Climate Change: Our Warming Earth

Climate Change: Our Warming Earth — page 7
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