Well, it'd be nice if they'd even attempt to create an answer. First, one has to frame how the impact will be measured: CO2 produced? petroleum products consumed? other factors such as poop on the ground? shoes/clothes/furniture destroyed? toys purchased? extra food processing required to make dog food?

Then, lifespan calculations need to be made.

On the overall, I think SUVs cost more - especially due to the cost of construction and products used. Given that they get less efficient with age, the environmental impact is probably something like an inverted bell curve.

Not even a close call.

Dogs live about 10-13 years, assume the same for SUVs.

SUVs indisputably have a higher production cost. (Assume we just talk about marginal cost to environment of +1 SUV and not even about the cost of setting up the SUV plant; likewise, assume cost of +1 puppy, setting aside cost of mom and dad dogs.) I don't even believe you could rationally argue otherwise.

For arguments sake I will even concede that a dog and a SUV have the same annual impact on the environement. How (1) a SUV and dog could give off the same amount of CO2 or (2) producing dog food would cost as much as drilling oil, with the resulting geopolitical impact, or (3) a SUV -- which routinely run over and cripple school children -- and a dog -- which on occasion might give a child a small bite -- possibly have the same impact just boggles the mind. But I'll even concende, for now, that the two are even -- just to show you how bad of a question this is.

Disposal costs. Again, not even close. Try burying a dead SUV and a dead dog, after he has passed on (due to natural causes) to doggy heaven, in your yard. Just try and tell me that you it took the same effort and your yard looks the same either way. Then give it a couple years. Come back and tell me which one works out better for you.

The only way you could even make it close is some make believe world were you warp the issue into marginal environment cost of a SUV vs. a minivan and a dog vs. an empty petless existence.

Seriously, what does it take to get a job with the MIT econ department? Is Boston so cold that no one else will take this job? Is it the sports teams?