the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 Aug 2025
Beyond MAGT: learning more from permafrost thermal monitoring data with additional metrics
Abstract. Metrics such as the mean annual ground temperature (MAGT) and active layer thickness (ALT) are used to monitor and quantify permafrost change. However, these have limitations including those arising from the effects of latent heat, which reduce their sensitivity. We investigated the behaviour of existing and novel metrics derived from temperature observations (TSP metrics) using an ensemble of more than seventy 120-year simulations. We evaluated which TSP metrics provide new insight into permafrost change and evaluated how reliably each one indicates changes in sensible, latent, and total heat contents for different levels of sensor quality. We also quantified the effect of sensor placement on the magnitude of observed MAGT trends.
Based on this, we recommend a parsimonious set of five TSP metrics that provide a better picture of permafrost thaw than MAGT alone. These are: height of the permafrost table (TOP), depth of zero annual amplitude (dza), thermal integral (τ), mean annual ground temperature (MAGT), and mean annual surface temperature (MAGST).
We observed depth-related differences in MAGT warming rates of more than 0.23 °C dec-1 in 50 % of 10-year observation periods for observation depths between 10 m and 20 m. The magnitude of these differences roughly corresponds to the mean warming rate reported for discontinuous permafrost. The effect of sensor depth on warming trends is found to be greatest in ice-poor soils. These results illustrate the challenge of interpreting the magnitude of observed ground temperature trends.
Our results can be used to inform permafrost monitoring strategies and help contextualize observed trends. Consistent metrics can be produced from observed and simulated thermal data via the "tspmetrics" library available on the Python Package Index (PyPi).
Competing interests: SG is the owner of Cryogeeks (13756378 Canada Inc.), which distributes GeoPrecision equipment, referred to in this study for describing sensing systems. The authors declare that they have no other competing interests.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
(1504 KB) - Metadata XML
-
Supplement
(1549 KB) - BibTeX
- EndNote
Status: final response (author comments only)
-
RC1: 'Comment on egusphere-2025-2658', Anonymous Referee #1, 19 Jan 2026
-
AC1: 'Reply on RC1', Stephan Gruber, 31 Jan 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-2658/egusphere-2025-2658-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Stephan Gruber, 31 Jan 2026
-
RC2: 'Comment on egusphere-2025-2658', Anonymous Referee #2, 22 Jan 2026
The manuscript by Brown & Gruber addresses how permafrost temperature trends from bore holes are measured and analyzed. As the authors correctly note, most reported trends are simply borehole ground temperature trends at a particular depth and therefore do not account for effects such as changes in latent heat. The manuscript proposes new metrics that, alongside MAGT, may provide a better picture or quantitative description of permafrost thaw than MAGT alone.
I therefore applaud the objectives and reasoning behind this study. The manuscript provides a comprehensive analysis of how the proposed metrics vary with permafrost type (warm/cold) and over time. I believe the study is worth publishing after the authors address several points that are currently unclear or need improvement.
Major points to address
- Some of the proposed metrics are not completely clear to me. I have noted specific questions below.
- Several sections are overly lengthy and would benefit from more concise writing, particularly the Introduction. Throughout the text, there are some redundancies which should be addressed
- The manuscript relies mainly on simulated time series (ERA) forcing a heat flow model (GlobSim) to derive and present the new metrics and then includes a case study that does not add much new information. Consider removing Section 5 or integrating it into the Discussion.
Detailed comments
- p. 5, chapt. 2.4: I do not fully understand the discussion about the talik. Please rephrase for clarity.
- p. 6: There are many equations — check whether all are necessary. Some measures are commonly known and do not need to be written out.
- p. 7, chapt. 2.8: I do not follow this paragraph; please clarify or rewrite.
- p. 10, last paragraph: Delete this paragraph, it is not necessary.
- p. 11, l. 275: Delete this paragraph. You do not need to continually preview what comes next.
- Figure 1: This is a nice figure. Consider indicating that the first six boxes represent “cold” sites and the next boxes “warm” sites. Alternatively, place cold sites in the left column and warm sites in the right column to facilitate comparison.
- p. 13: You have a subsection 4.3.1 but no 4.3.2. Either remove the subheading for 4.3.1 or add the missing subsection.
- p. 4.5: This paragraph contains some redundancy — please tighten it.
- Figure 3: I do not understand this figure; please improve the caption and figure clarity or simplify the presentation.
- p. 4.9: I do not follow this section completely. Why is this point important? Also, Fig. 4 is not readable — improve resolution and labeling.
- p. 4.10: Consider deleting this summary section; it seems unnecessary.
- Chapter 5: See comment above about possibly removing this section. If you keep it, provide a map showing site locations — many readers will not know where “Schilthorn” and the other sites are located.
- l. 571–572: The purpose of these lines is unclear, especially the sentence in line 572. Please reword or delete.
- Chapt. 6.3: The comment about bedrock sites echoes the original objective of the PACE boreholes, if I recall correctly — consider mentioning that here.
- Chapt. 6.5: The discussion seems to indicate talik development. If that is the intended message, state it clearly; if not, consider removing this paragraph.
- Conclusions: Provide clear, concise conclusions, preferably as bullet points, rather than a long paragraph with references and summaries.
The manuscript addresses an important topic and presents useful new metrics. After clarifying the points above, tightening the text, and improving figure clarity, the manuscript looks ok for me.
Citation: https://doi.org/10.5194/egusphere-2025-2658-RC2 -
AC2: 'Reply on RC2', Stephan Gruber, 31 Jan 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-2658/egusphere-2025-2658-AC2-supplement.pdf
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 2,008 | 275 | 44 | 2,327 | 35 | 65 | 67 |
- HTML: 2,008
- PDF: 275
- XML: 44
- Total: 2,327
- Supplement: 35
- BibTeX: 65
- EndNote: 67
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
This study proposes and seeks to demonstrate the use of novel metrics derived from temperature observations to complement commonly used metrics such as mean annual ground temperature (MAGT) and active layer thickness (ALT), with the goal of improving the quantification of permafrost change, especially by better accounting for the effects of latent heat. The authors investigate the behaviour of existing and novel metrics using an ensemble of more than seventy 120 year simulations. They also apply these metrics to observations and discuss issues associated with sensor deployment and resolution. I think the topic is of interest and value to the community, and I strongly agree with the authors that new metrics need to be explored and proposed. I believe the real value and usefulness of new or improved metrics can only be assessed through their adoption, or lack thereof, in future studies. The work presented by the authors is detailed and appears correct with regard to the calculations and testing performed. I therefore have only minor comments.
Minor comments:
In the abstract (lines 11–14), the text reads as if it presents a finding related to MAGT, but it does not discuss how other metrics may be more suitable, particularly with respect to uncertainty versus informative value. Later in the paper (L.389), there is some discussion of the value of the “annual thermal integral” in this context. Consider revising the abstract to more clearly highlight what the new metrics can contribute.
In the abstract and the introduction, consider clarifying that MAGT is generally inferred at a single depth and is sometimes compared across sites at different depths. I found this background somewhat unclear.
L.550: Few details are provided on the model. Consider adding a few sentences describing the processes represented in the active layer and talik, if present (for example, advection). Please also explain how freeze thaw energy is represented in the model. While some details are provided in the Supplementary Material, the main text lacks basic information on the model type.
The use of a model may influence the results if the model has limitations in representing certain ongoing hydro thermal processes. Consider clarifying potential weaknesses and their implications (for testing the value of the metrics).