"Hi, I am from Houghton MI. I read your letter to the editor today (4/28) and Iam hoping that you can set aside your "know all about it" attitude about how and why the earth is warming and answer one simple question for me. It is the same question that I have asked many times to many people and have yet to get a decent answer. Here it is;
If humans are causing global warming as you claim, why is there global warming on other planets? you know planets without human life.
Hope you respond, thanks"
I've already addressed the fact that I'm being criticized by somebody who's hiding behind the veil of internet anonymity in a response to their comment. If you'd like to see it, you can search the blog to find it. What? I'm not going to make things that easy for you.
First, I'd like to start by pointing out the glaring error that this person made in stating their argument. If there is one thing that anybody learns from reading this post, let it be this: You cannot make a statement, fail to provide any data, evidence, or supporting arguments for your statement, and expect people to take you seriously. Well...I suppose you could expect people to take you seriously, but you will be sorrily disappointed when you find out that nobody actually does take you seriously. However, I will be setting this aside because I kind of feel like responding, despite the complete and utter lack of provided evidence.
After doing a little research on the topic, I've found that proponents of the "other planets are warming too" argument generally cite Mars, Jupiter, Pluto, Neptune, and Neptune's largest moon (Triton) as supporting evidence.
Ian McClintock provides us with this quote from his paper directed to the National Farmer's Federation of Australia in June 2009.
"Further evidence that CO2 is not the principle driver of warming on this planet is provided by the simultaneous warming of other planets and moons in our solar system, despite the fact that they obviously have no anthropogenic emissions of greenhouse gasses. Mars, Triton, Pluto and Jupiter all show global warming, pointing to the Sun as the dominating influence in determining climate throughout the solar system." (link)Before I get into the details dealing with each of the named bodies, I'd like to address a general problem with the "other planets are warming too" argument. The problem is called the Inverse Square Law of Electromagnetic Radiation. This law tells us that the intensity of electromagnetic radiation is inversely proportional to the square of the distance from that body. In equation form it looks like this.
Where i is the measured intensity of electromagnetic radiation at a distance of 1d from the source. This tells us that Mars (the closest of the planets in question) receives approximately 43.2% of the electromagnetic radiation of Earth, since Mars is 1.52 Astronomical Units (AU) from the Sun. Jupiter receives 3.7% the level of electromagnetic radiation as Earth, while Neptune (Triton's distance varies, so I'll use Neptune's distance as an average) receives 0.11% of the radiation, and Pluto a scant 0.06% of the level of radiation of Earth. So, logic tells us that since the planets in question receive such a comparatively minuscule quantity of radiation, that the impact on the planet's weather and temperature is likewise minuscule compared to that of Earth.
Annual global temperature change (thin light red) with 11 year moving average of temperature (thick dark red). Temperature from NASA GISS. Annual Total Solar Irradiance (thin light blue) with 11 year moving average of TSI (thick dark blue). TSI from 1880 to 1978 from Solanki. TSI from 1979 to 2009 from PMOD. (Image Credit: Skeptical Science.)
The graph above demonstrates another major flaw in the "other planets are warming too" argument. The implication of the argument is that the Sun and its radiation are responsible for the increase in temperatures. However, as the graph clearly shows, global temperatures continue to rise, despite a decrease in the levels of radiation emitted by the Sun over the past 30 or so years.
Yet another problem with the "other planets" argument is atmosphere. The Earth's atmosphere is unique. It is comparatively thick and (though it also reflects more of the Sun's radiation than other planets) holds in a greater quantity of the Sun's electromagnetic radiation. This is what, ultimately, keeps the planet livable. Without the atmosphere, we'd fry from the radiation in a matter of minutes. The problem is that the release of entropy by human consumption is added to the entropy from the Sun's heat and cannot escape the atmosphere. I'll refer you all back to the "clogged sink" analogy that I'm so fond of. There's a finite rate at which water can leave a clogged sink. If you put water into the sink faster than it can drain out, the sink gets fuller. Likewise, if you put entropy into the atmosphere faster than it can leave the atmosphere, the Earth gets warmer. Other planets don't have this issue because their atmospheres are significantly thinner, weaker, and of a different composition than that of Earth. Subsequently, entropy can leave the system significantly more quickly than here on Earth.
Getting into the specifics of the planets, I'd like to start close and move out from there. Research has shown that the temperature of Mars is primarily driven by the albedo of surface dust and dust storms. Albedo is the scientific term for the ability of an object to reflect the light and radiation of the Sun. The reflection of the Sun's radiation logically causes temperature drops. Pictures taken of the surface of Mars in 1977 and again in 1999 show that in 1999, the surface of Mars was darker (meaning less reflection). This is something that proponents of the argument love to bring out in support of their stance. However, what they often fail to mention is that the 1977 image was taken just after a global dust storm and the 1999 image was taken just before the dust storm. This information from a wonderful paper by Dr. M. Richardson from CalTech, which can be found here.
With regards to Jupiter, the available research shows that the climate of Jupiter is driven by the Red Giant's internal heat. What happens is that when a number of smaller storms merge into one big storm (think of the Big Red Spot and the lesser known Red Oval), the planet loses the ability to properly regulate its own temperature. See research from Philip Marcus of UC Berkley here.
The issue with Neptune is, likewise, rather easy to understand. We've only been gathering information on the climate of Neptune since 1950 and a year on Neptune lasts over 169 Earth Years. This 60 year observation period is equivalent to observing 4.3 months of an Earth year and drawing a conclusion of the weather of the planet. We have simply not been gathering data of Neptune for a long enough period to put forth more than a vague guess as to what the weather is like. Making an assessment of the global climate of Neptune and whether or not it is changing is quite impossible at this point in time.
Triton, Neptune's largest moon, was visited by Voyager in 1998. Since that time, recorded data shows that the temperature is, indeed, warming. However, Triton is approaching what is known as an extreme southern summer, a phenomena that happens every few hundred years , which causes temperatures to rise to the highest point of the cycle, much like late August does to the Midwest. From Dr. J.L. Elliot of MIT.
Pluto (I feel bad for you Pluto. You're still a planet to me.) has only undergone a warming trend for the past approximately 14 years. This, given that Pluto's year is just over 248 Earth years, is akin to just over 20 Earth days. Saying "Late July is warmer than early July." isn't exactly much of an observation of global climate, is it? When this considered along side of Pluto's extreme axis tilt and significantly more elliptical orbit than other planets, it is clear that there isn't much that is known about the climate of Pluto, let alone the change of climate. Check out the paper by Dr. Sromovsky from the University of Wisconsin here.
So how to I respond to the "other planets are getting warmer" argument? The answer is simple, I don't. There is not enough empirical evidence available to make an even remotely accurate assessment of the climate of other planets for this argument to be considered valid.