This Friday will mark a memorable moment in the history of climate diplomacy. It’s when the world comes together in New York to sign up to the climate agreement agreed in Paris at the end of last year. Over 150 nations, including over 60 Heads of State, will confirm their determination to start properly getting to grips with climate change after more than 20 years of half-hearted and ineffective posturing.

As they do, President Obama has chosen instead to be here in the UK to add his voice, diplomatically, to an issue of critical importance to everyone this side of the Atlantic: whether the UK is better off in or out of the EU. He will simultaneously take the opportunity to wish the Queen a happy birthday. But let’s be clear, he’s not here for a slice of cake!

Many Brexit campaigners have already expressed their objections to President Obama joining the fray, conscious perhaps that their own parochial, mean-minded rhetoric will not compare well with Obama’s bigger vision of a better future. It’s so sad that we need to look to a leader from outside our shores (albeit President of the most powerful country in the world) to open-up perspectives beyond the ‘battleground of fear’ in which campaigners on both sides are now so obstinately entrenched.

Obama’s intervention has been so widely trailed as to leave little room for surprises. But the legitimacy of such a contribution is surely pretty solid. Comments from Boris Johnson that he’s the last person to talk to Europeans about ‘pooling sovereignty’ are both ignorant and risible, given that the USA’s constitution is based on a complex set of federal/state power-sharing relationships. He absolutely understands that the world needs a unified, outward-looking, generous-hearted Europe (with the UK at its heart), in addressing so many of today’s global challenges.

And climate change has to be top of that list of ‘wicked issues’. The UK has always punched above its weight on the international stage when it comes to climate leadership – something that we can and should be rightly proud of. But the UK’s leadership has always been both enabled and amplified by the EU’s overall positioning on climate change, particularly in terms of negotiations with developing and emerging countries on climate finance. It’s that spirit of shared diplomacy that underpins the Paris Agreement, and now is not the time to put all of this at risk.

And this is a substantial risk for the UK, as has been pointed out by a whole host of leading environmentalists, business groups and academics. The recent report from the Environmental Audit Committee spelled out in clear terms the impact that Brexit would have on environment policy in general. In the words of Mary Creagh MP, Committee Chair:

“Environmental problems don’t respect borders…the overwhelming evidence is that EU membership has improved the UK’s approach to the environment and ensured that the UK’s environment has been better protected.”

But it’s on climate in particular that we stand to lose most, and there are many in the Brexit camp who are not only aware of that, but have factored it in as one of their most important benefits that would arise from a No vote in the Referendum.

The overlap between ‘little Englander’ advocates for Brexit, and out-and-out climate deniers is startling. Be it Owen Paterson, Lord Lawson, John Redwood, Christopher Booker, Matt Ridley or James Delingpole – among others – they proudly wear both badges. And that’s even before we get on to Nigel Farage and some of the more extreme UKIP leaders.

This is not to say that the British public, or the UK’s strong party-political consensus on climate change, would allow the denialist wing of the Tory Party to have its way on climate change. And, to be fair, it would still be perfectly possible for the UK to sustain its admirable track record on international climate leadership whether or not we were in the EU. But that role would be significantly diminished outside of the EU’s wider climate endeavours.

So will Cameron and Obama touch on this tomorrow? At one level, it’s unfortunate they’re not both in New York to demonstrate solidarity with the world coming together in ratifying the Paris Agreement. But being in London, speaking up for that same agenda and for the wider benefits of international solidarity versus Brexit-style isolationism, sends a pretty powerful message in its own right.