Conservative estimates from peer reviewed models now suggest there is a greater than 65% probability that global temperatures will exceed 1.5 degrees Celsius above preindustrial levels by the year 2100. Other models predict more than a two degree Celsius increase during the same time period. Throughout the 21st century, global temperatures higher than today are a virtual certainty and are expected to continue to rise beyond the year 2100. While these impacts are global, their influence on the Arctic is particularly concerning, and there is already evidence of their impact. The impacts of climate warming on the Arctic's cryosphere will be substantial. The extent of Northern Hemisphere sea ice has decreased continuously since 1950, or even earlier. The area covered by seasonal snow in the Northern Hemisphere is also decreased, as is the area covered by glaciers. Snow, sea ice, and glacier ice all have high albedo and reflect as much as 90% of solar radiation back to space. Where sea ice is absent, the ocean absorbs up to 90% of this energy. Likewise, the land surface absorbs more radiation when snow or glacier ice is absent, further enhancing warming. Microscopic black carbon soot from fossil fuel burning is also a very important warming agent for the Arctic. Globally, atmospheric black carbon absorbs solar radiation, adding about 0.6 watts per square meter of energy. But is all off set by reflective dust and aerosols. But when black carbon is deposited on snow, glacier ice, or sea ice, it decreases the albedo and enhances melting. On a global scale, black carbon on snow and ice adds only 0.04 watts per square meter of energy. But locally, as in the arctic, even this small increase can greatly speed up melting and substantially shorten the winter season. The IPCC findings show that Northern Hemisphere sea ice extent has decreased continuously since 1950. Select the statement or statements that best describe the Arctic sea ice melting. Select all the answers you think are correct. A, the melted ice will increase snowfall and lead to glacier growth. B, ocean water will absorb more heat than ice, causing increased ice melt. C, black carbon soot increases the albedo but is insignificant to ice melt. D, black carbon soot decreases the albedo and enhances snow and ice melt. Both B and D are correct. Global temperature increases that melts ice and snow lead to decreased albedo and the absorption of additional energy that enhances melting. This positive feedback causes enhanced local temperature increases. The 2005 Arctic Climate Impact Assessment, using IPCC data and methodology, estimates that average temperatures in the Arctic will increase by as much as seven degrees Celsius by the year 2100. The impact of this is likely to be severe. With warmer temperatures there will be less snow and ice, as well as longer seasons. Permafrost landscapes will begin to melt, leading to changing ecosystems and species migration, as well as infrastructure damage. CO2 and methane, that have been stored in permafrost for tens of thousands of years, will be released, further enhancing global warming. Arctic coastal communities will become subject to erosion as a result of decreased sea ice. Melting glaciers and ice sheets will return water that has been stored on land to the ocean, contributing to rising sea levels around the world. Arctic residents who practice traditional ways of life will need to rapidly adapt to this changing environment that may affect their food sources. Although changes may be dramatic, there's reason to be optimistic about the ability of indigenous communities to adapt, as we'll see in lesson four. We've come to the end of lesson two, but come back soon for lesson three, where we'll learn all about the snow, ice, and glaciers of the Arctic. [MUSIC] [SOUND] [MUSIC]