snow, electric flashes of lightning or the blush of a sunset.
The swirling currents of Earth’s aerial and terrestrial oceans interact to create our planet’s many weathers and different climates, and these dictate the conditions for life. Perhaps the most significant of these global weathers is the Hadley Cell, a pattern of hot moist air that dumps reliable rains on the lush equatorial belt, generating the planet’s highly biodiverse tropical rainforests and swamps, while leaving parched deserts to the immediate north and south. The impact of this system can be seen from space as a sharp delineation of green to brown.
But life on Earth also dictates the atmospheric condition and its weathers. The world’s first atmosphere was hydrogen and water vapour – it took around 2 billion years for the gas of life, oxygen, to pervade the air, courtesy of the early photosynthesisers. Those ancient blue-green algae, which survive today as unremarkable-looking stromatolites, used energy from the sun to make sugars from carbon dioxide, in the process releasing oxygen as a waste product.
The continual breathing of Earth’s living organisms, from tiny ants to massive trees, depletes the atmosphere’s oxygen and replaces it with carbon dioxide and water vapour. During daylight hours, especially in the summer, this respiratory exchange is offset by the photosynthesis of the world’s terrestrial and oceanic forests of trees and algae. The various feedbacks between biota and air have created an atmosphere of roughly 78% nitrogen and 21% oxygen with the remainder being a mix of noble gases, carbon dioxide and traces of others.
It is into this intricate relationship that humanity has stormed, adding enough warming gases to the atmosphere to shift the delicate equilibrium of the past millennia and change global climate for centuries to come.
The atmosphere acts as a blanket against the unimaginably cold temperatures of outer space, and the main gas responsible for these cosy conditions is carbon dioxide. Carbon dioxide is invisible because sunlight passes straight through the molecule. However, it is opaque to the infrared rays that heat travels in, so, like the glass in a greenhouse, it warms the air. Sunlight travels unhindered through the atmosphere until it hits the surface of the Earth. If that surface is very reflective – like a shiny white glacier – then most of the rays will bounce straight back as light. But if the surface is dark – like black rock, soil or ocean – then this energy is absorbed as heat, which radiates into the atmosphere as infrared rays that can’t pass through the carbon dioxide. In this way, heat gets trapped bouncing between the atmosphere and the Earth, warming them both and sustaining life.
We know from fossil records that the planet’s climate has swung between tropical prolificacy that saw metre-long insects, and ice ages that killed off the majority of life forms. These catastrophic big freezes were the result of massive events like meteor hits or supervolcano eruptions that filled the atmosphere with so much dust that sunlight couldn’t penetrate to the planet and killed the animals that produce that all-important carbon dioxide. At such times, the concentration of carbon dioxide in the atmosphere dropped as low as 160 parts per million (ppm) molecules.
For the past half a million years – the world into which humans evolved – the carbon dioxide concentration has hovered between 200 ppm (during ice ages) and the comfortable 280 ppm of the Holocene. Historically, the main fuel humans used was wood, emitting the same amount of carbon dioxide that the tree absorbed during its growth. But in the Anthropocene, the vast majority of our energy comes from burning fossil fuels – emitting the huge stores of carbon dioxide from plants and creatures that died millions of years ago. As I write this, carbon dioxide concentrations in the atmosphere are 40% higher than pre-industrial levels – 400 ppm – the atmosphere is warmer, more energetic and holds more water, giving rise to more extreme weather. Scientists are saying that there is no longer such thing as ‘normal climate’, by which they mean what was normal for the Holocene.
We are also using the atmosphere as a repository for other gases released during combustion and for a range of other pollutants, including refrigerants that attack the ozone layer high in the stratosphere that protects us from UV rays.
And, in the Anthropocene, the atmosphere has also become humanity’s global voice. Just as visible light can travel through the air, so can sound, radio waves, and microwaves, enabling instant communication by radio, telephone and Internet. The atmosphere is as transparent to the human-generated pulses in the satellites it hosts as it is to the sun’s vital energy, and allows our species to traverse the globe virtually in seconds.
In 1932, King George V became the first monarch to deliver a Christmas Day message by radio to 20 million listeners from Britain to the outposts of the empire. In a script written for him by Rudyard Kipling, he addressed ‘men and women so cut off by the snows, the deserts, or the sea, that only the voices out of the air can reach them’. The atmosphere of the Anthropocene is now full of these ‘voices out of the air’. Imagine if we could see the beams emitted by our radios, laptops, televisions, mobile phones and other devices. For almost all of the planet’s 4.5 billion-year history, the atmosphere has been lit solely by extraterrestrial flares, like suns or meteors, or by electrical storms. Now, the skies are infused with artificial lights of different wavelengths as our devices communicate with each other and with us. And that’s just in the invisible spectrum. In the visible spectrum we have lit up our world so brightly that towns and cities can be seen from space at night and, for city dwellers, the stars fade into oblivion.
Satellites enable us to look down from space at our home as no eye has done before. The same cameras show us in unprecedented detail just how much we are changing our world. Using the Internet, we can pool our shared knowledge and intellectual resources to solve new problems, to cooperate in different ways and to transcend the geography of our planet to inhabit a virtual room no matter where we are physically.
The atmosphere has also become a playground for our aerial adventures, a medium for rapid and direct long-distance travel around and beyond our planet into space. Humans can now journey from London to Sydney in less than a day. We can trade between communities within time frames that allow fresh blueberries to be picked by a human in South Africa and eaten by another hours later in London.
Our technological invasion of the skies has allowed us to communicate across our species in a way that no other life form has. The atmosphere is un-ownable, common to all Earth-dwellers – it gives life with the first breath and life is extinguished with the last. In this chapter I look at how our changes to the atmosphere will help decide how societies develop over the coming decades.
I meet Mahabir Pun outside the tiny airstrip in Pokhara, some 200 kilometres west of Nepal’s capital Kathmandu. He is a shortish fellow in his mid-fifties with an inflatable ball of a stomach and thick black hair that emerges at extraordinary angles above his square face.
‘Gaia, come. Come!’ he says urgently, setting off ahead of me at a rapid pace and agitating his hair further, so that it stands wildly up on one side.
As I trot along behind him, people gather to watch the unusual spectacle of the pale, sweating foreign woman dressed for Arctic exploration with a bulging backpack following a local guy in light cottons and open sandals.
A political demonstration earlier in the week has led the Maoist government to impose a military-enforced curfew in the area, banning all vehicles including motorbikes, buses and taxis, so Mahabir has had to walk several kilometres to meet me. But here, as in every other place that lacks functional governance, people are resourceful. Casting a sly look around, Mahabir motions for me to get on one of two motorbike taxis, while he takes the other, and we speed off.
Pokhara is a lake town, shimmering within a halo of mountains. It is closest of anywhere in Nepal to achieving
