions. Letters to the Editor, The Times, London: REPRINTED IN Letters to the Editor, J Meteorol, 12, pp 348-8

~ (1989) London’s lowest barometric pressure in 167 years. Weather, 44, pp 221-5

~ (1993) Another new North Atlantic low pressure record. Weather, 48, pp 98-103

~ (2006) Barometric pressure during the Irish storm of 6-7 January 1839. Weather, 61, pp 22-27

~ (2006b) Britain’s highest barometric pressure on record is incorrect. Weather, 61, pp 210-1

~ (2007) The Lowest of the Lows … Extremes of barometric pressure in the British Isles, Part 1 – the deepest depressions. Weather, 62 (1), pp 4-14

~ (2007) The Highest of the Highs … Extremes of barometric pressure in the British Isles, Part 2 – the most intense anticyclones. Weather, 62 (2), pp 31-41

~(2008) The intense anticyclone over NW Russia, early January 2008. Weather, 63, pp 174-76

~ (2009) Long-term variations in extremes of barometric pressure in the British Isles. Weather, 64, pp 187-189

~ (2011) Barometric pressure during the Irish storm of 6-7 January 1839. Published online at http://www.irishmetsociety.org/jan-1839-storm

2012 global temperatures: still in medal zone!

2012 global temperatures: still in medal zone!

Another year has already passed. So let us comment what happened in 2012, initially at global scale and then zooming on Europe and on Italy. As usual, while we wait for the official data that will be published in the next two – three months from institutional sites (CRU, GISS, NASA, etc. – the detailed list can be found on last year’s post), the fastest method is to use the database NOAA/NCEP (in particular, I have used this site with monthly composites). I remember that these are not raw but processed data: in particular, they are averaged on a grid of 2.5 degrees in longitude and latitude, which is equivalent, at our latitudes, to a square of about 300 x 300 km2. It is therefore impossible to make local considerations using this type of data.

Surface temperature anomaly (°C) in 2012 with respect to the reference period 1981-2010. Data NOAA-NCEP.

Surface temperature anomaly (°C) in 2012 with respect to the reference period 1981-2010. Data NOAA-NCEP.

The annual mean anomaly (note that the graphs in this post, unless otherwise stated, are all referred to the thirty years 1981-2010, which is the most recent period, to account for the warming occurred in the last three decades) shows a positive mean value, with the highest values in the Arctic and Antarctic polar regions, over Canada and the United States, and a narrow strip of territory stretching from the Mediterranean to Siberia. The most evident negative anomalies are concentrated in three small areas (Alaska, Mongolia and a portion of the Antarctic coast). For the rest, the anomalies remain (in absolute) below 1°C, and are prevailingly positive in the northern hemisphere over south-central Europe and North America, and negative in part of Asia and Northwestern Europe, while in the southern hemisphere, excluding Antarctica, show a less clear signal.

Globally, the mean anomaly was 0.26 °C, i.e. 0.07 °C higher than that of 2011, equal to 0.19 °C. This value is in fifth place in the scale of thermal values calculated using the NOAA-NCEP data, 0.09 °C away from year 2005, which leads the list. In football jargon, we would say that 2012 has earned Europe League qualification. In absolute terms, however, the integral data on the grid points (weighted by their respective surface, of course) is 14.30 °C. This numerical value, however, should be corrected to make it compatible with the values of other datasets. I will shorthly explain here how. Referring to the data (Table and figure below), we can see how the data NOAA-NCEP result, on average, underestimated by about 0.35 °C. I underline here that, concerning the data GISS, CRU and NCDC, both in the table and in the figure, for the year 2012, the average values referred to the period December 2011 – November 2012, instead of the annual average, not yet available, have been used (however, looking at the values of the past years, the difference, in general, is not higher than 0.02 ° C).

