Climate Change: The Proof and the Process

Since what we call civilization began some 12,000 years ago, the mean temperature of Earth has not varied more than 1°C from the average. The forecast change in temperature of from 1.5 to 4°C (2.7 to 7°F) by 2100 has no equal in the recent history of the planet. Changes in the energy output of the sun, changes in the relative position of the sun and Earth, shifting locations of the continents, mountain building, volcanic eruptions, and changes in atmospheric composition all combine to cause our climate to change. Most of the changes in climate of the past can be explained by a combination of these processes. However, none of these natural changes, individually or collectively, explain the rapid change now taking place on Earth. Now these processes must be considered together with the impact of the human species. The species has grown to such an extent in numbers, and in per capita footprint, that the entire planet is being altered. That this is the case is well demonstrated by the extensive surface changes created by human activity. For instance, it has been known for decades that the human impact in cities is so great that a new set of climatic conditions is created. Now we know that the climate of the entire planet, from pole to pole, is being altered. Such extensive change has the potential to move our planet to a new stage unknown in human history and to change the entire human economic and cultural systems