It depends on your definion of Christian. In the western societies, those that have done and are doing much damage to the environment are often labelled Christian, often being respected members in churches. They have taken the advice to cultivate and reproduce but have mostly forgotten that our purpose has also been to be good stewards of the Earth.
Overpopulation is globally a problem, especially as climate change and greed are destroying locally the possibilities to produce sufficient crops. Yet, spreading education has had a positive effect on this problem as population growth has declined much or stopped in most parts of the world. At the moment, Africa is perhaps the most influential exception. This shows that positive changes can happen even without killing huge numbers of people.
Changing attitudes among Christians would probably have a great impact on the near future because there are a lot of Christians and many live in countries that pollute more than the global average. The reason climate change, loss of biodiversity and other global problems continue with the current rate is that even Christians are not willing to do much because ‘I could not stop the climate change’.