diff --git a/.github/workflows/create-condalock-file.yml b/.github/workflows/create-condalock-file.yml
index 52689e8693..bdca82b34f 100644
--- a/.github/workflows/create-condalock-file.yml
+++ b/.github/workflows/create-condalock-file.yml
@@ -28,21 +28,13 @@ jobs:
         with:
           auto-update-conda: true
           activate-environment: esmvaltool-fromlock
-          python-version: "3.12"
+          python-version: "3.13"
           miniforge-version: "latest"
           use-mamba: true
       - name: Show conda config
         run: |
           conda update -n base -c conda-forge conda
           conda --version
-          # setup-miniconda@v3 installs an old conda and mamba
-          # forcing a modern mamba updates both mamba and conda
-          # unpin mamba after conda-lock=3 release
-          # see github.com/ESMValGroup/ESMValTool/issues/3782
-          conda install -c conda-forge "mamba>=1.4.8,<2"
-          conda config --show-sources
-          conda config --show
-          conda --version
           mamba --version
       - name: Python info
         run: |
diff --git a/.github/workflows/install-from-conda.yml b/.github/workflows/install-from-conda.yml
index 4d30202dd4..562ba8c8e8 100644
--- a/.github/workflows/install-from-conda.yml
+++ b/.github/workflows/install-from-conda.yml
@@ -21,7 +21,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.11", "3.12"]
+        python-version: ["3.11", "3.12", "3.13"]
     name: Linux Python ${{ matrix.python-version }}
     steps:
       - uses: conda-incubator/setup-miniconda@v3
diff --git a/.github/workflows/install-from-condalock-file.yml b/.github/workflows/install-from-condalock-file.yml
index 86e04abd74..db3d4193e0 100644
--- a/.github/workflows/install-from-condalock-file.yml
+++ b/.github/workflows/install-from-condalock-file.yml
@@ -31,7 +31,7 @@ jobs:
     if: github.repository == 'ESMValGroup/ESMValTool'  # avoid GAs in forks
     strategy:
       matrix:
-        python-version: ["3.11", "3.12"]
+        python-version: ["3.11", "3.12", "3.13"]
       fail-fast: false
     name: Linux Python ${{ matrix.python-version }}
     steps:
diff --git a/.github/workflows/install-from-source.yml b/.github/workflows/install-from-source.yml
index ff4bbc469c..abc83596de 100644
--- a/.github/workflows/install-from-source.yml
+++ b/.github/workflows/install-from-source.yml
@@ -20,7 +20,7 @@ jobs:
     if: github.repository == 'ESMValGroup/ESMValTool'  # avoid GAs in forks
     strategy:
       matrix:
-        python-version: ["3.11", "3.12"]
+        python-version: ["3.11", "3.12", "3.13"]
       fail-fast: false
     name: Linux Python ${{ matrix.python-version }}
     steps:
diff --git a/.github/workflows/pypi-build-and-deploy.yml b/.github/workflows/pypi-build-and-deploy.yml
index d6df3626e6..7d57e2a87c 100644
--- a/.github/workflows/pypi-build-and-deploy.yml
+++ b/.github/workflows/pypi-build-and-deploy.yml
@@ -17,10 +17,10 @@ jobs:
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0
-      - name: Set up Python 3.12
+      - name: Set up Python 3.13
         uses: actions/setup-python@v1
         with:
-          python-version: "3.12"
+          python-version: "3.13"
       - name: Install pep517
         run: >-
           python -m
diff --git a/.github/workflows/run-tests-monitor.yml b/.github/workflows/run-tests-monitor.yml
index 6581ed1c21..86d734fc64 100644
--- a/.github/workflows/run-tests-monitor.yml
+++ b/.github/workflows/run-tests-monitor.yml
@@ -24,7 +24,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.11", "3.12"]
+        python-version: ["3.11", "3.12", "3.13"]
     name: Linux Python ${{ matrix.python-version }}
     steps:
       - uses: actions/checkout@v4
@@ -70,7 +70,7 @@ jobs:
