diff --git a/agenda/stats.py b/agenda/stats.py
index d9bdc51..c98cce9 100644
--- a/agenda/stats.py
+++ b/agenda/stats.py
@@ -9,6 +9,9 @@ from agenda.types import StrDict, Trip
 def travel_legs(trip: Trip, stats: StrDict) -> None:
     """Calculate stats for travel legs."""
     for leg in trip.travel:
+        stats.setdefault("co2_kg", 0)
+        if "co2_kg" in leg:
+            stats["co2_kg"] += leg["co2_kg"]
         if leg["type"] == "flight":
             stats.setdefault("flight_count", 0)
             stats.setdefault("airlines", Counter())
diff --git a/templates/trip/stats.html b/templates/trip/stats.html
index 8644aff..b463fd0 100644
--- a/templates/trip/stats.html
+++ b/templates/trip/stats.html
@@ -44,6 +44,9 @@
         {% endfor %} ]
       {% endif %}
     </div>
+    {% if year_stats.co2_kg %}
+      <div>Flight CO₂: {{ "{:,.1f}".format(year_stats.co2_kg / 1000.0) }} tonnes</div>
+    {% endif %}
     <div>Trains segments in {{ year }}: {{ year_stats.train_count or 0 }}</div>
     <div>Total distance in {{ year}}: {{ format_distance(year_stats.total_distance or 0) }}</div>
     {% if year_stats.distances_by_transport_type %}