The ember factory

The purpose of this application is to (re)produce burning ember diagrams of the style used in IPCC reports. The code is open-source. More information.

This application is written in Python, with the help of the ReportLab library (the web part is powered by the flask framework). The code is open-source and is available here: The ability of this application to reproduce several figures (independently) published by the IPCC was carefully tested. However, this is not a product of the IPCC (which is not responsible for projects or researches).

If it does not work as expected

We are sorry to hear that you have encountered a problem. We will do everything we can to help. Please have a look at 'It did not work! Why?' in the tutorial. Do not hesitate to provide feedback.

Development history

Although the web application and layout details were improved over time, there is no change affecting the translation of the risk levels provided as input to colours in the burning embers. The changes are recorded on (see Changelog). A short summary is provided below (from recent to old).

Recent news?

When an update is planned, it might be announced on

2023/07: Addition of SVG output, support for non-standard transition names

This update also fixes bugs and removes the requirement for the flask-session module.
(version 1.8.2)

2023/04: Support for detailed risk transitions, simplifications and corrections

The update provides support for complex descriptions of transitions, which may involve one or both of the following:

In addition, there is a minor bug fix, and:

(version 1.7.1)

2021/09: Support for 'overlapping transitions', corrections for technical issues

It is now possible to define 'overlapping transitions', i.e. generate embers with 'uncertainty ranges' that span across each other (e.g. it might be that risk is above or below 'high' at a given level). Technical changes enable files to be opened in recent versions of Adobe Illustrator (...).
(version 1.6)

2021/01: Additional layout options

Optional secondary axis (on the right, typically with a different scale), minor tick marks (unlabelled ticks between the main axis ticks), tick marks instead of horizontal grid lines, legend for confidence levels (experimental).
(version 1.5)

2020/12: Improvements, full documentation of the parameters, bug fixes for specific cases

File format download options (PDF/PNG/JPEG) are added. Cases where the vertical scale ('hazard') has limits significantly different from the usual "0 to +5°C", such as for CO2 concentrations in ppm, are now much better handled (bug fix). Coding improvements provide more clarity for future development. All parameters are documented in a way that is fully consistent with how they work (the same file provides online documentation and default values).
(version 1.4)

2020/08: Median value in the transitions and better handling of input file issues

An optional median, or 'midpoint' between the start and end of each transition, is added in the 'Basic format'. This results in the 'standard template' provided in the Tutorial. Input files containing missing data, errors, or other unexpected characteristics are better handled.

2019/11 - 2020/05: Initial development

This software was created by Philippe Marbaix at the end of 2019 (based on an earlier 'AR5-related' back-of-the-envelope version). The first objective was to produce figure 3 of Zommers et al. (2020; Burning Embers: Towards more transparent and robust climate change risk assessments. Nature Reviews Earth & Environment.

Help is welcome to further improve the application. All contributions will be recognised :-). For more information, please e-mail