     runs-on: "macos-latest"
     strategy:
       matrix:
-        python-version: ["3.11", "3.12"]
+        python-version: ["3.11", "3.12", "3.13"]
         architecture: ["x64"]  # need to force Intel, arm64 builds have issues
       fail-fast: false
     name: OSX Python ${{ matrix.python-version }}
diff --git a/.github/workflows/test-development.yml b/.github/workflows/test-development.yml
index 2283a8abdb..a9f58b251a 100644
--- a/.github/workflows/test-development.yml
+++ b/.github/workflows/test-development.yml
@@ -27,7 +27,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.11", "3.12"]
+        python-version: ["3.11", "3.12", "3.13"]
     name: Linux Python ${{ matrix.python-version }}
     steps:
       - uses: actions/checkout@v4
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index d2369a3041..07d35604a2 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -21,7 +21,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.11", "3.12"]
+        python-version: ["3.11", "3.12", "3.13"]
     name: Linux Python ${{ matrix.python-version }}
     steps:
       - uses: actions/checkout@v4
@@ -34,7 +34,7 @@ jobs:
           python-version: ${{ matrix.python-version }}
           miniforge-version: "latest"
           use-mamba: true
-          mamba-version: "2.0.5"  # https://github.com/conda-incubator/setup-miniconda/issues/392
+          mamba-version: "2.0.8"  # https://github.com/conda-incubator/setup-miniconda/issues/392
       - run: mkdir -p test_linux_artifacts_python_${{ matrix.python-version }}
       - name: Record versions
         run: |
@@ -82,7 +82,7 @@ jobs:
     if: github.repository == 'ESMValGroup/ESMValTool'  # avoid GAs in forks
     strategy:
       matrix:
-        python-version: ["3.11", "3.12"]
+        python-version: ["3.11", "3.12", "3.13"]
         architecture: ["x64"]  # need to force Intel, arm64 builds have issues
       fail-fast: false
     name: OSX Python ${{ matrix.python-version }}
diff --git a/doc/sphinx/source/conf.py b/doc/sphinx/source/conf.py
index de7feb4775..682377468c 100644
--- a/doc/sphinx/source/conf.py
+++ b/doc/sphinx/source/conf.py
@@ -112,6 +112,12 @@
 # The full version, including alpha/beta/rc tags.
 release = __version__
 
+# a lot of issues with importing esmvaltool modules due to
+# "incorrect" locale settings' this looks like a fix
+# see https://github.com/python/cpython/issues/133967
+import locale
+locale.setlocale(locale.LC_ALL, 'C')
+
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
 # language = None
diff --git a/environment.yml b/environment.yml
index 6a8fe6b418..59948524b8 100644
--- a/environment.yml
+++ b/environment.yml
@@ -49,7 +49,7 @@ dependencies:
   - prov
   - pyproj >=2.1
   - pys2index  # only from conda-forge
-  - python >=3.11,<3.13
+  - python >=3.11,<3.14
   - python-cdo
   - python-dateutil
   - pyyaml
diff --git a/environment_osx.yml b/environment_osx.yml
index 44a7b63fcf..10a70bcf89 100644
--- a/environment_osx.yml
+++ b/environment_osx.yml
@@ -49,7 +49,7 @@ dependencies:
   - prov
   - pyproj >=2.1
   - pys2index >=0.1.5  # only from conda-forge; https://github.com/ESMValGroup/ESMValTool/pull/3792
-  - python >=3.11,<3.13
+  - python >=3.11,<3.14
   - python-cdo
   - python-dateutil
   - pyyaml
diff --git a/setup.py b/setup.py
index 1d39c2d12e..5e64149752 100755
--- a/setup.py
+++ b/setup.py
@@ -220,6 +220,7 @@ def read_description(filename):
         "Programming Language :: Python :: 3",
         "Programming Language :: Python :: 3.11",
         "Programming Language :: Python :: 3.12",
+        "Programming Language :: Python :: 3.13",
         "Topic :: Scientific/Engineering",
         "Topic :: Scientific/Engineering :: Atmospheric Science",
         "Topic :: Scientific/Engineering :: GIS",