Reblogged from Watts Up With That:
Guest Post by Willis Eschenbach
As a result of a tweet by Steve McIntyre, I was made aware of an interesting dataset. This is a look by Vinther et al. at the last ~12,000 years of temperatures on the Greenland ice cap. The dataset is available here.
Figure 1 shows the full length of the data, along with the change in summer insolation at 75°N, the general location of the ice cores used to create the temperature dataset.
Figure 1. Temperature anomalies of the Greenland ice sheet (left scale, yellow/black line), and the summer insolation in watts per square metre at 75°N (right scale, blue/black line). The red horizontal dashed line shows the average ice sheet temperature 1960-1980.
I’ll only say a few things about each of the graphs in this post. Regarding Figure 1, the insolation swing shown above is about fifty watts per square metre. Over the period in question, the temperature dropped about two and a half degrees from the peak in about 5800 BCE. That would mean the change is on the order of 0.05°C for each watt per square metre change in insolation …
From about 8300 BCE to 800 BCE, the average temperature of the ice sheet, not the maximum temperature but the average temperature of the ice sheet, was greater than the 1960-1980 average temperature of the ice sheet. That’s 7,500 years of the Holocene when Greenland’s ice sheet was warmer than recent temperatures.
Next, Figure 2 shows the same temperature data as in Figure 1, but this time with the EPICA Dome C ice core CO2 data.
Figure 2. Temperature anomalies of the Greenland ice sheet (left scale, yellow/black line), and EPICA Dome C ice core CO2 data, 9000 BCE – 1515 AD (right scale, blue/black line)
Hmmm … for about 7,000 years, CO2 is going up … and Greenland temperature is going down … who knew?
Finally, here’s the recent Vinther data:
Figure 3. Recent temperature anomalies of the Greenland ice sheet.
Not a whole lot to say about that except that the Greenland ice sheet has been as warm or warmer than the 1960-1980 average a number of times during the last 2000 years.
Finally, I took a look to see if there were any solar-related or other strong cycles in the Vinther data. Neither a Fourier periodogram nor a CEEMD analysis revealed any significant cycles.
And that’s the story of the Vinther reconstruction … here, we’ve had lovely rain for a couple of days now. Our cat wanders the house looking for the door into summer. He goes out time after time hoping for a different outcome … and he is back in ten minutes, wanting to be let in again.
My best to all, rain or shine,
Reblogged from Watts Up With That:
Public Release: 3-Jan-2019
Melting ice sheets release tons of methane into the atmosphere, study finds
University of Bristol
Melting ice sheet release tons of methane into the atmosphere, study finds
The Greenland Ice Sheet emits tons of methane according to a new study, showing that subglacial biological activity impacts the atmosphere far more than previously thought.
An international team of researchers led by the University of Bristol camped for three months next to the Greenland Ice Sheet, sampling the meltwater that runs off a large catchment (> 600 km2) of the Ice Sheet during the summer months.
As reported in Nature, using novel sensors to measure methane in meltwater runoff in real time, they observed that methane was continuously exported from beneath the ice.
They calculated that at least six tons of methane was transported to their measuring site from this portion of the Ice Sheet alone, roughly the equivalent of the methane released by up to 100 cows.
Professor Jemma Wadham, Director of Bristol’s Cabot Institute for the Environment, who led the investigation, said: “A key finding is that much of the methane produced beneath the ice likely escapes the Greenland Ice Sheet in large, fast flowing rivers before it can be oxidized to CO2, a typical fate for methane gas which normally reduces its greenhouse warming potency.”
Methane gas (CH4) is the third most important greenhouse gas in the atmosphere after water vapour and carbon dioxide (CO2). Although, present in lower concentrations that CO2, methane is approximately 20-28 times more potent. Therefore smaller quantities have the potential to cause disproportionate impacts on atmospheric temperatures. Most of the Earth’s methane is produced by microorganisms that convert organic matter to CH4 in the absence of oxygen, mostly in wetlands and on agricultural land, for instance in the stomachs of cows and rice paddies. The remainder comes from fossil fuels like natural gas.
While some methane had been detected previously in Greenland ice cores and in an Antarctic Subglacial Lake, this is the first time that meltwaters produced in spring and summer in large ice sheet catchments have been reported to continuously flush out methane from the ice sheet bed to the atmosphere.
Lead author, Guillaume Lamarche-Gagnon, from Bristol’s School of Geographical Sciences, said: “What is also striking is the fact that we’ve found unequivocal evidence of a widespread subglacial microbial system. Whilst we knew that methane-producing microbes likely were important in subglacial environments, how important and widespread they truly were was debatable. Now we clearly see that active microorganisms, living under kilometres of ice, are not only surviving, but likely impacting other parts of the Earth system. This subglacial methane is essentially a biomarker for life in these isolated habitats.”
Most studies on Arctic methane sources focus on permafrost, because these frozen soils tend to hold large reserves of organic carbon that could be converted to methane when they thaw due to climate warming. This latest study shows that ice sheet beds, which hold large reserves of carbon, liquid water, microorganisms and very little oxygen – the ideal conditions for creating methane gas – are also atmospheric methane sources.
Co-researcher Dr Elizabeth Bagshaw from Cardiff University added: “The new sensor technologies that we used give us a window into this previously unseen part of the glacial environment. Continuous measurement of meltwater enables us to improve our understanding of how these fascinating systems work and how they impact the rest of the planet.”
With Antarctica holding the largest ice mass on the planet, researchers say their findings make a case for turning the spotlight to the south. Mr Lamarche-Gagnon added: “Several orders of magnitude more methane has been hypothesized to be capped beneath the Antarctic Ice Sheet than beneath Arctic ice-masses. Like we did in Greenland, it’s time to put more robust numbers on the theory.”
This study was a collaboration between Bristol University, Charles University (Czechia), the National Oceanography Centre in Southampton, Newcastle University, the University of Toronto (Canada), the Université Libre de Bruxelles (Belgium), Cardiff University (UK), and Kongsberg Maritime Contros (Germany). It was funded by the Natural Environment Research Council (NERC), with additional funds from the Leverhulme Trust, the Czech Science Foundation, the Natural Sciences and Engineering Research Council of Canada, and the Fond de Recherche Nature et Technologies du Québec (Canada).
Paper: ‘Greenland melt drives continuous export of methane from the ice sheet bed’ by Guillaume Lamarche-Gagnon, Jemma L. Wadham, et al. Nature, Doi: 10.1038/s41586-018-0800-0
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