diff --git a/.cirrus.yml b/.cirrus.yml
index e7688d22c5..13e95f7397 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -120,6 +120,8 @@ test_minimal_task:
       PY_VER: 3.6
     env:
       PY_VER: 3.7
+    env:
+      PY_VER: 3.8
   name: "${CIRRUS_OS}: py${PY_VER} tests (minimal)"
   container:
     image: gcc:latest
@@ -143,6 +145,8 @@ test_full_task:
       PY_VER: 3.6
     env:
       PY_VER: 3.7
+    env:
+      PY_VER: 3.8
   name: "${CIRRUS_OS}: py${PY_VER} tests (full)"
   container:
     image: gcc:latest
@@ -172,9 +176,7 @@ gallery_task:
   << : *CREDITS_TEMPLATE
   matrix:
     env:
-      PY_VER: 3.6
-    env:
-      PY_VER: 3.7
+      PY_VER: 3.8
   name: "${CIRRUS_OS}: py${PY_VER} doc tests (gallery)"
   container:
     image: gcc:latest
@@ -204,7 +206,7 @@ doctest_task:
   << : *CREDITS_TEMPLATE
   matrix:
     env:
-      PY_VER: 3.7
+      PY_VER: 3.8
   name: "${CIRRUS_OS}: py${PY_VER} doc tests"
   container:
     image: gcc:latest
@@ -240,7 +242,7 @@ linkcheck_task:
   << : *CREDITS_TEMPLATE
   matrix:
     env:
-      PY_VER: 3.7
+      PY_VER: 3.8
   name: "${CIRRUS_OS}: py${PY_VER} doc link check"
   container:
     image: gcc:latest
diff --git a/docs/iris/gallery_code/general/plot_anomaly_log_colouring.py b/docs/iris/gallery_code/general/plot_anomaly_log_colouring.py
index 846816aff7..7a6405b4b0 100644
--- a/docs/iris/gallery_code/general/plot_anomaly_log_colouring.py
+++ b/docs/iris/gallery_code/general/plot_anomaly_log_colouring.py
@@ -68,14 +68,14 @@ def main():
     # Create a 'logarithmic' data normalization.
     anom_norm = mcols.SymLogNorm(
         linthresh=minimum_log_level,
-        linscale=0,
+        linscale=0.01,
         vmin=-maximum_scale_level,
         vmax=maximum_scale_level,
     )
     # Setting "linthresh=minimum_log_level" makes its non-logarithmic
     # data range equal to our 'zero band'.
-    # Setting "linscale=0" maps the whole zero band to the middle colour value
-    # (i.e. 0.5), which is the neutral point of a "diverging" style colormap.
+    # Setting "linscale=0.01" maps the whole zero band to the middle colour value
+    # (i.e., 0.5), which is the neutral point of a "diverging" style colormap.
 
     # Create an Axes, specifying the map projection.
     plt.axes(projection=ccrs.LambertConformal())
diff --git a/docs/iris/src/developers_guide/gitwash/git_links.inc b/docs/iris/src/developers_guide/gitwash/git_links.inc
index f219d013a6..9a87b55d4d 100644
--- a/docs/iris/src/developers_guide/gitwash/git_links.inc
+++ b/docs/iris/src/developers_guide/gitwash/git_links.inc
@@ -28,6 +28,6 @@
 .. _git config: http://schacon.github.com/git/git-config.html
 
 .. _linux git workflow: http://www.mail-archive.com/dri-devel@lists.sourceforge.net/msg39091.html
-.. _deleting master on github: http://matthew-brett.github.com/pydagogue/gh_delete_master.html
+.. _deleting master on github: https://matthew-brett.github.io/pydagogue/gh_delete_master.html
 
 .. |emdash| unicode:: U+02014
diff --git a/docs/iris/src/further_topics/metadata.rst b/docs/iris/src/further_topics/metadata.rst
index e6d6ebc57a..ab6a6450b4 100644
--- a/docs/iris/src/further_topics/metadata.rst
+++ b/docs/iris/src/further_topics/metadata.rst
@@ -258,12 +258,12 @@ create a **new** instance directly from the metadata class itself,
     >>> DimCoordMetadata._make(values)
     DimCoordMetadata(standard_name=1, long_name=2, var_name=3, units=4, attributes=5, coord_system=6, climatological=7, circular=8)
 
