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How do we know where the carbon is coming from?

Keeling curve

Keeling curve vs prediction based on fossil fuel origin (from Scripps)

In 1957, Charles Keeling of Scripps Institution of Oceanography began regular measurements of carbon dioxide concentration at Mauna Loa, Hawaii. By 1960, he was already in a position to report a steady increase, together with seasonal variations. In the northern atmosphere, CO2 concentration falls during the spring and summer growing season, but recovers during autumn and winter as vegetable matter decays. This sawtooth pattern is superposed, however, on a steady overall increase.

The Keeling curve and beyond

Scripps Institution of Oceanography

Scripps Institution of Oceanography, from Birch Aquarium ((Invertzoo via Wikipedia)

Charles Keeling died in 2005, but the work is being continued by his son Ralph. When I visited Scripps in 1995, I saw Charles Keeling’s original curve, ink on graph paper, on the wall in the corridor outside his office. That curve has now been designated a National Historic Chemical Landmark, and there are commemorative plaques both at Scripps and at the Mauna Loa Observatory. Charles Keeling’s original paper, freely available here, goes into meticulous detail regarding sample collection, calibration, precautions taken to prevent local contamination, and comparisons between the Mauna Loa data and those that numerous other sites, including the Antarctic and samples collected from an aircraft.

By 1985, the record had been extended backwards in time by analysis of air bubbles trapped in ice cores, with dates ranging from the 1980s to the 1600s and earlier. These dates overlap Keeling’s data, and take us back to pre-industrial times. Before long, the ice core record had been extended to an 160,000 years, taking us into the Ice Ages, while further work has pushed it back to 800,000 years. We have estimates going back far beyond that, but employing indirect methods and with higher uncertainty.

Ice core record

Atmospheric CO2, 1700 – 2014; NASA via Forbes. Click to enlarge. Note that the zigzags for atmospheric data are not error bars, but annual fluctuations.

During the Ice Ages, carbon dioxide played a dual role, as product and as agent. The temperature oscillations at this time were driven primarily by subtle changes in the Earth’s motion (so-called Milankovitch cycles). But carbon dioxide is less soluble at higher temperatures (which is why your carbonated drink fizzes inside your mouth). And so in the first place the rise and fall of temperature led to a rise and fall of carbon dioxide in the atmosphere, as the oceans released and reabsorbed the gas. But then, the changes in carbon dioxide concentration amplified the original effect, since more carbon dioxide acting as a greenhouse gas makes the Earth lose heat less efficiently into space.

To summarise the results, current levels of CO2 are the highest they have been for over twenty million years. In the centuries leading up to 1800, Read the rest of this entry

Then and now; Darwin, Agassiz, global warming, and lakes that vanish overnight

Glen Roy is a valley in the Western Scottish Highlands, just south of the Great Glen (home to Loch Ness), and draining through Glen Spean to Loch Linnhe, an inlet of the Atlantic. It is remarkable for the presence of the Roads, a series of parallel, almost horizontal, grooves in the hills on the sides of the glen. Clearly shorelines; but of what body of water? And why are there more than one of them?

DarwinRoads

From Darwin, C. R., Philosophical Transactions of the Royal Society 129: 39-81, 1839. Observations on the parallel roads of Glen Roy, and of other parts of Lochaber in Scotland, with an attempt to prove that they are of marine origin.

Darwin thought the Roads represented vanished marine shorelines, one above the other as the result of vertical movement. Agassiz explained them, rather, as successive shorelines of a glacial lake, now vanished because the retaining glacier has melted away. If so, and if global warming is real, we might expect to see vanishing lakes today, as the glaciers retreat. We can, and we do, as my friend Peter Hess explains.

IMG_4396

Sedimentary (greywacke) erratic (approx. height 1 m) on glaciated slopes around Dunglass Crag, near Glasgow, transported from original location some 30 km to the North

Charles Darwin visited the Glenroy area in 1838, two years after his return from his round the world voyage on the Beagle. During that voyage, he had examined the geology as well as the plants and animals of the places he visited, and among them was the coastal area of Chile. This is marked by raised beaches inland where once had been shoreline, and Darwin correctly described these as the effects of uplift, which we now know to be driven by plate tectonics. So it was natural that Darwin should have applied a similar explanation to the Roads, suggesting that the Cairngorms, like the Andes, were a zone of uplift, and that the Roads were ancient beaches of the Atlantic, now some ten miles away. The alternative theory, that they represented shorelines of an ancient lake, ran up against a seemingly conclusive objection; such a lake could only have formed if there had been a barrier across the valley, but there was no trace of this.

