A new time series of September Arctic sea ice extent from 1935 to 2014

[diablobanquisa]

We have just published a new paper in the spanish journal Revista de Climatología. This paper presents a new time series of September Arctic sea ice extent from 1935 to 2014:

– Download full text (pdf, in spanish)

– Download extent data values (csv)

– Download gridded data (netcdf)


Abstract

Since 1979 satellite-borne passive microwave sensors have provided a continuous and consistent record of Arctic sea ice extent. This record shows a significant downward trend, particularly at September, when Arctic sea ice reaches its annual minimum. Records before 1979 exist, but are not consistent with the satellite record and have limited reliability, specially before 1953. We present a new time series of September Arctic sea ice extent from 1935 to 2014 that includes data for the Siberian sector (AARI operational charts) not used previously in the Arctic wide existing time series (Walsh, HadISST). The new record has been adjusted to be consistent with satellite data. The trend for 1935-2014 is -3.5% decade, while the trend for the satellite era is -13.3% decade. However, the trends since 1935 until early 1980s are positive and statistically significant. The trends turn negative in the 1990s, reaching statistical significance from 2006 onwards. The lowest annual minimum in the pre-satellite era is higher than any annual minimum after 2001.


Methodology

STEP 1: We adjust HadISST (1953-1978) to match the satellite data, using the same method employed  by Meier et al. 2012 . However, we also adjust the gridded data, instead of adjusting only the extent values:


Arctic sea ice concentration for September 1960. Left: original HadISST. Right: HadISST adjusted to match the satellite data.



STEP 2: We incorporate AARI data into previously adjusted HadISST (1953-1978):


Arctic sea ice extent for September 1960. Left: adjusted HadISST. Right: adjusted HadISST + AARI.



STEP 3: We extend back the time series to 1935, combining AARI data with a climatology (calculated on the basis of the correlation between sea ice extent and temperature):


Left: September climatology for the 1935-1952 period . Right: Arctic sea ice extent for September 1952, after the incorporation of AARI data into the climatology.



Results

September Arctic sea ice extent since 1935 to 2014:





September Arctic sea ice extent since 1935 to 2014. Red: this work. Black: Meier et al. Blue: HadISST:





Median September Arctic sea ice extent for the lowest decade of the pre-satellite era (1935-1944, left) and for the lowest decade of the satellite era (2005-2014, right):





September Arctic sea ice extent since 1935 to 2014. Black: this work. Blue: HadISST. Grey band: estimated sea ice extent using a regression of September SIE on Arctic temperature data (Apr-Sept., 70-90N, CRUTEM4) based on the correlation between sea ice extent and temperature during the satellite era:





Trend (black line) for periods starting in 1935 and ending the plotted year for September. The green, blue and red lines represent the 99% confidence level according to three different methods:



 

https://diablobanquisa.wordpress.com/2016/01/14/new-time-series-september-arctic-sea-ice-extent-1935-2014/




 

[Neven]

Thanks for posting this here on the forum, Diablo. I'm going to repost it on the ASIB later today.

[diablobanquisa]

Thank you so much, Neven, I would be honoured (although I'm not sure if this deserves so much)

[Pmt111500]

<Diablo>, definitely worth a post on the main ASI Blog, imo. There likely was quite a lot more of old ice in the Arctic during 1930s-1950s than today, so I'm a bit sceptical of the lowest values in the early days of the record. I cannot though see any obvious reason why the Arctic couldn't have been like you've stated in the article. And further, as you've managed to get this to match the satellite record, there's something in your study for everyone, but the best experts, I think.

[diablobanquisa]

<Diablo>, definitely worth a post on the main ASI Blog, imo. There likely was quite a lot more of old ice in the Arctic during 1930s-1950s than today, so I'm a bit sceptical of the lowest values in the early days of the record. I cannot though see any obvious reason why the Arctic couldn't have been like you've stated in the article. And further, as you've managed to get this to match the satellite record, there's something in your study for everyone, but the best experts, I think.

Thank you!

[diablobanquisa]

A couple of extras for the readers of the Forum:


- Timeseries updated until 2015:





- Left column: lowest minimum during the pre-satellite era (1952, top) and lowest minimum during the satellite era (2012, bottom). Right column: highest minimum during the pre-satellite era (1963, top) and highest minimum during the satellite era (1996, bottom):

[Neven]

Post is up on the ASIB.

[Pmt111500]

Why would the ice have increased until 1970s? Are you of the opinion that the sulfates blocked more of the incoming radiation in the Arctic than elsewhere? Of course that behavior could be because of some long cyclical variation like PDO, if it effects t's differently over midlatudes and arctic. The Soviet industries at least in the northwest Europe weren't too clean, but now they've cleaned up on many pollutants at least somewhat so that might be collaborating in the current decline of ice. But, I wouldn't still want acid rain or snow here.

[diablobanquisa]

I don't know. Our main goal was to develop a time series as consistent as possible. The reasons behind the ice behaviour are out of the scope of our work.
 

[Pmt111500]

Thanks for the response.

[solartim27]

Here is a similar article, going back to 1850
https://www.carbonbrief.org/guest-post-piecing-together-arctic-sea-ice-history-1850/amp

[logicmanPatrick]

Here is a similar article, going back to 1850
https://www.carbonbrief.org/guest-post-piecing-together-arctic-sea-ice-history-1850/amp

Bump!

That 'bump' is a geek/nerd response to a post or comment suggesting that it deserves a wider readership.  Thanks for the link, and a very belated 'muchas gracias' to diablobanquisa.