Global Warming
Global warming is the observation that Earth’s average temperature is gradually increasing. We see that temperature is closely correlated with greenhouse gas concentrations in the atmosphere, especially carbon dioxide. There is a tremendous body of evidence indicating that Earth is getting warmer and that the warming trend we see is caused by an enhanced greenhouse effect.
Earth’s current temperature is about 0.74 °C (1.34 °F) higher than it was 100 years ago, and the warming trend is continuing. Will it keep getting warmer and warmer? Scientists use computer models to make future predictions. These models are based on assumptive future fossil fuel use, and other factors that could influence climate like clouds, the amount of smog in the air, and the role of the oceans. They also use data from Earth’s ancient climate to make assumptions about the future climate. None of these factors are certain, so computer models give us only predictions based on our best assumptions and present knowledge. Climate is very complex and it is difficult to make exact predictions of future climate.
However, we can say with absolute certainty that global carbon dioxide levels are rising. We know that these rises are caused by human activity and that carbon dioxide is a powerful greenhouse gas. The following points relate past climate changes and current increased carbon dioxide levels to current global warming.
- Earth’s temperature has gone up and down several times in its long history. There have been ice ages alternating with times of tropical beaches over much of the globe.
- All of our evidence indicates that the warming we are experiencing now is much more widespread and much more rapid than any other warming that we know of in geologic history.
- The magnitude of warming we have experienced in the last century would have taken thousands of years without the onset of the Industrial Revolution and widespread fossil fuel combustion.
- We had millennia of little change in global carbon dioxide levels and then meteoric rises in just a few decades. That has to be influenced by human activity.
