Underground temperatures trends

[Bernard]

I just posted this, a bit off-topic, on another thread about permafrost warming.
https://forum.arctic-sea-ice.net/index.php/topic,2546.msg186586.html#msg186586
But thought it was worth a topic by itself.

The global warming could also be measured anywhere in underground, whether this underground is frozen or not. At depths around 20m, the temperature is mostly stable year-round, and is close to the mean ground temperature. It's a bit of work to borehole at such depths, but not that much, and there are quite a lot of caves worldwide where the temperature could be measured.
Given the stability of underground temperatures year-round, to have interesting series it would not even be necessary to measure it on a daily basis.

Anyone knows science papers on such topics?

[Bernard]

This one is behind a paywall
https://www.sciencedirect.com/science/article/pii/S0921818100000047

Evidence of climate warming from underground temperatures in NW Italy

Abstract

The ground surface temperature (GST) history in NW Italy was reconstructed for the last three centuries by means of temperature–depth data recorded in a borehole in 1982. The results indicate relatively warmer periods in the 18th century and at the end the 1970s. A more recent set of underground temperature data was recorded in 1996. The comparison with the earlier thermal logging shows an evident temperature increase in the uppermost 80 m. Two different inversion techniques yield a subsurface temperature increase of 0.8–1.0 K since the 1980s. The inferred climatic model is consistent with the air temperature variations recorded at the Genoa University meteorological station.

[Bernard]

https://www.thewire.in/the-sciences/climate-records-captured-underground-confirm-indian-landmass-is-warming
The science paper is available at  https://www.currentscience.ac.in/Volumes/115/08/1567.pdf

[wili]

Thanks for these, Bernard.

We have learned that over 90% of global warming has actually been warming of oceans. But I have never seen something that quantifies what portion of warming has actually gone into heating the land itself. If anyone has such info, I thank them in advance for sharing...

[Bernard]

This 2003 publication (free access) indicates state-of-the art studies as far as 1971.
The general method is called underground temperature inversion.

Abstract

Data are used to demonstrate two effects apparent in ground surface temperature histories coming from inversions of borehole temperatures: apparent climatic warming and apparent climatic stability. Unrecognized local terrain effects, such as spatial or temporal change in land cover, cause warming locally. Where there is seasonally frozen ground, the ground temperature is not coupled to freezing air temperatures due to both latent heat of moisture in the ground and snow cover. Consequently, average ground temperatures can be much warmer than average air temperatures, and changes in average air temperatures result in much smaller changes in average ground temperatures. This produces apparent climatic stability when past air temperatures are inferred from borehole temperatures. However, increases in summer air temperatures, such as those due to deforestation, are well coupled to the ground temperature, causing the average ground surface temperature to increase, even in colder climates.

https://journals.ametsoc.org/doi/abs/10.1175/1087-3562%282003%29007%3C0001%3AICCFUT%3E2.0.CO%3B2

[Bernard]

Thanks for these, Bernard.

We have learned that over 90% of global warming has actually been warming of oceans. But I have never seen something that quantifies what portion of warming has actually gone into heating the land itself. If anyone has such info, I thank them in advance for sharing...

Good question indeed. I've not yet found mention of this aspect of the question in the papers I've unearthed (sorry for the pun) so far. Focus of those papers is rather on assessing the history of ground temperature changes based on the speed of their diffusion in the underground (about 10m/year, or 1km/century).

[Bernard]

A last paper for today, this one is just awesome! The great astronomer Cassini started gathering underground temperatures data in the late 18th century.

https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/joc.1211

Abstract

Careful temperature measurements performed from 1783 to 1852 in underground galleries, 28 m below the Paris Observatory, are compared with current measurements performed in a limestone quarry, 20 m below ground surface, and with local and European surface temperature records. When averaged using a backward 11-year moving window, the surface temperature time series looks similar and exhibits the already well-known 1 °C temperature increase over the last century. In addition, since about 1987, a steeper increase of about 0.07 °C per year is noticed on all surface records.
Underground temperatures, unaffected by surface fluctuations and averaging procedures, show a 0.9 °C increase and thus confirm the trend indicated by the surface records. The averaged time series of the temperature in Paris and of the Wolf number, an indicator of sunspot activity, were reasonably well correlated till 1987 but deviated significantly from each other after that date. The long-term connection between surface temperature and solar cycles is further supported by a temporal analysis of the frequency content at 11 years and 5.5 years. Visual correlations between temperature and sunspot numbers, unconvincing when using recent records, appear more striking with underground data from 1783 to 1852. This analysis suggests that solar activity played an important role in temperature changes till the last century, but that different processes, possibly related to human-induced changes in the climate system, have been taking place lately with increasing intensity, especially since 1987.

