How a certain narrow-mindedness within the environmental movement could lead to policies that, if applied on a broad scale, would result in net environmental harm:
Anti-nuclear bias. Electricity generation is the biggest source of GHGs. Expansion of nuclear energy would save lives and protect habitat now and greatly reduce CO2 emissions from power plants. When nuclear power plants fail, they do so dramatically. But the technology keeps improving and the risks keep decreasing. Even with the old technology, the cumulative damage done to people and the environment throughout the history of nuclear power has been much less than what is wrought by coal and natural gas every year (mainly through air pollution). Of course, renewables like wind and solar should play a part in the battle against global warming but only nuclear energy has the potential to deliver reliable power at the scale the global economy requires while greatly reducing the carbon emissions that so endanger our planet. As Obama's Council of Advisers on Science and Technology put it "achieving low-carbon goals without a substantial contribution from nuclear power is possible, but extremely difficult..”
Organic agriculture. Organic agriculture is less productive overall and so organic farms require more land than those that use conventional methods. See, for instance http://www.nature.com/news/organic-farming-is-rarely-enough-1.10519 :” Crop yields from organic farming are as much as 34% lower than those from comparable conventional farming practices, the analysis finds. Organic agriculture performs particularly poorly for vegetables and some cereal crops such as wheat, which make up the lion’s share of the food consumed around the world.” Both to expand habitat for endangered species and to have more of the planet forested, we need to make agriculture more productive, not less. Conventional farmers are already getting better and better at reducing the environmental impact of farming, e.g., large expansion of no-till farming in the last decade, use of cover crops, less burning of crop residue, measures to reduce fertilizer run-off, plus less and more targeted use of pesticides and fertilizer.
Localism. This is the idea that our food should be locally produced for a variety of reasons, from romantic ideas about community to reducing CO2 from long-haul transport. Problem is, any specific locality is only appropriate for a few types of crops so locally-sourced produce and cereals are simply not feasible on any significant scale. Localizing would also mean forsaking comparative advantage in agriculture and require more inputs to grow a given quantity of food, including more land and more chemicals—all of which come at a cost of carbon emissions. Also, for more people to reap the “benefits” of locally sourced foods, the population would have to spread out and “de-urbanize” - requiring that they commute longer distances to work and increase cultivated and developed lands overall. Plus, smaller trucks with less storage space often emit more CO2 per unit transported than those big-ass long-hauls, because the latter transport so much more stuff per haul. Efficiency matters. For more on this, see: http://freakonomics.com/2011/11/14/the-inefficiency-of-local-food/ or read the wonderful book, “The Locavore’s Dilemma: In Praise of the 10,000 mile Diet”.