The Sea Ice Monster: it's a scaly thing

By Steve Goddard and Anthony Watts

If you zoom in far enough, most anything looks scary, like this picture of a human head louse.

http://img.metro.co.uk/i/pix/2009/05/BugDS_450x300.jpg

Electron micrograph of a human head louse. Photo credit: Last Refuge, via Metro.co.uk

But when you look at it in the scale of our normal experience, not so much.

http://www.cm.edu.gt/nurse/articles/LiceInfoSheet_files/image001.jpg

Actual size of the three lice forms compared to a penny Photo credit: CDC

Be it lice or ice, the scale of presentation matters.

There is often criticism of cherry picking when it comes to time scales of climate data. In the case of satellite sea ice data presentation, both time scale and vertical scale are magnified. There’s only about 30 years of satellite ice data, whereas Arctic sea ice has been around for millions of years. Vertical scale is magnified to show the smallest fluctuations. Willis Eschenbach made and excellent point about scale when he comparatively demonstrated the scale of ice melt in Greenland in his essay: On Being the Wrong Size. When compared to the bulk volume of ice, the current Greenland melt is statistically insignificant.

There has been a lot of talk about commercial shipping opportunities through the “soon to be ice free” Arctic. These are normally based on highly magnified graphs published by organisations like NSIDC, similar to the one below.

average monthly data from 1979-2009

A different view emerges when you take the raw data from NSIDC’s web site and plot it on graphs with a more appropriate vertical scale. Done that way, the downwards trend for April ice is 0.039 million km²/year.

The surprise of scale?

When you calculate the slope, it suggests that April sea ice extent won’t reach zero until the year 2385.

Oh, that can’t be right. How about May? May will be ice free in the year 2404, only 394 years from now. (The US is 234 years old. Copernicus was placed on the “Catholic Forbidden index” 394 years ago.)

June will be ice free in the year 2296.

July will be ice free by the year 2151.

August will be ice free by the year 2103

September will be ice free by the year 2065. (Note that September 2009 was right on the trend line.)

All of the data and plots are available here in this Google online spreadsheet.

September is the minimum and ice starts to freeze up again. No chance of an ice free Arctic in October. But something must be wrong. The experts said that the Arctic would be ice free by 2008, and that it would be ice free by 2013.

“Our projection of 2013 for the removal of ice in summer is not accounting for the last two minima, in 2005 and 2007,” the researcher from the Naval Postgraduate School, Monterey, California, explained to the BBC. “So given that fact, you can argue that may be our projection of 2013 is already too conservative.” “In the end, it will just melt away quite suddenly”

NSIDC director, Dr. Mark Serreze also says this in this 5/20/10  Globe and Mail article:

“We are going to lose the summer sea-ice cover. We can’t go back.”

Dr. Serreze is still on the ‘death spiral’. He hasn’t changed his tune.

While skeptics see cycles, by saying “we can’t go back” Dr. Serreze apparently assumes the linear trend will continue to zero.

You can see from the graphs above how ridiculous those claims are. Even if the current trends continue, there is no reason to expect an ice free Arctic anytime in the next 50 years. And even more interesting to me is the fact that September, 2007 was really not that interesting. It was only 1.5 standard deviations off the trend line, i.e. almost following the 30 year trend.

All of the the main Arctic ice experts underpredicted the 2009 minimum, except for WUWT – which predicted it correctly and early.

http://www.arcus.org/search/seaiceoutlook/2009_outlook/summary_report/downloads/pan-arctic/figure-1.pdf

—————————————————————-

Science is the belief in the ignorance of the experts

-Richard Feynman

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That had me going for a second. I though there was a decrease in “Arctic sea lice”!

BillD

No doubt, predicing when the arctic will become ice-free in late summer is difficult and full of uncertainty. The main question for this post is whether the decline in ice will stay linear.
My part of the US midwest is expecting highs in the mid 80s (°F) all week. Warm, but perhaps not too extreme for spring. However, I was really surprised by the posting of R. Gates (4:57 pm, May 23) in the previous post on arctic ice. Gates linked to the forecast for Venetie, Alaska, which above the arctic circle, where predicted highs for the next week range from 78-85 °F. Spring temps in the 80s in May must be a little unusual above the arctic circle. Vinetie is inland, so coastal areas will undoubtably be cooler. Still, I would not want to bet on such a steady, gradual and linear melting of ice.
Here is the forecast for a town in central Alaska:
http://www.weather.com/outlook/travel/businesstraveler/tenday/99781?par=Google&site=earth.google.com&promo=0&cm_ven=bd_select&cm_cat=Google&cm_pla=earth.google.com&cm_ite=map

JB

Isn’t this a moot point, I read on here that sea ice is recovering, so all these trendlines will eventually go flat and then slope upwards, no?

