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Record low sea ice extent in the Chukchi Sea (nsidc.org)
65 points by jesperlang 10 days ago | hide | past | web | favorite | 45 comments





The Chukchi Sea is directly north of the Bering Strait. Choice excerpt, spacing added:

>We also suggested a possible role of a strong oceanic heat inflow to the Chukchi Sea via Bering Strait.

>In support of this view, in the summer of 2017, Rebecca Woodgate of the University of Washington, Seattle, sailing on the research vessel Norseman II, recovered mooring data that indicated an early arrival of warm ocean water in the strait, about a month earlier than the average. This resulted in June ocean temperatures that were 3 degrees Celsius (5 degrees Fahrenheit) above average.

>Higher ocean temperatures in summer plays a large role in the timing of when the ice will form again in winter. There is likely a considerable amount of heat remaining in the top layer of the ocean, which will need to be lost to the atmosphere and outer space before the region becomes fully ice covered.


Just a reminder: When floating ice melts in water the level of the water does not rise. https://www.youtube.com/watch?v=aOCqHRpQh88

Melting is a proxy for warmer waters. Water becomes less dense (e.g. expands) as it warms above 0C (a little bit less for salt water). When you have a volume the size of the oceans, a small increase is a big surface volume change.

The bigger deal is that ice is very reflective. Reflected light energy promotes cooler temperatures.

Water is far less reflective, and so it absorbs significantly more incoming light energy, providing a general warming effect.


Edit: this paragraph is full of lies. -- There are a lot of things to be worried about with global warming, but I have never heard the density of ocean water listed among them. Water at 24 C is 0.002 less dense than water at 14 C. Since 10 C swings in global temperatures would long have caused catastrophes in other domains, I don't think we'll be much bothered by this small of a change in ocean density.

Please enlighten me if I am incorrect. Edit: thanks, all. I stand corrected.


Yes, actually it is a significant factor.

https://en.wikipedia.org/wiki/Sea_level_rise

> Based on figures from between 1993–2008 two thirds (68%) of recent sea level rise has been attributed by melting ice, and roughly one third has come from thermal expansion.

https://www.ipcc.ch/publications_and_data/ar4/wg1/en/faq-5-1...

> During recent years (1993–2003), for which the observing system is much better, thermal expansion and melting of land ice each account for about half of the observed sea level rise, although there is some uncertainty in the estimates.


If I'm correct (not a hydrologist) 0.002 decrease in density translates to a 2M (~6 feet) sea level rise per KM of ocean. Some quick googling suggest that the average ocean depth is close to 4KM.

So even small changes can have noticeable effect, particular when it's combined with other changes.


I'd be interested to hear more on this. Is this warming uniform throughout the entire depth? Does the change in density impact the ocean uniformly or mostly on the top layer where the pressure is less?

Take everything with a huge grain of salt here, I'm far from an authority on any of this, some of it I don't really grasp myself.

> Is this warming uniform throughout the entire depth?

I don't believe so, I think various ocean layers are practically on different planets. But I don't think it makes a difference, less warming at lower levels just means more warming at higher levels, producing the same effect.

> Is this warming uniform throughout the entire depth?

I don't think so, this is where waters uncompressability comes into play.


A 0.002 relative change in density is actually quite a lot, if you consider that the oceans are 12,000 feet deep on average.

Just a reminder: the climate is a dynamic system with many feedback loops, one of the most prominent feedback systems is albedo (amount of light reflected or absorbed). Snow/ice cover (on land or sea) reflects sunlight, cooling the Earth. Bare ground or water absorbs sunlight, warming the Earth. Melting of arctic sea ice is a positive feedback loop that will increase warming and can lead to a progression toward a different climate equilibrium (a warmer one) that could be hard to break out of even if CO2 levels come down.

How much sunlight does the Arctic get?

I've seen discussion that the heat lost from the relatively warm ocean water when not covered by ice exceeds the additional heat absorbed by low albedo, suggesting that lack of ice cover is actually a net negative feedback.

I have no personal calculations as to the magnitude of either effect, but I am skeptical of positive feedback loops, as they are inherently unstable. Note that we get significant ice loss every summer, followed by rapid gains in ice, which seems to cast doubt on the significance of any positive feedback.


Of course the sea ice normally returns every winter. Even at a modest 50 degrees of latitude, the insolation in summer is 6 times higher than in winter [1], so over short timescales, seasonal effects are so huge that they obscure the effects of any positive or negative feedback loops. That doesn't mean those loops don't exist and can't be significant over larger timescales.

[1]: http://www.applet-magic.com/insolation.htm


Right, so you have high insolation for some number of days. This provides heat at a rate of 300-500 W/m2 at peak, but that peak drops off, so the average insolation over the course of the year is low in polar areas. This is a positive feedback of open water (albedo ~.1 vs ice ~.6) and is limited by the duration of high insolation over open water. The maximum insolation is at the summer solstice (June) when there has been a smaller decline in arctic ice area (10%? http://nsidc.org/arcticseaicenews/charctic-interactive-sea-i...) By the date of low ice extent in September, the sun is getting pretty low for polar areas (low angle, low duration, low insolation - see the equinox data in your link: http://www.applet-magic.com/insolation.htm)

Open water loses heat much more rapidly than ice-covered water, with the rate dependent on temperature, wind speed, etc. One study found open water heat flux was about 250 W/m2 vs 75 for ice pack in March/April (http://onlinelibrary.wiley.com/doi/10.1029/94JC02485/abstrac...). I didn't find references to give averages or graphs over a year.

