by Bill Bryson
In the face of such tactics, the IPCC assessment reports are intended to be the best achievable statement of current scientific consensus. But ‘consensus’ is not necessarily built over conclusions but the confidence we have in a host of possible conclusions. With that kind of information policymakers can make risk-management decisions by weighing both the possible outcomes and the assessed levels of confidence – we know it well, sort of know it, or hardly know it at all. Scientists should just say what we do know and don’t, and not leave something out because it isn’t a well-established consensus yet. It is the job of society, through its officials, to make the risk-management decisions informed by our conclusions and accompanying confidence estimates.
Again, the groups preparing IPCC reports had many hot, contentious discussions on that issue. Working Group I, for example, initially balked at the notion of including subjective estimations, and then embraced it, but then said that they needed to have finer gradations, because they had real data, not just subjective judgments, and they wanted to have a 99 per cent and a 1 per cent. There were also interesting disciplinary differences. Linda Mearns at the National Center for Atmospheric Research, one of the few lead authors in two working groups, helped reconcile the physical scientists in Working Group I who were leery of subjectivity and risk management and the ecologists and social scientists in Working Group II who felt that society, not scientists, should choose how to take risks after all the possible conclusions were reported. It took us quite a long time to get both sides to first understand and eventually respect the other point of view. My role was not to endorse one or the other, but rather to be sure all our reporting was explicit about assumptions, so we could have a ‘traceable account’ of all underlying processes behind important conclusions. That process is building, but is not yet complete across the IPCC or the scientific community in general.14
WHERE NEXT?
As I’ve said, normally science strives to reduce uncertainty through data collection, research, modelling, simulation, and so forth. The objective is to overcome the uncertainty completely – to make known the unknown. Short of that, new information may narrow the range of uncertainty. No doubt further scientific research into the interacting processes that make up the climate system can reduce uncertainty about the response to increasing concentrations of greenhouse gases. This is very unlikely to happen quickly, however, given the complexity of the global climate and the many years of high quality data which will be needed. Meanwhile, even the most optimistic ‘business-as-usual’ emissions pathway is projected to result in dramatic, dangerous climate impacts. That means making policy decisions before this uncertainty is resolved, rather than using it to justify delaying action.
Risk management also means understanding what is truly uncertain, and what is not. Sometimes critics claim that there should be no strong climate policy until the science is ‘settled’ and major uncertainties resolved, whereas supporters of strong policies suggest the science is already ‘settled enough’ and it is time to proceed with action to reduce risks. The science which demonstrates a significant warming trend over the past century is settled; moreover, it is virtually settled that the past several decades of warming have been largely caused by human activity and that much more is being built into the emissions pathways of the twenty-first century. Sounds like the ‘settled already’ side has won the debate: warming is occurring and human activities are the primary driver of recent changes.
That leaves the uncertainty about how severe warming and its impacts will be in the future, especially when projections for ‘likely’ warming by 2100 vary by a factor of six. The task then is to manage the uncertainty rather than master it, to integrate uncertainty into climate research and policy-making. This kind of risk-management framework is often practised in defence, health, business and environmental decision-making. But the thresholds for action often seem lower. The US has a military arm, of course, and although I may not like everything we do with it, I don’t know anybody who says you should get rid of it because a nation has to have security precautions, even against only very low probability – but potentially dangerous – threats. Well, the climate change threat is not 1 per cent. It’s more than 50 per cent for many really significant troubles, and maybe 10 per cent for absolutely catastrophic troubles.
In my personal value frame, it is already a few decades too late for having implemented some policy measures against such risks. Had we begun mitigation and adaptation investments decades ago, when a number of us advocated them,15 the job of remaining safely below dangerous thresholds would be easier and cheaper. Similarly, beyond a few degrees Celsius of warming – at least an even bet if we remain anywhere near our current course – it is likely that many ‘dangerous’ thresholds will be exceeded. Strong action is long overdue, even if there is a small chance that by luck climate sensitivity will be at the lower end of the uncertainty range and, at the same time, some fortunate, soon-to-be-discovered low-cost, low carbon-emitting energy systems will materialise. For me, that is a high-stakes gamble not remotely worth taking with our planetary life-support system. Despite the large uncertainties in many parts of the climate science and policy assessments to date, uncertainty is no longer a responsible justification for delay.
Adapted in part from S.H. Schneider, Science as a Contact Sport (2009a) and S.H. Schneider and M.D. Mastrandrea, ‘Managing Climate Change Risk’ (2009b).16
1IPCC: N. Nakicenovic and R. Swart (eds), Emissions Scenarios – A Special Report of Working Group III of the Intergovernmental Panel on Climate Change (Cambridge, Cambridge University Press, 2000).
