1 ) 

Atmosphere warms up → more vegetation grows in warmer environments→ CO₂ removed from atmosphere → reduces warming.

2 ) 

Atmosphere warms → sea ice melts → more sunlight allows phytoplankton to photosynthesise more in oceans → CO₂ removed from atmosphere → limits atmospheric warming.

3 ) 

Sea ice melts → darker surfaces exposed → less solar radiation reflected → more insolation absorbed → temperatures rise → more melting.

4 ) 

Temperatures rise → increased evaporation of water → increased cloud formation → more precipitation falls as snow → snow reflects incoming solar radiation → less warming.