More on climate change The Teacher’s Guide for the article on Mt. Kilimanjaro (see References, below) says about climate change that:
Climate change refers to the long-term shift in average weather as a result of changes in the atmosphere-ocean-land system that affects a region’s weather. Long-term changes in climate are actually normal. The Cretacous period (120 million-90 million years ago) in North America was marked by vegetation that grows only in warm climates and the age of dinosaurs. On the other hand, massive ice sheets prevailed about 21,000 years ago. In the last 650,000 years there have been seven cycles in which glaciers have advanced and retreated. These variations took place over long time periods and over large land masses. Students should not confuse climate change with unusual isolated local weather events, like snow in normally balmy regions.
So we know that the gases described in the previous section of this Teacher’s Guide are present in the Earth’s atmosphere in increasing concentrations. And we know that these gases trap heat to a greater extent than normal and that on average the Earth’s temperature has risen about 1.4 oF in the last century. The central question is this: Is the Earth’s climate changing as a result?
Before we get to that issue, a word or two about weather vs. climate. Weather is a description of the conditions in the atmosphere at a given time and place. Most of what we call weather takes place near the surface of the Earth in the troposphere. When we think of weather we think of temperature, precipitation, clouds and wind, for example. Climate, on the other hand, is a description of atmospheric conditions over longer periods of time and over larger geographic areas. While weather changes frequently climate tends to remain on average fairly stable unless some force or forces—like large volcanic eruptions or significant changes in greenhouse gas concentrations—shift the climate.
Climate change, then, refers to any significant change in the measures of climate lasting for an extended period of time. In other words, climate change includes major changes in temperature, precipitation, or wind patterns, among other effects, that occur over several decades or longer. What are these indicators of climate change and what is their status? The EPA lists 26 of these climate change indicators. Below are brief summaries of the data for the twenty indicators that are related to physical factors in the environment. For the complete listing and extensive graphs that accompany the data, see http://www.epa.gov/climatechange/science/indicators/. References to charts and graphs in the summaries that follow have been omitted.