Part of the problem is that the sledgehammer certainty of the opening third undermines the notion of what follows - however good-hearted it may be - and Fox struggles to wrestle back control of his nebulous travelogue. In a similar style to his previous work, Fox jumps off on a personal crusade - this time sparked by a tree that he'd helped rear as a child being blighted by pests thriving in warmer winters - to speak to leading experts, capturing testimonies on a variety of cameras with the image quality shifting dramatically between one interview and the next, not to mention a barrage of news clippings and simulation videos that pop up between them to illustrate various ominous points. This is like a patchwork video diary take on An Inconvenient Truth but a little less dry and a little less polished, but no less dramatic. Indeed, being in amongst the people affected gives him some moving and unique moments that a mere science lesson would not and cannot; his visit to some of the homes devastated by Hurricane Sandy is particularly poignant, not least when a community activist lambastes the deadliness of the US's economic divide.
Fox meets a group of representatives from various Pacific Islands banded together as the 'Climate Warriors' who attempt to disrupt coal transport from the Australian port of Newcastle by blocking the exit with flotilla of kayaks and dinghies led by a hard-carved wooden raft from Vanuata - the event and those involved, are one of the film's clear high points. However, these little episodes, captured with admirable gumption and resolve, form no cogent whole. Apart from a cursory couple of lines of hackneyed voice-over in the closing minutes, there's little sense of what exactly Fox is aiming to achieve. He even states his intention outright; to "find the people who'd found this place of despair and got back up." That despair is brought on - both in filmmaker and audience by the various talking heads who occupy the first third and explain, in no uncertain terms, that time is almost up.
The only way to save human civilisation (someone points out that 'saving the planet' is a misnomer - it would be fine without us), they assert, is to make radical, wholesale changes to modern society in the next three to four years. Yet nothing that Fox does here seems to address this issue in any but the most tangential way. There's no doubt that the people that Fox singles out are worthy of his cameras attention, but it doesn't equate to a coherent feature film as much as an enormously wasted opportunity. Someone says to him late on that perhaps a total societal collapse will be humanity's chance to refocus - the dire premonition aside, refocusing might have done How to Let Go of the World the world of good.
The 2016 Sundance Film Festival takes place between 21-31 January. Follow our coverage here.
Ben Nicholson | @BRNicholson