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So obviously, if you have a battleship parked in low orbit, you're not in an ideal situation. The guns can blast cities to rubble and whatnot.
What sort of secondary effects would that be likely to have? Would five kilometers of metal entering low orbit interfere with weather patterns? What about the heat from engines, to give enough thrust to move the thing? Would bombardment raise the surface temperature enough to be noticed? Would there be a 'nuclear winter' effect from blasting enough of the dirt into the sky during a bombardment?
I know 40K runs on loose science at the best of times, but I'm just interested to think about that sort of thing from a fluff/RPG context.
In BFG I'm pretty sure that getting too close to a planet results in running the risk of getting sucked into the atmosphere, which isn't exactly an ideal situation for an unprepared 3 mile long hunk of metal... Nor would it end well for the unsuspecting citizens waiting below...
Aye, ships in BFG entering low orbit (which is necessary both for bombardment as well as launching dropships) have to counteract gravity with their engines or they crash. The only ships that can actually land on the surface are transports and escorts.
Other than that, I don't think any side effects are ever mentioned in GW fluff, though I'm certain a number of licensed sources will be able to provide suggestions in the form of their individual author's opinion.
During the invasion of Gereon in one of the Gaunts Ghosts novels the presence of so many landing craft and other ships in the upper atmosphere completely screws the ecosystem for a bit, causing storms and such. I think similar effects happen in some other novels as well, though I cannot recall specifics.
A lance strike shoul be clean; they're energy beams after all, the pressure wave caued by the beams parting the atmosphere will cause collateral damage while the beams themselves will completely vaporise the target and act like a needle on the ground, leaving a molten crater. A torpedo strike will have radioactive aftereffects, since they're nuclear, being ship-grade plasma explosives and all. As for an Astartes bombardment cannon, the magma bombs are cleaner than torpedos, since they're more like FAEs rather than micro-nuclear/tactical nuclear explosives.
I should have left him there. He had served his purpose. He owed me nothing - yet he gave himself to me willingly. Why? I know not. He is nothing more than a pathetic human. An inferior race. A mon-keigh. But still I broke off my wings so that I might carry him easier. I took him from that place, into the snowstorm where our tracks will not be found. He is heavy. And he is dying. And he is slowing me down. But I will save him. Why? I know not. He is still warm. I can feel his blood ebbing across me. For every beat of his heart, another, slight spill of heat. The heat blows away on the winter wind. His blood is still warm. But fading. And I have spilled scarlet myself. The snow laps greedily at our footsteps and our lifeblood, covering them without a trace as we fade away.
'She sat on the corner, gulping the soup down, uncaring of the heat of it. They had grown more watery as of late she noted, but she wasn't about to beggar food from the Imperials or the "Bearers of the Word." Tau, despite their faults at least didn't have a kill policy for her race.'
In Titanicus, when a two titan transport craft (each being "a few km long" according to the text) entered the lower orbit of a planet, it caused massive ecological perturbations, especially concerning storms, wind patterns and the like. Those atmospheric problems were only temporary though.
And during the first battle for Armageddon (the battle fought against Angron), Imperial forces blasted away a huge chunk of the engines of Angron's Spacehulk. This massive set of reactors entered the orbit of the nearby Pelucidar planet. This chunk of reactors was so big it survived atmospheric entry into Pelucidar and crash-landed on the planet. The mixture of plasma fuel and warp energies contained within the engine was released in Pelucidar's atmosphere and completely screwed up the planet's ecosystem, rendering this world uninhabitable for humans.
So yeah, a battleship entering the atmosphere of a planet can be quite dangerous for this planet's ecosystem.
"How many more worlds do we sacrifice? How many more millions or billions do we betray before we turn and fight?" - attributed to Captain Leoten Semper of Battlefleet Gothic - Gothic War, the evacuation of Belatis.
If commanding a Titan is a measure of true power, then commanding a warship is like having one foot on the Golden Throne - Navy saying.
Standard bombardment with Macrocannons and Lances (the preferred methods of surface bombardment) causes catastrophic damage to the surface given the velocity at which these shells are propelled, but while they probably approach or surpass Atomic Bomb level of damage, I doubt it will cause much permanent damage to the planet.
The Imperium doesn't regularly bombard a planet like that though. They want everything intact for resources/infrastructure reasons. It's why they'll willingly waste tens of thousands of men just to save a factory or what have you. Lives are cheap in the Imperium.
I think Abnett gives us the most detailed effects of ships in low orbit, or entering the atmosphere of a planet, plus the effects their null-fields and engine thrust has on the ecosystem. None of these are precisely good, causing all sorts of freak weather patterns and such, but don't cause any lasting harm.
Orbital bombardment, on the other hand, can really mess things up for quite a while, what with the energy weapons removing (or adding) vast amounts of moisture from the atmosphere and what not.
It is best to be a pessimist. You are usually right and, when you're wrong, you're pleasantly surprised.
This isn't a question you can answer without determining the scale of bombardment. From the fluff planetary bombardments can range from fairly modest stuff like we see in 13th Legion (battleship wipes out thousands of troops and vehicles to give the 13th Legion a clear path to a fortress, but doesn't wipe them out in the process) to megaton level bombardments (planetstrike, battle of MAcragge), to orbital strikes that wipe out continents. The effects of each one of those (and anything in between) can differ depending on the amount of enery involved, the kinds of wepaons involved and how they work (even when you have lasers, effects can differ dependign on if its a pulsed laser or continuous wave laser), the duration of bombardment, etc.
Just to give you an idea, IIRC thunderstorms, hurricaines and tornadoes tend to involve nulcear scale energies in totality, the reason they differ from nukes is that they expend the energy over a larger area and a prolonged period of time.
Waiting for my shill money from Spiral Arm Studios
A Battleship in low orbit isn't going to have an appreciable effect on the atmosphere just by being there. The atmosphere is too thin that high up to result in any pressure differential felt on the ground.
Bombardments and Landing craft however will cause massive pressure waves.
Self-proclaimed evil Cat-person. Dues Ex Felines
Cato Sicarius, after force feeding Captain Ventris a copy of the Codex Astartes for having the audacity to play Deathwatch, chokes to death on his own D-baggery after finding Calgar assembling his new Eldar army.
Except the null-gravity generators that press the "thin atmosphere" at that altitude down into the lower atmosphere at a distance of several hundred, to several thousand, kilometers.
It is best to be a pessimist. You are usually right and, when you're wrong, you're pleasantly surprised.
Lynata wrote:Aye, ships in BFG entering low orbit (which is necessary both for bombardment as well as launching dropships) have to counteract gravity with their engines or they crash. The only ships that can actually land on the surface are transports and escorts.
Other than that, I don't think any side effects are ever mentioned in GW fluff, though I'm certain a number of licensed sources will be able to provide suggestions in the form of their individual author's opinion.
From Last Ditch (latest Ciaphas Cain novel).
They crash land a freight ship on a planet, the pressure bow wave alone pulped half an ork army along with the surface of a mountain when they were at full speed.
DIE HERITICS 
