Methods

This page describes the methodologies used for estimating the year where the glacier is ‘mostly gone’ and for the glacier projection visualizations. The detailed explanations provided below are somewhat technical and might be challenging for non-scientists, but we have included them here to ensure full transparency.

Overview

We simulate individual glacier thickness and volume projections from 2000 to 2100 using climate scenarios (climate models and emission scenarios) from CMIP5 and CMIP6 and large-scale glacier models. We primarily focus on 2.7°C global warming above pre-industrial by 2100, as this represents the predicted real-world outcome of current policies and actions. For comparison, we also include projections under the 1.5°C target of the Paris Agreement. We chose climate scenarios with a range of ±0.2°C from 1.5°C or 2.7°C.

The warming levels are defined as the 2071–2100 global mean temperature difference relative to 1850–1900, with a 0.69°C warming from 1850–1900 to 1986–2005 (ref. IPCC AR6).

Definition of a glacier being ‘mostly gone’

We define ‘mostly gone’ as the year when either less than 10% of the glacier’s 2020 volume or less than 0.01 km³ is expected to be left - whichever threshold is crossed first. While small ice patches might persist beyond this year, the landscape will be very different compared to the current one. This 10%-threshold is considered appropriate for the Alps and regions with similar glaciers in terms of geometry. Using both thresholds ensures we can define ‘mostly gone’ for both, relatively large Alpine glaciers and those already very small today.

It is important to note that positive feedback mechanisms, such as localized warming due to glacier retreat, are not accounted for in large-scale glacier models. This means that, while the glacier changes we use here are the most reliable projections available, the actual glacier retreat may occur faster.

Threshold definition differences

We find that our definition of a glacier being ‘mostly gone’ is, in the median, 9 years earlier in the Alps when using the two thresholds (<10% or <0.01 km³) compared to just using <10%. Compared to using only the <10% threshold, the maximum difference can mean a glacier is mostly gone 73 years earlier and that fewer glaciers survive until the end of the century.

Changing the definition from a 10% threshold to a 5% threshold results in glaciers being ‘mostly gone’, in the median, four years later, and max. 34 years later. For approximately 40 glaciers, the remaining glacier volume in 2100 is between 5% and 10%, meaning these glaciers would survive until the end of the century under the 5% threshold.

Likely range

The likely range describes the spread of projections and is defined as the 17th to 83rd percentiles, consistent with IPCC AR6.
If the data follow a Gaussian distribution, this range corresponds approximately to one standard deviation (±1σ) from the mean, capturing about 68% of the available projections.

Glacier projection data sources and models

The 2020 glacier volume, year where we estimate the glacier to be mostly gone, and global and regional glacier volume change projections are derived from these three glacier models (specific model versions and data further summarized in Zekollari et al. (2024)) by simulating each of the >200,000 glaciers individually:

OGGM v1.6.1
- Data: DOI
- Documentation: OGGM
- Details:
  - CMIP5 and CMIP6 available.
  - Includes less-used climate models and overshoot emission scenarios.
  - For 2.7±0.2°C: n=14 climate scenarios
  - For 1.5±0.2°C: n=11 climate scenarios
PyGEM-OGGM
- Data: DOI
- Documentation: PyGEM
- Details:
  - CMIP5 and CMIP6 available.
  - Same scenarios as presented in Rounce et al., 2023.
  - For 2.7±0.2°C: n=7 climate scenarios
  - For 1.5±0.2°C: n=9 climate scenarios
GloGEM
- Data: DOI
- Documentation: Huss & Hock (2015)
- Details:
  - CMIP6 only.
  - For 2.7±0.2°C: n=3 climate scenarios
  - For 1.5±0.2°C: n=4 climate scenarios

The 3D glacier thickness projections are based solely on OGGM simulations and visualized using the Glacier:3D-Viz tool. These 3D projections differ slightly from the other estimates, which are based on a combination of three glacier models.

Note that these glacier projections are based on global glacier models that use globally available glacier observation data. Data that are only available for a few glaciers (i.e., only geodetic but no in-situ observations directly used) is not included. As a result, the models perform better on a global scale than at the individual glacier scale. Although some important processes at the individual glacier scale are not represented, we present individual glacier results here for educational purposes. In addition, the per-glacier and regional volume in 2020 is not an observed volume but a modelled volume (it is the glacier model median estimate of the multi-climate-model medians).

Results aggregation

For the 2020 glacier volume, deglaciation year, and regional glacier volume change projections, we present the median and the likely range across all available combinations of glacier models and climate scenarios. Since OGGM includes more climate scenarios, its projections contribute the most weight to the overall results.

The mean global warming above pre-industrial across all combinations of glacier models and climate scenarios is:

1.57°C for the 1.5±0.2°C range.
2.71°C for the 2.7±0.2°C range.

