For example, a decrease in solar activity coupled with an increase in volcanic activity is thought to have helped trigger the Little Ice Age between approximately and , when Greenland cooled from to the s and glaciers advanced in the Alps.
But several lines of evidence show that current global warming cannot be explained by changes in energy from the Sun:. A simplified animation of the greenhouse effect.
Greenhouse Effect 101
Not enough greenhouse effect: The planet Mars has a very thin atmosphere, nearly all carbon dioxide. Because of the low atmospheric pressure, and with little to no methane or water vapor to reinforce the weak greenhouse effect, Mars has a largely frozen surface that shows no evidence of life. Too much greenhouse effect: The atmosphere of Venus, like Mars, is nearly all carbon dioxide.
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But Venus has about , times as much carbon dioxide in its atmosphere as Earth and about 19, times as much as Mars does , producing a runaway greenhouse effect and a surface temperature hot enough to melt lead. The above graph compares global surface temperature changes red line and the Sun's energy that Earth receives yellow line in watts units of energy per square meter since Eleven-year averages are used to reduce the year-to-year natural noise in the data, making the underlying trends more obvious.
Over the same period, global temperature has risen markedly.
It is therefore extremely unlikely that the Sun has caused the observed global temperature warming trend over the past half-century. Images of Change. Explore a stunning gallery of before-and-after images of Earth from land and space that reveal our home planet in a state of flux.
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Climate Time Machine. Travel through Earth's recent climate history and see how increasing carbon dioxide, global temperature and sea ice have changed over time. Credit: NASA.
The findings, published this week in the journal Geophysical Research Letters , were obtained with a model similar to the type used to predict future climate change on Earth. Venus today is a hellish world. There is almost no water vapor. Temperatures reach degrees Fahrenheit degrees Celsius at its surface. However, Venus is closer to the sun than Earth and receives far more sunlight. With no water left on the surface, carbon dioxide built up in the atmosphere, leading to a so-called runaway greenhouse effect that created present conditions.
Greenhouse effect on other planets?
Previous studies have shown that how fast a planet spins on its axis affects whether it has a habitable climate. A day on Venus is Earth days. However, newer research has shown that a thin atmosphere like that of modern Earth could have produced the same result. That means an ancient Venus with an Earth-like atmosphere could have had the same rotation rate it has today.