Clouds aloft
Moist air cools and water condenses or freezes into cloud particles. A cloud can exist without producing snowfall at the ground.
🥶 Snowball Earth
Reduce sunlight and greenhouse warming, then compute the ice-albedo feedback.
Modeled ice expands; snowfall stays regional and moisture-limited.
Building the laboratory: star, orbit, planet, atmosphere...
What actually happens
This experiment gives Earth 94% of its present sunlight, removes the model's greenhouse warming, and keeps cloud cover at Earth's 60% starting value. The energy-balance calculation then iterates temperature, reflectivity, and ice cover until it reaches a much colder equilibrium.
Geology records major Snowball Earth episodes around 700 million years ago, when ice may have reached tropical latitudes. Volcanic carbon dioxide is one proposed route out of those frozen states, but that carbon cycle and the thaw are outside this simulator.
The globe maps the computed global ice fraction onto colder, wetter, and more polar surfaces first. Falling particles appear only where a simplified regional tendency finds cold air, moisture, and cloud together. They explain where snow is plausible, not live weather or the order in which ancient ice sheets grew. Tropical ice in the final picture does not mean that snow is falling everywhere.
How the simulation unfolds
Each step is labeled so you can tell a calculated result from an explanatory visual or wider scientific context.
- Changed input
Weaken the warming inputs
Sunlight is set to 94% of modern Earth and the greenhouse control is set to zero.
- Computed
Ice raises reflectivity
The energy-balance model iterates temperature, albedo, and global ice fraction to a cold equilibrium.
- Illustrated
Cold, moist clouds can make snow
Regional climate tendencies place flakes under suitable cold clouds, while warm lower air makes rain and deeply frozen dry air suppresses snowfall.
- Scientific context
A cold world can also be dry
Ancient tropical ice is plausible, but widespread ice does not imply active snowfall in every region.
How snow forms: clouds, falling snow, and accumulated ice are different
The animation separates what is in the air from what is falling and what has already collected on the surface. Snowfall follows regional climate tendency, not live weather or a forecast for a real place.
Falling snow
Ice crystals grow and fall only where a cold lower atmosphere overlaps plausible moisture. A frozen desert can still be too dry for frequent snow.
Accumulated surface ice
Snow and ice can remain after precipitation stops. Their bright surface reflects more sunlight, reinforcing the modeled ice-albedo feedback.
A mature Snowball Earth can be both globally icy and extremely dry. White ground does not mean snow is actively falling everywhere, and the Sahara is not treated as a permanently snowy region.
What is computed, illustrated, and not modeled
Calculated by the lab
- Average absorbed energy
- Global surface temperature
- Ice fraction and albedo feedback
Shown to explain the result
- Climatology-weighted clouds and snowfall
- Suitability-ranked placement of global ice
Outside this model
- Individual storms or forecasts
- Regional ice-sheet growth
- Carbon-cycle recovery and elapsed time
Model scope: Global ice is computed, while regional snowfall and ice placement use teaching heuristics. This is not live weather or an ancient climate reconstruction.