Comment by the_third_wave | Hacker News Reader

Comment by the_third_wave | Hacker News Reader

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This year has seen both a high melt [1] as well as a high accumulation [2] of snow, the balance of which currently lies clearly at the positive end - Greenland has far more accumulated snow than average. These images come from the Danish polar portal [3] which I assume to be a canonical source given that Greenland is a Danish province.

The explanation with the images reads as follows:

The map illustrates what the ice sheet’s total surface gains and losses have been over the year since 1 September compared to the period 1981-2010. It does not include the mass that is lost when glaciers calve off icebergs and melt as they come into contact with warm seawater.

The animation shows one frame every seven days going back to the previous 1 September.

The blue curve shows the current season, whilst the red curve shows the corresponding development for the 2011-12 season, when the degree of melting was record high.

The dark grey curve traces the mean value from the period 1981-2010.

The light grey band shows differences from year to year. For any calendar day, the band shows the range over the 30 years (in the period 1981-2010), however with the lowest and highest values for each day omitted.

[1] http://polarportal.dk/fileadmin/polarportal/meltarea/MELTA_c...

[2] http://polarportal.dk/fileadmin/polarportal/surface/SMB_comb...

[3] http://polarportal.dk/en/greenland/surface-conditions/

FYI, there's a school of thought which has concluded that global warming will lead to another glacial period within the current ice age, because higher temperatures disrupt ocean currents -- particularly the Gulf Stream, which redistributes warm water from the Gulf of Mexico to northern Europe. As the Gulf Stream makes its deposits of warm water along the coasts of Great Britain and northwest Europe, it keeps the temperatures in northwest Europe warmer than in eastern Canada, even though they both are roughly the same distance from the equator. The hypothesis is that, if Arctic ice melts as a result of global warming, huge amounts of fresh water will pour into the North Atlantic and slow down the Gulf Stream, cooling Europe, and triggering a feedback loop with colder and longer European winters, and more and more ice building up on the planet's surface.[a][b]

[a] The book "Ice Age" by Cambridge-trained astrophysicist John Gribbin and his wife Mary has a good high-level overview of this school of thought: https://reanimus.com/store/?item=1420

[b] Recent studies of circulation in the North Atlantic already show a significant reduction in currents flowing north from the Gulf Stream: https://www.realclimate.org/index.php/archives/2020/09/new-s...

As far as I can tell the slowdown or cessation of the gulf stream will not lead to an "ice age" but to a cooling of north-western Europe. The climate there will be more comparable to that of the southern part of Alaska. While to the inhabitants of this region it may feel like an "ice age" the difference is that in an ice age the global average temperature goes down while this is not the case for the above scenario. It is quite possible - likely, even - for some regions to end up with lower average temperatures while the average global temperature increases.

My understanding is that we're already in an ice age -- specifically, we're in an inter-glacial period of an ice age. What you call the "cooling" of northwest Europe would be a glacial period within this ice age.

We're in an interglacial, awaiting a new ice age. If history [1] is anything to go by we're at the trailing end of the warmest period of the Holocene epoch [2]. Depending on how this interglacial develops the temperature will either gradually decrease into a new ice age (i.e. follow the same pattern as the Pleistocene) or rebound for a second peak (like the Pliocene, Eocene and Paleocene interglacials). At the end of the Holocene interglacial the ice will return for the remainder of the epoch.

[1] https://upload.wikimedia.org/wikipedia/commons/c/c9/Co2_glac...

[2] https://upload.wikimedia.org/wikipedia/commons/c/ca/Holocene...

I believe you are using the terminology incorrectly. According to Wikipedia, we currently are in an an ice age that began approximately 2.6 million years ago:

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

Within this ice age, we've had glacial and inter-glacial periods. For example, Europe's "Little Ice Age" was a glacial period within this ice age:

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

Currently, we're in an inter-glacial period.

Could be, I interpret "interglacial" literally, as being "between two ice ages". Were we in an actual ice age the same etymology would produce the term "intraglacial", a word I've never seen but that might be because written language was not yet a thing when there were people living in that circumstance.

> Could be, I interpret "interglacial" literally, as being "between two ice ages"

Pretty sure the literal interpretation of 'interglacial' is 'between glaciation.'

Literal 'between two ice ages' would be 'inter-ice age.'

There is a conflict between the popular and scientific meaning of "ice age" that seems to be tripping the two of you up. If you are going to get into a semantic debate about related meanings, you should clarify the specific meaning you ate intending.

I don't think there is a need for any debate, it is after all clear what we mean: an ice age is the whole cycle (interglacial + glacial), glacial is the period of maximum ice coverage, interglacial is the period of minimum ice coverage. In the common vernacular "ice age" equals the glacial period.

Are there any climatologists who have written about Gribbin's Ice Age idea? Not that I think he's necessarily wrong, but I am a little extra skeptical when an expert in an adjacent area of research is positioned as a contrarian to the mainstream of another field. For whatever reason (overconfidence? credentialism? inexperience?) this always seems to produce sketchy science.

I think there is a reluctance to discuss this, given the politicisation of the entire problem, and inevitable confusion. But note that global warming did get changed to "climate change" a decade or so back. Unfortunately this particular aspect gets very geopolitical, very fast, on any contemplation about which regions benefit from the two states. The ice core record itself is very clear, we´re towards the end of an interglacial period of the dominant 100k year ice age cycle, caused by small cyclic differences in the earths position vis a vis the sun over that period.

As to what happens next, the generally accepted theory at the moment is that the rise in CO2 combined with differences in the orbital inclination this cycle make an ice age onset unlikely. However know enough to read between the lines, the known unknowns if you like, and it's clear we don't know nearly enough about what actually causes glacial onset, or why it appears to happen so quickly. One could also go a bit further and comment that all interglacials seem to have a pattern of increasing CO2 (although not nearly to the extent we have triggered), until an abrupt drop. The Ocean Circulation theory originated out of the Wood´s Hole Research Lab a few years back.

The wiki page is good, and has the relevant papers linked:

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

> a little extra skeptical when an expert in an adjacent area of research is positioned as a contrarian to the mainstream of another field.

Thanks for putting words to something I've always noticed.

I think it comes from overconfidence borne of expertise in one or a few other fields. A pop culture example would be Elon Musk thinking he understands virology and epidemiology because he knows a lot about rockets, computers, and other non-living engineering systems.

> This year has seen both a high melt as well as a high accumulation of snow, the balance of which currently lies clearly at the positive end - Greenland has far more accumulated snow than average.

Seems to apply for the whole northern hemisphere. Look at the diagrams for 'the current Northern Hemisphere snow water equivalent relative to the long-term mean and variability' (GCW/FMI SWE Tracker) at https://globalcryospherewatch.org/state_of_cryo/snow/

Last year this diagram was similar.

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