Consensus and consequences

The following brief communication was published on the The Cryosphere Discussions website two days ago: Does it matter exactly when the Arctic will become ice-free?

It's a good question, albeit a rhetorical one. The authors argue that a "robust definition of ice-free may reduce confusion in the community and amongst the public", and start by asking what the exact definition of ice-free is.

We consider four plausible definitions of the date of an ‘ice-free Arctic’. We apply the commonly-used threshold, for which northern hemispheric sea ice extent (defined as the total area of ocean with a sea ice fraction greater than 15%) is less than 1 million km2. The threshold of 1 million km2, rather than zero, is used because ice can be expected to remain for some time along the northern coast of Greenland, whilst for navigational purposes the central Arctic is ice-free. The ‘first ice-free year’ is then defined as:

A. The first year that at least one day is ‘ice free’.
B. The first year when the September mean is ’ice free’.
C. The first time the final year of a 5 year running mean of September monthly mean extents is ice-free.
D. The final year of 5 consecutive September monthly means which are ’ice-free’.

The question is an interesting one to ponder, and not just from a scientific perspective. Still, discussing the exact definition of ice-free may itself become a smoke screen that shrouds a more important issue, and thus cause even more confusion. Fortunately, the authors seem to be aware of this when they state in their paper's final paragraph:

Many of the impacts of decreasing ice cover will be felt irrespective of the precise date when the Arctic is declared seasonally ice-free.

I've said it before, and I'll say it again: An ice-free Arctic isn't some starting shot after which the consequences of Arctic sea ice loss spring into action. They already did so a while ago, but we're just not seeing it clearly as the signal hasn't crossed the bounds of natural variability for long enough yet.

Of course, scientists wouldn't be scientists if they wouldn't try to make things clearer. And thus they investigate things like the release of methane from permafrost and clathrates, changes in atmospheric patterns and melting rates of Greenland's ice sheet and glaciers, as these are all logically and mutually linked to Arctic sea ice loss.

Coincidentally, a paper was just published on the Journal of Climate website, by Liu, J., Z. Chen, J. Francis, M. Song, T. Mote, and Y. Hu.

Its title and abstract:

Has Arctic sea-ice loss contributed to increased surface melting of the Greenland ice sheet?

In recent decades, the Greenland ice sheet has experienced increased surface melt. However, the underlying cause of this increased surface melting and how it relates to cryospheric changes across the Arctic remain unclear. Here we show that an important contributing factor is the decreasing Arctic sea ice. Reduced summer sea ice favors stronger and more frequent occurrences of blocking-high pressure events over Greenland. Blocking highs enhance the transport of warm, moist air over Greenland, which increases downwelling infrared radiation, contributes to increased extreme heat events, and accounts for the majority of the observed warming trends. These findings are supported by analyses of observations and reanalysis data, as well as by independent atmospheric model simulations using a state-of-the-art atmospheric model that is forced by varying only the sea ice conditions. Reduced sea ice conditions in the model favor more extensive Greenland surface melting. We find that a positive feedback between the variability in the extent of summer Arctic sea ice and melt area of the summer Greenland ice sheet, which affects the Greenland ice sheet mass balance. This linkage may improve the projections of changes in the global sea level and thermohaline circulation.

Things aren't fine until the Arctic is ice-free (whatever your definition). The consequences of Arctic sea ice loss will most probably become worse when the Arctic is ice-free, but we may be able to prevent it from getting even worse after that, and eventually reverse the process. Together.

Comments

[Joe Wentrup]

I opt for A. To create awareness you have to be in the media - and recent arctic records have always been measured and have raised attention in terms of "first year in history".

[Aaron Lewis]

There was a time when continuous and competent Arctic sea ice separated the Arctic atmosphere from the Arctic ocean. From continent to continent, the atmosphere was cold and dry, allowing heat to radiate off freely. Greenland was also cold and dry.

Now, the diminished and cracked sea ice allows water vapor (latent heat) to move into the Arctic atmosphere. This reduces the amount of heat radiated off, so that heat from the Arctic Ocean is trapped. A warmer Arctic means that latent heat from the south is not condensed and radiated off.

Water vapor in the Arctic atmosphere changes the density of the air, impacting global atmospheric circulation patterns.

Loss of sea ice is long process of partition and equilibrium. The effects began when ice began to diminish and crack, allowing water vapor into the atmosphere. Increasing water water vapor in the Arctic atmosphere changes our weather. Today most our infrastructure was designed using engineering standards based on the climate of 50 years ago. Cracks in ice affect people, NOW.

Some horses can get out of a barn if the barn door is closed, but not latched. Measuring whether the barn door is 12 feet open or a full 16' open does not really tell you much whether your animals can get out of the barn. At this point the Arctic barn door (ice separating air and water) is open enough that all the “weather animals” can come and go as they please. As a result, for the last few years we have seen weather patterns never before seen, and which were not included in our engineering basis of design. The 4 options are about measuring the width of the barn door opening as the horses come and goes.

The important question about sea ice is, “Can water vapor move from the ocean to the atmosphere?” At this point, the ice is both diminished and fractured, and water vapor can move from the Arctic Ocean into the Arctic Atmosphere. AGW unlatched the Arctic Barn Door at least 20 years ago.

More water vapor in the Arctic atmosphere means more precipitation on Greenland. In 1970, rain on Greenland was almost unknown. Starting in 2002, I tracked rain on Greenland for for 60 consecutive months, and rain was reported somewhere on Greenland every month. If it is raining, then there is water vapor in the air, and water vapor melts ice.

