Times are good for the Scottish National Party just now: the party's public approval ratings are high and support for its ultimate raison d'être, independence, is on the rise. But the majority of Scots have not yet been convinced that the SNP can translate its crowd-pleasing performance as a devolved government into the kind of leadership a sovereign state would need. And the problems it faces were illustrated by the environmental policies that came up for discussion at its spring conference this month.

Historically, the SNP's image has always been too strongly linked with backing business development and with Scotland's oil to be seen as particularly green. In recent years, it has worked hard to change that, but the issues raised at the conference did more to highlight the difficulties faced by a devolved government than they did to advance the SNP's environmental cause.

A fringe meeting ambitiously titled "The Greening of Our Policies" turned out to be devoted to the Scottish government's rather cosmetic "war on litter". Scotland's environment minister, Michael Russell, announced an initiative that will encourage councils to hand out more fines for dumping rubbish, and more radically, will offer firms such as Tesco the opportunity to sponsor areas with litter problems. In return for funding clean-up operations, they will be able to put up signs showing the company's logo. Time was also made for a brief aside about the problem of bins with small openings - the minister pointed out that people aiming to throw rubbish into these receptacles often miss. It was a fair point; and, more broadly, it's true that in a country whose economy relies heavily on tourism, plastic bags in hedgerows and filthy beaches potentially can be major problems. But whether replacing rubbish with corporate branding has any kind of aesthetic advantage wasn't discussed, and neither was the question of whether an event that dealt only with the most superficial of environmental issues really deserved such lofty billing.

At the other end of the scale, Alex Salmond mentioned the £10m Saltire Prize for innovation in marine technology, which was launched in Washington, DC during last month's Scotland Week, in his keynote speech. The prize is the biggest of its kind, and Salmond announced to an audience of whooping Nationalists that Scotland has "a quarter of Europe's marine renewable resource and the ambition and determination to harness this clean, green energy". What he failed to note was that the SNP controls only the waters within 12 miles of the coast because the Scottish Marine Bill, announced by the party last June, is apparently still in development. So the Scottish government cannot consent to the use of any wave technology that is designed for use more than 12 miles offshore - in other words, it may not be able to utilise the technologies that are funded by the Saltire Prize.

Leading a devolved government, the SNP are trapped between their remit as a national party and their desire to become the party of "a global Scotland". To achieve this, Salmond and the rest of his cabinet need to engage with the environment as a global issue. But funding marine innovations when Scotland lacks jurisdiction over its own waters, and dressing up a litter initiative as policy "greening", simply underline the SNP's limitations.

In an attempt to appear more engaged globally, the party has made impressive pledges to reduce carbon emissions by 3 per cent each year and to recycle 85 per cent of Scotland's rubbish. But it remains to be seen whether the SNP keeps these promises or not.

And if it fails, it will be left with a series of environmental policies that leave the party looking insular and weak.