Yes! Bitcoin can be mined by computers through a very complex mathematical algorithms. These computers from miners all over the world need tremendous amount of energy to perform such processes.
According to Digiconimist, the Bitcoin networks estimated power use is 30.14TWh a year. This means the electricity consumption of Bitcoin network has exceeded the power produced by the largest Windfarm in Europe.
Since electricity generation is one of the leading source of greenhouse gases, we could tell that Bitcoin greatly affects or environment.