The Environmental Protection Agency echoes what many of the sources from this lesson have already stated - the planet's climate is changing and the data is clear that the root is human activity.
- Greenhouse Gases
The min greenhouse gases on Earth are CO2, NO2 and CH4. All of these gases as produced naturally, but they are also produced or emitted through human activity as well (agriculture, fossil fuels or livestock). These gases contribute to our warming trend by acting as insulators for the solar energy that strikes Earth as well as the infrared radiation that is emitted from our warm planet.
- Solar Activity
If the greenhouse effect is largely dependent on the solar energy that reaches Earth, then certainly changes in the Sun's output would have direct consequences for our climate. But evidence shows that the Sun's activity has been generally consistent, except for a stretch of time in the mid 20th century, and that doesn't account for the continued changes today.
- Reflectivity
The composition of the surface of our planet determines how much solar energy is absorbed as heat and how much is reflected back into space. Our oceans act as large, dark heat sinks for solar radiation. Whereas our white polar ice caps and glaciers on land act as solar reflectors. These reflectors get smaller and smaller with a warming planet, and our large dark heat sinks get bigger and bigger, warming our planet in a positive feedback loop.