Arguments
Global warming on Mars, ice caps melting
What the science says...
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Martian climate is primarily driven by dust and albedo and there is little empirical evidence that Mars is showing long term warming. |
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Climate Myth...
Mars 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.
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 Viking 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.
Last updated on 5 October 2016 by John Cook. View Archives
Thinking 'outside the box' is a school not often visited by some. In all the discussions of planetary global warming (i.e. Earth, Mars Jupiter, Saturn, Pluto) very little attention is given to our solar system's travel above, below, and around the galactic plane on its cyclical route round the Galaxy. (approx 240k+ years). Conditions along the path are hard to predict since historic records are only now being established. Therefore any theories or calculations of planetary temperatures from volcanic, atmospheres, rings of dust, or human intereactions, etc. must include calculations of the density and position of materials encountered along our solar systems path and its interactions with the Sun's activities. These conditions make it extremely difficult to predict any astronomical algorithm's absolute forecasting the reason for Earth's warming trends. In other words, the best thought humans put forth probably has not reached a definite answer in totallity to the question, "Why is Earth warming?"
Whether travels on the galactic path had anything to do with past climate change is harder to decide, but we can see clearly that it has very little to do with post-1970 climate change. Why? because we have good measurements of the climate determinants. The only "space" factor affecting climate is TSI, whether from change of angle, change of solar luminense or "space dust". This is accurately measured by satellites since 70's and is stable if not decreasing (see "its the sun" argument), and yet the earth warms. Why look to weird, unknowable, out-there sources of warming when there is a perfectly reasonable, physically plausible solution coming right out of the smoke stack? Or to put it another way, we have measurably increased the energy flux onto the surface of the earth with increased GHGs. What mechanism do you propose by which this would not cause warming?
We have NOT been measuring the other planets temperatures systematically since the 70's.... and I did not state the the majority of EARTH warming does originate with our mismanagement of the planet. I was only stating that IF other planets in our system might all be experiencing warming, then we should look at other possibilities be they "weird" or undiscovered!
Novemdecellist @33, there is a very simple reason to think that our motion through the galaxy has very little do do with current changes in climate. Specifically, it will take us 1360 years to travel just one light year at our current rate of travell. In the direction we are travelling, there are no nebulae to obscuring local stars, so we know the nearest nebula to be many light years away. Apparently the nearest nebula of any sort, L134, is around 300 light years away, and not in our direction of travel.
It follows from this that the radiation, and molecular density of the space through which we are travelling has not changed appreciably in hundreds of thousands of year; and will not change appreciably for hundreds for thousands more years except in the cases of nearby supernovas. And if it is not changing, it is not the cause of change.
And also worth noting (as this and articles on other planets show) that real evidence for climate change on the other planets is somewhat lacking. See the intermediate versions.
Also worth noting are the astronomers - who spend their careers looking at the stars, including spectral and intensity measurements. If we had entered a nebula (that was somehow unobserved at a distance) the reduction in starlight over the last 40 years would have been quite noticeable. Not to mention spectral changes in sunlight, measured either from the surface or from satellite.
Given a complete lack of evidence for a hypothesis of interstellar dust/climate interaction, I would classify it on the same level as "climate elves".
Novemdecillist... Is there something to give you indication that others are not thinking outside this particular box? I would suggest that scientists have made careers out of looking into a wide range of boxes to see if there could possibly be other explanations for what they see. In fact, other planets warming would be one of the first in a long series of other boxes researchers would check into.
Tom Curtis #29:
If all the photos in your figure 3 were taken close to opposition (when Mars is closest to the Earth), each of them must have been taken about 780 days later than the previous one, or one Martian year plus 93 days. That is like taking photos of the Earth with 415 days intervals or 50 days later every year.
Based on the surface markings it seems to me that the photo from 2001 must have been taken close to northern hemisphere autumn equinox on Mars, corresponding to late September on Earth.
That means that the photos from 1995, 1997 and 1999 roughly corresponds to late April, mid June and early August respectively (spring and summer in NH), while the photos from 2003 and 2005 corresponds to early November and late December (spring and summer in SH).
In other words, the changes in this photo sequence are simply caused by the seasons, and have nothing to do with any climate change on Mars!
I wonder how this guy Nasif Nahle would explain away that?
HK @40, you raise a very good point. It is likely that most of the differences between polar cap size in Mar's observations will be due to seasonal cycles, something Nahle has failed to consider (along with the majority of the evidence on the changes in the size of Mars's icecaps over time.
Thank you for a quick response, Tom!
Yes, it is meaningless to use photo sequences like that as proof of climate change on Mars unless the photos are taken close to one Martian year (687 days) apart. In the 2005 photo, the south polar cap (mostly frozen CO2) had been exposed to the midnight sun for nearly 6 months. No wonder it had almost disappeared!
Hi There, I know it has been a couple of years, but since bad arguments against AGW tend to stick around, I recently tried to explain to someone how mars' specific characteristics make it a bad earth analog in this case. I was then tripped up by the fact that we do use Venus as an analog for the greenhouse effect. I'm sure there's an explanation of how these things do not refute each other, how it isn't hypocritical to use both concepts in explaining our understanding of AGW, but I'm having trouble wording it. Can anyone help me out. Why do we accept Venus as an example in support of AGW hypothesis, but reject Mars as an example in opposition. Thanks!
I think you need to explain your problem a little more. GHG play a part on both Venus and Mars. Exactly the same equations are used to calculate the change of surface temperature due to GHE on Venus, Mars, Earth (or any other planet). Try here for detailed comparisons. I dont see a claim that is using Venus to support AGW and Mars to reject it.
@43,
I would request a link to where Venus is used as an example of the greenhouse effect, thanx !!
Well Venus is hardly an "analog". It is often used as an example of a "runaway greenhouse effect" - positive feedback boiling oceans and then remaining too hot for condensing of any GH gases. Note that scientific opinion so far is that there is no chance of this happening here due to anthropomorphic activities.
A good discussion of Venus' greenhouse effect is here, by Chris Colose.
GPWayne, your link to Fred Thompson in the green box no longer works.
[GT] Thanks, we will update the link.
Dutchwayne @49 - you are certainly correct that Mars is a far simpler climate system. But given the very great differences between it and Earth, it is therefore a much poorer comparison to Earth's system. So therefore what useful information can be gained in the comparison, which could not be better obtained elsewhere?
For instance: solar activity is better measured directly by Earth satellite, rather than by observation of its effects on a planet which is (varyingly) 60 million to 400 million Km from Earth.