BEIJING, March 14 (Xinhuanet) -- Earth's not the only planet in solar system that's heating up; so is Mars, Jupiter and Pluto. And some scientists say global warming is the sun's fault, not man's.

    Others argue such claims are misleading and create the false impression rapid global warming is a natural phenomenon, media reported Wednesday.

    While evidence suggests fluctuations in solar activity can affect climate on Earth, and has done so in the past, the majority of climate scientists and astrophysicists agree the sun should not be blamed for the current and historically sudden increase in global temperatures.

    Habibullo Abdussamatov, the head of space research at St. Petersburg's Pulkovo Astronomical Observatory in Russia, recently linked the attenuation of ice caps on Mars to fluctuations in the sun's output. Abdussamatov also blamed solar fluctuations for Earth's current global warming trend. His initial comments were published online by National Geographic News.

    "Man-made greenhouse warming has [made a] small contribution [to] the warming on Earth in recent years, but [it] cannot compete with the increase in solar irradiance," Abdussamatov told LiveScience in an email interview last week. "The considerable heating and cooling on the Earth and on Mars always will be practically parallel."

    Abdussamatov's critics contend Mars'recent warmup is more likely due to natural variations in the planet's orbit and tilt. On Earth, these wobbles, known as Milankovitch cycles, are thought to contribute to the onset and disappearance of ice ages.

    "It's believed that what drives climate change on Mars are orbital variations," said Jeffrey Plaut, a project scientist for NASA's Mars Odyssey mission. "The Earth also goes through orbital variations similar to that of Mars."

    Charles Long, a climate physicist at Pacific Northwest National Laboratories in Washington, says Abdussamatov's theory that solar fluctuations are causing global warming is nonsense.

    "That's nuts," Long said in a telephone interview. "It doesn't make physical sense that that's the case."

    Long's team published a study in 2005 in the journal Science showing Earth experienced a period of "solar global dimming" from 1960 to 1990. During that timeframe solar radiation hitting our planet¡¯s surface decreased. Then from the mid-1990s onward, the trend reversed and Earth experienced a "solar brightening."

    These changes were not likely caused by fluctuations in the output of the sun, Long explained, but rather increases in atmospheric clouds or aerosols that reflected solar radiation back into space.

    Others have pointed out anomalous warming on other worlds in our solar system.

    Benny Peiser, a social anthropologist at Liverpool John Moores University who monitors studies and news reports of asteroids, global warming and other potentially apocalyptic topics, recently quoted in his daily electronic newsletter the following from a blog called Strata-Sphere:

    "Global warming on Neptune's moon Triton as well as Jupiter and Pluto, and now Mars has some [scientists] scratching their heads over what could possibly be in common with the warming of all these planets ... Could there be something in common with all the planets in our solar system that might cause them all to warm at the same time?"

    In fact, scientists have alternative explanations for the anomalous warming on each of these other planetary bodies.

    The warming on Triton could be the result of an extreme southern summer on the moon, a season that occurs every few hundred years, as well as possible changes in the makeup of surface ice that caused it to absorb more of the sun's heat.

    Researchers credited Pluto's warming to possible eruptive activity and a delayed thawing from its last close approach to the sun in 1989.

    And the recent storm activity on Jupiter is being blamed on a recurring climatic cycle that churns up material from the gas giant's interior and lofts it to the surface, where it is heated by the sun.

    "The small measured changes in solar output and variations from one decade to the next are only on the order of a fraction of a percent, and if you do the calculations not even large enough to really provide a detectable signal in the surface temperature record," said Penn State meteorologist Michael Mann.

    The link between solar activity and global warming is just another scapegoat for human-caused warming, Mann told LiveScience.

    "Solar activity continues to be one of the last bastions of contrarians," Mann said. "People who don't accept the existence of anthropogenic climate change still try to point to solar activity."

    (Agencies)