Only a year later, the Swiss naturalist Louis Agassiz visited the area. He had just published his Ice Age theory, and in the Highlands he found plenty of evidence to support it; scratches on bedrock caused by the passage of glaciers, erratics (boulders far from their parent rock formations),  and moraines (piles of rock rubble that had been carried by glaciers, left in place when the glacier melted).

IMG_4366

A glacier-sculpted landscape. The hard basalt of Dunglass Crag, an ancient volcanic plug, has protected the softer rock downstream (right in photograph) from erosion

Evidence of this kind is not difficult to find throughout much of Scotland. I saw some of it myself earlier this month a few miles from Glasgow as a student on Glasgow University extension course (see illustrations). Agassiz realised that his ice age theory also provided the correct answer to the mystery of the Roads. Yes, there had been a lake, and yes, the roads did represent the shorelines at different times, carved into the sides of the valley by fierce freeze-thaw cycles. As for the barriers holding the lake in place at different levels over the course of time, they were a series of long vanished glaciers.

We now know that Agassiz was basically correct. Indeed, we can trace a whole series of glaciations, not just a single ice age. And Darwin was right in thinking that the area has experienced uplift; it could not fail to do so as the weight of ice above it melted away.

IMG_4377

Poorly sorted rubble deposited by the glacier near the foot of the Crag

Later Darwin was to write of his paper on the Roads as his greatest blunder. He had visited Snowdonia in North Wales in 1831, as a student companion of the noted geologist Adam Sedgwick, who had been looking for fossils. In his Autobiography (p. 70) he laments how

“neither of us saw a trace of the wonderful glacial phenomena all around us; we did not notice the plainly scored rocks, the perched boulders, the lateral and terminal moraines. Yet these phenomena are so conspicuous that … a house burnt down by fire did not tell its story more plainly than did this valley.”

But it took Darwin several years to reach this point, and even then he persisted for a while with hybrid explanations, in which icebergs rather than retreating glaciers had deposited at least some of the erratics.

OLYMPUS DIGITAL CAMERA

“Darwin’s boulders” in Cwm Idwal, Snowdonia, North Wales. Darwin had recognise these as glacial by 1842

Agassiz rejected Darwin’s concept of evolution when it was published twenty years later, but this does not seem to have diminished Darwin’s respect for him. Belief in the fixity of species was, in the 1860s, understandable conservatism, even if now, 150 years later, it is no more than deliberately cultivated ignorance.

The present is key to the past. It follows that the past can increase our understanding of the present. And so it is in this case. The glaciers of Switzerland are receding. Those of the southern Andes are receding even faster. Among them is Chile’s Colonia glacier, which dams a lake, Lake Cachet 2, some 3 square kilometers in area. As the glacier shrinks and weakens, it becomes progressively less able to hold back the water of the lake, which now periodically bursts through; on one recent occasion, the lake emptied itself overnight.

lake-cachet-670

Lake to sandy valley overnight

The overflow channel through which the vanished Loch Roy must have drained can still be detected as an abrupt narrow valley in the surrounding hillsides. The draining of Lake Cachet II sent 200,000 tonnes of water overnight down Chile’s main river, and caused giant waves as far as the Pacific Ocean, 60 miles away.

Since Agassiz and Darwin examined the roads of Glen Roy, the earth’s mean surface temperature has increased by roughly 1oC, with another 0.5oC in the pipeline even if emissions were to be stabilised at the same levels as in the year 2000.

Which, of course, they won’t be.

