There’s no joy in it but it’s got to be done. We have to press ahead with harvesting the tidal energy of the River Severn, despite the havoc it is likely to wreak on local wildlife, because these days there is no such thing as local wildlife.

When we talk about living in a globalised world, we don’t usually think about nations sharing wildlife. But we are now getting other people’s fish. Bluefin tuna and anchovies are increasingly common in British waters and no doubt we’ll be getting into fights with foreign fishing fleets about them soon. Elsewhere, species of Japanese coral are migrating northwards. A few weeks ago, Australian scientists issued a report into the ocean biodiversity in their region. Rather shockingly, their tropical fish are moving away – those that aren’t dying off in the rapidly warming water are migrating southwards, following the plankton that are being carried on currents that are rising in strength.

You won’t be surprised to hear that the blame for all this flux lies with global warming. Rising temperatures leave the inhabitants of the ocean no choice but to embrace change. Paradoxically, though, taking measures to combat global warming – such as building the Severn barrage to reduce our dependence on fossil fuels – will also force changes on the natural world. It’s now a question of whether we value our creatures more than everyone else’s.

The Severn provides Britain with a golden opportunity to exploit lunar power. The moon’s pull causes earth’s water to bulge out from the surface and the geometry of the Severn creates a bigger bulge than most. The difference between its high and low tide is the second largest in the world; only Canada’s Bay of Fundy can beat the Severn’s 14-metre pile of water.

Hold that heap of water back until just the right moment and the resulting torrent on release is a renewable source of energy. A Severn barrage would provide enough lunar electricity to power 5 per cent of Britain’s homes, equivalent to three nuclear or gas-fuelled power stations. It would also last three times longer – at least. According to projections, the barrage could operate for over a century, compared to the few decades of lifetime offered by a nuclear plant.

A cross-party group of MPs is backing a campaign for the barrage to be built and David Cameron has recently instructed the Energy Secretary, Ed Davey, to look at the proposal. It still might not take off, however. That is because, from a local perspective, it will be an environmental tragedy.

As with any hydroelectric project, holding back the water floods areas that would usually be dry. In the case of the Severn barrage, many of those areas are mudflats designated as sites of special scientific interest: feeding grounds for important bird species. It’s also worth mentioning that forcing the water through electricity-generating turbines at high pressure cannot help but hurt fish populations, too.

No pain, no gain

The consortium looking to build the barrage has come up with a design that, it claims, reduces mudflat loss by 60 per cent and operates at lower pressures, easing the toll on the Severn’s fish. Perhaps there are other mitigation efforts that can be made, such as constructing artificial mudflats at the water’s new edge. Either way, it is hard to see how we can justify holding back the barrage now. We will have to sacrifice some of our cherished natural environment.

As far as carbon-free, sustainable energy generation goes, this is the low-hanging fruit. If we don’t grab it, our continued emissions will have a similar, maybe greater, impact on biodiversity in other places. Yes, it will hurt but when did it become OK to save our wildlife at the expense of everyone else’s?