Fred Hoyle - The Black Cloud

“What am I to tell London?”

“That’s up to you. You certainly ought to tell ’em about evacuating high mountain districts even though there aren’t any high enough to matter in Britain. But I leave it to your judgement how much of the rest you tell ’em.”

“Not very nice, is it?”

“No. If you find it getting you down I’d recommend a talk with one of the gardeners, Stoddard by name. He’s so slow that nothing would worry him, not even the atmosphere being sprayed off.”

By the third week in January the fate of Man was to be read in the skies. The star Rigel of Orion was obscured. The sword and belt of Orion and the bright star Sirius followed in subsequent weeks. The Cloud might have blotted out almost any other constellation, except perhaps the Plough, without its effect being so widely noted.

The Press revived its interest in the Cloud. “Progress reports’ were published daily. Bus companies were finding their Night-time Mystery Tours increasingly popular. “Listener research’ showed a threefold increase in the audience for a series of B.B.C. talks on astronomy.

At the end of January perhaps one person in four had actually observed the Cloud. This was not a suffficient proportion to control public opinion, but it was sufficient to persuade the majority that it was high time that they took a look for themselves. Since it was scarcely possible for a majority of town dwellers to move at night into the country, suggestions were made for the shutting off of town lighting systems. These were at first resisted by municipal authorities, but resistance only served to change polite suggestions into strident demands. Wolverhampton was the first town in Britain to impose a nightly black-out. Others quickly followed, and by the end of the second week in February the London authorities capitulated. Now at last the population at large was starkly aware of the Black Cloud, as it clutched like a grasping hand at Orion, the Hunter of the Heavens.

A closely similar pattern of events was repeated in the U.S., and indeed in every industrialized country. The U.S. had the additional problem of evacuating much of the western states, since a considerable area of populated territory there lies above 5,000 feet, the safe limit set in the Nortonstowe report. The U.S. Government had of course referred the matter to its own experts, but their conclusions turned out not to differ significantly from those of Nortonstowe. The U.S. also undertook to organize the evacuation of the Andean republics of South America.

The agrarian countries of Asia were strangely unmoved by the information supplied to them through the United Nations. Theirs was a ‘wait and see’ policy, which might really be said to have been the wisest course of all. For thousands of years the Asian peasant had been accustomed to natural disasters — ‘acts of God’ as the lawyers of the West called them. To the oriental mind drought and flood, marauding tribes, plagues of locusts, disease, were to be suffered passively, and so was the new thing in the sky. In any case life offered them little and consequently was not set at an unduly high price.

The evacuation of Tibet, Sinkiang, and Outer Mongolia was left to the Chinese. With cynical indifference nothing at all was done by them. The Russians, on the other hand, were punctilious and prompt in their evacuation of the Pamirs and of their other highland areas. Indeed genuine efforts were made to shift the Afghans, but Russian emissaries were driven out of Afghanistan at pistol point. India and Pakistan also spared no effort to ensure the evacuation of the part of the Himalaya south of the main watershed.

With the coming of spring in the northern hemisphere the Cloud passed more and more from the night sky to the day sky. So, although it was spreading rapidly outside the constellation of Orion, which was now completely obscured, its presence was far less obvious to the casual observer. The British still played cricket, and dug their gardens, as indeed did the Americans.

The widespread interest in gardening was favoured by an exceptionally early summer which started in mid-May. Apprehension was widespread certainly, but it was lulled to a vague outline by week after week of wonderfully clear sunny weather. Vegetable crops were ready for eating in late May.

The Government was not nearly so pleased by the excellent weather. The reason underlying it was ominous. Since its first detection, the Cloud had by now completed about ninety per cent of the journey to the Sun. It had of course been realized that more and more radiation would be reflected by the Cloud as the Sun was approached, and that a consequent rise of temperature would take place on the Earth. Marlowe’s observations suggested that there would be little or no increase in the amount of visible light, a prediction that turned out to be correct. Throughout the whole of the brilliant spring and early summer there was no noticeable increase in the brightness of the sky. What was happening was that light from the Sun was impinging on the Cloud and being re-radiated as invisible heat. Fortunately, not all the light impinging on the Cloud was re-radiated in this fashion, otherwise the Earth would have become entirely uninhabitable. And fortunately quite a large fraction of the heat never penetrated inwards through our atmosphere. It was reflected and bounced back into space.

By June it became clear that the temperature of the Earth was likely to be raised everywhere by some thirty degrees Fahrenheit. It is not commonly realized how near the death temperature a large fraction of the human species lives. Under very dry atmospheric conditions a man can survive up to air temperatures of about 140° Fahrenheit. Such temperatures are in fact attained in a normal summer in low-lying regions of the Western American desert and in North Africa. But under highly humid conditions, the death temperature is only about 115° Fahrenheit. Temperatures at high humidity up to 105° Fahrenheit are attained in a normal summer down the eastern seaboard of the U.S. and sometimes in the Middle West. Curiously, temperatures at the equator do not usually run above 95° Fahrenheit, although conditions are highly humid. This oddity arises from a denser cloud cover at the equator, reflecting more of the Sun’s rays back into space.

It will accordingly be appreciated that the margin of safety over much of the Earth amounts to no more than 20°, and in some places to very much less than this. An additional rise of 30° could be viewed therefore only with the greatest apprehension.

It may be added that death results from the inability of the body to get rid of the heat that it is constantly generating. This is necessary in order to maintain the body at its normal working temperature of about 98° Fahrenheit. An increase of body temperature to 102° produces illness, 104° produces delirium, and 106° or thereabouts produces death. It may be wondered how the body can manage to rid itself of heat when it happens to be immersed in a hotter atmosphere, say in an atmosphere at 110°. The answer is by evaporation of sweat from the skin. This happens best when the humidity is low, which explains why a man can survive at higher temperatures in low humidity, and indeed why hot weather is always pleasanter when the humidity is low.

Evidently much would depend in the days to come on the behaviour of the humidity. Here there were grounds for hope. The heat rays from the Cloud would raise the temperature of the surface of the land more rapidly than the sea, and the air temperature would rise with the land while the moisture content of the air would rise more slowly with the sea. Hence the humidity would fall as the temperature rose, at any rate to begin with. It was just this initial fall of humidity that produced the unprecedented clarity of the spring and early summer in Britain.