Long story, short: There is excellent observational evidence that loss of sea ice competence affects GL melt. A fractured tea cup is not a “tea cup”, and fractured sea ice does not behave as traditional competent sea ice.

[jdallen_wa]

Nice commentary, Aaron.

I think you've also put your finger on a key point: Our civil engineering and domestic architecture was designed for the climate of 50 years ago, not what is evolving.

We can see the consequences of that in many of this winter's weather events across the US, Britain and elsewhere.

I think coping with it will be a huge, previously unforeseen problem. The cost of infrastructure changes required will be enormous.

[AbbottisGone]

@ arron,

You say, '...water vapor melts ice.'

Is this what we should ultimately be worried about?

[Chris Reynolds]

Aaron, Neven,

Hanna 2012 "Increased Runoff from Melt from the Greenland Ice Sheet: A Response to
Global Warming"
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.466.1641&rep=rep1&type=pdf

That finds that Greenland run off is mainly dominated by the intensity of the Greenland Blocking index and resultant high pressure -> clear skies -> increased surface insolation. This has been particularly strong since 2007.

This intensity in GBI since 2007 has been a result of increased Arctic Dipole anomaly in the summer. The Arctic Dipole has a role in wider weather impacts. e.g. European summer rainfall.
http://iopscience.iop.org/article/10.1088/1748-9326/8/4/044015;jsessionid=0A4A9F25F83E744C73E02A07025624AB.c4.iopscience.cld.iop.org

Overland et al find suggestions of wide impacts. (Overland et al "The recent shift in early summer Arctic atmospheric circulation")

QUOTE
The suggestion that recent (2007–2012) magnitudes of the early summer AD pattern are associated with enhanced North America and Greenland blocking events in the 700 hPa composite height field (Figure 3c) may imply a mechanism linking high-latitude change with mid-latitude weather in early summer...

...The June
2012 700 hPa geopotential height and temperature patterns (not shown) are similar to the Russian heatwave of 2010 [Dole et al., 2011], and the anomalous circulation may also have contributed to dryness and forest fires plaguing central and western US during the 2012 summer. Meanwhile, an enhanced southward dip in the jet stream leeward of the increased ridging over Greenland has caused generally cool wet summers in the U.K. since 2007, with record rains and floods in 2007 and 2012 [e.g., Hanna et al., 2008b; Met Office, 2012].
/QUOTE

We often concentrate on N America, Europe and Eurasia. But the effects are found in east Asia...

Wu et al find a link betwee the Arctic Dipole and summer rain in China.
http://link.springer.com/article/10.1007/s11434-008-0229-1

Zuo et al find predictablilty of China's winter cold with sea ice extent
http://link.springer.com/article/10.1007%2Fs00382-015-2966-6
Which leads onto a growing body of study showing potential linkage between low summer sea ice and cold winters.

e.g.
Honda "Influence of low Arctic sea-ice minima on anomalously cold Eurasian winters"
http://onlinelibrary.wiley.com/doi/10.1029/2008GL037079/full
and
Cohen "Arctic warming, increasing snow cover
and widespread boreal winter cooling" http://web.mit.edu/jlcohen/www/papers/Cohenetal_ERL12.pdf

All this is before we get to the issue of extreme weather and the planetary wave linkage to Arctic Amplification.
http://web.mit.edu/jlcohen/www/papers/Cohenetal_NGeo14.pdf
(Just look at the author list on that - it's a who's who of the leading experts in the issue)

***

There is a growing picture of year-round weather impacts across the entire northern hemisphere due to the loss of Arctic sea ice. Some of the details remain to be sorted out, but the overall pattern is clear.

Determining the criteria for declaring an ice free Arctic is useful. I'd favour <1M km^2 as the first year of ice free, that may be followed by some years above 1M, I can't decide between Ridley et al's C and D for determining when the transition to a seasonal pack is complete.

But Neven is correct, the consequences of sea ice loss are already here and are already having impacts.

Anyway, rambling over, back to lurking.

[Tor Bejnar]

It always serves us when we see you un-lurk, Chris!

If my opinion counted, I'd advocate for A & D. "A" for first ice free autumn, "D" for 'the transition' is complete.

[Jon Hurn]

That we are even discussing the event is indicative on how much the situation has changed in the last 20 years.

[Chris Reynolds]

Tor,

Thanks, I've had to withdraw from most discussions and have barely been to the forum because I'm now in management, so I'm cash rich :D, but time (and energy) poor :( . Ho hum.

I'm the only one of the management team without a status car. VBEG

Anyway, yes, I think I'd like D, but for the purposes of betting it puts a payout even further into the future. So for betting I'd prefer the first year.

That rambling on weather impacts is symptomatic of a building urge to re-read loads of papers get up to date with some more, and do a map of impacts. It's also driven by things like this:

https://farm2.staticflickr.com/1472/25566758986_6f6de0e27b_o.png

The winter just gone (2016) and winter 2014 have been absolutely insane! Is it linked to the Arctic? I don't know.

Jon,

Indeed, in the 1990s it was being discussed in the literature whether the decline in ice extent was part of a cycle (with the 1930s). The impact of AGW was considered in doubt by serious scientists.

Nobody serious thinks that way now.

[StuartP]

http://www.bbc.co.uk/programmes/b07142ls#play

The infinite Monkey Cage covers global warming.