Joe Bastardi

I also predicted a smaller ice melt season for 08 and 09 ( the accuweather.com pro site has my archives). This year I have a major ice melt season forecasted though, even as global temps turn rapidly down. But dont fool yourself, this will be almost back to the 2007 min before its over this year. However a major recovery will occur in the coming two years so the min in 11 and 12 will be a greater extent than 09. NH ice is in a recovery, but in a herky jerk one step down , 2 steps up fashion. The real turn in this will come in 10-15 years when the AMO joins the PDO with cyclical cold in tandem.
JB

James Sexton

JB says:
May 24, 2010 at 3:38 am
“Isn’t this a moot point, I read on here that sea ice is recovering, so all these trendlines will eventually go flat and then slope upwards, no?”
Yep, as like most things in nature, one can expect to see a sine wave eventually.

Joe,
Thanks. Your forecast is noted and bookmarked.

Today's State Extremes
State Highs:
Tanana	55°F
Northway	55°F
Fairbanks	54°F
Nenana	54°F
Haines	53°F
State Lows:
Tin City	24°F
Point Lay	24°F
Shishmaref	26°F
Savoonga	26°F
Noatak	26°F
JB

James, how long before we see that sine wave? 2 years, 5 years, 30 more years?

Mike McMillan

I think a couple ice free or at least passable months along the Northwest Passage would be a good thing, saving saving many tons of bunker oil for our shipping companies.
I’ve never been a fan of polar bears anyway.

EV

BillD…a couple things: the NWS forecast for that part of Alaska is about 10 degrees cooler than what you have linked on weather.com. I have noticed that weather.com comes up with interpolated data to produce their forecasts which in many cases are way off the mark. Furthermore, Venetie, Alaska is NOT representative of the entire arctic, where much lower 500 mb heights can be seen across areas north of Alaska this week, and even across western and southwestern Alaska (remember it’s a big, big state).

Al Gore

Now before we get all blasé about these long, long projections of meltdown: won’t somebody think of our children’s children’s children’s children’s children’s children? Also, we must remember that if previous (alarmist) trends are anything to go by, then we can safely assume that before too long it will be considered to be “worse than we thought” and that we’ll soon have to be worrying about our children’s children’s children’s children’s children. We must act NOW! And by “we” I mean “you” and by “act” I mean “pay.”

PJB

I am very afraid. What if this “cyclical” downturn reverses and the cycle goes back to an upward climb?
I live in the Canadian Shield. I don’t want to be under 3 km of ice (just too much pressure to bear…)
Won’t somebody get hot for a warmer, kinder world?
Won’t somebody think of the chilled wren?
😉

Vincent

Joe Bastardi:
“The real turn in this will come in 10-15 years when the AMO joins the PDO with cyclical cold in tandem.”
So we’ll have to put up with alarmist bleatings for another 10-15 years? Groan!

Henry chance

I can’t tell how much wind and currents shape extent of the ice. It sure looks like next winter will be cold. Last fall Edmonton Alberta had 46 below zero. It really shows us when they complained of balmy weather in Vancouver, it was not widespread.

jcrabb

So the IPCC is correct expecting the Arctic to be Summer ice free some time after 2050.

Ulric Lyons

@Joe Bastardi says:
May 24, 2010 at 3:48 am
I too predicted the last two cold winters. There should be a lot of ice melt by this Autumn, I would expect global temps to rise this year. The AO is theoretically positive till 2035, exceptions like last winter though, are of a greater magnitude than the cycle itself. The next two winters coming, I don`t see getting particularly cold till February, so ice build up will not be so much. 2012/13 winter looks mild, but 2014/16/17/18/20 winters are looking hard.

Enneagram

It´s the same with global temperatures, where the Y axis is always shown in 0.1 degrees increments, being really a straight line as in the present case, where any small increase in ice extent will straighten the curve.

