Global freight accounts for about the same amount of Co2 as Japan, Canada, Germany and Mexico combined. That is three billion metric tonnes of Co2 produced each year by road, rail, air and shipping. One solution might be solar-powerd airships. Several research projects are trying to get them off the ground. These solar airships would travel at 9,000m where photovoltaic cells are up to 30 per cent more efficient.

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Source: Al Jazeera