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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Pluto warms while the sun cools

What the science says...

Select a level... Basic Intermediate
And the sun has been recently cooling.

Climate Myth...

Pluto is warming

"Some people think that our planet is suffering from a fever. Now scientists are telling us that Mars is experiencing its own planetary warming: Martian warming. It seems scientists have noticed recently that quite a few planets in our solar system seem to be heating up a bit, including Pluto." (Fred Thompson)

This argument is part of a greater one that other planets 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.

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:

  • 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.
  • 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.
  • 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.
  • 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.

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.

Last updated on 15 September 2010 by gpwayne.

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Comments 1 to 4:

  1. Two questions: 1. Where are the scientific citations for "What the science says..." section? 2. The following statement has major logical flaws: "Any Plutonian warming cannot be caused by solar variations as the sun has showed little to no long term trend over the past 50 years and sunlight at Pluto is 900 times weaker than it is at the Earth." First off, why is it necessary for the sun to undergo long term variations over several decades for solar variations to affect Pluto? That is, why are short term variations completely irrelevant? For an extreme example, let's say the temperature of the sun doubled overnight and stayed that way for a year, only to fall back down to normal the next year. Does anyone seriously believe that such an extreme (but temporary) solar temperature jump wouldn't affect Pluto's temperature? Secondly why does the fact that the sunlight is 900 times weaker on Pluto necessitate that Pluto is not warming due to solar variations? Presumably the fact that Pluto is 500 times smaller in mass than the Earth with essentially no atmosphere plays a role, no?
  2. Intermediate tab text is missing.

  3. I have seen no mention that Pluto was closer to the sun in 1988 than in 2002. In fact, according to the Wikipedia entry on Pluto, perihelion came on September 5, 1989. If it is true that, despite this, Pluto warmed up, this calls for further measurements — or a search of the literature for newer temperature measurements.

    Perhaps the following excerpt from  is overly simplistic: " At its warmest, when it is closest to the sun, Pluto can reach temperatures of minus 369 degrees Fahrenheit (minus 223 degrees Celsius)." Perhaps there is a delayed reaction as the planet continues to heat up due to being much closer to the sun than usual. Perhaps the increased temperature as Pluto approaches perihelion has atmospheric effects including a greenhouse effect. More discussion is needed!

  4. The commenters above only show they have not read the materials below and others related to TSI variations.

    Pnyikos says "More discussion is needed!"

    No, it's not. If the sun's output was to increase enough to cause a temperature increase on Pluto so large that it would be observable from Earth, we might as well kiss our bunnies good-bye. The effect would be seen on Earth first and would be of such concern that discussions about Pluto would be delayed until the emergency abates. There is no way that the sun could warm Pluto and we see nothing on Earth first. That is the height of idiocy. Variations on Pluto are going to tell us things about Pluto, not about Earth. We watch the sun closely from here and its output variations are so minute that we could not effectively measure them before satellites. Get real. The Pluto argument is the most grotesque piece of nonsense ever spewed up by deniers. Only one with no quantitative thinking skills whatsoever could be swayed by such drivel.

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