# How a giant floating landmass might affect the weather?

I'm building up a world with floating islands. They don't move much and generally stay around the same area. However, would this affect the weather?

Essentially, I have giant floating rocks in the atmosphere(similar to earth) which will not go higher than 14 km above sea level. The mechanics behind the floating islands do not affect anything other than the islands themselves whatever they might be. The islands can range from the average size of a family car to about 500 sq meters.

Some of the islands can clump to gather to form 'super' islands and there are on average about 50-100 individual islands every mile or so.

I can't solve the problem with wind erosion so negate it for the moment and assume that someone(me) performs maintenance now and then.

• Are there some special atmospheric conditions on those islands ? For example a dome with a higher pressured atmosphere to allow life on a 14km high island ? Furthermore how big are your islands ? Commented Aug 25, 2016 at 13:41
• "Don't move much" == do they at least move their own diameter? I.e., island that's 5 miles across moves around in an area greater than 10 miles wide? If not, there will be parts of the surface that will be permanently shadowed/twilight and cut off from precipitation. Commented Aug 25, 2016 at 13:46
• No, as said these are really just regular islands if you exclude the way they float. So while life won't exist on a 14km high island, it would exist on maybe a 1km high island. The islands can range from the average size of a family car to about 500 sq meters
– Skye
Commented Aug 25, 2016 at 13:46
• @JohnFeltz umm they might move a few meters but nothing more, i really won't want them to knock down mountains or something. i don't intend to make them too big. is 1000 sq meters a big area? never mind , I'm changing it to 500 sq meters
– Skye
Commented Aug 25, 2016 at 13:47
• How many of them? What's the ratio of island surface to regular land surface? One island 30m x 30m every 40 square kilometers won't do anything: 1000 of them will. Commented Aug 25, 2016 at 13:51

Given the back-and-forth in comments & your edits, I don't see any global weather issues. If many of the floating islands are low in the atmosphere (tree-top level), you'll have issues of erosion on the surface where all the rain from a 500 square meter surface drizzles down in a sheet around the island, but if they're higher than that the sheets of water will disperse.

The only effect I can see locally deals with snowmelt. Snow would stay stuck to the top of the mountains, and would melt off and fall as rain, instead of melting more gently into the water table. More erosion, more flooding during the thaw, and some artesian aquifers wouldn't be recharged as well - which means fewer springs.

If the material of the floating rocks is generally the same as the surface (same rocks/soil, same amount of vegetation), then it shouldn't affect the planetary albedo - but if the rocks are all mirror-surfaced or dark black, then you'd see a change on the order of 1 part per thousand in the albedo. Enough to shift growing regions north or south, but it's a fantasy world and you can just specify that stuff by fiat (ie adjust the sun & the atmosphere to compensate).

Depending on the height of the floating landmass they may not receive much rain. Rain clouds (stratus) are at 6,500 ft (1.98 km) or lower. Landmasses above this may not receive much rain, and any lower than 2 km would block portions of the earth from receiving rain beneath their floating mass.

However thunderheads (cumulonimbus) can reach up to 50,000 ft (15.24 km) and have hail, lightning, and torrential rain. So with this type of cloud it is fully possible for higher floating islands to receive heavy rain and other intense weather conditions.

Floating islands present a different condition than mountains which have a base and cause air to go up cool and lose its moisture. With no base the islands won't catch as much air (and their shape may not be conducive in making air rise) so most weather should be natural and unaffected by the floating islands, ie carried by the wind. Especially the smaller islands, if they range from average size of a family car, then you can compare them to hot air balloons or planes which are bigger than a car and don't affect the weather at all.

Something else to keep in mind is the freezing level, about 2 degrees C per 1000 ft (.31 km). So if on the surface its 75 deg F (23 deg C) the freezing level is about 11,500 ft (3.5 km). Any floating island above this height will most likely not have rain but snow and ice.

A floating island would only affect local immediate weather conditions, mostly underneath. Cooling underneath, light sensitive things affected, spillover from the island impacting the terrain, etc..

You would need to get up in size to begin affecting weather globallyl. The island shadow will change growing conditions underneath, with the impact increasing over time. Sufficient surface area coverage would alter the wind streams (currents if over the ocean) which form the weather patterns, and affect evaporation. In a dry environment, blocking the light might result in a desert underneath, but in a moist environment might result in endless field of mold and decay, or field of snow.

Not to mention being an easy way to throw rocks.