Once again, the "prophets of apocalypse" are forgetting the most precious natural resource that exists: human creativity. As the bitcoin market increases and attracts bigger companies, the competition for the fastest mining machines will eventually lead to more investment on improving the power efficiency of current processors. And this will not only benefit bitcoin mining, but also any other heavy processing tasks. It can even improve the energy consumption of cell phones, for example, and that would lead to more durable batteries, which is another pollution source today. And, if the mining costs begin to reach the value of their rewards, the interest in mining will simply diminish, reducing the amount of complexity and again making it profitable. That's simply supply and demand, and it was not invented with bitcoin. It's a concept motivated by basic human instincts, and has been present in our lives since pre-history.