# Extraterrestrial Global Warming?

*Published:* 2007-05-03
*Author:* Bill Chameides

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 \[PDF\]](http://www.environmentaldefense.org/documents/5544_SolarActivity_One-pager.pdf).)

![Solar Energy Output](/climate411/wp-content/files/2007/05/solar_energy.jpg)

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.