Annual mean values and anomalies for the three major databases, in comparison with the values calculated by the database grid points NOAA-NCEP used in this post. 2012 mean values, for the databases CRU, GISS and NCDC, refer to the period December 2011 - November 2012 and are shown in italics. The last column shows the NOAA-NCEP values "corrected" by adding the average difference in the 1981-2010 thirty years between the average of the other three databases and the average NOAA-NCEP, equal to 0.35 °C.

Annual mean values and anomalies for the three major databases, in comparison with the values calculated by the database grid points NOAA-NCEP used in this post. 2012 mean values, for the databases CRU, GISS and NCDC, refer to the period December 2011 – November 2012 and are shown in italics. The last column shows the NOAA-NCEP values “corrected” by adding the average difference in the 1981-2010 thirty years between the average of the other three databases and the average NOAA-NCEP, equal to 0.35 °C.

Let us note here that, in the past year, the CRU database has been slightly modified (see for example here), so some numerical values may slightly differ from previous assessments. In any case, the comparison reveals that, more or less, all databases are in agreement on the measurements and show the 2012 as warmer than the average of the most recent thirty years. On the other hand, the first year colder than period 1981-2010, for three databases on four, is the 2000 …, while to find the first year colder than period 1981-2010 for all four databases, it is necessary to go back to 1996!

Annual average values for the three major databases, in comparison with the gridded values calculated by the database NOAA-NCEP used in this post.

Annual average values for the three major databases, in comparison with the gridded values calculated by the database NOAA-NCEP used in this post.

However, beside the classifications, which can not be devoided by errors (observational, of average, station selection, interpolation, etc..), it is interesting to see how, if we take the ten-year period 2003-2012, it contains eight of the ten warmest years.

The signal is not present only at the surface: in fact, the map at 500 hPa (level corresponding to about 5500 m a.s.l., i.e. in the middle of the troposphere) shows values a bit smaller but still of the same sign, indicating that the warming occurred in the whole troposphere and not only of the surface stations (or of the boundary layer).

500 hPa temperature anomaly (°C) in 2012 with respect to the reference period 1981-2010. Data NOAA-NCEP.

500 hPa temperature anomaly (°C) in 2012 with respect to the reference period 1981-2010. Data NOAA-NCEP.

Let us go now to examine the graphs related to individual seasons. The winter 2011-2012, which includes December 2011, shows a strong warming on the Arctic regions, with maximum values between Svalbards and Siberia larger than 16 °C, but is also great on Canada and the United States, while practically all the Central Asia (from Caspian Sea to Korea), West Africa and the areas around the Bering Strait show anomalies of -4/-5°C. Unlike the Arctic, however, Antarctica shows less significant and more varied values, and also part of Greenland has recorded temperatures below average.

Surface temperature anomaly (°C) in 2012 with respect to the reference period 1981-2010. Data NOAA-NCEP.Surface temperature anomaly (°C) in 2012 with respect to the reference period 1981-2010. Data NOAA-NCEP.

Surface temperature anomaly (°C) in 2012 with respect to the reference period 1981-2010. Data NOAA-NCEP.Surface temperature anomaly (°C) in 2012 with respect to the reference period 1981-2010. Data NOAA-NCEP.

Concerning the spring 2012, different warm areas are noticeable on the Antarctic mainland, while in the Arctic only the area above the Eurasia maintains strongly positive anomalies, in both cases with values of 6°C or more. Other hot spots are the United States and much of Europe, as well as north-western Asia and part of Greenland. Areas with strong negative anomaly practically do not exist, except for part of Alaska and a portion of Antarctic coasts.

Surface temperature anomaly (°C) on the period March - May 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

Surface temperature anomaly (°C) on the period March – May 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

Summer 2012 is the season with the more moderated extreme anomalies. Almost the entire northern hemisphere has the land warmer than average, with rare exceptions (Great Britain and Scandinavia in Europe, and a small Siberian region over Mongolia in Asia), while in the southern hemisphere the oceans show more positive anomalies, and negative ones are present in the western parts of South America and Africa, and Australia. The most negative anomalies, however, are recorded on the Antarctic coastal areas, with values lower than -3°C, while inside there is the largest positive anomaly (more than 4°C).