-It is also possible to easily convert ``metadata`` to an `OrderedDict`_
+It is also possible to easily convert ``metadata`` to an `dict`_
 using the `namedtuple._asdict`_ method. This can be particularly handy when a
 standard Python built-in container is required to represent your ``metadata``,
 
     >>> metadata._asdict()
-    OrderedDict([('standard_name', 'longitude'), ('long_name', None), ('var_name', 'longitude'), ('units', Unit('degrees')), ('attributes', {'grinning face': '🙃'}), ('coord_system', GeogCS(6371229.0)), ('climatological', False), ('circular', False)])
+    {'standard_name': 'longitude', 'long_name': None, 'var_name': 'longitude', 'units': Unit('degrees'), 'attributes': {'grinning face': '🙃'}, 'coord_system': GeogCS(6371229.0), 'climatological': False, 'circular': False}
 
 Using the `namedtuple._replace`_ method allows you to create a new metadata
 class instance, but replacing specified members with **new** associated values,
@@ -943,7 +943,7 @@ such as a `dict`_,
 
     >>> mapping = latitude.metadata._asdict()
     >>> mapping
-    OrderedDict([('standard_name', 'latitude'), ('long_name', None), ('var_name', 'latitude'), ('units', Unit('degrees')), ('attributes', {}), ('coord_system', GeogCS(6371229.0)), ('climatological', False), ('circular', False)])
+    {'standard_name': 'latitude', 'long_name': None, 'var_name': 'latitude', 'units': Unit('degrees'), 'attributes': {}, 'coord_system': GeogCS(6371229.0), 'climatological': False, 'circular': False}
     >>> longitude.metadata = mapping
     >>> longitude.metadata
     DimCoordMetadata(standard_name='latitude', long_name=None, var_name='latitude', units=Unit('degrees'), attributes={}, coord_system=GeogCS(6371229.0), climatological=False, circular=False)
@@ -1000,7 +1000,6 @@ values. All other metadata members will be left unaltered.
 .. _NetCDF: https://www.unidata.ucar.edu/software/netcdf/
 .. _NetCDF CF Metadata Conventions: https://cfconventions.org/
 .. _NumPy: https://github.com/numpy/numpy
-.. _OrderedDict: https://docs.python.org/3/library/collections.html#collections.OrderedDict
 .. _Parametric Vertical Coordinate: https://cfconventions.org/Data/cf-conventions/cf-conventions-1.8/cf-conventions.html#parametric-vertical-coordinate
 .. _rich comparison: https://www.python.org/dev/peps/pep-0207/
 .. _SciTools/iris: https://github.com/SciTools/iris
diff --git a/docs/iris/src/installing.rst b/docs/iris/src/installing.rst
index fbe59858a4..723c172fac 100644
--- a/docs/iris/src/installing.rst
+++ b/docs/iris/src/installing.rst
@@ -16,8 +16,8 @@ any WSL_ distributions.
 
 .. _WSL: https://docs.microsoft.com/en-us/windows/wsl/install-win10
 
-.. note:: Iris currently supports and is tested against **Python 3.6** and
-          **Python 3.7**.
+.. note:: Iris is currently supported and tested against Python ``3.6``,
+          ``3.7``, and ``3.8``.
 
 
 .. _installing_using_conda:
diff --git a/lib/iris/coords.py b/lib/iris/coords.py
index 76ca83cd96..2f46b529f3 100644
--- a/lib/iris/coords.py
+++ b/lib/iris/coords.py
@@ -579,7 +579,21 @@ def shape(self):
         return self._values_dm.shape
 
     def xml_element(self, doc):
-        """Return a DOM element describing this metadata."""
+        """
+        Create the :class:`xml.dom.minidom.Element` that describes this
+        :class:`_DimensionalMetadata`.
+
+        Args:
+
+        * doc:
+            The parent :class:`xml.dom.minidom.Document`.
+
+        Returns:
+            The :class:`xml.dom.minidom.Element` that will describe this
+            :class:`_DimensionalMetadata`, and the dictionary of attributes
+            that require to be added to this element.
+
+        """
         # Create the XML element as the camelCaseEquivalent of the
         # class name.
         element_name = type(self).__name__
@@ -882,6 +896,20 @@ def cube_dims(self, cube):
         return cube.cell_measure_dims(self)
 