Joe

Meanwhile, in Central Ontario, we have been basking in an abnormal warm trend since February. Most of the low pressures systems and storms are forced lower and away to the coast. Low 30 degree celcius for the next 3 days.
This is the same system that reaches to Greenland. Last week we had 2 nights of minus 6 degrees celcius which killed off some of the crops growing early.
Seems to me that the oscillating trends are getting more wild and closer in fluctuations.

geo

I think 2007 was anomalous, and that’s why we are going to get an unprecedented (in the satellite age) 3 years in a row of minimum extent growth.
I’m still sitting on 6.0-6.2M for minimum this year. The concentrations in the central core are still holding up very well compared to any previous year you look at since 1980 for this date (tho 2009 is not availabe at Cryosphere to look at because of an issue they had last spring/summer). It’s the central core that actually matters for minimum, because that’s the only place ice survives past minimum in any great quantity. There are large swaths of the core that are still north of 80% concentration that were below 80% in 2006-2008 (for instance).

BillD says:
May 24, 2010 at 3:35 am

However, I was really surprised by the posting of R. Gates (4:57 pm, May 23) in the previous post on arctic ice. Gates linked to the forecast for Venetie, Alaska, which above the arctic circle, where predicted highs for the next week range from 78-85 °F.

Your link was to the weather channel (click on the monthly data, their software can’t handle days without a sunrise – having written software to compute such info, their errors are amusing).
The NWS says:
Monday…Partly cloudy. Isolated afternoon thunderstorms west of beaver. Highs 70 to 75. Northeast winds 10 to 20 mph.
Monday Night…Partly cloudy. Isolated evening thunderstorms west of beaver. Lows near 45. Northeast winds 10 to 15 mph.
Tuesday…Mostly sunny. Highs around 75. Northeast winds 10 to 15 mph.
Wednesday…Mostly sunny. Highs near 75.
Thursday…Mostly sunny. Highs near 75.
Friday…Mostly sunny. Highs near 80.
Saturday…Mostly sunny. Highs near 75.
http://forecast.weather.gov/MapClick.php?zoneid=AKZ220
I don’t have time to hunt down records for the area this morning.

Wren

Is Arctic “ice extent” a measure of the surface area covered by ice, regardless of the ice’s depth, and therefore not a measure of the total amount of ice ? If so, what the researcher from the Naval Postgraduate School said seems reasonable:
“In the end, it will just melt away quite suddenly”
I would agree, since I have observed that a thin sheet of ice covering a pond can disappear quickly while a thick sheet takes a while to disappear.
I would agree with the continued gradual melting implied in the above graphs (e.g., June will be ice free in the year 2296) if the “ice extent” measure accounts for the depth or thickness of Arctic ice. If it doesn’t, the ice could be gone much sooner than the graphs imply.
While summers might see little or no Arctic ice in the future, I would expect the ice to be back in Winter , although thinner and possibly allowing navigation by ships during more months.

mcfarmer

beware the graph that does not show a zero at the x or y axis

As a parent who has suffered through the ongoing lice epidemic in eastern secondary schools, I can tell you that head lice are terrifying – at any scale.

Warren in Minnesota

In the posting titled: “WUWT Arctic Sea Ice News #6”, there was an interesting comment from commieBob who said, “The ice melts from the bottom up. Very roughly, it takes a certain air temperature to maintain a certain thickness of ice”. He continued that from March to May the “ice went from more than six feet to around two feet but you couldn’t tell it from the top of the ice.”
If his statements are correct, then I think that rather than the area of ice, the volume of the ice could be a better measurement of annual variation of temperature. However, I don’t see any data or discussion of measurements of the thickness of the ice over the entire area of the arctic.

latitude

Why do scientists feel like they have to give these predictions in the first place?
There is not one single person with one single active brain cell that would believe any of it.
chance of rain tomorrow – 50%
25 named hurricanes this year
human population will be X by year X…………..

Fred

“So the IPCC is correct expecting the Arctic to be Summer ice free some time after 2050.”
The IPCC can “expect” whatever it wants to expect. But it won’t happen.
IPCC expectations aren’t about facts or science, they are about fear-mongering and keeping their Gravy & Fame Train rolling. You see, the IPCC is really just people organized to take advantage of the Great Eco Scam, to get the next great Research Grant, to get one year closer to their pensions, too say whatever needs to be said to keep their jobs & the money rolling in and the flattering interviews on CNN, BBC & HufPo happening.
The IPCC is an Eco-Grifting organization, the people in it are best described as eco-pimps living off the avails off lies, deceits, half-truths, innuendo and fear mongering.
Their basic problem is Gaia, who they thought was on their side, refuses to cooperate with their greenie wannbe-ness & AGW theories & computer models.
They are hooped, time is proving them wrong. You have a choice – you can believe them or you can believe what is happening. But you can’t believe both – well you can, but then cognitive dissonance would be a forte.
History will not be kind to them, not kind at all.