[johnm33]

Thanks for this Bernard, I'm paticularly interested to see if there's any data about permafrost warming from below, and the activation of microbe specie as the temperature rises.

[Bernard]

Thanks for this Bernard, I'm paticularly interested to see if there's any data about permafrost warming from below, and the activation of microbe specie as the temperature rises.

Maybe you should check the more specific threads about permafrost at
https://forum.arctic-sea-ice.net/index.php/board,20.0.html

[Bernard]

Default serious papers about it, I tried a napkin computation of the Underground Heat Content growth under the conservative hypothesis of 1K growth in surface temperature over the past century.

According to different papers previously quoted, the diffusion of the mean ground temperature on such a time scale would reach depths around 100 m. So I try below to asses the energy needed to heat up by 1K the first 100 m of bedrock all over continents.

I take mean values for granite or similar rocks :

heat capacity ~ 25 J/mol/K
molar mass ~ 60 g/mol
density ~ 2.5 g/cm³

Continents being about 1.4x10⁸ km² gather to a depth of 100 m a volume of 1.4x10⁷ km³, a mass of 3.5x10²² g, around 6x10²⁰ mol.

To heat this up 1K, you need to transfer 1.5x10²² J, or 15 zettajoules.

This is one order of magnitude (less than 5%) smaller than the ~400 zettajoules added to Ocean Heat Content since 1940, according to https://www.carbonbrief.org/state-of-the-climate-new-record-ocean-heat-content-and-growing-a-el-nino

But not small enough to ignore it in any accurate assessment of global warming.

[TerryM]

Thanks Bernard.


An interesting measurement. I'd think that ground temps would have an effect on moisture content, possibly effecting root growth, which in turn might cause shifts in albedo and shading that could act as an unrecognized feedback.


I'd expect this to be strongest in arid environments. Regions that might need to be abandoned to desertification in the not too distant future.
Terry

[Richard Rathbone]

Thanks for these, Bernard.

We have learned that over 90% of global warming has actually been warming of oceans. But I have never seen something that quantifies what portion of warming has actually gone into heating the land itself. If anyone has such info, I thank them in advance for sharing...

Good question indeed. I've not yet found mention of this aspect of the question in the papers I've unearthed (sorry for the pun) so far. Focus of those papers is rather on assessing the history of ground temperature changes based on the speed of their diffusion in the underground (about 10m/year, or 1km/century).

That would be 1km per 10,000 years if its 10m/year. Diffusion scales with L/T^2. (the further in a change has got, the weaker the gradient driving it gets and the slower it progresses, just like the sea ice grows more slowly as it thickens)

[Bernard]

Focus of those papers is rather on assessing the history of ground temperature changes based on the speed of their diffusion in the underground (about 10m/year, or 1km/century).

That would be 1km per 10,000 years if its 10m/year. Diffusion scales with L/T^2. (the further in a change has got, the weaker the gradient driving it gets and the slower it progresses, just like the sea ice grows more slowly as it thickens)

From the above quoted article at
https://www.thewire.in/the-sciences/climate-records-captured-underground-confirm-indian-landmass-is-warming

"The depth to which the temperature profile is disturbed in a given time period is governed by Earth’s thermal diffusivity. For typical rocks, a thermal front driven by surface temperature can plunge up to about 15 meters in one year, 160 meters in 100 years and 500 meters in 1,000 years. In other words, the surface ground temperature history of Earth over the last millennium is captured in the uppermost 500 meters of the crust."

[Tor Bejnar]

A slippery slope: How climate change is reshaping the Arctic landscape
Phys.org article about study by Antoni Lewkowicz, University of Ottawa, published in Nature Communications

Increasing ground temperatures in the Arctic are indicators of global climate change, but until recently, areas of cold permafrost were thought to be relatively immune to severe impacts. A new study ... shows that areas of cold permafrost can be vulnerable to rising summer temperatures.
…
… recorded an astounding sixty-fold increase in the number retrogressive thaw slumps—landslides caused by the melting of the ice in the permafrost—on Banks Island over the past three decades.
...

[gerontocrat]

Well spotted, that man.

If this is happening on this scale on Banks Island, are there a few million km2 of Tundra elsewhere where the same is happening? I know one does not extrapolate from the particular to the general, but......

A slippery slope: How climate change is reshaping the Arctic landscape
Phys.org article about study by Antoni Lewkowicz, University of Ottawa, published in Nature Communications

Increasing ground temperatures in the Arctic are indicators of global climate change, but until recently, areas of cold permafrost were thought to be relatively immune to severe impacts. A new study ... shows that areas of cold permafrost can be vulnerable to rising summer temperatures.
…
… recorded an astounding sixty-fold increase in the number retrogressive thaw slumps—landslides caused by the melting of the ice in the permafrost—on Banks Island over the past three decades.
...