Abstract The polar ice sheets, their surrounding land fringes and oceans (68 × 10 6  km 2 ; 13% of Earth's surface) are hot spots for carbon cycle perturbation under future climate change due to glacier retreat, rising meltwater fluxes, reduced sea ice, thawing permafrost, warming land‐surfaces and increased precipitation. Here we assess carbon stored and exchanged with the atmosphere (as carbon dioxide and methane) across an expansive bipolar ice‐to‐ocean domain. We show that the polar regions harbor large reserves of carbon stored in sediments, rocks and the ocean, which differ in their reactivity and turnover times: 5,300–22,200 PgC of organic carbon and 5,600–8,600 PgC of inorganic carbon. These carbon reservoirs include potential reserves of marine and subglacial methane hydrate (80–570 PgC), which could become destabilized under future warming scenarios. Oceans (270–360 PgC) and ice sheets (14–96 PgC Greenland, 5,000–21,000 PgC Antarctica) dominate organic carbon stores, with smaller (but regionally important) stocks found in ice sheet land fringes (13–58 PgC). Estimates of natural CO 2 and CH 4 fluxes from these polar regions to the atmosphere present high uncertainty but highlight oceanic CO 2 sinks in Greenland (−110 to −49 TgC‐CO 2 a −1 ) and in the ICE and SPSS biomes of the Southern Ocean (−480 to 55 TgC‐CO 2 a −1 ), with potential CH 4 sources associated with the Greenland Ice Sheet. Such high uncertainty in polar carbon reservoirs and fluxes is important to resolve if future feedbacks between the polar regions, Earth's carbon cycle and climate are to be conclusively determined. Plain Language Summary Around 13% of the Earth's surface is covered by ice sheets, their neighboring land fringes, fjords and oceans in the polar regions. These environments are undergoing unprecedented rapid change due to warming of the atmosphere and oceans, but there is poor understanding of the amount of carbon that is stored and how it is exchanged with the atmosphere as greenhouse gases (GHGs). Our study quantifies for the first time the stores and fluxes of carbon beneath, in and around polar ice sheets, and speculates on how they might change with 21st century warming. We show vast stores of inorganic and organic carbon (>10,000 billion tonnes), and active emissions of greenhouse gases to and from the atmosphere. These regions are likely small sources of methane gas to the atmosphere and overall sinks for atmospheric CO 2 . Narrowing uncertainty in these greenhouse gas emissions is important given forecast climate‐driven changes in the polar regions, which have the potential to dramatically shift greenhouse gas emissions to the atmosphere. Key Points Polar ice sheets, land fringes and oceans host vast carbon reserves (>10,000 billion tonnes, Gt) but with high uncertainty Polar ice sheets and their surrounding oceans are likely net sinks for CO 2 and small sources for CH 4 Future climate‐driven changes in the polar regions have the potential to influence CO 2 and CH 4 fluxes to the atmosphere