Editor's note: We're pleased to welcome Jason Leggett to the Green Options writing team. A civil engineer based in Huntsville, Alabama, Jason started blogging about climate science, and the myths surrounding it, last December at his blog Reasic. He now also writes for Celsias. We're very happy to have him on board, and to bring back our "Green Myth-Busting" series.

Myth: Mars is warming primarily due to the Sun and therefore, Earth's recent changes in climate are also due to solar activity.

Fact: This theory is based on satellite images that show that the ice caps at the Martian south pole are retreating. According to the theory, Mars has very little atmosphere, so a greenhouse effect can be ruled out. Therefore, the Sun must be causing warming on Mars. If that's true, then it must also be causing warming on Earth:

In 2005 data from NASA's Mars Global Surveyor and Odyssey missions revealed that the carbon dioxide "ice caps" near Mars's south pole had been diminishing for three summers in a row. Habibullo Abdussamatov, head of space research at St. Petersburg's Pulkovo Astronomical Observatory in Russia, says the Mars data is evidence that the current global warming on Earth is being caused by changes in the sun. "The long-term increase in solar irradiance is heating both Earth and Mars," he said. Abdussamatov believes that changes in the sun's heat output can account for almost all the climate changes we see on both planets. Mars and Earth, for instance, have experienced periodic ice ages throughout their histories. "Man-made greenhouse warming has made a small contribution to the warming seen on Earth in recent years, but it cannot compete with the increase in solar irradiance," Abdussamatov said.

There are several problems with Abdussamatov's theory, but I'll just point out the two biggest holes I've found. The first problem is that it is controversial. The mainstream theory is that Mars' warming can be explained by changes in its orbit and tilt, much like Earth's Milankovitch Cycles:

The conventional theory is that climate changes on Mars can be explained primarily by small alterations in the planet's orbit and tilt, not by changes in the sun. "Wobbles in the orbit of Mars are the main cause of its climate change in the current era," Oxford's Wilson explained. All planets experience a few wobbles as they make their journey around the sun. Earth's wobbles are known as Milankovitch cycles and occur on time scales of between 20,000 and 100,000 years. These fluctuations change the tilt of Earth's axis and its distance from the sun and are thought to be responsible for the waxing and waning of ice ages on Earth. Mars and Earth wobble in different ways, and most scientists think it is pure coincidence that both planets are between ice ages right now. "Mars has no [large] moon, which makes its wobbles much larger, and hence the swings in climate are greater too," Wilson said.

The second problem with this theory is that there is an overwhelming amount of scientific research that supports the mainstream theory that increased greenhouse gas concentrations are the primary drivers of our climate. On page 4 of SPM1 for the IPCC's latest report, there is a chart that lists each of the components that affect our climate, including their corresponding values, which quantify their contributions. The components are called radiative forcings, and each forcing's effect is measured in watts per meter squared (W/m^2). According to the chart, carbon dioxide is the dominant forcing at 1.66 W/m^2, while the Sun's effect, called solar irradiance, is much smaller at only 0.12 W/m^2. The latter can also be verified by a simple calculation.

The funny thing about this myth is that it is hypocritical. Many skeptics do not trust or appreciate the massive amounts of data that we have collected here on our planet via land, sea, weather balloon, satellite, and proxy measurements, and yet three photos of one secton of Mars convince them that the Sun is warming not only Mars but also Earth.