(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: Global warming is happening on Mars and Pluto as well. Since there are no SUVs on Mars, CO2 can’t be causing global warming.

Answer: Warming on another planet would be an interesting coincidence, but it would not necessarily be driven by the same causes.

The only relevant factor the earth and Mars share is the sun, so if the warming were real and related, that would be the logical place to look. As it happens, the sun is being watched and measured carefully back here on earth, and it is not the primary cause of current climate change.

As for the alleged extraterrestrial warming, there is extremely little evidence of a global climate change on Mars. The only piece I’m aware of is a series of photographs of a single icy region in the southern hemisphere that shows melting over a six year period (about three Martian years).

Here on earth we have direct measurements from all over the globe, widespread glacial retreat, reduction of sea ice, and satellite measurements of the lower troposphere up to the stratosphere. To compare this mountain of data to a few photographs of a single region on another planet strains credulity. And in fact, the relevant scientists believe the observation described above is the result of a regional change caused by Mars’ own orbital cycles, like what happened during the earth’s glacial cycles.

See Global Warming on Mars? from RealClimate for much more detail about this issue.

Turning to the outer reaches of the solar system: in the icy cold and lonely Kuiper Belt was observed a difference in Pluto’s atmospheric thickness, inferred from two occultation observations 14 years apart. But a cursory glance at Pluto’s orbit and atmosphere reveals how ridiculous it is to draw any conclusions about climate, much less climate change, from observations spanning less than even a single season, let alone enough years to even establish the climate’s normal state.

Anyone trying to draw conclusions about what is happening here on earth from all this might as well be from another planet.

Back to Mars for a quick summary:

On Earth, we have poles melting, surface temperature rising, tropospheric temperatures rising, permafrost melting, glaciers worldwide melting, CO2 concentrations increasing, borehole analysis showing warming, sea ice receding, proxy reconstructions showing warming, sea level rising, sea surface temperatures rising, energy imbalance, ice sheets melting, and stratospheric cooling, all of which leads us to believe the earth is undergoing global warming driven by an enhanced greenhouse effect.

One Mars we have one spot melting, which leads us to believe that … one spot is melting.

Forgive me for not being reassured.