Global_Temperature_Anomaly.svg

Global mean surface temperature change from 1880 to 2015, relative to the 1951–1980 mean. The black line is the annual mean and the red line is the 5-year running mean

Darwin’s drawing of the Roads from Darwin Online.  Dunglass Crag, photos by author. Darwin’s boulders photographed by Michael Roberts. Lake Cachet II images via NCSE. Global temperature anomaly graph from NASA GISS via Wikipedia

More on receding glaciers at World Glacier Monitoring Service  and the US Government’s National Snow and Ice Data Center

h/t Michael Roberts, Dana Nuccitelli, Peter Hess. An earlier version of this post appeared in 3 Quarks Daily.

Darwin, Agassiz, and Global Warming; The Case of the Vanishing Lake

Darwin thought the parallel “Roads” of Glen Roy represented vanished marine shorelines, one above the other as the result of vertical movement. Agassizexplained them, rather, as successive shorelines of a glacial lake, now vanished because the retaining glacier has melted away. If so, and if global warming is real, we might expect to see vanishing lakes today, as the glaciers retreat. We can, and we do, as a recent blog post by my friend Peter Hess explains.

Glen Roy is a valley in the Western Scottish Highlands, just south of the Great Glen (home to Loch Ness), and draining through Glen Spean to Loch Linnhe, an inlet of the Atlantic. It is remarkable for the presence of the Roads, a series of parallel, almost horizontal, grooves in the hills on the sides of the glen. Clearly shorelines; but of what body of water? And why are there more than one of them?

From Darwin, C. R. 1839. Observations on the parallel roads of Glen Roy, and of other parts of Lochaber in Scotland, with an attempt to prove that they are of marine origin.  Philosophical Transactions of the Royal Society 129: 39-81, through Darwin Online

Charles Darwin visited the area in 1838, two years after his return from his round the world voyage on the Beagle. During that voyage, he had examined the geology as well as the plants and animals of the places he visited, and among them was the coastal area of Chile. This is marked by raised beaches inland where once had been shoreline, and Darwin correctly described these as the effects of uplift, which we now know to be driven by plate tectonics. So it was natural thatDarwin should have applied a similar explanation to the Roads, suggesting that the Cairngorms, like the Andes, were a zone of uplift, and that the Roads were ancient beaches of the Atlantic, now some ten miles away. The alternative theory, that they represented shorelines of an ancient lake, ran up against a seemingly conclusive objection; such a lake could only have formed if there had been a barrier across the valley, but there was no trace of this.Only a year later, shortly after going public with his Ice Age theory, the naturalist Louis Agassiz visited the area. In the Highlands he found plenty of evidence to support his idea; scratches on bedrock caused by the passage of glaciers, erratics (boulders far from their parent rock formations), and moraines (piles of rock rubble that had been carried by glaciers, left in place when the glacier melted). He considered the Roads further evidence of this; yes, there had been a lake, and yes, the roads did represent the shorelines at different times, carved into the sides of the valley by fierce freeze-thaw cycles. As for the barriers holding the lake in place at different levels over the course of time, they were a series of long vanished glaciers.

We now know that Agassiz was basically correct, although we now speak of a series of glaciations rather than a single Ice Age, and although Darwin was right in this; that the area has in addition experienced uplift, as the weight of ice above it has melted away.

Later Darwin was to write of this as his greatest blunder, describing in his Autobiography how in Wales he had missed the evidence of glaciation all around him, and generously acknowledging Agassiz for having come up with the correct explanation.

Agassiz rejected Darwin’s concept of evolution when it was published twenty years later because he believed in the fixity of species, but this does not seem to have diminished Darwin’s respect for him. What is now nothing but a deliberately cultivated ignorance was then, with so much less evidence available, no more than an understandable conservatism.

The overflow channel through which the vanished Loch Roy must have drained can still be detected as an abrupt narrow valley in the surrounding hillsides. The draining of the vanished lake in South America sent a surge through its own channel, down Chile’s main river, and caused giant waves as far as the Pacific Ocean, 60 miles away.

Lake to sandy valley overnight (from Peter Hess posting on NCSE blog site)

The glaciers of Switzerland are receding. Those of the southern Andes are receding even faster. Since Agassiz and Darwin examine the roads of Glen Roy, the earth’s mean surface temperature has increased by roughly 1oC, with another 0.5oC in the pipeline even if emissions were to be stabilised at the same levels as in the year 2000.

Which, of course, they won’t be.

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