diff --git a/half-earth/resources/tile_types/developed.tres b/half-earth/resources/tile_types/developed.tres
index 211c470..70a9358 100644
--- a/half-earth/resources/tile_types/developed.tres
+++ b/half-earth/resources/tile_types/developed.tres
@@ -8,3 +8,4 @@ Name = "Developed"
 BuildLabel = "[D]eveloped"
 Key = 68
 Color = Color( 0.372549, 0.372549, 0.372549, 1 )
+HeatGeneration = 0.1
diff --git a/half-earth/resources/tile_types/wild.tres b/half-earth/resources/tile_types/wild.tres
index 238de57..eae570c 100644
--- a/half-earth/resources/tile_types/wild.tres
+++ b/half-earth/resources/tile_types/wild.tres
@@ -8,3 +8,4 @@ Name = "Wild"
 BuildLabel = "[W]ild"
 Key = 87
 Color = Color( 0, 0.545098, 0.0196078, 1 )
+HeatGeneration = -0.025
diff --git a/half-earth/scripts/WorldGrid.cs b/half-earth/scripts/WorldGrid.cs
index 661b202..d454cb3 100644
--- a/half-earth/scripts/WorldGrid.cs
+++ b/half-earth/scripts/WorldGrid.cs
@@ -40,7 +40,7 @@ public class WorldGrid : Node2D
             {
                 var tile = _tiles[x, y];
                 var material = tile.material;
-                material.SetShaderParam("t", tile.value);
+                material.SetShaderParam("t", tile.temperature);
             }
         }
     }
@@ -100,7 +100,7 @@ public class WorldGrid : Node2D
             {
                 var tile = new Tile();
                 tile.isHighlighted = false;
-                tile.value = 0.0f;
+                tile.temperature = 0.0f;
                 tile.type = _startTileType;
 
                 var node = TileScene.Instance<Node2D>();
@@ -122,6 +122,7 @@ public class WorldGrid : Node2D
 
     public void _on_Clock_OnTick(int ticks)
     {
+        GenerateHeat();
         Diffuse();
     }
 
@@ -135,13 +136,27 @@ public class WorldGrid : Node2D
     private void GetNeighbourTemperatures(int x, int y, out float nx, out float ny, out float px, out float py)
     {
         // default value
-        var t = _tiles[x, y].value;
+        var t = _tiles[x, y].temperature;
 
-        nx = x > 0 ? _tiles[x - 1, y].value : t;
-        px = x < Size - 1 ? _tiles[x + 1, y].value : t;
+        nx = x > 0 ? _tiles[x - 1, y].temperature : t;
+        px = x < Size - 1 ? _tiles[x + 1, y].temperature : t;
 
-        ny = y > 0 ? _tiles[x, y - 1].value : t;
-        py = y < Size - 1 ? _tiles[x, y + 1].value : t;
+        ny = y > 0 ? _tiles[x, y - 1].temperature : t;
+        py = y < Size - 1 ? _tiles[x, y + 1].temperature : t;
+    }
+
+    private void GenerateHeat()
+    {
+        for (int x = 0; x < Size; x++)
+        {
+            for (int y = 0; y < Size; y++)
+            {
+                var tile = _tiles[x, y];
+                var type = tile.type;
+                tile.temperature += type.HeatGeneration;
+                _tiles[x, y] = tile;
+            }
+        }
     }
 
     private void Diffuse()
@@ -150,7 +165,7 @@ public class WorldGrid : Node2D
         {
             for (int y = 0; y < Size; y++)
             {
-                float t = _tiles[x, y].value;
+                float t = _tiles[x, y].temperature;
                 var D = DiffusionCoefficient;
 
                 GetNeighbourTemperatures(
@@ -161,7 +176,10 @@ public class WorldGrid : Node2D
                     out var py);
 
                 // current value
-                _nextValues[x, y] = TransferHeat(t, D, nx, ny, px, py);
+                var temperature = TransferHeat(t, D, nx, ny, px, py);
+                // TODO: what if it's really really cold out?
+                temperature = Mathf.Max(0, temperature);
+                _nextValues[x, y] = temperature;
             }
         }
 
@@ -169,7 +187,7 @@ public class WorldGrid : Node2D
         {
             for (int y = 0; y < Size; y++)
             {
-                _tiles[x, y].value = _nextValues[x, y];
+                _tiles[x, y].temperature = _nextValues[x, y];
             }
         }
     }
diff --git a/half-earth/scripts/tile/Tile.cs b/half-earth/scripts/tile/Tile.cs
index 70560a0..e247129 100644
--- a/half-earth/scripts/tile/Tile.cs
+++ b/half-earth/scripts/tile/Tile.cs
@@ -3,7 +3,7 @@ using Godot;
 public struct Tile
 {
     public bool isHighlighted;
-    public float value;
+    public float temperature;
     public ShaderMaterial material;
     public TileType type;
 }
\ No newline at end of file
diff --git a/half-earth/scripts/tile/TileType.cs b/half-earth/scripts/tile/TileType.cs
index c6dc2ab..8d8e777 100644
--- a/half-earth/scripts/tile/TileType.cs
+++ b/half-earth/scripts/tile/TileType.cs
@@ -14,6 +14,9 @@ public class TileType : Resource
     [Export]
     public Color Color { get; private set; }
 
+    [Export]
+    public float HeatGeneration { get; private set; }
+
     public override string ToString()
     {
         return Name;