Water Demands - can they be met? 
http://www.ers.usda.gov/publications/eib-economic-information-bulletin/eib99.aspx
 
Are Biofuels Damaging to the Environment?
http://blogs.princeton.edu/chm333/f2006/biomass/home.html
 
Is mass extinction taking humans with it?
http://blogs.scientificamerican.com/guest-blog/can-humans-survive-mass-extinction/
http://www.newsweek.com/sixth-mass-extinction-upon-us-can-humans-survive-63237