Seasons and sea ice

A world with monthly climate renders through its year. Twelve months of temperature and precipitation decide how wet the ground is, how green the low vegetation looks and where snow lies, and the sea freezes and thaws with them. Monthly climate comes from a World Climate Lab import: see Working on a globe for bringing one in.

The planet above was generated in Gleba, with climate from World Climate Lab. Dayside rendered the colour.

Climate month#

Climate month sits in the Colour group of the section editor, in the Colour section of the Whole-world passes dialog, and beside the World Climate Lab row under Source maps. It offers Annual and Month 1 to Month 12.

• The twelve months are equal parts of the planet's year, starting at its January-equivalent orbital position. A planet with a longer or shorter year keeps twelve months, each covering a twelfth of its year.
• Monthly temperature and precipitation drive ground moisture, the condition of low vegetation and snow cover. Annual keeps the year-round appearance.
• Vegetation follows the climate with a 45-day response, and the cycle wraps from month 12 back to month 1, so green-up lags the warmth that drives it.
• Climate is worked out at up to 1024 × 512 for the whole world and laid onto the section, so monthly patterns are broad.
• A world without monthly data renders the annual appearance and says so in the render's warnings: Climate month requested without WCL monthly maps; using annual appearance.

The monthly model is an appearance model. It runs a repeated climatological year with a bounded soil-water store and degree-month snowmelt. It does not simulate weather, individual frosts or glacier dynamics.

While a month is selected, Vegetation state is greyed out, because the month already decides how green the vegetation is.

Play seasonal previews#

Play seasonal previews, under Climate month in the section editor, renders each month in order and holds each one for 0.75 seconds. Pause seasonal playback keeps the current month; a render that has already started is allowed to finish.

Inspect climate and export masks#

Inspect climate & export masks is a collapsible panel in the section editor's Colour group, and in the World Climate Lab row of Source maps for the whole world. Choose a climate month first; the panel then shows the selected field for that month.

• Climate field picks the field to inspect: Temperature at WCL terrain, Total precipitation, Soil moisture, Vegetation greenness, Snow cover, the snow and growing-month summaries, and the monthly, annual, minimum and maximum sea-ice fields.
• Play climate maps steps through the months for that field, holding each loaded month for 0.75 seconds. Choosing a month by hand pauses it.
• Show on globe / map draws the field over the globe or flat map, with Overlay opacity. While shown, the climate overlay takes precedence over the guide and settlement overlays.
• Download climate masks saves a ZIP of 16-bit PNG maps for the selected month, each with a file giving its units and a mask of where it is valid.
• Download all 12 months + GIF saves every climate field for the whole year, with a looping preview of the selected field.
• Download field GIF saves just the animation. GIF previews use 256 colours; the numeric maps keep full 16-bit precision.

The masks use the World Climate Lab terrain and climate resolution rather than the section's own pixel grid.

Seasonal exports#

A section export can write a whole year, or chosen months, in one job, each month in its own folder with a looping GIF preview. Choose Climate sequence in the export dialog. The details are in Exporting.

Sea ice#

Sea ice only ever appears on the ocean. Ice that stays frozen all year forms a solid pack crossed by long leads; ice that lasts part of the year, and ice near open water, breaks into floes. The floes themselves are procedural: their pattern is generated from the ice share, so a map says where ice is and how much of the sea it covers, and the render draws the pack, the leads and the floes.

Where the ice comes from#

A world can take its ice from three places.

1. A World Climate Lab import. When the import carries twelve monthly ice maps, each climate month draws its own. When it carries only the annual snow and ice cover, Dayside estimates each month from that annual fraction and the monthly air temperature: freezing ramps in between -1.8 °C and -9.8 °C, with a 60-day lag for delayed freeze and thaw, and the annual mean is held to the imported coverage wherever the temperatures support ice.
2. An uploaded map. Under Source maps, Sea ice · optional takes a 2:1 greyscale PNG, 8 or 16 bit. Read it as a Mask (black open water, white ice, greys fade the ice out) or as Ice fraction (each grey is the share of the sea covered, drawn as pack ice with openings). World Climate Lab's snow_ice_cover.png is an ice-fraction map.
3. Painted ice. The Sea ice layer of the globe's World brush paints a share of ice from 0 to 100%, over ocean only. Apply sea ice publishes it over the world's own ice in every month; unpainted sea keeps the ice it has. Remove painted ice takes it back off and leaves uploaded or imported ice untouched.

An uploaded map is the same in every month. On a world that already has seasonal ice from World Climate Lab, the upload row warns you:

• with estimated seasonal ice: THIS WORLD HAS SEASONAL ICE FROM WCL · AN UPLOAD REPLACES IT IN EVERY MONTH, and the seasons are lost until you remove the upload;
• with twelve monthly ice maps: THIS WORLD HAS MONTHLY ICE FROM WCL · AN UPLOAD ONLY SHOWS IN THE ANNUAL VIEW.

To change ice in every month on such a world, paint it with the world brush instead.

The Sea ice group#

The section editor's Sea ice group sits between Sea and Snow & ice. The same dials appear in the Sea section of the Whole-world passes dialog for the globe.

Under Advanced:

Reset sea ice returns every dial to its default.