Chapter One 6 Average global temperatures on Earth rose 1 53 degrees Fahrenheit 0 85 C between 1880 and 2012 1 More than half of this warming has occurred since 1979 Higher temperatures are causing rapid melting of Arctic and Antarctic ice and mountain glaciers decreases in overall snow cover warmer oceans and rising sea levels They are also making extreme weather events more frequent These stronger storms worse droughts and floods and heavier snowfalls lead to human deaths and destruction of property People are seeing the results of global warming on Earth and in their own lives Many species may go extinct as a result of climate change At least 97 percent of climate scientists now agree this warming most likely results from human activities 2 A key cause is the burning of fossil fuels When fossil fuels are burned they release gases into the atmosphere including carbon dioxide This Cameras designed to monitor Arctic glaciers have recorded direct evidence of increased melting The Hockey Stick OF CLIMATE
and other gases help the atmosphere retain more heat from the sun warming the planet This concept reached broad acceptance in the scientific community relatively recently Throughout the 1900s scientists wondered whether increased levels of carbon dioxide and other gases could actually raise global temperatures They debated whether humans could really change the climate and if so how significantly What Is the Hockey Stick Graph In 1998 Michael Mann of the University of Massachusetts decided to follow the evidence Along with Raymond S Bradley also of the University of Massachusetts and Malcolm K Hughes of the University of Arizona he analyzed data for ancient climates in the Northern Hemisphere The scientists used data from fossil tree rings ice cores and ancient corals These objects can be studied measured and analyzed to determine the approximate temperatures during the time they formed They combined this ancient data with modern thermometer readings collected since the mid-1800s The result was a continuous reconstruction of Northern Hemisphere temperatures going back 1,000 years Mann and his colleagues published their report in the scientific journal Geophysical Research Letters One key part of the report was a graph showing average Northern Hemisphere temperatures over the last millennium It soon became known as the hockey stick graph Temperatures were relatively flat for the first 900 years This made up the long handle of the hockey stick In the last century and especially in the last several 8
9 decades the graph spiked sharply upward creating the stick’s blade The graph was featured in the 2001 report of the Intergovernmental Panel on Climate Change IPCC a scientific body set up by the members of the United Nations It became an iconic illustration of human influence on climate Mann summarized its significance The graph told a simple story that a sharp and highly unusual rise in atmospheric Mann has become a major public face for the issues surrounding climate change
