Since the canard that since Mars is warming anthropogenic warming here on earth must be false pops up again and again (like in whack-a-mole), I think it appropriate to post something about it.
The only thing possibly linking a warming on Earth and Mars (if there were a common cause) is variations of the sun’s radiation. This hasn’t changed much in at least the last 30 years, apart from the 11year solar cycle:
It is clearly visible that even those cyclic changes are small – about 1 W/m2. To compare with forcings by the greenhouse effect, this has to divided by four, because the 1367 W/m2 apply only to a surface perpendicular to the direction of the sun (like at the equator without absorption by the atmosphere), while forcings are calculated for the whole surface of the earth. The greenhouse forcings (the additional effect by manmade GHGs) are at about 1.5 W/m2. Compare this with 0.25 – and it is irrelevant anyway, because these changes go up and down.
Moreover, in the last few years, it has gone down, not up. But we just observed the warming on Mars in just those last few years.
Now there is a new paper (for those fortunate enough to have a subscription) published in Nature that explains the warming trend on Mars with changes in the albedo. It is cited in Scientific American:
Snapshots over the past three decades have shown vast regions of the Red Planet’s surface have brightened or darkened by 10 percent or more, reflecting about 20 percent of incoming sunlight in total. To determine if albedo (reflectivity) changes affect the climate, researchers compared Viking orbiter photos from 1976 to 1978, which mapped the planet’s bright and dark spots, to those from 1999 to 2000, when the Mars Global Surveyor discovered a darker Mars.
See also this post by William M. Connolley.
Changes in albedo can have an effect. I have a small C program that calculates the expected temperature with
T = pow((solconst/(d * d))/(4*SIGMA)*(1.0 - albedo), 0.25);
With the values d (distance) = 1.53 AU, solconst = 1367 W/m2 (at 1 AU), SIGMA = 5.6704×10−8 (metric), and albedo = 0.16 the temperature gets 215.65K (-57.5C). With just 1 percent point increase in albedo (0.17) it gets 215.00K (-58.14C). We disregard the greenhouse effect on Mars here – which is there, but small (the average temperature on Mars is about 10 degrees higher).