The average Arctic land surface air temperature for the past year, from October 2014 to September 2015, is the warmest since 1900. Driven by summertime ocean heating in ice free waters and increased solar heating of snow-free land, the Arctic is warming faster than the rest of the globe. In 2015, the September Arctic sea ice minimum extent was 29% less than the 1981-2010 average. The maximum sea ice extent in winter was the lowest in the satellite record. Moreover, thick winter sea ice that is four or more years old, declined from 20% of the ice pack in 1985 to 3% in 2015. Summer sea ice retreat exposes more of the ocean to solar heating, contributing to rising upper ocean temperatures throughout the Arctic, with profound impacts on the marine ecosystem and threatening ice-associated marine mammals. Walruses are forced to haul-out on land which is distant from their food sources, rather than on sea ice. The Arctic marine environment is changing as small Arctic fish and organisms that live near the sea bottom are now mixing and competing with larger, more mobile fish species from the south. Spring snowmelt marks the transition from the reflective wintertime snow cover to heat-absorbing snow-free ground, and coincides with increasing solar radiation during the lengthening days of the high latitude spring. June snow cover has declined since 1979, and was the second lowest on record in 2015. There is a strong connection in weather between the Arctic and mid-latitudes. From fall 2014 to spring 2015, warm winds from the south brought unusually warm temperatures to Alaska, causing the second worse fire season on record for those months. Cold temperatures from Arctic sources were a feature of eastern North America in winter and spring. Arctic river discharge has been increasing since 1979, putting increasing amounts of fresh water into the Arctic Ocean and impacting coastal and ocean chemistry, biology and circulation. River discharge is especially important in the Arctic because Arctic rivers transport 10% of global river discharge even though the Arctic Ocean is only 1% of the global ocean. Terrestrial vegetation productivity and above-ground biomass have been decreasing since 2011, impacting uptake of atmospheric carbon dioxide through photosynthesis, surface energy and water exchanges, plant-herbivore interactions, and the state of the active layer and permafrost. Ice loss from the Greenland ice sheet is a principal source of sea level rise. Melt area in 2015 exceeded more than half the ice sheet on July 4 for the first time since the exceptional melting of 2012. And glaciers terminating in the ocean showed an increase in ice velocity and a decrease in area. Taken together, 2015 shows a continuing set of major changes in the Arctic.