First, as arctic snow and ice melt, the darker land and ocean surfaces that are revealed absorb more of the sun's energy, increasing arctic warming. Second, in the Arctic, a greater fraction of the extra energy received at the surface due to increasing concentrations of greenhouse gases goes directly into warming the atmosphere, whereas in the tropics, a greater fraction goes into evaporation. Third, the depth of the atmospheric layer that has to warm in order to cause warming of near-surface air is much shallower in the Arctic than in the tropics, resulting in a larger arctic temperature increase. Fourth, as warming reduces the extent of sea ice, solar heat absorbed by the oceans in the summer is more easily transferred to the atmosphere in the winter, making the air temperature warmer than it would be otherwise. Finally, because heat is transported to the Arctic by the atmosphere and oceans, alterations in their circulation patterns can also increase arctic warming.

1. As snow and ice melt,  darker land and ocean surfaces absorb more solar energy.
2. More of the extra trapped energy goes directly into warming rather than into evaporation.
3. The atmospheric layer that has to warm in order to warm the surface is shallower in the Arctic.
4. As sea ice retreats, solar heat absorbed by the oceans is more easily transferred to the atmosphere.
5. Alterations in atmospheric and oceanic circulation can increase warming.

First, as arctic snow and ice melt, the darker land and ocean surfaces that are revealed absorb more of the sun's energy, increasing arctic warming. Second, in the Arctic, a greater fraction of the extra energy received at the surface due to increasing concentrations of greenhouse gases goes directly into warming the atmosphere, whereas in the tropics, a greater fraction goes into evaporation. Third, the depth of the atmospheric layer that has to warm in order to cause warming of near-surface air is much shallower in the Arctic than in the tropics, resulting in a larger arctic temperature increase. Fourth, as warming reduces the extent of sea ice, solar heat absorbed by the oceans in the summer is more easily transferred to the atmosphere in the winter, making the air temperature warmer than it would be otherwise. Finally, because heat is transported to the Arctic by the atmosphere and oceans, alterations in their circulation patterns can also increase arctic warming.

1. As snow and ice melt,  darker land and ocean surfaces absorb more solar energy.
2. More of the extra trapped energy goes directly into warming rather than into evaporation.
3. The atmospheric layer that has to warm in order to warm the surface is shallower in the Arctic.
4. As sea ice retreats, solar heat absorbed by the oceans is more easily transferred to the atmosphere.
5. Alterations in atmospheric and oceanic circulation can increase warming.