Extraterrestrial Global Warming?

Warming in the solar system has become a hot topic these days, and I’ve been getting lots of questions that go something like this: I’ve read that other planets have global warming. There are no SUVs on other planets, so the warming must be due to increased energy from the sun. Doesn’t that mean that Earth’s warming is also due to increased solar energy?

The short answer is, whatever warming there may be on other planets is not due to changes in the Sun. Scientists have thoroughly investigated this possibility, and in nearly 30 years of satellite observations, we’ve seen no increase in overall solar output. (For more on this, see our article on global warming and solar activity [PDF].)

Solar Energy Output

Solar variation cannot explain global warming on any planet, including Earth. So what’s up with our neighbors?

Some sort of warming does seem to be occurring on Mars. The permanent ice cap on the South Pole of Mars has been shrinking. This may indicate a global warming trend or just a regional change. We don’t know for sure, because we don’t have direct global temperature measurements. But let’s say global temperatures on Mars are rising. If the sun isn’t causing it, then what is?

Because of its elliptical course around the Sun, thin atmosphere, and lack of ocean, Mars exhibits large swings in climate over the course of its year, and from year to year. These swings can be amplified by huge dust storms that sweep across the planet. And indeed a recent paper in Nature observed that exceptionally strong Martian dust storms kicked up the light-colored, reflective dust on the planet’s surface, exposing the darker, less reflective basaltic rock underneath. This would decrease the amount of sunlight reflected by the planet, causing it to warm – not because of changes on the sun, but because of changes on the planet itself.

Reading this, you might ask: Could reduced reflectivity, rather than greenhouse gases, explain the Earth’s warming?  The answer is no. As with solar output, we’ve been monitoring the Earth’s reflectivity for decades, and changes in our planet’s reflectivity can’t explain the warming trend.

There also has been some discussion of global climate trends on Pluto, but that’s a real stretch. Two measurements about 15 years apart show a temperature increase on Pluto, but Pluto takes almost 250 years to make a complete orbit around the Sun. Fifteen years on Pluto is equivalent to less than a month on Earth. Imagine declaring a climate trend on Earth using one month of measurements!

The other planets in our solar system are great laboratories for studying climate. But what happens on Mars or other planets does not change our understanding of what’s causing global warming on Earth.

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  1. K.C. Weber
    Posted May 14, 2007 at 3:57 pm | Permalink

    I am writing to respond to Dr. Bill Chameides’ article attempting to disprove Extraterrestial Global Warming, the fact that other planets are warming also, not just the earth.

    In his article he states, “The short answer is, whatever warming there may be on other planets is not due to changes in the Sun. Scientists have thoroughly investigated this possibility, and in nearly 30 years of satellite observations, we’ve seen no increase in overall solar output.”

    This is incorrect. Studies show that the sun’s radiation has increased by .05 percent per decade since the late 1970’s.

    Now, this increase is only important if it has been going on for a century or more. But, we have only been able to monitor this output since the development of observations through satellite technology.

    I’m not saying that the sun is the only reason for global warming. Mankind is definitely a contributor. But, the sun’s influence cannot be so easily dismissed. especially by such an inaccurate statement.

    K.C. Weber

  2. Posted May 14, 2007 at 5:59 pm | Permalink

    I don’t know what studies you’re referring to, but the IPCC’s latest report states that “Continuous monitoring of total solar irradiance now covers the last 28 years. The data show a well established 11-year cycle in irradiance that varies by 0.08% from solar cycle minima to maxima, with no significant long-term trend.” (See section TS.2.4 on page 30 of the Technical Summary.)

    Over a much longer time frame (since 1750), the IPCC estimates that the sun has had a small warming effect (0.12 watts per square meter). That’s still tiny compared to man-made factors. The net effect of greenhouse gases (which cause warming) and aerosols (which cause cooling) is a lot of warming: 1.6 watts per square meter.

    For more on global warming and the sun, you can also see my earlier post about global dimming.

  3. K.C. Weber
    Posted May 15, 2007 at 3:59 pm | Permalink

    This is K.C. Weber again, and I would like to add another point or two on the importance of the sun in a discussion on global warming.

    First of all, the sun is the largest body in our solar system, several times larger than the largest planet, Jupiter, and many, many times larger than the Earth. Not only is its gravity holding all the planets, asteroids, and comets in orbit, but various forms of its energy constantly go to the farthest reaches of the solar system.

    I’m not sure how much the sun contributes to global warming, but we can’t be blind and say that it has no effect on the planet’s temperature. If there was no effect, there would be no life on Earth. Visitors to Alaska can see an example of the sun’s energy interacting with the Earth when they see the Northern Lights. This is radiation from the sun interacting with the Earth’s magnetic field around the poles. Another example is when there are strong solar flares on the sun’s surface. At times like this there are often interruptions in the Earth’s communications and electrical power. If an astronaut were in orbit during a time of increased solar activity, the radiation would be dangerous to him.

    Earth and all the planets are constantly hit by many forms of solar energy, and we are still learning which of them causes variations in a planet’s temperature and climate. In my study of science, I have come to the conclusion that the sun is affecting the Earth and other planets in ways we have not yet discovered yet.

    Now, my love of science has made me an optimist. The more I learn, the more I realize how fantastic our universe is. It causes me to often see things in very positive ways. In environmental talk, I often hear of all that we need to give up and do without. I have a different viewpoint, however. In my opinion, the do without mentality is no good. We need to think of what we can do to improve our lifestyle not take away from it. Rather than denying that the sun has anything to do with global warming, let’s learn how to tap the sun’s variety of energies in ways that we haven’t imagined yet. Or go the other direction. There is untapped energy at the Earth’s core if we could learn how to tap it.

    Now, even though I do not feel that our use of carbon based fuel is the main cause of global warming, I feel its use is becoming somewhat ancient. Rather than saying we should do without, let’s take positive action to bring our world up to speed and make it a better place where we will have more energy to live on, not less.

    K.C. Weber

  4. prohb
    Posted May 30, 2007 at 1:24 pm | Permalink

    Dear KC,
    Unfortunately, I do not agree with you about humans not being the main contributor to present day global warming. I say unfortunately because I wish you were right. It would be so much easier for us. But I have always been taught that when you make a mistake…you fess up. It’s time for us to “fess up” and take responsibility and do something, as a species, about global warming. I have studied this issue for years…listening to both sides and my conclusion is that: Yes, there are normal cycles and astonomical events which can affect climate, BUT, human activity in the form of adding carbon to the atmosphere is speeding up the process and causing more intense events. Also, believe it or not, I am an optimist too….we have responded to situations (notice I didn’t say crisis) before. This time, though, we have to change our paradigm about what progress really is….and about how what we do affects everything else. Being an optimist does not take away our responsibility.
    About myself – I am a teacher, trained as a scientist, of middle school and high school students (one of my responsibilities is debate coach). As a teacher and parent I am convinced we can raise our children to be resilient and courageous problem-solvers while still finding the beauty, joy, and excitement of the world around us. Let’s show them that climate change is a situation to deal with and not a crisis. That is what makes us human. Sincerely, Rick Glatz, New Hampshire

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