The current greenhouse gases we have to contend with are mostly carbon dioxide (CO2) and methane (CH4). Methane eventually breaks down into CO2; but, before it does, it is many times more potent of a greenhouse gas than carbon dioxide is.
Once CO2 is released into our biosphere, it remains on the loose for many centuries (only very gradually diminishing). So, even if we completely stopped releasing all CO2 and CH4 emissions today, the current level of global warming would remain constant. Thus, the rate of ice melting and sea level rise will continue unabated. Also, the rate of permafrost melting and its release of methane will continue on and on. Indeed, when enough permafrost has melted and released enough methane, there is the danger of it becoming a self-perpetuating cycle in conjunction with oceanic methane hydrate release (especially if we haven’t ceased fossil fuel usage in time).
Note: The increased rate of the melting of the Greenland and Antarctic ice sheets, plus the calving of glaciers, are graphic demonstrations of global warming. Visual images of the effects of permafrost melting are another: