Climate myths: Mars and Pluto are warming too

Tools

See all 26 climate myths in our special feature.

There have been claims that warming on Mars and Pluto are proof that the recent warming on Earth is caused by an increase in solar activity, and not by greenhouses gases. But we can say with certainty that, even if Mars, Pluto or any other planets have warmed in recent years, it is not due to changes in solar activity.

The Sun's energy output has not increased since direct measurements began in 1978 (see Climate myth special: Global warming is down to the Sun, not humans). If increased solar output really was responsible, we should be seeing warming on all the planets and their moons, not just Mars and Pluto.

Our solar system has eight planets, three dwarf planets and quite a few moons with at least a rudimentary atmosphere, and thus a climate of sorts. Their climates will be affected by local factors such as orbital variations, changes in reflectance (albedo) and even volcanic eruptions, so it would not be surprising if several planets and moons turn out to be warming at any one time.

However, given that a year on Mars is nearly two Earth years long, and that a year on Pluto lasts for 248 Earth years, it is rather early to start drawing conclusions about long-term climate trends on the outer bodies of the Solar System.

What do we know? Images of Mars suggest that between 1999 and 2005, some of the frozen carbon dioxide that covers the south polar region turned into gas (sublimated). This may be the result of the whole planet warming (see Mars images hint at recent climate swings).

Dwarf planet

One theory is that winds have recently swept some areas of Mars clean of dust, darkening the surface, warming the Red Planet and leading to further increases in windiness – a positive feedback effect (see Dust blamed for warming on Mars).

There is a great deal of uncertainty, though. The warming could be a regional effect. And recent results from the thermal imaging system on the Mars Odyssey probe suggest that the polar cap is not shrinking at all, but varies greatly from one Martian year to the next, although the details have yet to be published.

Observations of the thickness of Pluto's atmosphere in 2002 suggested the dwarf planet was warming even as its orbit took it further from the Sun. The finding baffled astronomers at the time, and the cause has yet to be determined.

It has since been suggested that this is due to a greenhouse effect: as it gets closer to the sun Pluto may warm enough for some of the methane ice on its surface to turn into a gas. This would cause further warming, which would continue for a while even after Pluto's orbit starts to take it away from the Sun.

If you would like to comment on this article, visit our blog.