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The Planets Suite: Is There Climate Change in Outer Space?

September 16, 2010

Other planets in the solar system are warming?

The argument is this; other solar bodies are warming. If this is happening throughout the solar system, clearly it must be the sun causing the rise in temperatures – including here on Earth. In which case – it’s not us!

It is curious that the theory depends so much on sparse information – what we know about the climates on other planets and their history – yet its proponents resolutely ignore the most compelling evidence against the notion. Over the last fifty years, the sun’s output has decreased slightly: it is radiating less heat. We can measure the various activities of the sun pretty accurately from here on Earth, or from orbit above it, so it is hard to ignore the discrepancy between the facts and the sceptical argument that the sun is causing the rise in temperatures.


TSI from 1880 to 1978 from Solanki. TSI from 1979 to 2009 from PMOD.

But if the sun’s output has levelled off or even diminished, then what is causing other planets to warm up? Are they warming at all?

The planets and moons that are claimed to be warming total roughly eight out of dozens of large bodies in the solar system. Some, like Uranus, may be cooling. All the outer planets have vastly longer orbital periods than Earth, so any climate change on them may be seasonal. Saturn and its moons take 30 Earth years to orbit the Sun, so three decades of observations equates to only 1 Saturnian year. Uranus has an 84-year orbit and 98° axial tilt, so its seasons are extreme. Neptune has not yet completed a single orbit since its discovery in 1846.

This is a round-up of the planets said by sceptics to be experiencing climate change:

  • Mars: the notion that Mars is warming came from an unfortunate conflation of weather and climate. Based on two pictures taken 22 years apart, assumptions were made that have not proved to be reliable. There is currently no evidence to support claims that Mars is warming at all. (Specific aspects of the ‘Mars’ argument are addressed in a separate Skeptical Science post “Global Warming on Mars?“)
  • Jupiter: the notion that Jupiter is warming is actually based on predictions, since no warming has actually been observed. Climate models predict temperature increases along the equator and cooling at the poles. It is believed these changes will be catalysed by storms that merge into one super-storm, inhibiting the planet’s ability to mix heat. Sceptical arguments have ignored the fact this is not a phenomenon we have observed, and that the modelled forcing is storm and dust movements, not changes in solar radiation.
  • Neptune: observations of changes in luminosity on the surface of both Neptune and its largest moon, Triton, have been taken to indicate warming caused by increased solar activity. In fact, the brightening is due to the planet’s seasons changing, but very slowly. Summer is coming to Neptune’s southern hemisphere, bringing more sunlight, as it does every 164 years.
  • Pluto: the warming exhibited by Pluto is not really understood. Pluto’s seasons are the least understood of all: its existence has only been known for a third of its 248 -year orbit, and it has never been visited by a space probe. The ‘evidence’ for climate change consists of just two observations made in 1988 and 2002. That’s equivalent to observing the Earth’s weather for just three weeks out of the year. Various theories suggest its highly elliptical orbit may play a part, as could the large angle of its rotational axis. One recent paper suggests the length of Pluto’s orbit is a key factor, as with Neptune. Sunlight at Pluto is 900 times weaker than it is at the Earth.

Claims that solar system bodies are heating up due to increased solar activity are clearly wrong. The sun’s output has declined in recent decades. Only Pluto and Neptune are exhibiting increased brightness. Heating attributed to other solar bodies remains unproven.

Footnote: this post was written for SkepticalScience as part of an ongoing project to add ‘basic’ rebuttals of common climate change denial arguments. References for all statements can be found in the intermediate discussion “Global warming on other planets in the solar system”.

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5 Comments leave one →
  1. G. Thomas Farmer, Ph.D. permalink
    September 16, 2010 8:55 pm

    Even if the other planets in the solar system system are heating up, it is not relevant to the Earth’s warming, which is mainly due to the burning of fossil fuels. Unless one believes in Martians, Venutians, etc. and a fossil-fuel based economy on those other heavenly bodies.
    A great site, Graham!

  2. elsa permalink
    September 16, 2010 10:47 pm

    Dr Farmer is quite right. Even if the other planets were warming it would not demonstrate that any earthly warming is not due to CO2.

    That would be a bit like saying if you were ill at the same time as your neighbour had polio that you must have polio. It is also like saying that such warming as has taken place has ocurred at the same time as CO2 levels have risen therefore the CO2 caused the warming.

  3. Graham Wayne permalink*
    September 17, 2010 8:09 am

    Dr. Farmer – thank you Sir! Most kind.

    Elsa – Good morning my dear. Actually, if all the planets could be shown to be warming synchronously – including Earth – then it would cast doubt on the AGW theory. Sceptics believed they did indeed have evidence that this ET warming was occuring in the same time-frame as climate change on Earth. The obvious culprit in that scenario would be increased TSI, which would affect all bodies in the solar system (the amount of effect depending on distance from the sun).

    This argument has frequently been raised in fora I contribute to, and as I pointed out here, it is the levelling of TSI in recent decades that defeats the argument outright, let alone the fact that most of the reported ‘warming’ (8 counts so far) is actually wrong anyway.

  4. January 14, 2011 9:00 am

    Does anyone know what the many bodies in our solar system are doing – warming, cooling or no trend?

  5. Graham Wayne permalink*
    January 14, 2011 9:32 am

    As far as I could tell when researching the article, there seems to be no specific trend. However, the information is incredibly patchy and sparse, and the periodicity of what measurements we do have is so long that any trend may be impossible to discern. We don’t have the instruments from which better data can be derived – photographs are unreliable, as the Mars farrago demonstrated – and other data we get is incidental; ‘drive-by’ measurements taken as part of some other initiative or study, usually from satellites on their way somewhere else. Contemporary surface data from Mars doesn’t help much, because we don’t have an historic data series from which to derive a trend.

    However, we do know that the sun’s output has been flat (or diminishing) for several decades – starting to pick up again now – so I believe we can draw some modestly accurate inferences from that.

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