Vulnerable Earth: hits from space and other disasters
In the little squeak of time which is a human life, the surface of the Earth seems to change very little. Seasons come and go, storms and droughts follow each other, plants and animals are born or die, and the world looks broadly the same. Yet stretch time to hundreds, thousands or millions of years, and the Earth looks very different: an almost spherical rock with a thin tissue of life around it, spinning with others in space round a sun, in a galaxy among galaxies, in a universe among universes of unimaginable size and complexity.
Yet so it is. No wonder that until people began to get a different sense of time some 250 years ago, the vulnerability of the Earth was wrapped up in stories often involving the moods of a not always benevolent creator. We can now stand back and see the shocks to the Earth system, whether from outside or inside, which is its - and our own - true history.
Today I will begin with natural disasters from beyond the Earth; then go for some from within the Earth; and then some caused by the small but destructive animal species which is ourselves. I will say something at the end about what, if anything, we can do to anticipate, prevent, or otherwise cope with them.
Disasters from space range from the very big to the very small. Probably the biggest of all such objects was that which hit the young Earth more than 4 billion years ago, and led to the creation of the Moon. Since then there has been an intermittent barrage of asteroids, meteorites, planetesimals and comets, many of them dating to the very early days of the Earth. Looking at the Earth's surface, over 180 hit structures have been identified, ranging from big to small craters in all parts of the Earth. The barrage, which mostly comes from the swarm of objects which circle the Sun from between the planets Mars and Jupiter, has not been constant.
It is now believed that there was a collision between a major object among them known as Baptistina and other asteroids around 160 million years ago, which has caused the shower of smaller objects since then. Baptistina is still about 40 kilometres across, and the objects which derive from it are identifiably rich in carbon. Normally the atmosphere and magnetic field of the Earth act as a protective shield against most objects from space, and some of us have seen glowing showers of tiny objects which have been deflected. But some hit the Earth at different angles or burn up or explode at high altitudes. The main effects of those which hit or get close to the surface are craters, blast waves, tsunamis, injection of material into the atmosphere and a rich variety of electromagnetic shocks.
I spent some happy months in a government Task Force on Potentially Hazardous Near Earth Objects 13 years ago. This enabled me to see many of the effects of hits for myself, ranging from the Barringer Crater in Arizona to the disturbance of a field in a village near to mine in the Cotswolds. We were also able to see a film of the comet Shoemaker-Levy colliding with the planet Jupiter in July 1994. As the comet entered Jupiter's gravitational field, it broke into fragments, resulting in multiple impacts, one fragment alone created a fireball as big as the Earth.
I suppose that the most famous hit was one that took place in Yucatan in Mexico some 65 million years ago. An object with a diameter of about 10 kilometres struck Chicxulub digging out a crater traceable today with a diameter of around 180 kilometres. It threw up a cloud of vaporized and molten rock over North America. The consequent dust in the upper atmosphere darkened and drastically cooled the whole Earth, damaging the process of photosynthesis on the surface.
When the dust settled, the temperature swung the other way. Water vapour and carbon dioxide in the atmosphere caused a runaway greenhouse effect. The temperature of the Earth could have risen by as much as 10 degrees C for around half a million years. It is no wonder that all living creatures were affected, and that a high proportion, including the dinosaur family, perished. Extinctions of this magnitude are a disaster for some, but obviously an opportunity for others. The evolution of mammals, including ourselves, would not have taken place without it.
You will have heard about the hit from the meteor named Chelyabinsk, probably some 17 to 20 metres across, which hit Russia on 15 February this year, fortunately causing relatively little damage except broken walls and windows; but about 1,500 people were still injured, mostly by flying glass. By an extraordinary coincidence an asteroid some 45 metres across streaked past the Earth about 27,000 kilometres from Earth on the same day. Only 13 years previously, there was a hit over Lake Tagish in the Yukon in 2000 when an object of around 5 metres in diameter exploded at an altitude of 25 kilometres. It caused a long and bright fireball, a loud bang, a shower of fragments, and an electromagnetic pulse which led to a loss of power transmission on the ground below.
A bigger event took place at Tunguska in Siberia in 1908. This object had a diameter of around 60 metres and its blast wave destroyed some 2,000 square kilometres of forest in Siberia. It lit up the night sky across most of the northern hemisphere, and in Belgium was likened to a great red glow after sunset as if from a huge distant fire. Had it struck London, there would have been little left. Until recently astronomers feared a hit from a meteor named Apophis of comparable size in 2029, but latest calculations show that it is likely to miss us. There is another still remote possibility of a 120 metre diameter asteroid hitting us in 2048.
You will wonder how often big or small objects hit the Earth. The answer is that no one knows. In the past big hits have occurred at roughly 100 million year intervals but something could happen at any time. In the United States, Hawaii, Australia, Chile and elsewhere much research has taken place recently, and so far no asteroids of more than a kilometre in diameter have been identified on a track to hit the Earth. But there are thousands of many shapes and sizes smaller than 1 kilometre across which could hit us at any time.
