Arquivo da tag: Termodinâmica

Winter is coming: Researchers uncover the surprising cause of the little ice age (Science Daily)

Cold era, lasting from early 15th to mid-19th centuries, triggered by unusually warm conditions

Date: December 15, 2021

Source: University of Massachusetts Amherst

Summary: New research provides a novel answer to one of the persistent questions in historical climatology, environmental history and the earth sciences: what caused the Little Ice Age? The answer, we now know, is a paradox: warming.

New research from the University of Massachusetts Amherst provides a novel answer to one of the persistent questions in historical climatology, environmental history and the earth sciences: what caused the Little Ice Age? The answer, we now know, is a paradox: warming.

The Little Ice Age was one of the coldest periods of the past 10,000 years, a period of cooling that was particularly pronounced in the North Atlantic region. This cold spell, whose precise timeline scholars debate, but which seems to have set in around 600 years ago, was responsible for crop failures, famines and pandemics throughout Europe, resulting in misery and death for millions. To date, the mechanisms that led to this harsh climate state have remained inconclusive. However, a new paper published recently in Science Advances gives an up-to-date picture of the events that brought about the Little Ice Age. Surprisingly, the cooling appears to have been triggered by an unusually warm episode.

When lead author Francois Lapointe, postdoctoral researcher and lecturer in geosciences at UMass Amherst and Raymond Bradley, distinguished professor in geosciences at UMass Amherst began carefully examining their 3,000-year reconstruction of North Atlantic sea surface temperatures, results of which were published in the Proceedings of the National Academy of Sciences in 2020, they noticed something surprising: a sudden change from very warm conditions in the late 1300s to unprecedented cold conditions in the early 1400s, only 20 years later.

Using many detailed marine records, Lapointe and Bradley discovered that there was an abnormally strong northward transfer of warm water in the late 1300s which peaked around 1380. As a result, the waters south of Greenland and the Nordic Seas became much warmer than usual. “No one has recognized this before,” notes Lapointe.

Normally, there is always a transfer of warm water from the tropics to the Arctic. It’s a well-known process called the Atlantic Meridional Overturning Circulation (AMOC), which is like a planetary conveyor belt. Typically, warm water from the tropics flows north along the coast of Northern Europe, and when it reaches higher latitudes and meets colder Arctic waters, it loses heat and becomes denser, causing the water to sink at the bottom of the ocean. This deep-water formation then flows south along the coast of North America and continues on to circulate around the world.

But in the late 1300s, AMOC strengthened significantly, which meant that far more warm water than usual was moving north, which in turn cause rapid Arctic ice loss. Over the course of a few decades in the late 1300s and 1400s, vast amounts of ice were flushed out into the North Atlantic, which not only cooled the North Atlantic waters, but also diluted their saltiness, ultimately causing AMOC to collapse. It is this collapse that then triggered a substantial cooling.

Fast-forward to our own time: between the 1960s and 1980s, we have also seen a rapid strengthening of AMOC, which has been linked with persistently high pressure in the atmosphere over Greenland. Lapointe and Bradley think the same atmospheric situation occurred just prior to the Little Ice Age — but what could have set off that persistent high-pressure event in the 1380s?

The answer, Lapointe discovered, is to be found in trees. Once the researchers compared their findings to a new record of solar activity revealed by radiocarbon isotopes preserved in tree rings, they discovered that unusually high solar activity was recorded in the late 1300s. Such solar activity tends to lead to high atmospheric pressure over Greenland.

At the same time, fewer volcanic eruptions were happening on earth, which means that there was less ash in the air. A “cleaner” atmosphere meant that the planet was more responsive to changes in solar output. “Hence the effect of high solar activity on the atmospheric circulation in the North-Atlantic was particularly strong,” said Lapointe.

Lapointe and Bradley have been wondering whether such an abrupt cooling event could happen again in our age of global climate change. They note that there is now much less Arctic sea ice due to global warming, so an event like that in the early 1400s, involving sea ice transport, is unlikely. “However, we do have to keep an eye on the build-up of freshwater in the Beaufort Sea (north of Alaska) which has increased by 40% in the past two decades. Its export to the subpolar North Atlantic could have a strong impact on oceanic circulation,” said Lapointe. “Also, persistent periods of high pressure over Greenland in summer have been much more frequent over the past decade and are linked with record-breaking ice melt. Climate models do not capture these events reliably and so we may be underestimating future ice loss from the ice sheet, with more freshwater entering the North Atlantic, potentially leading to a weakening or collapse of the AMOC.” The authors conclude that there is an urgent need to address these uncertainties.

This research was supported by funding from the National Science Foundation.

Journal Reference:

  1. Francois Lapointe, Raymond S. Bradley. Little Ice Age abruptly triggered by intrusion of Atlantic waters into the Nordic Seas. Science Advances, 2021; 7 (51) DOI: 10.1126/sciadv.abi8230

Thermodynamics, W.H. Auden and Philip K. Dick (Immanent Forms)

JUNE 5, 2015 – 

I was struck this morning by the similarity between two twentieth-century passages about entropy. The first is from W.H. Auden’s poem “As I Walked Out One Evening,” and the second from Philip K. Dick’s Do Androids Dream of Electric Sheep. If I was a betting man, I’d put money on PKD having read Auden. The cupboard and the teacup, especially, drew my attention, but it is also worth noting that the passage in PKD immediately precedes J.R. Isidore’s vision of the “tomb world,” a variation on Auden’s “land of the dead.”

