Final answer:
Global warming is evidenced by rising global temperatures, receding glaciers and polar ice fields, increase in greenhouse gases present in the current atmosphere, and climactic changes over the years detected through natural records like tree rings.
Step-by-step explanation:
There are several pieces of evidence that indicate global warming exists. The first indication is that global land and ocean temperatures have been showing a consistent warming trend since the late 1800s. This trend is a direct result of an increase in greenhouse gas levels due to the constant burning of fossil fuels since the start of the Industrial Revolution.
Secondly, an indirect evidence comes from the visible effects of global warming such as the receding of glaciers and polar ice fields. The shrinking McCarty glacier in Alaska, for example, had completely disappeared by the summer of 2004.
The third proof is the increase in earth’s temperature as predicted by scientists based on the levels of greenhouse gases present in the current atmosphere. The increase in the earth’s temperature has been supported by data from climate models.
Lastly, historical evidence like analyzing the number of annual rings in trees also points to climactic changes over the years, serving as another indirect testament to global warming.
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