Melting the Polar Caps
Melting the Martian Polar Caps
The mechanism is a feedback loop, and it is the reason every warming proposal points here first. Warm the cap; CO2 sublimes; atmospheric pressure rises; a thicker CO2 atmosphere traps more heat; the cap warms further. Left alone Mars sits in the stable cold branch of that loop. Push it hard enough — with mirrors, with aerosols, with gases — and it runs on its own.
Radar sounding from Mars Reconnaissance Orbiter established the size of the buried deposit, and it is genuinely large: comparable in mass to the entire present-day atmosphere. Sublimating it is the cheapest single step in terraforming, because the planet does the work once the trigger is pulled.
And then the loop stops. Doubling 6 millibars gives 12 millibars. The Armstrong limit — the pressure below which water boils at human body temperature — is 63 millibars, a factor of five higher still, and a comfortable breathing mixture needs about 250. The polar caps are the biggest lever available and they move the needle from 0.6% of Earth to 1.2%.
Jakosky and Edwards settled the wider question in 2018. Adding every accessible CO2 source on Mars — polar ice, adsorbed gas in regolith, carbonate minerals within reach — gets to no more than about 7% of Earth's sea-level pressure, and most of even that is locked in deposits that cannot readily be mobilised. This is why current work has shifted from "terraform Mars" to "warm regions of Mars".
The case for
The planet does the work
Sublimation is self-sustaining once triggered. No sustained industry is needed — only enough forcing to tip the cap out of its stable cold state.
It is the largest reservoir in reach
The buried south-polar CO2 deposit is comparable in mass to the entire present atmosphere, making it the single biggest volatile source on the planet.
It compounds every other method
A thicker CO2 atmosphere strengthens the greenhouse effect of everything else, so the caps multiply mirrors, aerosols and gases rather than competing with them.
It releases water too
The caps are layered CO2 and water ice. Warming them supplies both atmosphere and the water that any biological stage depends on.
The case against
It runs out almost immediately
Full release takes Mars from about 6 to about 12 millibars. The Armstrong limit is 63. The biggest lever on the planet delivers roughly a fifth of what is needed just to stop water boiling in your blood.
Most of the CO2 is unreachable
Jakosky and Edwards found that every accessible source together caps out near 7% of Earth pressure, with the bulk locked in carbonate rock nobody can mobilise at planetary scale.
CO2 is not breathable at any pressure
Thickening the atmosphere with carbon dioxide raises pressure and temperature but makes the air more toxic, not less. It buys pressure suits off, not helmets.
Solar wind takes it back
Without a magnetosphere the released atmosphere erodes away again. The loss is slow — hundreds of millions of years — but any permanent solution eventually needs a shield.
| Trigger forcing | +5 K over the pole | e.g. a 125 km orbital mirror |
| Yield | ~2× the atmosphere | From ~6 to ~12 mbar |
| Ceiling, all sources | ~7% of Earth | Jakosky & Edwards, 2018 |
| Gas per millibar | 3.89 × 10¹⁵ kg | Global mean surface pressure |
What happens if you melt the Martian polar caps?
Releasing the buried south-polar CO2 would roughly double atmospheric pressure, from about 6 millibars to about 12, and warm the planet through a stronger greenhouse effect. It would not come close to a pressure a human could survive unsuited.
Is there enough CO2 on Mars to terraform it?
No. Jakosky and Edwards showed in 2018 that processing every accessible source would raise pressure to at most about 7% of Earth's, and most of that CO2 is locked in deposits that cannot be mobilised with any foreseeable technology.
How much gas does one millibar of Martian pressure need?
About 3.89 × 10¹⁵ kg of atmosphere per millibar of global mean surface pressure — roughly four trillion tonnes for each millibar.