An Arctic Sea Ice Energy Budget for the Last Interglacial

As the Earth warms, the Arctic Ocean is expected to be dominated by thin ice that forms and melts each year, with little thick multiyear ice. To understand the Arctic response under such conditions, we study the Last Interglacial period, 127,000 years ago, when changes in Earth's orbit caused the Arctic to receive more sunlight in spring and summer. Using nine state-of-the-art climate models, we investigate how energy moved between the atmosphere, ocean, and sea ice during this period, compared with pre-industrial conditions. We examine how much energy reached the surface, how much was reflected or absorbed, and how this energy was stored in the ocean. We find that differences in summer sea-ice cover between models are mainly driven by how much of the additional sunlight reaches the surface, and how much melting the ice changes the proportion that is reflected. Some extra energy is absorbed by the ocean, and later released in autumn. This delays regrowth, though winter ice area eventually returns. Although today's Arctic warming is driven mostly by greenhouse gases, our results show that accurately representing surface energy processes is essential for predicting how quickly summer sea ice will disappear in a warmer future.