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Global warming on Mars, ice caps melting

The skeptic argument...

Martian North Polar Cap. NASA/JPL.

Scientists are telling us Mars is experiencing its own planetary warming. NASA says the Martian South Pole's ice cap has been shrinking for three summers in a row. Maybe Mars got its fever from earth. If so, I guess Jupiter's caught the same cold, because it's warming up too, like Pluto. I wonder what all those planets, dwarf planets and moons in our SOLAR system have in common. Hmmmm. Solar? (source: The Fred Thompson Report).

What the science says...

Martian climate is primarily driven by dust and albedo and there is little empirical evidence that Mars is showing long term warming.

The primary empirical evidence for long term, global warming on Mars comes from Fenton 2007. Fenton compared a composite snapshot of Mars from 1977 taken by the Voyager spacecraft to a 1999 image compiled by the Mars Global Surveyor (referencing work from Geissler 2005). The 1977 snapshot showed a brighter planet. In 1999, the planet had a lower albedo, with prominent darker regions in the southern mid and high latitudes. Using the albedo changes in a general circulation model, Fenton calculated a 22 year global warming trend of 0.65°C.


Figure 1: Snapshots of Mars 1977 (top) and 1999 (bottom). Image courtesy of Geissler 2005.

Fenton attributed the warming to surface dust causing a change in the planet's albedo. Martian dust plays a major role in the planet's climate (Kahn 1992). Solar variations are not the main driver of Martian climate. Nevertheless, an important question remains: is the interpretation of long term global warming on Mars correct?

A broader view of Martian climate change

To put these results in proper perspective, an understanding of what drives Martian climate is required. Global dust storms increase the surface albedo by settling brighter dust on dark surfaces. Within a year after a dust storm, various wind systems remove the dust and Mars returns to a normal, lower albedo.

The 1977 snapshot was taken after a global dust storm had deposited dust over the southern latitudes, lightening the planet surface. Before the storm, the planet had albedo comparable to recent measurements (Szwast 2006).

Fenton drew conclusions about long term climate by comparing two end points. This led to the classic error of mistaking weather for climate (similar to the recent global cooling argument). When you look at the broader data, there is no discernable long term trend in albedo:


Figure 2: Comparison of data sampling by Fenton 2007 (left, comparing 2 end points) and the full sample of data (courtesy Mark Richardson).

The apparent long-term warming between the 1970's and 1990's is largely a consequence of the timing of the two snapshots used. The "brighter" 1977 snapshot was immediately after a global dust storm when the planet was temporarily lighter. The "darker" 1999 snapshot was of the planet in it's usual state. There is little evidence that Mars is undergoing decadal-scale, long term global warming. In fact, following the 2001 global dust storm, the southern hemisphere was brighter than in 1977 (Szwast 2006).

Conclusion

The empirical evidence isn't conclusive on whether global warming is happening on Mars. However, to answer the question on whether the sun is causing Earth's global warming, there is plentiful data on solar activity and Earth's climate. Many papers have examined this data, concluding the correlation between sun and climate ended in the 70's when the modern global warming trend began.

So the argument that Martian warming disproves anthropogenic global warming fails on two points - there is little empirical evidence that Mars is warming and Mars' climate is primarily driven by dust and albedo, not solar variations.

Planet wide dust storm

A good example of how dust affects Mars climate: over 2007, Mars suffered a titanic dust storm that engulfed the entire planet. The dust storm contributed to a temporary warming effect around Mars, raising the temperature of the atmosphere by around 20-30°C. Interestingly, whereas the atmosphere of the planet heats up, the surface of the planet cools down because it receives much less solar heat.

Acknowledgements

Many thanks to Mark Richardson for his advice and materials on Martian climate. Thanks also to Jon for the heads-up on Mark Richardson's latest AGU presentation.