     def xml_element(self, doc):
+        """
+        Create the :class:`xml.dom.minidom.Element` that describes this
+        :class:`CellMeasure`.
+
+        Args:
+
+        * doc:
+            The parent :class:`xml.dom.minidom.Document`.
+
+        Returns:
+            The :class:`xml.dom.minidom.Element` that describes this
+            :class:`CellMeasure`.
+
+        """
         # Create the XML element as the camelCaseEquivalent of the
         # class name
         element = super().xml_element(doc=doc)
@@ -2229,14 +2257,26 @@ def nearest_neighbour_index(self, point):
         return result_index
 
     def xml_element(self, doc):
-        """Return a DOM element describing this Coord."""
+        """
+        Create the :class:`xml.dom.minidom.Element` that describes this
+        :class:`Coord`.
+
+        Args:
+
+        * doc:
+            The parent :class:`xml.dom.minidom.Document`.
+
+        Returns:
+            The :class:`xml.dom.minidom.Element` that will describe this
+            :class:`DimCoord`, and the dictionary of attributes that require
+            to be added to this element.
+
+        """
         # Create the XML element as the camelCaseEquivalent of the
         # class name
         element = super().xml_element(doc=doc)
 
-        element.setAttribute("points", self._xml_array_repr(self.points))
-
-        # Add bounds handling
+        # Add bounds, points are handled by the parent class.
         if self.has_bounds():
             element.setAttribute("bounds", self._xml_array_repr(self.bounds))
 
@@ -2613,7 +2653,20 @@ def is_monotonic(self):
         return True
 
     def xml_element(self, doc):
-        """Return DOM element describing this :class:`iris.coords.DimCoord`."""
+        """
+        Create the :class:`xml.dom.minidom.Element` that describes this
+        :class:`DimCoord`.
+
+        Args:
+
+        * doc:
+            The parent :class:`xml.dom.minidom.Document`.
+
+        Returns:
+            The :class:`xml.dom.minidom.Element` that describes this
+            :class:`DimCoord`.
+
+        """
         element = super().xml_element(doc)
         if self.circular:
             element.setAttribute("circular", str(self.circular))
@@ -2754,7 +2807,17 @@ def __add__(self, other):
 
     def xml_element(self, doc):
         """
-        Return a dom element describing itself
+        Create the :class:`xml.dom.minidom.Element` that describes this
+        :class:`CellMethod`.
+
+        Args:
+
+        * doc:
+            The parent :class:`xml.dom.minidom.Document`.
+
+        Returns:
+            The :class:`xml.dom.minidom.Element` that describes this
+            :class:`CellMethod`.
 
         """
         cellMethod_xml_element = doc.createElement("cellMethod")
diff --git a/lib/iris/cube.py b/lib/iris/cube.py
index c3f77c9288..f280891fde 100644
--- a/lib/iris/cube.py
+++ b/lib/iris/cube.py
@@ -225,6 +225,7 @@ def __getslice__(self, start, stop):
 
     def xml(self, checksum=False, order=True, byteorder=True):
         """Return a string of the XML that this list of cubes represents."""
+
         doc = Document()
         cubes_xml_element = doc.createElement("cubes")
         cubes_xml_element.setAttribute("xmlns", XML_NAMESPACE_URI)
@@ -239,6 +240,7 @@ def xml(self, checksum=False, order=True, byteorder=True):
         doc.appendChild(cubes_xml_element)
 
         # return our newly created XML string
+        doc = Cube._sort_xml_attrs(doc)
         return doc.toprettyxml(indent="  ")
 
     def extract(self, constraints):
@@ -755,6 +757,59 @@ class Cube(CFVariableMixin):
     #: is similar to Fortran or Matlab, but different than numpy.
     __orthogonal_indexing__ = True
 
