So here I am, writing this on a flight out to join Forum for the Future colleagues in New York (I know, I know…), pondering, as always, how to manage the advocacy challenge that lies ahead.

I'm leaving on the day the British media went into overdrive on the latest data from the Arctic on the extent of melting in the summer sea ice. Superlatives abound: 'worst ever', 'unprecedented', 'no known comparison in at least three million years' etc. But the thing that really grabbed me in all the coverage was the personal testimony of some of the scientists involved: shocked, horrified and astonished as they clearly are at the prospect of an ice-free summer Arctic by 2030 – decades earlier than the same scientists were predicting just a few years ago.

A comment from a Cambridge University sea ice researcher says it all: "this is staggering. It's disturbing, scary that we have physically changed the face of the planet."

Scary. A word that's hopelessly understated, and yet seriously difficult to use effectively – especially in the US.

In his acceptance speech at the Republican Convention, Presidential Candidate Mitt Romney mentioned climate change only once, and used speech marks around it to demonstrate his contempt for Barack Obama's marginally more committed position.

It's election time, and both parties still get a lot of money from the oil, coal and gas lobbies. Money talks louder than science or even basic reason. Just check out the official platform of the Republican Party in Texas: "We strongly oppose all efforts of the extreme environmental groups to disrupt and stop the oil and gas industries. We believe the Environmental Protection Agency should be abolished. We support the freedom to continue to use and manufacture incandescent light bulbs. We strongly support the immediate repeal of the Endangered Species Act. We strongly oppose the listing of the dune sage brush lizard either as a threatened or an endangered species."

Now that is scary. Especially if you're a dune sage brush lizard.

Fortunately, I suspect I won't have to deal with any Texas Republicans on this visit, though I have in the past. But I will be engaging with many people who may still describe themselves as 'climate sceptics', if not full-on 'denialists'.

No doubt I'll end up moderating the message to avoid alienating them. To ensure that 'scary' doesn't lead to denial rather than enlightenment. Keeping people on side is a precondition of making any progress on sustainability issues.

I feel bad about that. All the more so having just read the latest broadside from the redoubtable Kevin Anderson at Manchester University, taking to task the vast majority of climate scientists for their mealy-mouthed inability to tell it as it really is: "Contrary to the claims of many climate sceptics, scientists repeatedly and severely underplay the implications of their analyses. When it comes to avoiding a 2°C rise, 'impossible' is translated into 'difficult but doable', whereas 'urgent and radical' emerge as 'challenging' – all to appease the god of economics. Put bluntly, climate change commitments are incompatible with short to medium-term economic growth."

He's right about this. In one way or another, many of us are now involved in playing down the full horror of accelerating climate change. I even do it with my own children, both of whom have started to ask me how, after 40 years trying to narrow the gap between what needs to be done and what is being done, I haven't collapsed into utter despair!

"Never too late", I tell them. Not as in "never too late" to avoid some pretty horrendous shocks to the system, but "never too late" to avoid total apocalyptic meltdown.

I spent much of my summer holiday reading books by people wrestling with that very demarcation line, including the latest reworking of the original (1972) Limits to Growth analysis by Jorgen Randers. This time round, he's casting his somewhat gloomy Norwegian perspective out to 2052, and here's his conclusion.

"Don't let the prospect of impending disaster crush your spirits. Don't let the prospect of a suboptimal long-term future kill your hope. Hope for the unlikely! Work for the unlikely! Remember, too, that even if we do not succeed in our fight for a better world, there will still be a future world. And there will still be a world with a future – just less beautiful and less harmonious than it could have been."

I suspect I'll avoid even those uplifting exhortations in the US. Just too scary!

• Jonathon Porritt is Founder Director of Forum for the Future