We must also reckon with other much neglected influences on the Earth from space. Events inside and outside our galaxy, for example the explosion of a supernova, can generate bursts of immensely destructive radiation from the Sun, our friendly neighbourhood hydrogen bomb. Occasional coronal injections, or concentrated solar flares, as in 774, 1859 and 1989, could have such effects as the disruption of electronic communications systems. Finally there are the changing relationships in the Earth's orbit - variations in wobble, tilt and spin known as the Milankovitch effect - which profoundly affect the Earth's climate, and its current propensity to dip in and out of ice ages. Our present warm period - the Holocene - began about 11,700 years ago. It won't go on for ever.
This brings me to disasters from within the Earth. The slow movement of tectonic plates usually gives time for ecosystems and the species which compose them to move or adapt to change. But passing over thresholds can sometimes have dramatic effects on the behaviour of winds, oceans and currents, and of course the living organisms adapted to them. A good example is the joining of North and South America some 4 million years ago, which led to drastic changes in the direction of ocean currents, and thus climate world wide.
Associated with tectonic plate movements are volcanoes and earth movements. We are unused to major volcanic eruptions. The eruptions of the Siberian Traps some 250 million years ago, and the Deccan Traps 65 million years ago, both possibly associated with extraterrestrial impacts, changed the surface conditions of the planet. The eruption of Mount Toba in Indonesia some 73,000 years ago, which put enormous quantities of dust into the atmosphere, may have helped trigger a renewal of glacial conditions within the last ice age, and changed the development of our own species. By comparison the eruption of Tambora in 1815, which led to the famous 'year without a summer', that of Krakatoa in 1883, that of Mount St Helens in 1980, that of Mount Pinatubo in 1991, and that of Eyjafjallajokull in Iceland in 2011, each with its specific global effects, were relatively minor. Possible locations for the next one include the Iceland (again), Yellowstone National Park and New Madrid in the United States.
Earthquakes are part of the same pattern. Mostly their effects, however destructive, are local. Some 10,000 people a year are killed by earthquakes, usually by buildings falling in on them, but sometimes they can combine with tsunamis to cause much greater damage. Tsunamis and major floods are a constant feature of history. Underwater landslides can be precipitated by many factors, including earth tremors. One such off Norway, known as the Storegga Slide, caused a giant wave to hit eastern Scotland and the Shetland Islands some 8,000 years ago. It may also have broken the last land connection between Britain and the continent. Recently there has been concern about the possibility that part of the Cumbre Vieja volcano in the Canary Islands might collapse into the sea, creating a tsunami with a height of up to 40 metres, which could hit the east coast of the United States.
Then there are disasters in the living world. If the widespread extinctions at the Permian/Triassic boundary 250 million years ago and those of the Cretaceous/Tertiary boundary (in other words Chicxulub) 65 million years ago, had not taken place, nothing like the world we know today, and the human species within it, could have existed.
One point is worth adding, the product of recent and continuing research. To a considerable exent, and operating on Darwinian principles, organisms tend to create and maintain a living environment most favourable to them. The Earth system behaves as a single, self regulating system, comprised of physical, chemical, biological and even human components. In a word this is Gaia theory. At present we are pressing Gaia hard without fully understanding the possible consequences.
This brings me to the role of our own animal species, and our influence on the condition, living and otherwise, of the Earth's surface. A periodical visitor from outer space would find more change in the last 250 years than in the last 2,000 and more changes in the last 20 years than in the last 250. The association between humans and their environment, including the micro-world in and around them, has changed at every stage of human evolution: from hunter gatherers to farmers, from country to city dwellers, and from tribal groups to complex hierarchical societies.
But the most radical divide was the beginning of the industrial revolution in Britain. Before then the effects of human activity were local, or at worst regional, rather than global. All civilizations of the past cleared land for cultivation, introduced plants and animals from elsewhere, and caused a variety of changes. It is no wonder that there are proposals to reclassify the geological past so that the Holocene epoch would end some 250 years ago, and a new Anthropocene epoch, to mark the increasing changes brought about by our own species, would follow it. High among them is the almost incredible multiplication of human numbers: in my own lifetime there has been a rise from 2.5 billion to 7 billion today, with the prospect of even 9 billion by 2050.
Our ability to influence other species has given us a profound conceit of ourselves. Yet our use of other species is coupled with an amazing ignorance of how many natural systems work, their astonishing interconnectedness, and our own total reliance on natural services. There have been some 30 urban civilizations before our own. All eventually crashed. Why?
