diff --git a/cmd/esc/cli/cli_test.go b/cmd/esc/cli/cli_test.go
index bcb65279..859aa82e 100644
--- a/cmd/esc/cli/cli_test.go
+++ b/cmd/esc/cli/cli_test.go
@@ -1203,7 +1203,8 @@ func (c *testPulumiClient) EnvironmentExists(
 	projectName string,
 	envName string,
 ) (bool, error) {
-	return false, nil
+	_, ok := c.environments[path.Join(orgName, projectName, envName)]
+	return ok, nil
 }
 
 func (c *testPulumiClient) CreateEnvironmentOpenRequest(
diff --git a/cmd/esc/cli/env.go b/cmd/esc/cli/env.go
index cf67cee6..065ee0b4 100644
--- a/cmd/esc/cli/env.go
+++ b/cmd/esc/cli/env.go
@@ -109,6 +109,14 @@ func (r *environmentRef) String() string {
 	return s
 }
 
+func (cmd *envCommand) warnIfAmbiguousTwoPartRef(refString string) {
+	fmt.Fprintf(
+		cmd.esc.stderr,
+		"warning: environment reference %q is ambiguous (could be <project>/<environment> or <org>/default/<environment>); prefer <org>/<project>/<environment>.\n",
+		refString,
+	)
+}
+
 func (cmd *envCommand) parseRef(refStr string) environmentRef {
 	var orgName, projectName, envNameAndVersion string
 
@@ -223,6 +231,10 @@ func (cmd *envCommand) getNewEnvRef(
 		}
 	}
 
+	if existsLegacyPath {
+		cmd.warnIfAmbiguousTwoPartRef(cmd.envNameFlag)
+	}
+
 	if !existsProject && existsLegacyPath {
 		return legacyRef, args, nil
 	}
@@ -279,6 +291,10 @@ func (cmd *envCommand) getExistingEnvRefWithRelative(
 		legacyRef.envName,
 	)
 
+	if existsLegacyPath {
+		cmd.warnIfAmbiguousTwoPartRef(refString)
+	}
+
 	// Require unambiguous path if both paths exist
 	if exists && existsLegacyPath {
 		return ref, ambiguousIdentifierError{
diff --git a/cmd/esc/cli/testdata/env-ambiguous-two-part-warning.yaml b/cmd/esc/cli/testdata/env-ambiguous-two-part-warning.yaml
new file mode 100644
index 00000000..6719a996
--- /dev/null
+++ b/cmd/esc/cli/testdata/env-ambiguous-two-part-warning.yaml
@@ -0,0 +1,15 @@
+run: |
+  esc env get test-org/env --definition
+environments:
+  test-org/default/env:
+    values:
+      string: esc
+
+---
+> esc env get test-org/env --definition
+values:
+  string: esc
+
+---
+> esc env get test-org/env --definition
+warning: environment reference "test-org/env" is ambiguous (could be <project>/<environment> or <org>/default/<environment>); prefer <org>/<project>/<environment>.