The Single Biggest Problem With the Younger Dryas Impact Hypothesis: Uniformitarian Impact Craters, Part Cinq

The Single Biggest Problem With the Younger Dryas Impact Hypothesis: Uniformitarian Impact Craters, Part Cinq

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Guest commentary by David Middleton

  • YDIH = Younger Dryas Impact Hypothesis
  • YDB = Younger Dryas Boundary

Last month I shot a big hole in the latest YDIH paper.  This Science News article shoots another big hole in it.  The irony is that both of these particular holes were preexisting conditions: The contradictory data were either unknown to or ignored by the YDIH proponents.

Why won’t this debate about an ancient cold snap die?

Despite mainstream opposition, a controversial comet impact hypothesis persists

BY CAROLYN GRAMLING 2:00PM, JUNE 26, 2018

[…]

Geologists call this blip of frigid conditions the Younger Dryas, and its cause is a mystery. Most researchers suspect that a large pulse of freshwater from a melting ice sheet and glacial lakes flooded into the ocean, briefly interfering with Earth’s heat-transporting ocean currents. However, geologists have not yet found firm evidence of how and where this happened, such as traces of the path that this ancient flood traveled to reach the sea (SN: 12/29/12, p. 11).

But for more than a decade, one group of researchers has stirred up controversy by suggesting a cosmic cause for the sudden deep freeze. About 12,800 years ago, these researchers say, a comet — or perhaps its remnants — hit or exploded over the Laurentide Ice Sheet that once covered much of North America (SN: 6/2/07, p. 339).

[…]

The latest salvo came in March, when West and more than two dozen researchers published a pair of papers in the Journal of Geology. The papers include data from ice cores as well as sediment cores from land and sea. The cores contain signatures of giant wildfires that support the idea of a widespread burning event about 12,800 years ago, West says.

[…]

The March papers focus mainly on the wildfires, a long-standing aspect of the original hypothesis. Greenland ice cores show peaks in ammonium dating to the onset of the Younger Dryas, which the researchers say, suggests large-scale biomass burning. These data were previously presented in 2010 by astrophysicist Adrian Melott of the University of Kansas in Lawrence and colleagues. They suggested that the ammonium ions in those ice cores could be best explained by an extraterrestrial impact. A similar spike dating to 1908 — the year of the airburst over Siberia — had also been found in those same cores. The papers also describe finding peaks in charcoal that date to the start of the cold snap.

“The big thing here is a careful comparison of [many possible impact markers], normalized to the same dating method,” says Melott, one of the authors on the new impact papers. Those markers, including previously described evidence of microspherules, iridium and platinum dust, are consistent with having been caused by the same event, he says.

However, Jennifer Marlon, a paleoecologist and paleoclimatologist at Yale University and an expert on biomass burning, has taken her own look at sediments in North America dated to between 15,000 and 10,000 years ago. She sees no evidence for continent-wide fires dating specifically to the onset of the Younger Dryas.

“I’ve studied charcoal records for many years now,” Marlon says. In 2009, she and colleagues reported data on charcoal and pollen in lake sediments across North America. Importantly, the sediment records in her study encompassed not only the years of the Younger Dryas cold episode, but also a few thousand years before and after.

Her team found multiple small peaks of wildfires, but none of them were near the beginning of the Younger Dryas. “Forests burn in North America all the time,” she says. “You can’t find a cubic centimeter of sediment in any lake on this continent that doesn’t have charcoal in it.”

070718_cg_dryas_inline_6_graph_730070718_cg_dryas_inline_6_graph_730

Missing peak: Charcoal records from 15 lake sediment cores from across North America show how often fires occurred at each site over 5,000 years. The records show no peak in burning about 12,800 years ago, as would be expected if there were continent-scale fires.

Such fires could be triggered by rapid climate change, when ecosystems are quickly reorganizing and more dead fuel might be available. “That can cause major vegetation changes and fires,” Marlon says. “We don’t need to invoke a comet.”

