Temperature (Below Zero)

The temperature in Subnautica: Below Zero is a major environmental game mechanic that the player must manage. Extreme temperatures (both hot and cold) are harmful to the player.

Temperatures and rate of exposure can be affected by the weather conditions. The current weather and forecast can be seen in a base Control Room. Robin's current warmth is indicated by a temperature gauge in the HUD. This gauge will switch places with the Oxygen gauge when the player is in a cold environment.

Robin also indicates her temperature through rubbing her hands and making teeth-chattering sounds.

Cold
Certain consumables boost the player's warmth, such as the Spicy Fruit Salad, Fevered Pepper and the Thermos. Thermal Lilies, Steam Vents and hot springs can be found on the surface to provide warmth to the player.

The Cold Suit exists to protect the player from low temperatures, and the PDA will warn the player about cold weather and hypothermia (extremely low heat in the body)

Heat
The player starts taking damage from temperatures above 50°C. The UI will indicate that the player is too hot by showing glowing orange lines on the edges of the screen. The player can increase their thermal resistance to 70°C if they are wearing a Reinforced Dive Suit.

Energy Generation
High temperatures can be used to generate energy for Seabases through the Thermal Plant; because these are external generators that have to be placed at specific locations to work (any source above 25°C, which can be found in the HUD of the Prawn Suit or on the Thermal Plant), the Seabase needs to be close, or otherwise connected via Power Transmitters.

The Prawn Suit can generate energy from heat using the Thermal Reactor upgrade (any source above 30°C).

Fumaroles
Fumaroles are large volcanic structures found only in the Purple Vents and Deep Purple Vents biomes. They can be seen bursting from their rocky shell and spewing a violet stream of smoke. Unlike most thermal structures in Below Zero, the Fumaroles will burn the player when they are close to them.

Hot Springs
Hot springs are flatbeds of water located all over the Delta Island. Some hot springs contain Crystalline Sulfur lining their edges. When standing in a Hot Spring the player’s temperature increases.

Hydrothermal Spires
Hydrothermal Spires are a type of hydrothermal Vent; chimney-like structures that emit black material resembling smoke. They are found commonly in the Thermal Spires and the Thermal Spires Caves and in lower number in the Crystal Caves, East Arctic, Koppa Mining Site, Tree Spires and near Marguerit Maida's Base. They produce heat that can be harnessed for energy, but are not harmful to the player.

Hydrothermal Vents
Hydrothermal Vents are large, narrow thermal structures located in the Arctic Kelp Caves, Crystal Caves, Deep Twisty Bridges, and the underwater portion of the Glacial Basin. The area around Hydrothermal Vents is generally charred, showing their extreme heat output. Many vents have nearby resources such as Diamond, Lithium, Magnetite, or Gold Outcrops. It is unknown what effect Hydrothermal Vents will have on the player in the future, but they will likely act similarly to geysers.

Lava Geysers
Lava Geysers are areas of the ocean floor that spew out lava and steam. Every few seconds, the craters erupt, throwing steam and chunks of lava into the waters surrounding them. They can only be observed from a distance, as their eruptions will cause massive damage to the player if they get too close. Approaching the area near a Lava Geyser can hurt the player due to the extreme amount of heat they put out.

Steam Vents
Steam Vents are surface vents channeling gas out from underground pockets. The vents are only active for a few seconds at a time, and intermittently start and stop spewing gas. The player can use these vents to increase their Temperature by standing on or near them. Steam Vents can also be used to launch the Snowfox in the air.

Thermal Lilies
Thermal Liliess are land-dwelling Flora species found near Outpost Zero, on Delta Island, and on various floating icebergs in the Shallow Twisty Bridges and both Arctic biomes. When a player is not near them they remain dormant with their petals folded around their eye. However, when the player approaches them, they will stare at the player and emit heat. If the player is too close to a Thermal Lily, it will slowly burn them.

Tree Spires
Tree Spires are large, heat sources that can be found exclusively in the Tree Spires biome and neighboring areas. They behave similarly to Hydrothermal Spires, spewing black smog and creating heat, though not being harmful to the player.