According to a February 28, 2009 article in National Geographic, Mars Hints at Solar, Not Human, Cause for Global Warming. From the article:

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.

Obviously Abdussamatov isn’t very popular.  His work hasn’t been “well received” by other climate scientists who would potentially be a) wrong and/or b) out of work if he is right.  “His views are completely at odds with the mainstream scientific opinion,” said Colin Wilson, a planetary physicist at England’s Oxford University.  Mainstream science thinks that Mars is wobbling, causing shifts in solar radiation to the poles.  Mar’s lack of a large moon makes it wobbles worse.

Abdussamatov also maintains that solar irradiance is decreasing, leading to a cold snap in 2040.  Perhaps the effect of CO2 in the air will balance with decreased solar irradiance leading to consistent temperatures over the next 50 years.

On another side, El Reg had an article 9 April 2009 stating that our clean air regulations and improvements to air quality is causing the increase in temperatures at the poles, not global warming.  More heat from solar radiation is making it through due to decreased sulfates and increased aerosols in the air.  Sooty aerosol from the Chinese traps some of the heat too… So we humans can decide whether we’re helping, hurting, or having no effect.