+    @classmethod
+    def _sort_xml_attrs(cls, doc):
+        """
+        Takes an xml document and returns a copy with all element
+        attributes sorted in alphabetical order.
+
+        This is a private utility method required by iris to maintain
+        legacy xml behaviour beyond python 3.7.
+
+        Args:
+
+        * doc:
+            The :class:`xml.dom.minidom.Document`.
+
+        Returns:
+            The :class:`xml.dom.minidom.Document` with sorted element
+            attributes.
+
+        """
+        from xml.dom.minidom import Document
+
+        def _walk_nodes(node):
+            """Note: _walk_nodes is called recursively on child elements."""
+
+            # we don't want to copy the children here, so take a shallow copy
+            new_node = node.cloneNode(deep=False)
+
+            # Versions of python <3.8 order attributes in alphabetical order.
+            # Python >=3.8 order attributes in insert order.  For consistent behaviour
+            # across both, we'll go with alphabetical order always.
+            # Remove all the attribute nodes, then add back in alphabetical order.
+            attrs = [
+                new_node.getAttributeNode(attr_name).cloneNode(deep=True)
+                for attr_name in sorted(node.attributes.keys())
+            ]
+            for attr in attrs:
+                new_node.removeAttributeNode(attr)
+            for attr in attrs:
+                new_node.setAttributeNode(attr)
+
+            if node.childNodes:
+                children = [_walk_nodes(x) for x in node.childNodes]
+                for c in children:
+                    new_node.appendChild(c)
+
+            return new_node
+
+        nodes = _walk_nodes(doc.documentElement)
+        new_doc = Document()
+        new_doc.appendChild(nodes)
+
+        return new_doc
+
     def __init__(
         self,
         data,
@@ -3399,6 +3454,7 @@ def xml(self, checksum=False, order=True, byteorder=True):
         doc.appendChild(cube_xml_element)
 
