The Top of the World

One might say that immensity is a philosophical category of daydream. Daydream undoubtedly feeds on all kinds of sights, but through a sort of natural inclination, it contemplates grandeur. And this contemplation produces an attitude that is so special, an inner state so unlike any other, that the daydream transports the dreamer outside the immediate world to a world that has the mark of infinity Gaston Bachelard, The Poetics of Space (1958)

The sun is shining, but the sky above is Bible black. It takes on colour only lower down, first deep violet, then, just above the encircling horizon, a band of blue and white. The descending, brightening sweep of colour gives a swelling curve to the sky.

Within that encompassing blue-white band, the bright-below Earth, too, is curved. It bends away in every direction towards its blue-lipped rim.

The only straight line in this whole vast, round, empty world is the wing.

You are 22 kilometres up, well inside the stratosphere – a realm which, although it is about as peripheral as a part of the Earth can be, plays a central role in the story to come. If climate geoengineering ever takes place, there is a good chance that it will take place up here, in the Earth's attic. If it does not take place, it may well be for fear of the damage it could do to this bright-lit void.

Even if it were not a crucial locale for geoengineering schemes, though, the stratosphere would still have much to recommend it as the starting point for a book about the environment, its protection and its politics. Its short history – it was discovered only in 1902 – weaves together threads of scientific exploration, military ambition and environmental concern. Beyond that, though, in its liminal way the stratosphere seems to me a perfect setting in which to begin a book which looks at the way the earthsystem works and ways it might work differently, a book about the boundaries between physical planets and imagined worlds.

You are an inhabitant of the Earth's surface who has, in all likelihood, seen more of that surface than your ancestors would have dreamed possible; you are probably the sort of person who can imagine crossing an ocean for a holiday: and so you think that you know the Earth. But less than a day's walk vertically above you, your planet offers an environment beyond your ken, a realm without local features or breathable air, a windy but oddly weatherless stack of atmospheric layers sliding around from equator to pole without storms or clouds. The rules that govern the workings of the lower atmosphere are turned on their head up here, and common-sense ideas about the world you have picked up on its surface hold no sway. In understanding the world below, science can feel like an optional extra. Here it is indispensable.

The stratosphere is closed – a volume of about 15 billion cubic kilometres with well-defined boundaries at its base and at its top. At the same time as being finite, though, it is all-encompassing – no bit of the world below lacks a stratosphere above, no trip beyond the world can avoid passing through it. In this, it is a realm not simply described by science, but oddly akin to science itself: limited but all-encompassing. Like the stratosphere, science is, in its way, alien to everyone; it is at the same time, and by the same measure, common to all, sheltering the just and unjust alike. It provides a viewpoint from which the world is bigger and stranger than it seems from the surface. The world thus revealed is more abstract, too, and there is no denying that something is lost in that. Yet a sort of universality is gained, and a liberating rootlessness.

I prize that rootlessness. I also worry about it. That is why, in our thinking, I would not have our scientifically informed imaginations waltz around this vast curving ballroom completely unconstrained, like dancing giants of the mind. That is why I insist, as you look out to the blue-white-bright horizon, that you also see the wing, straight and true and joined to your point of view. Because there must be a wing. With the exception of the very occasional balloon, it is only with wings that people rise this high into the stratosphere. And I would not ask you to picture this abstract not-quite-place, this featureless more-than-place, without also having you acknowledge the means by which people come to see such things.

There are stratospheres around other planets. Mars has one; so does Jupiter, and Saturn; Saturn's moon Titan is in the club, too. Spacecraft have measured their heights and their temperatures and sent profiles of them back to Earth – just as orbiters closer to hand have done for the Earth's own stratosphere. But that Earthly stratosphere is not just known from the outside, as the others are, in the planetary way; up here, on the wing, you see it from within, in the way that worlds are seen. There have been no births in this part of the world, though there have been deaths, and few have spent much time here. But what those few achieved here has had human impact. What could be seen from up here helped to determine the early course of the cold war. The damage that might be done to this thinnest of airs did much to define the evolving global environmental consciousness of the 1970s and 1980s. Nor do you have to enter this high realm to partake, a little, of its splendour. Everyone who has ever treasured the quality of light just after sunset, where the blue scattering of the stratosphere comes into its own, has felt their world touched by this planetary periphery. Like all stratospheres, that of the Earth is tied to what lies beneath it by gravity and radiative-transfer mechanisms and atmospheric dynamics. But there are also ties of history, politics and wonder.

A paramount expression of those ties is the wing, and that which the wing entails; the people who worked the moulding and riveting, who designed the cross section, who defined the mission, who built the company that built the aircraft, who elected the politicians who contracted for the aircraft to be built. Without all of them, you couldn't see all of this. Even in a daydream of almost empty immensity, I insist on this rule: you can't imagine the end without imagining the means. And the means are human.

The wing tip edges up. The harsh sun arcs gently across the sky.

Discovering the Stratosphere

The wing is shaped as it is, long, strong-shouldered but thin, because that is what it takes to lift you this high. You are as far above an everyday airliner as that airliner would be above the ground. The surface far below stretches in vast ambit. The horizon would be almost 600...