David L.

My in-laws bought a vacation home on the sound in NC in the 1980’s. Their house is built next to an ancient pile of oyster shells, built up over the past thousand years by natives who would canoe over to the island and have feasts until the colonists put a stop to that in the 1600’s. Between the house and the water’s edge is about 150 feet of marsh. My engineer father-in-law placed a white pole at the waters edge in 1985.
Today the pole is off the shore’s edge and completely surrounded by water. Some family members worry that errosion is going to take the house. He and I measured the distance of the pole to the shore and estimated a monthly shoreline loss of over one eighth inch! Wow, that sounds like a lot….over one eighth inch of errosion per month! But my father-in-law laughs because at that rate it will take almost 1000 years for the shoreline to make it to the back porch (which is near the 1000 year old garbage pile of oyster shells and broken pottery). So not only is the erosion rate meaningless in our lifetime it’s probably meaningless on the timescale of at least 1000 years since for thousands of years the shoreline has not exceeded the garbage pile of oyster shells.
Do you think it’s scarier to quote the erosion as one eighth inch per month, two inches per year, one millimeter per week, or one hundred and fifty feet in one thousand years?

Capn Jack

Now I happened back here again, but I clicked an (mermaids go figure)
But is it true that Jerry Lewis the great comedian is not dead , but a member of congress reprising his role as the nutty Professor scoring hot and not so hot from what Isaw, shielas.

Capn Jack

and everyone knows warmers can’t swim or surf, they are scared of open water but like to talk about it.
Gore can’t swim, he wears a plastic puddle duck.

harrywr2

BillD says:
May 24, 2010 at 3:35 am
“Gates linked to the forecast for Venetie, Alaska, which above the arctic circle, where predicted highs for the next week range from 78-85 °F. Spring temps in the 80s in May must be a little unusual above the arctic circle.”
Sunrise and Sunset for Venitie, Alaska
Sunrise for May 24th – 3:08 AM
Sunset for May 24th – 12:16 AM
They have 21 hours of sun right now. On June 3rd it’ll be 24 hours.
Having lived in Fairbanks there are only 2 seasons. Summer and Winter.
Their onset of winter is usually first snow(August/Sept). Summer is last melt(May).
Alaskan summers are absolutely fantastic. Unfortunately they don’t last long.

INGSOC

With alarmists, time scales aren’t the only things that are ridiculously short.

Marc77

If scientist cared to make a correlation between sea ice extent and the temperature of Greenland. And the coupled that with Greenland ice cores. I believe they would find the North pole has probably been ice free many times in the past.

JB
So apparently you think that the Arctic will be ice free by 2008. Nice call.

Tom in Florida

Joe Bastardi says: (May 24, 2010 at 3:48 am)
“… The real turn in this will come in 10-15 years when the AMO joins the PDO with cyclical cold in tandem.”
They way I see it you have two choices:
1. Check the sea ice graphs daily and worry. Continue to look for proof that you are right and “they” are wrong (doesn’t matter which side your are on). Then look back in 10 – 15 years and ask yourself “where did my life go?”
2. Realize you can’t do anything about it, don’t worry, be happy, take care of what really matters. Then look back in 10- 15 years and tell yourself “that was great, let’s keep going”.

Joe Bastardi wrote, “The real turn in this will come in 10-15 years when the AMO joins the PDO with cyclical cold in tandem.”
A question: Through what mechanism would the PDO impact Arctic sea ice? The PDO does not represent SST anomalies in the North Pacific, North of 20N. It represents the leading Principal Component of monthly SST anomalies in the North Pacific Ocean,
poleward of 20N. And before you say it impacts ENSO, the PDO lags ENSO. The PDO is, in effect, an aftereffect of ENSO, but it’s also impacted by Sea Level Pressure (and possibly volcanic eruptions), which is why it appears to have longer-term variability. Refer to:
http://bobtisdale.blogspot.com/2009/04/misunderstandings-about-pdo-revised.html
And:
http://bobtisdale.blogspot.com/2009/05/revisiting-misunderstandings-about-pdo.html
And:
http://bobtisdale.blogspot.com/2010/04/is-difference-between-nino34-sst.html
Second, the AMO may have peaked around 2005, which would mean the SST anomalies of detrended North Atlantic SST anomalies are dropping. And if we look at North Atlantic SST anomalies…
http://i40.tinypic.com/11j98bl.png
…we can see that they had been dropping for a few years, contributing less to Global Surface Temperature anomalies directly, and indirectly through teleconnections.
Second question: Isn’t it the fact that the variations of the SST anomalies of the North Atlantic are greater than global SST anomalies on a multidecadal basis that causes its contribution (or lack thereof) to global temperature, and not its sign?

