The burning of fossil fuels and other human activities are contributing to a rise in average global temperatures. In Alaska and other cold regions, these rising temperatures are leading to melting glaciers, a phenomenon known as glacial retreat. In Kenai Fjords National Park in Alaska, retreating glaciers have exposed rock, giving scientists an up-close view of primary succession at work. The most recently exposed rock is still bare; however, rocks that have been exposed longer are covered in moss and lichens. In regions that have been uncovered for longer periods of time, small plants and shrubs are growing. In areas that have been exposed for decades, cottonwood trees grow. Cottonwoods are shade-intolerant trees that grow rapidly. In regions that have been exposed for at least 100-200 years, a climax community with a wide variety of trees and plants grow. ANALYZE How do human societies influence natural processes such as primary succession?