Aerosols and Arctic sea ice loss

A great article was posted on the Guardian website yesterday, written by Dr John Abraham, in which he highlights research that shows that if it weren't for aerosols, Arctic sea ice loss would've been even greater:

Pollution is slowing the melting
of Arctic sea ice, for now

Human carbon pollution is melting the Arctic,
but aerosol pollution is slowing it down

NASA satellite photo of the minimum extent of Arctic sea ice in 2005 that occurred on September 21, when the sea ice extent dropped to 2,05 million square miles (53 094 969 million square kilometers). Photograph: HO/AFP/Getty Images

The Arctic is one of the “canaries in the coal mine” for climate change. Long ago, scientists predicted it would warm quicker than other parts of the planet, and they were right. Currently, the Arctic is among the fastest-warming places on the planet. Part of the reason is that as the Arctic warms, ice melts and ocean water is uncovered. The ocean is darker than ice so it in turn absorbs more sunlight and increases its warming. This is a feedback loop.

Another reason is that the Arctic doesn’t get that much sunlight so increased energy from the atmosphere has a bigger influence there than it would have elsewhere.

Scientists have looked to the Arctic for clues and hints of human climate change over the past decades. The fact that the Arctic is warming has led to a 70% reduction in the volume of summer sea ice – an enormous loss of ice.

Decline in September Arctic ice extent (not volume). Illustration: NASA

A recent paper just published in the Journal of Climate by the American Meteorological Society takes an in-depth look at how fast the Arctic ice is melting and why. According to the paper, the authors completed a detection and attribution study of Arctic sea ice decline from 1953 to 2012. That is 60 years of data that tell the picture of climate change. The “detection” part of this study was about detecting what long-term trends are apparent over these six decades. The “attribution” part of the study is figuring out what is the cause of the trends.

Why six decades? Well the authors wanted to go back as far as they could while still accessing high-quality records of the ice extent. They used three different sets of data that record the extent of ice in the region.

In terms of attribution, the authors looked for “fingerprints” of human activity. Humans emit greenhouse gases that trap heat. We know that and we have known that for a long time. Greenhouse gases make the Arctic warmer. But, other things are happening too. There are natural changes to the Arctic. There are also other human pollutants that affect the ice. For instance, humans emit small particles called “aerosols” that can get into the atmosphere and block sunlight. So, these human aerosol emissions can actually cause cooling. 

The authors concluded that the combined cooling effect from human aerosols was detected in all three datasets of ice. That means, it didn’t matter whose measurements you used – the effect of aerosol cooling was present. 

So how much of an effect do aerosols have? It turns out 23% of the warming caused by greenhouse gases was offset by the cooling from aerosols. Unfortunately, this isn’t good news. It means that if/when humans reduce our aerosol pollution, the warming in the Arctic and the ice loss there will be worse.

Read the rest of the article here (I get quoted at the end of it!).

Comments

[VaughnA]

I have mentioned the Air Pollution in World: Real-time Air Quality Index Visual Map previously on this blog.

http://aqicn.org/map/world/

One thing that I have particularly noticed is how much cleaner the air over China has become during the past 4 years. Yes, the air is cleaner in the summer but when I have compared seasonal data the winter data shows dramatic improvement with improvement during all seasons (sorry I do not have access to previous data at this time.)

Might this cleaner air also be a contributing factor to the heatwaves this summer?

I also need to mention the Arctic Sea Ice Forum for the continuing discussion on this topic: https://forum.arctic-sea-ice.net/index.php/topic,1384.0.html

[Rob Dekker]

Thanks Neven, and congrats on getting quoted in that article !
That's really cool !

I'd alway thought that aerosol had mostly a local cooling effect, so it is surprising that these guys (Mueller et al) find the signature of aerosol forcing in a regression model of Arctic sea ice decline. Very interesting, so it is unfortunate that their paper is under paid access.

Also, do you know if there is an overview of world wide aerosol emissions over the past 4 decades ? Has it reduced ? Or increased ? or stayed the same as the West reduced emissions while the East increased them ?

[michael sweet]

This is a free copy of Mueller et al:
https://dspace.library.uvic.ca/bitstream/handle/1828/7669/Mueller_Bennit_MSc_2016.pdf?sequence=1
Google Scholar shows free copies listed to the right hand side.

Neven, I rarely post here anymore but I read all the OP's and most of the comments. I think you do a great job of describing the main points of the melt season. If I want more detail I look at the forum. Keep up the good work!

[michael sweet]

This is a free copy of Mueller et al:
https://dspace.library.uvic.ca/bitstream/handle/1828/7669/Mueller_Bennit_MSc_2016.pdf?sequence=1
Google Scholar shows free copies listed to the right hand side.

Neven, I rarely post here anymore but I read all the OP's and most of the comments. I think you do a great job of describing the main points of the melt season. If I want more detail I look at the forum. Keep up the good work!

[Rob Dekker]

Thank you much, Michael, for finding that free copy of the paper.

I did not have enough time to read the paper in full yet, but just glancing over it, it seems to be a modeling exercise in CMIP5 models. Nothing wrong with that, but I wonder how they link it to actual observed sea ice decline (which is steeper than CMIP5 models predicted).

Allow me some time to read the rest of the paper and I will report back.

[Rob Dekker]

I reviewed the Mueller et al paper that is the basis of this ASIB post.
Here are the details :

https://forum.arctic-sea-ice.net/index.php/topic,1384.msg166919.html#msg166919

In summary : overall a great paper, with the notion that maybe they overestimated the influence of aerosols on Arctic Sea Ice extent by a factor of 1.7 - 1.8.

[Zakelwe]

If aerosols offset 23% of the value what percentage do more and more planes flying over Greenland and the Arctic do by making contrails /clouds ?

Is it bigger or smaller factor than aerosols?

Also planes emit a large amount of CO2 currently at the same time, so that has to be examined too.

[Diablobanquisa]

"Why six decades? Well the authors wanted to go back as far as they could while still accessing high-quality records of the ice extent. They used three different sets of data that record the extent of ice in the region."

One of the three data sets used by Mueller et al. is the one we published two years ago and that Neven kindly reblogged here: http://neven1.typepad.com/blog/2016/01/september-arctic-sea-ice-extent-1935-2014.html

(Journal article: https://doi.org/10.5281/zenodo.44756 , NetCDF file with the gridded data: https://doi.org/10.5281/zenodo.44757 , CSV file with the extent values: https://doi.org/10.5281/zenodo.44758)

Glad to see that our data are useful!