Whether or not the passage in PKD is a explicit allusion or homage to Auden, I find it interesting that PKD’s passage, which several times mentions the irradiated dust of nuclear fallout, so closely resembles Auden’s pre-nuclear poem. The psychological issue, in each case, is not humanity’s ability to destroy itself (despite the post-apocalyptic setting of Androids) but the problem of being, as Carl Sagan puts it, “a way for the cosmos to know itself.” How do we live with our knowledge of geologic or cosmological time–scales on which all of human history occupy a mere blip–and, simultaneously, assert the meaningfulness of individual lives? More after the break, but, first the passages:

W.H. Auden, from “As I Walked Out One Evening” (1940):

But all the clocks in the city

Began to whirr and chime:

‘O let not Time deceive you,

You cannot conquer Time.

‘In the burrows of the Nightmare

Where Justice naked is,

Time watches from the shadow

And coughs when you would kiss.

‘In headaches and in worry

Vaguely life leaks away,

And Time will have his fancy

To-morrow or to-day.

‘Into many a green valley

Drifts the appalling snow;

Time breaks the threaded dances

And the diver’s brilliant bow.

‘O plunge your hands in water,

Plunge them in up to the wrist;

Stare, stare in the basin

And wonder what you’ve missed.

‘The glacier knocks in the cupboard,

The desert sighs in the bed,

And the crack in the tea-cup opens

A lane to the land of the dead.

‘Where the beggars raffle the banknotes

And the Giant is enchanting to Jack,

And the Lily-white Boy is a Roarer,

And Jill goes down on her back.

Philip K. Dick, from Do Androids Dream of Electric Sheep (1968):

“he saw the dust and the ruin of the apartment as it lay spreading out everywhere–he heard the kipple coming, the final disorder of all forms, the absence which would win out. It grew around him as he stood holding the empty ceramic cup; the cupboards of the kitchen creaked and split and he felt the floor beneath his feet give.

Reaching out, he touched the wall. His hand broke the surface; gray particles trickled and hurried down, fragments of plaster resembling the radioactive dust outside. He seated himself at the table and, like rotten, hollow tubes the legs of the chair bent; standing quickly, he set down the cup and tried to reform the chair, tried to press it back into its right shape. The chair came apart in his hands, the screws which had previously connected its several sections ripping out and hanging loose. He saw, on the table, the ceramic cup crack; webs of fine lines grew like the shadows of a vine, and then a chip dropped from the edge of the cup, exposing the rough, unglazed interior.”

Nietzsche frequently and disparately writes about this problem in terms of “eternal recurrence”: the natural cycles of life and death that repeat themselves across long stretches of time dwarf the appearance of any individual member of a single species on one planet. In The Birth of Tragedy (an early work that Nietzsche distances himself from, but still a valuable touchstone in his thought), Nietzsche frames this as a problem of identification. We identify with our individual selves, but those selves are also part of the large natural cycles whose inevitable continuation will destroy the individual. We can attempt to identify with the cycle itself as a claim to immortality. As Sagan says, “Some part of our being knows this is where we came from. We long to return, and wecan, because the cosmos is also within us. We‘re made of star stuff.

On the other hand, identifying with the cosmos as a whole diminishes the significance of our own disappearance within the natural cycle. As homo sapiens sapiens we may be part of the terran biosphere in the solar system (itself a secondary star system formed from the stuff of previous supernovas), but as Carl or Friedrich or Wiston or Dick, our individual deaths, like our lives, are not interchangeable. Hannah Arendt, in The Human Condition (1958), refers to this quality as “uniqueness”: “In man, otherness, which he shares with everything that is, and distinctness, which he shares with everything alive, become uniqueness, and human plurality is the paradoxical plurality of unique beings.” We act together, speak together, and, in the process, we forge identities that are irreducible to our membership in a class of objects or a biological species. We exercise what Nietzsche calls the “principle of individuation”: we create individual selves that will never be repeated in the eternal recurrence of natural cycles.

Taking this a step farther, our potential identification with the cosmos as a whole is only possible because we have individual consciousnesses that can identify/form identities. Nietzsche argues that simply disavowing our individual selves in favor of universal being/becoming prevents the cosmos from knowing or being known. The individual (what he calls Apollonian) may be a temporary, fleeting form, but for us to experience our place within the universal (what he calls Dionysian), we must hold our individual selves in tension with those larger processes.

The highest forms of art are born, Nietzsche argues, when Apollo and Dionysus are locked in conflict. We are individuals who will die, and our unique lives will be gone. We are also part of, constitutive of, and coextensive with the dynamic unfolding of the universe as a whole. A few billion years from now, the sun will die and take the Earth (and Mercury and Venus) with it, but even that will not be the end of our story. The productive problem we face is finding meaning that can emerge from both biography and cosmology and their vast differences in scale.

Arendt has some very interesting things to say about entropy and the apparently miraculous rescue of human life and worldliness from the seemingly inevitable destruction of natural cycles. I am tempted to end with her, but, for this post, I want to give Auden the final word. His poem begins with lovers declaring that they will love forever, and the entropic wisdom of the cities chiming clocks interrupts those declarations. The meaning of that interruption, however, is not a simple rejection of subjective folly in favor of a more objective, longer view. It leaves the lovers (and the listeners who are left long after the lovers leave) with a peculiar form of responsibility:

‘O look, look in the mirror,

O look in your distress:

Life remains a blessing

Although you cannot bless.

‘O stand, stand at the window

As the tears scald and start;

You shall love your crooked neighbour

With your crooked heart.’

It was late, late in the evening,

The lovers they were gone;

The clocks had ceased their chiming,

And the deep river ran on.