         # Print our newly created XML
+        doc = self._sort_xml_attrs(doc)
         return doc.toprettyxml(indent="  ")
 
     def _xml_element(self, doc, checksum=False, order=True, byteorder=True):
diff --git a/lib/iris/plot.py b/lib/iris/plot.py
index 349f1fea10..b0159af9d6 100644
--- a/lib/iris/plot.py
+++ b/lib/iris/plot.py
@@ -1073,6 +1073,18 @@ def contourf(cube, *args, **kwargs):
             # any boundary shift.
             zorder = result.collections[0].zorder - 0.1
             axes = kwargs.get("axes", None)
+
+            # Workaround for cartopy#1780.  We do not want contour to shrink
+            # extent.
+            if axes is None:
+                _axes = plt.gca()
+            else:
+                _axes = axes
+
+            # Subsequent calls to dataLim.update_from_data_xy should not ignore
+            # current extent.
+            _axes.dataLim.ignore(False)
+
             contour(
                 cube,
                 levels=levels,
diff --git a/lib/iris/tests/__init__.py b/lib/iris/tests/__init__.py
index ac0d313d76..4a85e5cdb2 100644
--- a/lib/iris/tests/__init__.py
+++ b/lib/iris/tests/__init__.py
@@ -573,6 +573,10 @@ def assertXMLElement(self, obj, reference_filename):
         """
         doc = xml.dom.minidom.Document()
         doc.appendChild(obj.xml_element(doc))
+        # sort the attributes on xml elements before testing against known good state.
+        # this is to be compatible with stored test output where xml attrs are stored in alphabetical order,
+        # (which was default behaviour in python <3.8, but changed to insert order in >3.8)
+        doc = iris.cube.Cube._sort_xml_attrs(doc)
         pretty_xml = doc.toprettyxml(indent="  ")
         reference_path = self.get_result_path(reference_filename)
         self._check_same(
diff --git a/lib/iris/tests/results/analysis/sqrt.cml b/lib/iris/tests/results/analysis/sqrt.cml
index c6b9b88e9a..f8a1c48fc3 100644
--- a/lib/iris/tests/results/analysis/sqrt.cml
+++ b/lib/iris/tests/results/analysis/sqrt.cml
@@ -39,6 +39,6 @@
       </coord>
     </coords>
     <cellMethods/>
-    <data checksum="0x09ef96ca" dtype="float64" shape="(73, 96)"/>
+    <data dtype="float64" shape="(73, 96)" state="loaded"/>
   </cube>
 </cubes>
diff --git a/lib/iris/tests/results/imagerepo.json b/lib/iris/tests/results/imagerepo.json
index a7fd9e1faf..9ec5cf83fb 100644
--- a/lib/iris/tests/results/imagerepo.json
+++ b/lib/iris/tests/results/imagerepo.json
@@ -145,11 +145,11 @@
     ],
     "gallery_tests.test_plot_wind_speed.TestWindSpeed.test_plot_wind_speed.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/bcf924fb9306930ce12ccf97c73236b28ecec4cd3e29847b18e639e6c14f1a09.png",
-        "https://scitools.github.io/test-iris-imagehash/images/v4/e9e960e996169306c1ee9e96c29e36739e13c07d3d61c07f39a139a1c07f3f01.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/e9e960e996169306c1fe9e96c29e36739e13c06c3d61c07f39a139e1c07f3f01.png"
     ],
     "gallery_tests.test_plot_wind_speed.TestWindSpeed.test_plot_wind_speed.1": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/bcf924fb9306930ce12ccf97c73236b28ecec4cc3e29847b38e639e6c14f1a09.png",
-        "https://scitools.github.io/test-iris-imagehash/images/v4/e9e960e996169306c1ee9e86c29e36739e13c07d3d61c07f39a139a1c17f3f01.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/e9e960e996169306c1ee9e96c29e36739653c06c3d61c07f3da139e1c07f3f01.png"
     ],
     "iris.tests.experimental.test_animate.IntegrationTest.test_cube_animation.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/fe81957ac17e6a85817e6a85857e942a3e81957a7e81917a7a81d95ec17e2ca1.png",
@@ -210,13 +210,15 @@
     ],
     "iris.tests.test_mapping.TestBoundedCube.test_pcolormesh.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/fa81e535857e92ca8ec23d21b13ce15e7a811ea5c47e1a5ac17b652d3b05e4f2.png",
-        "https://scitools.github.io/test-iris-imagehash/images/v4/fa81c17a857e1ea5857e634a7a81cd257e8584da857e3b29817e68f47a81c791.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/fa81c17a857e1ea5857e634a7a81cd257e8584da857e3b29817e68f47a81c791.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/fa81c17a857e1ea5857e734a7a81cd257e8484da857e3b29817a68f47a81c799.png"
     ],
     "iris.tests.test_mapping.TestLimitedAreaCube.test_grid.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/bf80e2b1c17f1d0ac4f7c8d739a637202749699b6bb3ce3666e4b048944d9d89.png",
         "https://scitools.github.io/test-iris-imagehash/images/v4/bf80e2f1c17f1d0ac457c8d619a637213749699b6bb34e3666e4b04e944d9d89.png",
         "https://scitools.github.io/test-iris-imagehash/images/v4/ea05392995bac6d691ce3f21666569d86a96c6360ee195cb91e8ce54953b313b.png",