Surface temperature anomaly (°C) on the period June - August 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

Surface temperature anomaly (°C) on the period June – August 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

The fall 2012 shows a configuration with distinctly positive anomalies on Arctic areas (with maximum larger than 8°C and peaks of 10°C) and still positive on part of the continents in the northern hemisphere (except the region between Alaska and Canada and Central Asia) and Antarctica (with the exception of the Antarctic Peninsula and neighbour sea, which show the minima anomaly, lower than -4°C). In the southern hemisphere, there are some spots with slightly positive anomaly.

Surface temperature anomaly (°C) on the period September - November 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

Surface temperature anomaly (°C) on the period September – November 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

For completeness, we show also the image for the month of December 2012, which completes the analysis of the year, as the distribution of anomalies is singular. Obviously, being an average on only one month, the mean anomalies are larger. Northern America, Alaska and western Canada are colder than average (minimum around -5°C), while the eastern part, from the United States to Greenland, recorded positive anomalies of 2-3°C. In Eurasia, the areas close to the Arctic Ocean show very positive anomalies, over 10°C, while almost all continent, with the exception of Western Europe, and southeast Asia, show strong negative anomalies, with values between -5°C and -10°C. In the southern hemisphere, the anomalies are less noticeable: slightly negative in Argentina, Chile and Mauritania, and weakly positive in Brazil, South Africa, Australia and Ethiopia; positive, with peaks larger than 5°C over most of Antarctica.

Surface temperature anomaly (° C) on the month of December 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

Surface temperature anomaly (° C) on the month of December 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

Let us now look in more detail the situation on the European continent. Apart from the Arctic (where anomalies exceeded 6°C), we see that the whole Europe, with the exception of Portugal, Great Britain, Scandinavia, Baltic States and a small piece of Russia, was under a positive anomaly, albeit lower than 2°C. The hottest areas include south-eastern Italy, Greece, Romania, Bulgaria, the Black Sea and a strip between Armenia and Azerbaijan.

Surface temperature anomaly (° C) on the period December 2011-February 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

Surface temperature anomaly (° C) on the period December 2011-February 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

It is interesting, in this regard, to see also the map of the anomalies of geopotential height at 200 hPa (hereinafter called Z200), a level typical of the lower stratosphere. The graph shows a good correspondence between the positive thermal anomalies of temperature and those positive of Z200, while the negative anomalies of Z200 match with null or slightly negative anomalies of temperature.

200 hPa geopotential height anomaly (in m) relative to the period December 2011-February 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

200 hPa geopotential height anomaly (in m) relative to the period December 2011-February 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

This finding can also be generalized to a global scale, as the good symmetry between the map of thermal anomaly at ground level and that of the Z200 is still evident. These maps visualize the correlations between tropospheric and stratospheric circulation, not yet fully understood in their details but under study (among others, I cite this 2007 paper in which Cohen et al. discuss the events of interaction between the stratosphere and troposphere in the extratropical regions).

200 hPa geopotential height anomaly (in m) relative to the period December 2011 - February 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

200 hPa geopotential height anomaly (in m) relative to the period December 2011 – February 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

Recently, the National Oceanic and Atmospheric Administration (NOAA) said that, in the continental 48 states of the US, 2012 had an average temperature of 55.3°F (12.9°C), which eclipsed 1998, the previous record holder, by 1°F (0.55°C). The 1°F difference from 1998 is an unusually large margin, considering that annual temperature records are typically broken by just tenths of a degree Fahrenheit. In fact, the entire range between the coldest year on record, which occurred in 1917, and the previous record warm year of 1998 was just 4.2°F.

Let thus see a map centered on the US: the anomaly here tops to more than 3°C between Nebraska and Kansas, and the isotherm 1.5°C contains most of the US.