Comments

  1. Sediment cycles on Mars in resonance with Earth

    After computation of the astronomical Milankovitch cycles on deep sea cores for the last 2.4 Ma the same cycles revealed to exist in land sediment series: Long Term (last 2.4 Ma, Pleistocene) and Middle Term (last 127Ka, Last Interglacial - Last Glacial Time-span) Time Series after cycle computation with the newly developed ExSpect method. Moreover, the same calculation method proved useful for Short Term Time Series as well on sediments of the last 10.000 years (10Ka). The latter cycles as those obtained for ice and glacial lake deposits on Mars could also clearly be traced back in the planetary correlations computed by the NASA Goddard Space Flight Center. This points to an extra terrestrial astronomical forcing of the origin of all these cycles on both planets Earth and Mars.

    Which begs the next question - how would they know this without taking a sediment sample on Mars?
    Answer: they got one with the the Mars orbital satellite.
  2. Nice picture of the southern icecap by the way.
    [ Response: Thanks, it was either a photo of the icecaps or a picture of Fred Thompson. I think I made the right choice. ]
  3. Philippe Chantreau at 02:36 AM on 24 September, 2007
    Once again, it is useful to ask ourselves this question about other planets: how unusual is this (the recent southern ice caps sublimation)? This link gives a hint: http://www.msss.com/http/ps/seasons/seasons.html. Consider also that Mars' orbit takes about 589 days, letting us observe only three full seasonal cycles in 5 years.

    It has long been known that Milankovitch cycles are the best fit to the available evidence for historic glaciation-deglaciation cycles on Earth. The energy source, the Sun, is extra-terrestrial but there is no evidence that it got brighter or dimmer in proportions apt at changing our climate and in any case, that is not what Milankovitch cycles are. As far as I can recall, the energy received changes because of the planet getting closer, farther, or being oriented slightly different, which is a function of its orbit and precession; in that sense, extra-terrestrial is a little misleading, since these qualities could really be called intrinsic to the planet.

    The point of the paper cited by papertiger is that Earth and Mars' Milankovitch Cycles could be resonant. I wonder if anyone has tried to obtain some level of confirmation from pure celestial mechanics calculation. In any case, it is interesting but quite irrelevant to the current terrestrial warming, which does not correlate well with neither Milankovitch nor with the so-called Martian warming. That Martian warming is really a re-warming back to the kind of weather seen by the Viking crafts, and the Earth should now be heading for cooler climate if only Milankovitch was at play.
  4. Philippe Chantreau at 02:55 AM on 24 September, 2007
    This seems to be the best work so far on Mars' recent weather: Global warming and climate forcing by recent albedo changes on Mars
    [ Response: Thanks, this was the study I was refering to but I didn't have a direct link to the study. I've updated the page with the link added. ]
  5. Sunspot numbers are extremely crude indicator of solar activity and do not encompass many other manifestations of it (sorry adding the F10.7cm Radio Flux Index also won't do the trick). So repeating the argument that sunspot numbers have leveled out since 1950 doesn't necesseraly mean what you want it to mean (no additional inputs from the Sun in the Earth's or any other planet's climate). Also, focusing only on the total solar irradiance (TSI) as the only possible way in which solar activity influences Earth type planets' climates is just selective presenting/lack of knowledge (I hope it is the second, since the first would imply very bad things about your presentation of facts).

    In fact, there some quite viable hypothesis that explain how non-TSI manifestations of solar activity cause dust storms on Mars (by the way those are possible for the Earth as well). Obviously there is still to little data to confirm or reject them. By don't "get rid of" Mars just yet. Mars is actually quite good "test case" for the anthropogenic vs. natural warming debate. As a planet it is quite similar to the Earth in many important aspects and it is as close as ti the Earth as it gets in the solar system. Some of the main advantages for a possible "Mars test case" are: 1. There is no human activity there to influence the Marsian climate in any way, so we can discount that factor 2. there is no ocean to provide huge termal inertia, so solar effects will be much more immediate, 3. Marsian day is almost identical to Earth's day, 4. Marsian atmosphere is similar Earth's mid upper atmosphere, so this simplifies estimation of the solar effects quite a bit.

    The geometrical effects that you mention (orbit's eccentricity, axis tilt) are quite easy to correct for, much easier that cloud structure in the current climates for example.
  6. StanislavLem: An interesting post, but even better for me is that it lets me play skeptic for a change ;-) .