-        "https://scitools.github.io/test-iris-imagehash/images/v4/ea05392995bac6d691ea3f21666569d86a97c6320ee195cb91e8ce559539391b.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/ea05392995bac6d691ea3f21666569d86a97c6320ee195cb91e8ce559539391b.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/fa1585e885ea7a1785fa7a157a177a017a1585e817a885ea85e86a1785fa7a17.png"
     ],
     "iris.tests.test_mapping.TestLimitedAreaCube.test_outline.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/fa81857e857e3e80857e7a817a817a817a81817f7a81857e857e857e857e7a81.png",
@@ -226,7 +228,8 @@
     ],
     "iris.tests.test_mapping.TestLimitedAreaCube.test_pcolormesh.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/bf81e6b1c17e1d4884bfc8df39a43720374969db69b34e26c4e4b0ca904f9d89.png",
-        "https://scitools.github.io/test-iris-imagehash/images/v4/ea57396995a8c6d691ea3f25664569d86b16c63686ed958991ea4a549531393b.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/ea57396995a8c6d691ea3f25664569d86b16c63686ed958991ea4a549531393b.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/ea57396995a8c6d691ea3e25664569d96b16c63684e9958b91ea4a559431793b.png"
     ],
     "iris.tests.test_mapping.TestLimitedAreaCube.test_scatter.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/ea053d2e916ac2d9c4d894346b24f3477acf68ad39329ed8c696e136c1ab9a71.png",
@@ -257,7 +260,8 @@
     "iris.tests.test_mapping.TestLowLevel.test_simple.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/eae0943295154bcc844e6c314fb093ce7bc7c4b3a4307bc4916f3f316ed2b4ce.png",
         "https://scitools.github.io/test-iris-imagehash/images/v4/faa0e55c855fdce7857a1ab16a85a50c3ea1e55e856658a5c11837096e8fe17a.png",
-        "https://scitools.github.io/test-iris-imagehash/images/v4/faa0e55c855fdce7857a1ab16a85a50c36a1e55e854658b5c13837096e8fe17a.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/faa0e55c855fdce7857a1ab16a85a50c36a1e55e854658b5c13837096e8fe17a.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/faa0e558855fd9e7857a1ab16a85a51d36a1e55a854e58a5c13837096e8fe17a.png"
     ],
     "iris.tests.test_mapping.TestMappingSubRegion.test_simple.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/bd913e01d07ee07e926e87876f8196c1e0d36967393c1f181e2c3cb8b0f960d7.png",
@@ -395,7 +399,8 @@
     ],
     "iris.tests.test_plot.TestAttributePositive.test_2d_positive_down.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/fb946ba684e194fb901b3a0587641ad03b1ae7674e64c15a5b99c767c47e3a98.png",
-        "https://scitools.github.io/test-iris-imagehash/images/v4/fb946ba484e194dbc01f3665c0e4399a3f0fc2653f90c99e3f613e64c81e3f81.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/fb946ba484e194dbc01f3665c0e4399a3f0fc2653f90c99e3f613e64c81e3f81.png",
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@@ -588,7 +594,8 @@
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@@ -600,7 +607,8 @@
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@@ -618,7 +627,8 @@
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@@ -677,23 +687,27 @@
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@@ -815,7 +831,8 @@
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@@ -846,10 +863,12 @@
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+        "https://scitools.github.io/test-iris-imagehash/images/v4/be816a95907ae508c17e955ac07f3fa0945bc07f3f80c07f3aa36f01c0ff3f80.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/be816ab5907ae508c17e955ac07f3fa0945ac07f3f80c07f3aa32f81c0ff3f80.png"
     ],
     "iris.tests.test_quickplot.TestLabels.test_contourf_nameless.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/faa52ec1955ac536c0bf9e09c57edae69357e13f4e80c0da2f81618493da3f01.png",
-        "https://scitools.github.io/test-iris-imagehash/images/v4/be816af5907ee508c17e955ac03f3f809419c07f3f80c07f3a8b6f81c0ff3f80.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/be816af5907ee508c17e955ac03f3f809419c07f3f80c07f3a8b6f81c0ff3f80.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/be816ab5907ee508c17e975ac07f3fa09459c07f3f80c07f3a812f81c0ff3f80.png"
     ],
     "iris.tests.test_quickplot.TestLabels.test_map.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/ea5e618434ac36e5c1c9369b95b39c38c3a39a4fcee19a6e9b64cb609925cd25.png",
@@ -902,36 +928,45 @@
     ],
     "iris.tests.test_quickplot.TestLabels.test_pcolor.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/bb423d4e94a5c6b9c15adaadc1fb6a469c8de43a3e07904e5f016b57984e1ea1.png",
-        "https://scitools.github.io/test-iris-imagehash/images/v4/eea16affc05ab500956e974ac53f3d80925ac03f2f81c07e3fa12da1c2fe3f80.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/eea16affc05ab500956e974ac53f3d80925ac03f2f81c07e3fa12da1c2fe3f80.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/eea16abfc05ab500956e974ac13f3da0925ac07f3fa1c07e3fa12da1c25e3f80.png"
     ],
     "iris.tests.test_quickplot.TestLabels.test_pcolormesh.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/bb433d4e94a4c6b9c15adaadc1fb6a469c8de43a3e07904e5f016b57984e1ea1.png",
