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Messages - crandles

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Antarctica / Re: Rift in Larsen C
« on: July 09, 2018, 02:30:59 PM »
The 'monster' iceberg: What happened next?

Arctic sea ice / Re: How soon could we go ice free?
« on: June 16, 2018, 04:00:09 PM »
... If the models show a slowdown in the rate of decline as zero ice is approached and also the data is tending to show this recently...

Which models are you referring to? I've never seen a physics-based model with good predictive ability on this trend. True, there are models that don't work well, e.g. for the IPCC studies. If the model can't find the recent trend then it's not much use for predicting future trends.

Why do you say the data is showing a slowdown recently? If I look back at the linear fit of #97 then the residuals are all over the place and I don't see that trend. Based on the second plot, I suspect a quadratic fit would also curve downwards rather than upwards.

Lots of models. There are lots of graphs like attached below, some with many more model runs on them.

>" good predictive ability on this trend."

Clearly not they are all over the place on level of ice and also the trend. While some don't have enough data to see, all the model runs where you can see the change in trend where ice approaches zero is for the trend to get less steep as zero ice is approached.

Do we throw out all evidence because they are all over the place wrt level and trend? Or, do we say yes not much good for level or trend, but it looks like they all agree on trend in slope as zero ice is approached? So don't use them where they are bad but do use them for what they are good at, ie suggesting the change in trend as zero ice is approached declines.

>"Why do you say the data is showing a slowdown recently?"

The 4 parameter gompertz fit has a single inflection point. Whether I use Sept or April, that inflection point occurs in 2005. We have 12 years data since that inflection point. If there was only ~6 or fewer years data since the inflection point, I would be inclined to the opinion that 4 parameters might be too many parameters and I was overfitting. So just random residuals in last few years was allowing a better fit by using too many parameters. However with 12 years data past the infection point, that is too much data led and seems to me to be indicative that the data is showing a decline in the rate of decline.

See 4 parameter gompertz fit at top of this page.

>"If we're looking for a physical reason for a slowdown then I would point to the existence of a 'sanctuary region' against the North side of the CAA and Greenland where the ice hasn't melted out in any year."

Certainly wouldn't disagree with that being one physical reason, but I think there are lots of others.

I would tend to add in albedo feedback to this explanation (as well as deep water). In areas where ice moves out of the area, melting and ice movement allows albedo to drop and more sunlight energy be absorbed and this obviously helps additional melting. In contrast where ice piles up against Greenland & CAA, ice tend to move into area. So rather than melting and movement of ice causing extra area to open up, movement tend to close up areas opened by melting so it is much harder to get albedo drops to assist the melting.

If the ice retreats to a smaller area, that relevant area receives less sunlight energy so less volume melts seems quite possible. I guess this is complicated by winds bringing warmer temperature air so it isn't clear whether this accelerates or decelerates the volume of melt so maybe we need to look to the data and/or models?

Then there is oft discussed failure of MYI to make it around Beaufort gyre leading to rapid collapse of MYI to much lower proportion of the ice over a few years, but once we are down to these lower levels there is more FYI which almost completely recoveres itself each winter.

Are the people on these forums thinking through these reasonings and rejecting them because they don't believe they are significant compared to positive feedbacks they believe in? Or are they just rejecting the reasonings because it is just not exciting or they want to see catastrophic decline in sea ice or .... ?

Arctic sea ice / Re: How soon could we go ice free?
« on: June 16, 2018, 03:10:37 PM »
What observation? That the basic data clearly indicates a poof? That's not iffy. That must be the base assumption. In my opinion, the "iffy" assumption is to use a 2 dimensional, enthalpy ignoring mechanism to determine the first ice free Arctic. Any model that uses a "slab of ice" to analyse the past and make projections for the future is missing the big picture.

I'm not making any assumption, I'm only looking at the linear trends and that's what they show.

"I'm only looking at the linear trends" is just another way of saying 'if the linear trend continues' and that is an assumption you are making even if you want to try and say you are not making any assumption. FWIW I think you are making yourself sound ridiculous by clearly contradicting yourself.

As Ned W said

Yes, I agree with crandles.  Currently, some ways of extrapolating the past data show volume reaching zero before extent reaches zero.  There are three possible implications of that:

(1) Extent loss could speed up to match volume
(2) Volume loss could slow down to match extent
(3) Both extent and volume could change to reach zero at some other point

For some reason, a lot of people around here simply assume that (1) is the only possible outcome.  That's wrong. 

We both think the other is making big iffy assumptions. I think I have made the point and attempted clarification enough times, time to agree to disagree.

Arctic sea ice / Re: Arctic sea ice minimum early prediction
« on: May 30, 2018, 03:26:24 PM »
Like I asked above, and how I always vote.  Is there any good reason to vote anything other than the lowest?

Of course there is:

If too many people just go for the lowest and this turns out not to be the case, then this is setting up a 'those environmentalists are always crying wolf' defence for ff companies to continue not to act. Why hand them such a defence?

The forum / Re: Comments/posts can be liked now
« on: May 12, 2018, 02:24:58 PM »
Tried to like a post (link to do so visible) but now a pop up window says only people who have received 5 likes can like posts.

Policy and solutions / Re: Build, Baby, Build. In Fact, Overbuild.
« on: April 21, 2018, 10:55:51 PM »
I'll read the paper but 50% overbuilding is not enough.  Based on the data I've been able to use.

Wind and solar are dropping to $0.02/kWh.  Nuclear and storage are over $0.10/kWh.

We can greatly overbuild 2 cent generation before we start getting close to the cost of storage or nuclear.

2 cents * 1.5 (50% overbuilding) = 3 cents.

2 cents * 5 (500% overbuilding) = 10 cents.

I agree overbuilding makes sense. Less sure about 500% overbuilding 10 cents plus cost of maintaining distribution makes electricity expensive.

But even well before 100% overbuild, who gets paid what? Does the price come down to practically zero virtually all the time so there is no incentive to continue to overbuild? If those with contract for supply get paid but those without don't, why would anyone without contract for supply invest in something when rarely get any income?

Is there a possible market mechanism? Maybe some feature where solar PV and turbine owners are paid to switch off generation until point where indifferent between earning for supply of electricity and earning for turning off generation? Can this work to produce a reasonably efficient outcome? Can it be implemented if some currently have contracts for supply?

The forum / Re: Comments/posts can be liked now
« on: April 19, 2018, 12:32:43 PM »
Is there anyone who can see how many likes a particular post/comment receives?

Only for a brief period when it said who.

It would be nice to see which posts are liked. While I wonder if it tends to make the forum more of an echo chamber, it is worth trying it to see what happens.

The forum / Re: Comments/posts can be liked now
« on: April 18, 2018, 01:14:47 PM »
Have to hover over bar to see number of likes. Bar shows ratio of likes to posts.

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