maxwell

Hey guys,
thanks for the post. The presentation of data is often rife with problems stemming from the story the researchers want to tell. It’s not just an issue in climate science, but thanks for bringing it into context here.
The statement,
‘Note that September 2009 was right on the trend line.’
is meaningless, however. One cannot look at both the trend and a single point. That’s a point that just about every contributor has made in context to claims of ‘alarmists’ about single warm months or years in records or reconstructions.
Why do you guys you a double standard here?
Either it is acceptable to look at a single point in the context of a trend or it’s not, in general.

I respect opinion of Joe Bastardi, but present ice is in much better shape compared to 2007.
http://igloo.atmos.uiuc.edu/cgi-bin/test/print.sh?fm=05&fd=23&fy=2007&sm=05&sd=23&sy=2010
The biggest melt in 2007 was from the Bering strait side, which is well bellow normal now:
http://weather.unisys.com/surface/sst_anom.html

Ed Caryl

Nothing in nature is linear, so forget those linear trends. I’m believing Joe Bastardi, but wondering if he factors in the solar cycle. The current sunspot count is way below last year’s prediction, the solar wind is a gentle zephyr, and the NASA guys are hiding out on an update.

Even if the Northwest Passage were to become ice-free, it would not be evidence of man-made global warming. It could just as easily — and more scientifically — be explained by natural warming caused by the sun and ocean oscillations.
As Joe Bastardi points out, we won’t have to worry about an ice-free arctic. We’re now in a cool PDO (and moving towards a La Nina), the sun remains quiet, and there is a very real chance of a major volcanic eruption (Katla) in Iceland. In any event, we’re not looking at warmer temperatures over the next 20 or 30 years. In my humble opinion, we’re headed for a Dalton-like minimum.
You can read my recent story (link below) describing the climate events that may lead to the “The Triple Crown of Global Cooling.” Both Joe Bastardi and Joe D’Aleo contributed to the article.
http://www.examiner.com/x-32936-Seminole-County-Environmental-News-Examiner~y2010m5d19-Triple-Crown-of-global-cooling-could-pose-serious-threat-to-humanity

Bill Yarber

Most of you are talking about weather, not climate. Both impact artic sea ice extrent but only climate truly impacts long term trends as discussed in this article. And with only a 30 year data base, any cyclical trends of more than 20 years won’t be detectable by the human eye.
The Earth’s atmosphere is a huge ocean of gas that has many eddy currents that impact weather. Try an experiment. Fill your bath tub with water and wait an hour for most of the perturbations to die down. Then gently pore three small glasses of water color (red, green and blue) equal distance from each other (end, middle, end). Now gently stir the water surface and see how long it takes to get any end color to the other end. The color patterns will give you a glimpse of what is happening in the Earth’s atmosphere on a far grander scale. Suggest you don’t let your kids see you do this and definitely don’t let them take a bath in this water. 🙂

One thing for sure, the current interglacial will end, and the whole mess will be covered with several km of ice(lice?). And then what will we all do?
It’s been quite cold in Florida, the water has barely warmed in our pool. By this time it would normally be mid-80 degrees.
Scales need to be uniform, not designed to give the most fright per inch.

barry

I thought the sea ice recovered last month. Back to normal was the message from WUWT. I see that all indicators show the sea ice extent has dropped below average and is now near 2007 levels for this time of year.
Can we get an update on whether it has recovered or not?
I note that the projection above for an ice-free summer in the Arctic (2065), is sooner than projected in the IPCC AR4. The maximum earliest date projected by the IPCC, at the bottom edge of the fastest melt scenario, is 2070. The mid-range projection for the fastest melt scenario, is an ice-free summer by the early 22nd century. Has the IPCC been too conservative in their estimates?