Photo sources and licenses

Photographer: Max Baier
Date: 10.08.2020
Original URL: https://commons.wikimedia.org/wiki/File:Pasterze_202008.jpg
License: CC BY-SA 4.0

Photographer: Markus Strudl
Date: 09.08.2024

Photographer: Christoph Oberschmied (Agenzia per la Protezione civile)
Date: 2024
Original URL: https://geographie.uibk.ac.at/unicms/projects/glistt/gallery/index.html
Citation: Mit dem Download der Bilder erklären Sie, dass die Verwendung der Fotos der Ausstellung 'Goodbye Glaciers' gemäß der Richtlinie (EU) 2019/790 über das Urheberrecht erlaubt ist, dass ausdrücklich auf das Interreg VA Italien-Österreich 2014-2020 Projekt 'GLISTT' verwiesen werden muss und dass folgende Metadaten angegeben werden müssen: Gletscher und Name der Talschaft/Gebirgsgruppe, Vor- und Nachname des Fotografen, Aufnahmejahr des Fotos, Vor- und Nachname des Eigentümers oder des Archivs, aus dem das Foto stammt

Photographer: Steffen Flaischlen
Date: 07.09.2016
Original URL: https://de.wikipedia.org/wiki/Datei:Gaisbergferner_2016_-1.jpg
License: CC BY-SA 4.0

Photographer: Marin Kneib
Date: 9.2024
License: CC BY-SA 4.0

Photographer: Lambrecht A.
Date: 12.09.2006
Original URL: http://nsidc.org/data/glacier_photo/search/image_info/hintereisferner20060912
Citation: Lambrecht, A.. 2006. Hintereis Ferner Glacier: From the Glacier Photograph Collection. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.

Photographer: Rainer Prinz
Date: 08.09.2014
Original URL: http://nsidc.org/data/glacier_photo/search/image_info/hintereisferner20140908
Citation: Prinz, Rainer. 2014. Hintereis Ferner Glacier: From the Glacier Photograph Collection. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.

Photographer: Romeo Walser
Date: 08.10.2018
Original URL: https://commons.wikimedia.org/wiki/File:Rhonegletscher_Sept-2018a.jpg
License: CC BY-SA 4.0

Photographer: Andrea Kneib Walter
Date: 9.2024
License: CC BY-SA 4.0

Photographer: Michael Zemp
Date: 28.09.2013
Original URL: https://nsidc.org/data/glacier_photo/search/image_info/oberaar2013092801
Citation: Zemp, Michael. 2013. Oberaar Glacier: From the Glacier Photograph Collection. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.

Photographer: Pierre Zeiger
Date: 6.2024
License: CC BY-SA 4.0

Photographer: Ste Valentini
Date: 16.08.2011
Original URL: https://commons.wikimedia.org/wiki/File:Ghiacciaio_del_Careser.jpg
License: CC BY-SA 3.0

Photographer: Christian Casarotto (MUSE)
Date: 2024
Original URL: https://geographie.uibk.ac.at/unicms/projects/glistt/gallery/index.html
Citation: Mit dem Download der Bilder erklären Sie, dass die Verwendung der Fotos der Ausstellung 'Goodbye Glaciers' gemäß der Richtlinie (EU) 2019/790 über das Urheberrecht erlaubt ist, dass ausdrücklich auf das Interreg VA Italien-Österreich 2014-2020 Projekt 'GLISTT' verwiesen werden muss und dass folgende Metadaten angegeben werden müssen: Gletscher und Name der Talschaft/Gebirgsgruppe, Vor- und Nachname des Fotografen, Aufnahmejahr des Fotos, Vor- und Nachname des Eigentümers oder des Archivs, aus dem das Foto stammt

Photographer: Marin Kneib
Date: 19.09.2020
License: CC BY-SA 4.0

Photographer: Marin Kneib
Date: 28.09.2023
License: CC BY-SA 4.0

Photographer: Pierre Zeiger
Date: 7.202
License: CC BY-SA 4.0

Photographer: Stephan Peccini
Date: 04.09.2014
Original URL: http://nsidc.org/data/glacier_photo/search/image_info/gebroulaz2014090402
Citation: Peccini, Stephan. 2014. Gebraoulaz Glacier: From the Glacier Photograph Collection. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.
License: CC BY-NC-SA 4.0

Photographer: Bruno Jourdain
Date: 01.08.2019
License: CC BY-SA 4.0

Photographer: Pierre Zeiger
Date: 8.2023
License: CC BY-SA 4.0

Photographer: Matthias Huss
Date: 24.07.2009
Original URL: http://nsidc.org/data/glacier_photo/search/image_info/marmolada-20090724-huss
Citation: Huss, Matthias. 2009. Marmolada Glacier: From the Glacier Photograph Collection. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.

Photographer: Lilian Schuster
Date: 2024

Direction tool

Tool which helps, to mount individual signs pointing into the right direction.