-        "https://scitools.github.io/test-iris-imagehash/images/v4/eea16affc05ab500956e974ac53f3d80925ac03f3f81c07e3fa12da1c27e3f80.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/eea16affc05ab500956e974ac53f3d80925ac03f3f81c07e3fa12da1c27e3f80.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/eea16abfc05ab500956e974ac13f3da0925ac07f3fa1c07e3fa12da1c25e3f80.png"
     ],
     "iris.tests.test_quickplot.TestLabels.test_pcolormesh_str_symbol.0": [
-        "https://scitools.github.io/test-iris-imagehash/images/v4/eea16affc05ab500956e974ac53f3d80925ac03f3f80c07e3fa12da1c27f3f80.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/eea16affc05ab500956e974ac53f3d80925ac03f3f80c07e3fa12da1c27f3f80.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/eea16abfc05ab500956e974ac13f3da0925ac07f3fa1c07e3fa12da1c25e3f80.png"
     ],
     "iris.tests.test_quickplot.TestQuickplotCoordinatesGiven.test_non_cube_coordinate.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/fa816a85857a955ae17e957ec57e7a81855fc17e3a81c57e1a813a85c57a1a05.png",
         "https://scitools.github.io/test-iris-imagehash/images/v4/fe816a85857a957ac07f957ac07f3e80956ac07f3e80c07f3e813e85c07e3f80.png"
     ],
     "iris.tests.test_quickplot.TestQuickplotCoordinatesGiven.test_tx.0": [
-        "https://scitools.github.io/test-iris-imagehash/images/v4/ea856a95955a956ac17f950a807e3f4c951ac07e3f81c0ff3ea16aa1c0bd3f81.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/ea856a95955a956ac17f950a807e3f4c951ac07e3f81c0ff3ea16aa1c0bd3f81.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/ea856a95955a954ac17f950ac07e3f44951ac07e3f81c0ff3ea16aa1c0ff3e81.png"
     ],
     "iris.tests.test_quickplot.TestQuickplotCoordinatesGiven.test_tx.1": [
-        "https://scitools.github.io/test-iris-imagehash/images/v4/fa856a85957a957ac17e954ac17e1ca2950bc07e3e80c07f3e807a85c1ff3f81.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/fa856a85957a957ac17e954ac17e1ca2950bc07e3e80c07f3e807a85c1ff3f81.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/fa856a85957a957ac17e954ac17e0da2954bc07e3e81c07f3a806a85c1ff3f81.png"
     ],
     "iris.tests.test_quickplot.TestQuickplotCoordinatesGiven.test_tx.2": [
-        "https://scitools.github.io/test-iris-imagehash/images/v4/eafdeec9f729943032168d66d4cb896e9567497b81304aedc96514ad8d18669a.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/eafdeec9f729943032168d66d4cb896e9567497b81304aedc96514ad8d18669a.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/eaf9a6c9f728943032168d66d4cb8d2e9567497b81304aedc9e51e2d9d186ada.png"
     ],
     "iris.tests.test_quickplot.TestQuickplotCoordinatesGiven.test_tx.3": [
-        "https://scitools.github.io/test-iris-imagehash/images/v4/a6fb4b967f00950eb00f9d0f900fcd62dc7868f2c1bb3a909c266e34daa52f6c.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/a6fb4b967f00950eb00f9d0f900fcd62dc7868f2c1bb3a909c266e34daa52f6c.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/a6fa1e967f00950eb00f9d0f914fcdc2d560c9f3c1fb3a9084266e34daa52f6c.png"
     ],
     "iris.tests.test_quickplot.TestQuickplotCoordinatesGiven.test_tx.4": [
-        "https://scitools.github.io/test-iris-imagehash/images/v4/eaa9b549f756854ea0168d6ed556896dd8e909ed88290afdd9e97e008d6e2296.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/eaa9b549f756854ea0168d6ed556896dd8e909ed88290afdd9e97e008d6e2296.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/eaa9b529f756850ea0169566d1568d6dd86909ed88290afd9ded7e008d666ad6.png"
     ],
     "iris.tests.test_quickplot.TestQuickplotCoordinatesGiven.test_tx.5": [
-        "https://scitools.github.io/test-iris-imagehash/images/v4/aad73e0df78085ac840395ac9428d9fad56cd8f2906c48f2d0ec7a536a1737f3.png"
+        "https://scitools.github.io/test-iris-imagehash/images/v4/aad73e0df78085ac840395ac9428d9fad56cd8f2906c48f2d0ec7a536a1737f3.png",
+        "https://scitools.github.io/test-iris-imagehash/images/v4/aad73e0cf710952c840195acd528c1e2d1ecc9f3c1ec49f3c1ec6a536a1737f3.png"
     ],
     "iris.tests.test_quickplot.TestQuickplotCoordinatesGiven.test_x.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/a6ffb5097e84cde2224598d1649f8d6cd2388c76d0799867d009da76c9f8d866.png",
@@ -1025,4 +1060,4 @@
         "https://scitools.github.io/test-iris-imagehash/images/v4/82fe81987fdf77ffe0002addd4002805dd28df67d9a9d4625bfddc209841de20.png",
         "https://scitools.github.io/test-iris-imagehash/images/v4/82fa80997f547799a0037a00d52f0956ddaf9f7e98a1816e09f5d8260bfffe00.png"
     ]
-}
+}
\ No newline at end of file
diff --git a/lib/iris/tests/test_basic_maths.py b/lib/iris/tests/test_basic_maths.py
index c4d7b51a06..2d045c684f 100644
--- a/lib/iris/tests/test_basic_maths.py
+++ b/lib/iris/tests/test_basic_maths.py
@@ -554,8 +554,8 @@ def test_square_root(self):
 