Surface temperature anomaly (° C) on the period December 2011-February 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

Surface temperature anomaly (° C) on the period December 2011-February 2012 with respect to the 1981-2010 reference period. NOAA-NCEP data.

Now we would see some zooms in some meteorologically interesting periods. The year that has just ended was characterized, overall, by a series of significant weather phenomena. Among others, Italians remember the intense cold wave in first half of February (with extreme thermal values not seen since 1985-86 and, in some areas, heavy snowfalls also in the plains, that created serious problems), the very hot and dry summer in central and southern Italy (probably the warmest of the last 100 years, maybe second only to that of 2003) and the moderate cold wave in early December, which put an end to a long period of above-average temperatures.

Let us start from the first two weeks of February 2012. The thermal maps show Europe completely covered by a negative anomaly (except for part of Scotland and Ireland, and Iceland), with very low values: -12°C. In Italy, the North was the most abnormally cold zone, with values below the average of 7.5-10.5°C, while moving Southwards, the anomaly, even if negative, becomes less conspicuous. Notice also how the mitigating effect of the Mediterranean, who entered in the 2011 winter with temperatures well above average, such as to favors some flooding episodes and even the generation of a Mediterranean hurricane (medicane: see here) near Corsican coasts, was almost absent in the western part.

Surface temperature anomaly (°C) on the period 1 - 14 February 2012, compared to the 1981-2010 reference period. NOAA-NCEP data.

Surface temperature anomaly (°C) on the period 1 – 14 February 2012, compared to the 1981-2010 reference period. NOAA-NCEP data.

Also some Asiatic regions have experienced cold weather at the beginning of the year. The map of the anomalies in the first two months shows a sort of bipolar situation, with a large negative anomaly over most of central and southern Asia, with the exception of the extreme southeast, and another huge and large positive anomaly over Siberia and Arctic sea. It appears as the cold air was displaced southwards of its natural position, and also in this case the map of the Z200 anomaly (not shown) presents some similarities.

Surface temperature anomaly (°C) on the period January  – February 2012, compared to the 1981-2010 reference period. NOAA-NCEP data.

Surface temperature anomaly (°C) on the period January – February 2012, compared to the 1981-2010 reference period. NOAA-NCEP data.

Coming again to Europe, we continue with the warm months: the anomaly map shows a dipolar situation over Europe, with the northwestern part of the continent cold and the rest under the influence of a heat wave that, in Italy, recorded 1.5-2°C above average over the Adriatic regions, and values less than 1°C over the Alps (on this site there are some additional consideration on Italian summer). The most striking positive anomaly was recorded in a narrow strip of land included between Romania and the Black Sea.

Surface temperature anomaly (°C) on the period May-August 2012 compared to the 1981-2010 reference period. NOAA-NCEP data.

Surface temperature anomaly (°C) on the period May-August 2012 compared to the 1981-2010 reference period. NOAA-NCEP data.

Finally, we analyze the situation that characterized the other, most moderate, cold spell of the year, recorded in the first two weeks of December. As in the previous case, the 0°C isotherm contains almost all Europe, except the southern part and the Mediterranean.

Surface temperature anomaly (°C) on the period 1 - 14 December 2012 compared to the 1981-2010 reference period. NOAA-NCEP data.

Surface temperature anomaly (°C) on the period 1 – 14 December 2012 compared to the 1981-2010 reference period. NOAA-NCEP data.

Concerning the rest of the world, everybody remembers the Hurricane Sandy, which flooded entire districts of New York; or the drought in the U.S.; or the extensive flooding caused by tropical cyclones in Madagascar and the Philippines. Fewer people instead remember the Hurricane Nadine, which did not cause serious damages, but stationed off the Azores for over twenty days with the status of a hurricane, going round and round in these parts, and double-tapping islands and giving some concern to meteorologists who feared its explosive entrance in the Mediterranean, fortunately not occurred. Born on Sept. 7, and died on October 4, with its 23 days of life as tropical, subtropical and post-tropical cyclone, of which 21.75 as a tropical/subtropical system, Nadine is ranked as the fifth long-lived hurricane of the history.