The reasons range from damage to the environmental base on which they rested to the mounting costs in human, economic and organisational terms of maintaining them. Nor should we forget the effects of major epidemics such as the Black Death in the 14th century, the Great Plague of 1665, and the Great Flu of 1918, the more so when our very interconnectedness renders us particularly vulnerable. More recently we have become aware of the threat caused by climate destabilization, promoted by human-driven changes in the chemistry of the atmosphere. Global swarming of our species is matched by global warming of the atmosphere.
We do well to reflect that the Earth has never been in this situation before. But I do not want to leave you expecting doom. There is something that we can do about most of the categories of disaster that I have described. But there has to be a common theme to any response. These are global problems which will require global solutions.
Let us look first at the kind of disaster which looks furthest from human control: impacts from outer space. We looked into the possibilities in the report of the British Government Task Force of 2000, and NASA in the Untied States has initiated a major programme on the subject. Let us suppose that with the help of an improved telescope network on land and in space, we could with reasonable accuracy compute the next range of hits from space. We would have to reckon not only with the size, composition and orbit of an incoming object, but also with the possibility that it might enter into an ever diminishing circuit of the Earth before colliding with it. Our response would fall into two categories.
The first would comprise conventional measures of civil defence. Depending on the length of notice and the size and composition of the incoming object, people could move out of target areas to relatively safer areas elsewhere. The response of neighbouring countries to millions of refugees is hard to assess. Some form of international understanding would have to be reached if chaos were not to occur. A big problem would be how to feed a displaced population. A really big hit could lead to a darkened Earth which would affect growing seasons for food the world over.
The second is the more exotic prospect of planetary defence, either through destruction or through deflection of incoming objects. Destruction of an object by high-yield nuclear devices might be technically feasible, but would carry enormous risks of its own. Incomplete destruction of an object could subject the Earth to multiple impacts from pieces of the original body. We saw for ourselves what happened to Jupiter when Shoemaker-Levy broke into 21 pieces with 21 impacts.
More promising are the possibilities of deflection through modification of the object's orbit. What would be needed is a steady gentle push, not an explosive jolt: for example the mounting of sails on the object to harness the Sun's radiation pressure to push it from its course. Another possibility would be the use of mass drivers whose source of power would again be the Sun. To do either a number of major engineering problems would have to be solved, but this should not be impossible.
We are more used to disasters within the Earth system. There the remedies are less exotic. It is well within our capabilities to improve prediction and take measures to anticipate and mitigate catastrophes. Disasters such as the earthquakes in Turkey in 1999, in Iran in 2002, 2003 and 2013; in China, Haiti and Chile in 2009 and 2010; in Japan in 2010; and in China again last month, seem to pull people in communities together as never before, while those in other countries are often willing to send relief to those they have never seen or are never likely to meet.
Larger scale catastrophes would require international effort and administrative skills which are at present lacking. Obviously human ability to cope would depend on the resilience and good health of society in general. A world riven by war and degradation could easily be overwhelmed. Much would depend on the abilities of individual governments to manage at least within the areas of their responsibility.
There are related issues. Take human population increase. The overall rate is still rising, but in several parts of the world it is levelling off. The main factors are improvement in the status of women, better provision for old age, wider availability of contraceptive devices, lower child mortality, and better education, especially for girls and young women.
Take the atmosphere. We do not have to rely on systems of energy generation which affect weather and climate in a way that could put an overcrowded world at risk.
Take degradation of land and water. We know how to look after them both if we try. We do not have to exhaust top soils, watch them erode into the sea, rely upon artificial aids to nature, eliminate the forests with their natural wealth of species, or poison the waters, fresh and salt.
Nor do we have to run the risks we do in developing certain new technologies recently specified by Lord Rees.
In short we have to learn to think differently before it is forced upon us, and that means a new measure of global governance. So far global institutions remain feeble. Yet change in them is vital if we are to improve our understanding of natural ecosystems and rethink our value system.
This is a subject for another lecture. As a former British Ambassador to the United Nations, I am better aware than most of the enormous difficulties matched only by the need for radical change. So far we have the United Nations and its many agencies and associated bodies. The World Trade Organization, the International Monetary Fund and the World Bank are all institutions with real mechanisms for influencing government policy and public opinion. By contrast the 200 or more environmental agreements are dispersed and poorly coordinated, with different hierarchies of reference and accountability. I have long argued for the creation of a World Environment Organization to balance - and be a partner of - the World Trade Organization.
We could also create a global organization on Risk Management. Its job would mainly be to promote coordination, so far sadly lacking, between national agencies. It would cooperate with such bodies as the UN Committee on the Peaceful Uses of Outer Space. Like the Intergovernmental Panel on Climate Change, it would also suggest and if necessary direct action to cope with specific risks.
Above all let us remember how small and vulnerable we are. We are like microbes on the surface of an apple, on an insignificant tree, in an insignificant orchard, among billions of other insignificant orchards stretching over horizons beyond our sight or even our imagining.