         e = a ** 0.5
 
-        self.assertArrayEqual(e.data, a.data ** 0.5)
-        self.assertCML(e, ("analysis", "sqrt.cml"))
+        self.assertArrayAllClose(e.data, a.data ** 0.5)
+        self.assertCML(e, ("analysis", "sqrt.cml"), checksum=False)
         self.assertRaises(ValueError, iris.analysis.maths.exponentiate, a, 0.3)
 
     def test_type_error(self):
diff --git a/noxfile.py b/noxfile.py
index 7bfcc73dd7..dc365b59d7 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -19,7 +19,7 @@
 PACKAGE = str("lib" / Path("iris"))
 
 #: Cirrus-CI environment variable hook.
-PY_VER = os.environ.get("PY_VER", ["3.6", "3.7"])
+PY_VER = os.environ.get("PY_VER", ["3.6", "3.7", "3.8"])
 
 #: Default cartopy cache directory.
 CARTOPY_CACHE_DIR = os.environ.get("HOME") / Path(".local/share/cartopy")
diff --git a/requirements/ci/iris.yml b/requirements/ci/iris.yml
index e9adb956db..a76932b56e 120000
--- a/requirements/ci/iris.yml
+++ b/requirements/ci/iris.yml
@@ -1 +1 @@
-py37.yml
\ No newline at end of file
+py38.yml
\ No newline at end of file
diff --git a/requirements/ci/py38.yml b/requirements/ci/py38.yml
new file mode 100644
index 0000000000..da29d30d71
--- /dev/null
+++ b/requirements/ci/py38.yml
@@ -0,0 +1,51 @@
+name: iris-dev
+
+channels:
+  - conda-forge
+
+dependencies:
+  - python=3.8
+
+# Setup dependencies.
+  - setuptools>=40.8.0
+  - pyke
+
+# Core dependencies.
+  - cartopy>=0.18
+  - cf-units>=2
+  - cftime<1.3.0
+  - dask>=2
+  - matplotlib
+  - netcdf4
+  - numpy>=1.14
+  - python-xxhash
+  - scipy
+
+# Optional dependencies.
+  - esmpy>=7.0
+  - graphviz
+  - iris-sample-data
+  - mo_pack
+  - nc-time-axis
+  - pandas
+  - python-stratify
+  - pyugrid
+
+# Test dependencies.
+  - asv
+  - black=20.8b1
+  - filelock
+  - flake8
+  - imagehash>=4.0
+  - nose
+  - pillow<7
+  - pre-commit
+  - requests
+
+# Documentation dependencies.
+  - sphinx
+  - sphinxcontrib-napoleon
+  - sphinx-copybutton
+  - sphinx-gallery
+  - sphinx-panels
+  - sphinx_rtd_theme