Hurricane Nadine photographed on September 15, 2012 (left) and his track from the time of his birth until his death (right).

Hurricane Nadine photographed on September 15, 2012.

Hurricane Nadine photographed on September 15, 2012 (left) and his track from the time of his birth until his death (right).

Hurricane Nadine track from the time of his birth until his death.

Look at the map of the anomalies of sea surface temperature, we can see that, particularly during the period in which Nadine flew over the Atlantic, the anomalies became negative, sign of the potent activity of water mixing carried by the Nadine winds. That is why fishermen, in tropical areas, usually do not fear, but rather wait, and hope, the hurricanes, whose mixing effect cools the surface waters, favoring the fish abundance.

Sea surface temperature anomaly (°C) on the period 15 - 30 September 2012 compared to the 1981-2010 reference period. NOAA-NCEP data.

Sea surface temperature anomaly (°C) on the period 15 – 30 September 2012 compared to the 1981-2010 reference period. NOAA-NCEP data.

Worldwide, the 2012 reserved another resounding record: the marine Arctic ice cap has shrunk as never before in recent decades (see this post by Real Climate): the minimum area occupied by marine ice at the North Pole was only 3.41 million square kilometers, value smaller than one half the average of the last two decades of the twentieth century! Climatologists know well the ice-albedo positive feedback, one of the most important ones. Let us see, therefore, if it is possible to find a direct effect of this anomaly of Arctic marine ice cover on its surface temperatures (SST). Well, the answer is positive: the actual area free of ice is the one that shows the most noticeably positive thermal anomalies, more than 4°C, with a peak of more than 7°C near the islands of Novaya Zemlya. Without detailing here hypotheses that still need further evidence, however, it is impossible to not underline that the ice-free horseshoe structure that, in September, surrounds the Greenland, is also present in the SST thermal anomalies, and has also an impact on the field of sea-level pressure anomaly, whose maxima are shifted on the continents.

Ice extent on September 16, 2012 (from the site NSIDC).

Ice extent on September 16, 2012 (from the site NSIDC).

Sea surface temperature anomaly (°C), related to the period September-December 2012 and compared to the 1981-2010 reference period. NOAA-NCEP data.

Sea surface temperature anomaly (°C), related to the period September-December 2012 and compared to the 1981-2010 reference period. NOAA-NCEP data.

Surface pressure anomaly (hPa) related to the period September-December 2012 and compared to the 1981-2010 reference period. NOAA-NCEP data.

Surface pressure anomaly (hPa) related to the period September-December 2012 and compared to the 1981-2010 reference period. NOAA-NCEP data.

The fear, in this case, is that the scientific findings will be later than the disappearance, in September, of the Arctic sea ice. As it is can be seen below, it may be possible that this fact could happen as early as within 4-5 years …

Estimated sea ice minimum volume from UW PIOMAS, and regression curve.

Estimated sea ice minimum volume from UW PIOMAS, and regression curve.

Last, but not least, we will report another record in 2012. At the remote meteorological station in Barrow, Alaska, for the first time the monthly averaged atmospheric CO2 concentrations exceeded the threshold of 400 ppm (parts per million – that is, over a million molecules of air, more than 400 are CO2) in the months of April and May. We would like to stress that Barrow station is remote, i.e. away from CO2 sources able to influence the measurements. The threshold of 400 ppm is purely psychological, and probably, less than three years later, also the global average will exceed it; however, this figure represents a signal that can not be overlooked, especially considering that other greenhouse gases such as methane, are increasing and every year set a new record of concentration.

The NOAA observatory's atmospheric in Barrow, Alaska.

The NOAA observatory’s atmospheric in Barrow, Alaska.

Note: part of this post has been published in Italian language here.