    You do not specify what viable hypothesis explain how non-TSI manifestations of solar activity cause dust storms on Mars, so I can not address that, but I do not agree with your idea that the Martian atmosphere is a good test bed to allow observation of the effect of human activity. Off the top of my head, here are 4 major differences and, in my opinion, each one is enough to invalidate such a comparison without a large amount of research (i.e. several continuous martian weather stations).

    1) No magnetosphere so there is a direct ionization of atmospheric particles.

    2) I would disagree with your comparison about pressure. If you are looking at total atmospheric pressure, then Mars is more like the stratosphere. If you are talking about partial pressure of CO2, then the surface of Earth is the best we can get, but that is even too low. In any case, both of these do not produce some of the more important effects such as pressure broadening of the CO2 absorption spectrum.

    3) There is no water to speak of and thus the vertical thermal transport associated with water does not exist.

    4) Finally, the drivers also seem to be much different. Dust storms are a key part of the Martian climate as are sublimation winds from the poles. These have no equivalent on earth.

    Regards,
    John
  7. Will Nitschke (www.capitaloffice.com.au) at 10:32 AM on 19 December, 2007
    You wrote:

    "Mars has one of the highest orbital eccentricities of any planet in our solar system which causes much greater seasonal changes than on Earth."

    OK, but has the orbit of Mars changed in the last 30 years or the last 100 years to explain the extra warming? If the answer is 'yes' can you explain why and how? If the answer is 'no' then doesn't that point to an extra-planetary explanation? It seems in your article you begin by ruling out the sun, then suggest you're going to offer alternate explanations, then fail to do so. Yes the storms can cause the warming, but what is causing the extra turbulence in the atmosphere leading to the storms?
    [ Response: The orbit wouldn't have changed over a 30 year or 100 year period - orbital changes occur over much longer periods. By orbital eccentricity, I mean Mars' orbit is more elliptical than Earth's which is more circular. This means Mars's distance from the sun changes more dramatically through a Martian year which means its seasonal changes are more dramatic than Earth's. I thought the alternate explanation was clearly explained - dust storms reducing the planet's albedo. ]
  8. Will Nitschke (www.capitaloffice.com.au) at 12:38 PM on 19 December, 2007
    Thanks for the response, but it appears you only want to take the argument up to a fixed point. What's caused the *increase* in dust storms that is leading to higher temperatures? Obviously not the more elliptical orbit of Mars alone as this hasn't changed. Which only leaves an extra-planetary explanation, doesn't it? Your explanation only makes sense if the temperature of Mars was not showing a trend increase. Storm activity would therefore be relatively consistent over time and the temperature on Mars would be relatively consistent over time. But it isn't. If this is wrong (which is quite possible of course), you need to explain how these storm cycles can last decades and lead to decades of warming, and then presumably afterwards, decades of cooling, only by means of interactions within the Martian atmosphere itself.
  9. If Jupiter, the earth, Mars, Pluto and so forth are warming... then its the sun. These alternative feeble excuses are really clutching at straws.
  10. Wondering Aloud at 09:13 AM on 4 January, 2008
    I haven't seen anything on Jupiter system as a whole that would convince me it is warming to any significant extent, and Pluto is likely caused by orbital eccentricity it has been closer than average to the sun in recent years
  11. Philippe Chantreau at 14:01 PM on 15 January, 2008
    Mars cooled down signficantly between the Viking landings and the recent "warming" trend, while Earth was consistently warming throughout that time, making the correlation highly doubtful.

    Pluto has not been observed through a complete orbit yet, arguing about its "climate" is pointless. The observations match expectations from its seasonal cycle and the albedo changes seen since the 50s (likely due to collection of space materials). Furthermore, if the Sun could really throw out the energy to affect Pluto so much, we would be frying.

    There is no convincing evidence that Jupiter's "climate" (once again more a figure of speech than a observed reality) is prone to be affected by variations in TSI so minute that we had to have satellites around Earth to actually mesure them.

    Among the inner planets, Venus, most likely to show changes due to its proximity to the Sun and huge greenhouse effect is not showing any warming.
  12. It's not just Mars. Ever read the papers by the late Dr. Rhodes Fairbridge?

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