I would say Coconut milk is more environmentally friendly. Almond milk requires more water.
According to BBC, “Almond milk requires more water to produce than soy or oat milk. A single glass requires 74 liters (130 pints of water) – more than a typical shower. Rice milk is also comparatively thirsty, requiring 54 liters of water per glass. Heating the average UK home produces 2.34 tonnes of CO2eq annually, according to data from the Committee on Climate Change, and a passenger’s carbon footprint for a return flight from London to Malaga is 320kg CO2eq, based on figures from the Carbon Neutral calculator.
The land used to produce the annual consumption of each food is compared with the size of a double tennis court, 261 meters squared.”

According to Inhabitat.com,” Almond milk seems like a great milk alternative, its environmental impact is fairly high. The biggest problem with almonds is that they require a lot of water to produce. On average, it takes a little over a gallon of water to grow a single almond. Even worse, many almond growers are located in California, which has suffered extreme droughts over the past few years. Coconut milk is that it has a very low environmental impact. The farms are eco-friendly and use small amounts of water to produce coconuts. Coconut trees can also filter out carbon dioxide, which is great for combating greenhouse gases. Transportation and processing are the only environmental impacts to consider in the production of coconuts.”

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