The problem with the data in the recent papers, Marlon says, is that the researchers look only at a narrow time period, making it difficult to evaluate how large or unusual the signals really were. From her data, there appeared to have been more burning toward the end of the Younger Dryas, when the planet began to warm abruptly again.

“That speaks to my fundamental problem with the biomass burning part of the papers,” Marlon says. “I don’t understand why they’re zooming in. It’s what makes me skeptical.”

Holliday echoes that criticism. “Most of the time they sample only around this time interval,” he says. What would be more convincing, he says, are data from cores that span 15,000 to 20,000 years, sampled every five centimeters or so. “If this is a unique event, then we shouldn’t see anything like it in the last 15,000 years.”

West says that other peaks are irrelevant, because the impact hypothesis doesn’t imply that there was only one wildfire, just that one occurred around 12,800 years ago. He adds that the new papers suggest that Marlon and her colleagues didn’t correctly calibrate the radiocarbon dates for their samples. When done correctly, he says, one spike in fires that Marlon estimated at around 13,200 years ago actually occurred several hundred years later — right around 12,800 years ago.

[…]

Science News

Why won’t the YDIH debate die?  Mostly because it’s fun and also because its proponents tunnel-vision on the YDB and ignore any observations that are inconsistent with the YDIH.

While the YDIH has a lot of problems, this is the biggest…

West says that other peaks are irrelevant, because the impact hypothesis doesn’t imply that there was only one wildfire, just that one occurred around 12,800 years ago. He adds that the new papers suggest that Marlon and her colleagues didn’t correctly calibrate the radiocarbon dates for their samples. When done correctly, he says, one spike in fires that Marlon estimated at around 13,200 years ago actually occurred several hundred years later — right around 12,800 years ago.

This is analogous to the biggest problem with AGW: There is no genuine anomaly to explain.

The Medieval Warm Period, Holocene Climatic Optimum and Eemian are said to be irrelevant because past warming not driven by CO2 has no relevance to recent warming which surely must be driven by CO2.  Recent warming is simply not anomalous.

Temperature reconstruction (Ljungqvist, 2010), northern hemisphere instrumental temperature (HadCRUT4) and Law Dome CO2 (MacFarling Meure et al., 2006). Temperatures are 30-yr averages to reflect changing climatology.  The Good, the Bad and the Null Hypothesis.

Over the past 2,000 years, the average temperature of the Northern Hemisphere has exceeded natural variability (defined as two standard deviations (2σ) from the pre-1865 mean) three times: 1) the peak of the Medieval Warm Period 2) the nadir of the Little Ice Age and 3) since 1998.  Human activities clearly were not the cause of the first two deviations.  70% of the warming since the early 1600’s clearly falls within the range of natural variability.

While it is possible that the current warm period is about 0.2 °C warmer than the peak of the Medieval Warm Period, this could be due to the differing resolutions of the proxy reconstruction and instrumental data.

There is no wildfire anomaly associated with the YDB.  Even if you shift the dates, there’s no anomaly.  Because none of the peaks are anomalous.  An anomaly is a deviation from the norm.  If the norm is a fluctuation between wildfire frequencies of  0.0002 and 0.0003 peaks/site/year, a peak of 0.0003 peaks/site/year is not an anomaly, even it it was exactly at the YDB.  A YDB wildfire anomaly would significantly exceed (>2σ) the normal peak amplitude.

Note: The does not mean that it is incorrect to refer to HadCRUT4, GISTEMP, UAH or RSS as temperature anomalies.  The “norm” in these time series is an average temperature over a reference period.

A lot of the evidence for the YDIH has been very interesting.  Some of it has even been compelling.  However a lot of it has been poorly documented, unrepeatable, found to lack uniqueness and seriously unscientific (Carolina Bays… Argh).

 

Superforest,Climate Change

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