Gail Combs

I originally posted this at Arctic Sea Ice news #6 but it actually belongs here since it looks at the bogus use of statistics with relation to Arctic Sea Ice.
There are natural cycles of about 60 yrs (ocean) and 200 yrs (sun), but we only have data for about 30 yrs so there is no way in heck we have a good handle on the natural variability or what the “true average is”.
The graph uses data from 1979 to 2006 to compute the average. This is less than the thirty years that cover 1/2 an ocean cycle (In my numerous statistics classes I was taught to always use a minimum sample size of 30.) SO what part of the relevant ocean cycles does the average cover?
This Wiki graph – PDO (1650 – 1991) shows the PDO was mainly in a warm phase for 1979 to 2006. A more recent graph from NOAA shows there were only three years with a strongly negative PDO included in the infamous “average”.
This article shows both the arctic oscillation and the atmospheric pressure over the north pole were mainly positive.
And again the North Atlantic Oscillation was also strongly positive through the period. Wiki NAO graph
The AMO went from negative to positive during the time period. Wiki AMO graph
The sun has also been in a more active phase during that time period sunspots as proxy Here is a more complete look at the subject of the sun’s activity and TSI over time.
Not only is the “average” used for comparison a poor proxy for the “true mean” given it does not include a sampling of all the natural variability, but the gray area signifying “normal” is only one standard deviation from the average. Only 68% of data are within one standard deviation of the mean. So that is meant to cause alarm and mislead too.
The gray area should be 2.5 STD or at least 2 STD since 95% of individuals will have values within 2 standard deviations of the mean. I am sure those constructing the graph know this and that is why they chose to use only one standard deviation.
The “system” has been accumulating “heat” for thirty years. We are at the top of the sine curves starting on the downward slope. However just like you can not stop and turn an ocean liner like you can a quarter horse, you can not expect the “system” to change directions in a couple of years. I have no idea what the lag time is but given the changes we saw in the weather patterns last winter, I think the weather will be different (and become colder and colder) in the next thirty years than the last thirty. The whole darn subject and the graphs are very misleading and designed to cause alarm.
To be complete the cosmic ray count during the period. Note how 2009 has the highest cosmic ray count during the time period shown (1965 to 2009).

maxwell,
The statement “Note that September 2009 was right on the trend line” means that September, 2009 was right on the trend line.

barry
You must have missed this post from yesterday.
http://wattsupwiththat.com/2010/05/23/wuwt-arctic-sea-ice-news-6/

Flask

Maybe it’s just me, but I am more afraid of head lice than summers being ice-free in the Arctic.
Straight line extrapolation is a mug’s game.
If summers become ice-free, it still won’t be easy for shipping, there are bound to be lots of icebergs, and some years will have late break-up and early freeze-up.
In the Cenozoic, an interesting flora and fauna thrived in the then much warmer Canadian arctic archipelago.
PS – The sentence should read “Willis Eschenbach made an excellent point…”

R. Gates

Very interesting, but the assumption is the trend will be linear, rather than look something like this: (very unsophisticated graph, but gets the point across)
http://www2.norwalk-city.k12.oh.us/wordpressmu/precalc/files/2008/12/math.bmp
And taking a look at this graph, (even with the modest recovery of Sept. 2008-09 added in), we see that the trend is not linear at all:
http://newsimg.bbc.co.uk/media/images/45146000/gif/_45146192_ice_extent_466.gif
An ice free Arctic in September of 2065 would be unprecedented in human recorded history, and would have lots of other implications.
Finally, even if we all agree that the Arctic will be ice free sometime this century, two other entirely different issues are:
1)Will that be an overall good or bad thing for humans and all the other creatures that we share this planet with.
2) What the cause of the melt is? Is it AGW, or natural cycles?

jcrabb
We know from the historical record that climate trends are infinitely linear. That is why the glacial ice keeps getting deeper and deeper in Chicago, as the last ice age proceeds forwards.

Chris1958

Meanwhile, skeptical science tells us that the Greenland land mass is showing accelerated elevation because of the decreasing weight of overlying ice mass. I wonder if anyone has looked at their claims – it’s getting difficult to know who to believe these days.

Steven mosher

If the scientists should take care and caution in trusting their models, people would do well to take the same care and caution WRT simple linear models. That’s what fitting a straight line to the decline does. It creates a “model” of the ice that is strictly a function of prior ice extent and time. Nevertheless, you might want to throw some error bars on that “forecast”