The last issue of the Economist tackles some of the "holy cows" of the ecologist movement: Organic Food, Fair Trade and Local Production. I am recommending to read this :-)

https://www.economist.com/opinion/displaystory.cfm?story_id=E1_RPRTPSV

If you think you can make the planet better by clever shopping, think again. You might make it worse

.....If you are worried about the environment, you might buy organic food; if you want to help poor farmers, you can do your bit by buying Fairtrade products; or you can express a dislike of evil multinational companies and rampant globalisation by buying only local produce. And the best bit is that shopping, unlike voting, is fun; so you can do good and enjoy yourself at the same time......
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Farming is inherently bad for the environment:since humans took it up around 11,000 years ago, the result has been deforestation on a massive scale. But following the “green revolution” of the 1960s greater use of chemical fertiliser has tripled grain yields with very little increase in the area of land under cultivation. Organic methods, which rely on crop rotation, manure and compost in place of fertiliser, are far less intensive. So producing the world's current agricultural output organically would require several times as much land as is currently cultivated. There wouldn't be much room left for the rainforest.
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Fairtrade food is designed to raise poor farmers' incomes. It is sold at a higher price than ordinary food, with a subsidy passed back to the farmer. But prices of agricultural commodities are low because of overproduction. By propping up the price, the Fairtrade system encourages farmers to produce more of these commodities rather than diversifying into other crops and so depresses prices—thus achieving, for most farmers, exactly the opposite of what the initiative is intended to do. And since only a small fraction of the mark-up on Fairtrade foods actually goes to the farmer—most goes to the retailer—the system gives rich consumers an inflated impression of their largesse and makes alleviating poverty seem too easy.

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...local food....A study of Britain's food system found that nearly half of food-vehicle miles (ie, miles travelled by vehicles carrying food) were driven by cars going to and from the shops. Most people live closer to a supermarket than a farmer's market, so more local food could mean more food-vehicle miles. Moving food around in big, carefully packed lorries, as supermarkets do, may in fact be the most efficient way to transport the stuff.

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So what should the ethically minded consumer do? Things that are less fun than shopping, alas. Real change will require action by governments, in the form of a global carbon tax; reform of the world trade system; and the abolition of agricultural tariffs and subsidies, notably Europe's monstrous common agricultural policy, which coddles rich farmers and prices those in the poor world out of the European market. Proper free trade would be by far the best way to help poor farmers. Taxing carbon would price the cost of emissions into the price of goods, and retailers would then have an incentive to source locally if it saved energy. But these changes will come about only through difficult, international, political deals that the world's governments have so far failed to do.