However long the ocean remains open, it radiates excess heat at an increased rate vs ice pack - a negative feedback of open water, limited by the area and duration of open water.


True. But it does tell you that the ice is melting. Which indicates heat input.

It's not real.

It's real but it's not caused by us.

It's caused by us but the water does not rise.

The water does rise but that's actually good.

etc.


Well, one could bet in futures markets that coastal cities will flood, and so on.

Is there actually a viable way to currently do this?

Buy land at 50 ft. elevation? I only half kid.

I checked the elevation last time I bought a house. I'm not even kidding. 63' above sea level, worst comes to worst I'll have a beachfront property to sell when I want to buy my houseboat.

Yes I did as well. One of my requirements in shopping for a house was >50 feet above sea level. It won't matter in the short run but it definitely will matter in the long run. Unfortunately if the sea rises 20 feet, I will still have a house but my whole area will be a lot less lucrative...

We believe in freedom of expression, but let's censor/threaten whoever disagrees with us, because their opinions are harmful.

We believe in gaining a consensus, but you'd better believe what we say or else.


Based on what hasn't happened in recent decades, I'd say that climate-change deniers have won. So it goes.

If they have won, they have only won because the game has been given to them. It's clear to see that a lot of their arguments are just reactionary, as Florin_Andrei pointed out.

Mouseover text of https://xkcd.com/1357/ :

> I can't remember where I heard this, but someone once said that defending a position by citing free speech is sort of the ultimate concession; you're saying that the most compelling thing you can say for your position is that it's not literally illegal to express.


I think you're missing the point.

I am not defending a position. I was merely pointing out the irony in trying to force a consensus.

Also, there is a difference between thinking that people speaking freely is good for a society's health, and trying to win a legal/ego battle.

If people can't handle a relatively neutral discussion about such things, then they might as well say so up front. I can understand if people have run out of patience, but it's far from being one-sided.


Well it could be real depending on whose definition we're going by. I remember a teacher in school giving us pictures of skyscrapers buried in water. Is that realistic?

As for the cause, there is bound to be disagreement when you try to reduce it down to a single factor.

If the waters aren't muddied enough by these oversimplifications, along come the thought police to tell us that racism is to blame.

It's not hard to see why people think this discourse is a cover for something else.


> If the waters aren't muddied enough by these oversimplifications,

I didn't knew that papers were oversimplified, because you're talking about science, not the media, isn't?


He's not wrong. Why the down votes?

Downvotes don't mean “wrong”, they mean “not valuable contribution”. A well known fact that is tangential to the content of the article (the first paragraph of which states the reason this is important, which is not that the ice melting leads to or indicated sea level ride in the direct manner the downvoted comment dismissed) is not a valuable contribution.

It's because the discussion is derailing and completely misses the point. It's like commenting the wild fires in california with "hey, just a reminder, the burning of trees releases carbon dioxide"..

Loss of arctic sea ice has major implications, one of them is the affect on the jet stream. A discussion about that would have been much more fruitful. A brief explanation about this can be found here:

https://youtu.be/wE53Or56eNM?t=3304


Well, then just don't respond to him, or make this point that the sea ice melt is a problem for other reasons. Otherwise it looks like you are downvoting a scientific fact. To those on the skeptical side, like myself, this adds fuel to the fire.

I see you got downvoted too. So much for facts.

This is the sort of thing that makes me a "climate denier." If even basic science gets downvoted, how is the other side scientific?

Discussions about climate stories on HN have tended to get derailed by climate deniers injecting "facts" or little calculations/conjectures that seem to refute bodies of peer-reviewed science into the discussion.

And after a while this diversion of attention is irritating. Not a down voter, but I'd assume that's what's going on.

Now, about "the other side" being unscientific -- HN down vote behavior does not have much to do with the content of peer-reviewed scientific papers. So I don't agree with letting HN down voting behaviors drive your decision-making about climate science.

For climate science, a good place to start is the just-published 2017 (U.S.) National Climate Assessment, which helpfully summarizes the peer-reviewed science. See: https://science2017.globalchange.gov


It is sort of a sniff test. It is hard and time consuming for an individual to parse the validity of these studies. So people look for basic facts they know to be true, which seem to be contradicted by the global warming claims. One of these is that water displaces the same volume of water whether frozen or liquid. Thus it would appear melting sea ice would have no impact on sea levels.


The commend says 'floating ice' the link you point at says 'ice on land'. The commender is 100% right but apparently the HN crowd has a lot of people that just love to downvote (which is why downvoting should be banned).

The link the op points says:

"First, as the oceans warm due to an increasing global temperature, seawater expands—taking up more space in the ocean basin and causing a rise in water level."


The ice melting is not the cause of seawater warming. Ice melt may indicate seawater warming, but the OP is correct that in itself it does not affect sea levels.

Actually, because sea ice has a different albedo than exposed sea water [0], sea ice melting is a significant cause of seawater warming (seawater warming is also, of course, a cause of sea ice melting; this is a classic positive feedback loop.)

[0] https://nsidc.org/cryosphere/seaice/processes/albedo.html


Yes, the sea water absorbing more sunlight due to lack of reflecting ice could cause it to warm significantly. But this is indirectly caused by sea ice melting, and a more speculative connection between ice melt and water levels rising. Furthermore, I'd like to see hard numbers, since most of sea ice is under water and does not reflect sunlight.

Stick a piece of ice in a cup of water, mark the water level before and after the melt, and tell me what happens.

Thermal expansion effect in cup of water is a little smaller than the thermal expansion effect in the oceans

Thermal expansion is a separate issue. Ice melt in and of itself does nothing to raise water level.



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