3‘The Science of Climate Change’: Joint statement of sixteen national academies of science, 18 May 2001; http://royalsociety.org/displaypagedoc.asp?id=13619
4‘Global Response to Climate Change’: Joint science academies’ statement, 7 June 2005; http://royalsociety.org/displaypagedoc.asp?id=20742
5‘Sustainability, Energy Efficiency and Climate Protection’: Joint science academies’ statement, 16 May 2007;
6‘Climate Change and the Transformation of Energy Technologies for a Low Carbon Future’: Joint academies’ statement, June 2009; http://royalsociety.org/displaypagedoc.asp?id=34103
7 T. Kuhn, The Structure of Scientific Revolutions (Chicago, University of Chicago Press, 1962).
8 Oxford Environment Conference: ‘Climate Change: Potential for Interactions and Surprise’ Oxford University, Oxford, England, 15–16 July 1993.
9 S.H. Schneider, ‘The Future of Climate: Potential for Interaction and Surprises’ in T.E. Downing (ed.), Climate Change and World Food Security (Heidelberg, Springer-Verlag, 1996), NATO ASISeries 137: 77–113.
10 G. McBean, P. Liss and S. Schneider, ‘Advancing our understanding’ in J.T. Houghton, L.G. Meira Filho, B.A. Callander, N. Harris, A. Kattenberg and K. Maskell (eds), Climate Change 1995: The Science of Climate Change, Contribution of Working Group Ito the Second Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge, Cambridge University Press, 1996).
11 Houghton et al., ‘Summary for Policy Makers’ in J.T. Houghton, L.G. Meira Filho, B.A. Callander, N. Harris, A. Kattenberg and K. Maskell (eds), Climate Change 1995: The Science of Climate Change, Contribution of Working Group I to the Second Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge, Cambridge University Press 1996).
12 R.H. Moss and S.H. Schneider, ‘Uncertainties in the IPCC TAR: Recommendations to Lead Authors for More Consistent the Third Assessment Report of the IPCC (Geneva, World Meteorological Organization, 2000), pp. 33–51.
13Intergovernmental Panel on Climate Change (IPCC), Climate Change 2007: The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge and NY, Cambridge University Press, 2007).
14 S.H. Schneider, Science as a Contact Sport (Washington DC, National Geographic Press, 2009a), 295 pp.
15 Ibid.
16S.H. Schneider and M.D. Mastrandrea, ‘Managing Climate Change Risk
’. Chapter 15 in S.H. Schneider, A. Rosencranz, M.D. Mastrandrea and K. Kuntz-Duriseti (eds), Climate Change Science and Policy (Washington DC, Island Press, 2009b).
20 GREGORY BENFORD
TIME: THE WINGED CHARIOT
Gregory Benford is a Professor of Physics at the University of California, Irvine, and author of over thirty books, mainly science fiction. His novels include Timescape, Cosm, Beyond Infinity, What Might Have Been, The Sunborn and the six-volume Galactic Centre series. His non-fiction includes Deep Time and Beyond Human.
THE ROYAL SOCIETY IS 350 YEARS OLD, AND STILL GOING. SCIENCE, TOO, WILL GO ON. HOW LONG FOR? WELL, ANSWERING THAT QUESTION NEEDS A PROPER UNDERSTANDING OF TIME – SOMETHING WHICH, AS GREGORY BENFORD EXPLAINS, REMAINS ELUSIVE AFTER ALL THESE YEARS.
But at my back I always hear
Time’s winged chariot hurrying near;
And yonder all before us lie
Deserts of vast eternity.
– Andrew Marvell, To His Coy Mistress, 1652
When the Royal Society began, time seemed a simple, obvious subject, understood since ancient ages. To Isaac Newton and his colleagues, two long-standing traditions pervaded the idea of time.
The Greeks, like most ancient cultures, saw their world as not completely chaotic, though it could be capricious. Faith in a definite order in nature promised that it could be understood by human reasoning. To them, some physical processes, at least, had a hidden mathematical basis, and they sought to build a model of reality based on arithmetical and geometrical principles.
Adding to this Western tradition was the Judaic worldview, which had a timeline. God created the universe at some definite moment, arriving fresh and with a fixed set of laws. The Jews thought that the universe unfolds in a sequence running forward, which we now call linear time. Creation enabled evolution, which led forward in linear time to a future we could quite possibly change. This differed greatly from most other ancient cultures, which favoured cosmic cycles, probably by generalising from the march of the year’s seasons. In cyclic time everything ends, but eventually returns, so there is eternal recurrence.
These two ideas, time’s arrow vs. time’s cycle, persist today in physics and also emerge in our art and literature. Physics has constrained time, ordering the music, but the dance between these linear and cyclic views continues.
Four hundred years ago, Europeans assumed a God-created universe that unfolded in orderly ways, in linear time, but that did not mean that the universe always had to be as we see it now. Change was possible, but constrained by physical laws. Einstein once remarked that what most interested him was whether God had any choice in his creation. The Abrahamic religious tradition answered with a resounding yes. Further, they insisted on nature’s rationality, aided by mathematical principles. These were the only cultures to do so. This driving idea eventually altered the concept of time itself, as the cultural agenda played out in modern science.
EVOLVING TIME
Time has two faces.
First, our sense of it passing seems inevitable, an automatic intuition. Unlike space, in which we can move back and forth, time hammers on relentlessly. This is Intuitive Time.
Second, we frame our position in time, our historical era, by looking at our slowly changing landscapes, and our societies. These alter on the scale that we ourselves see as we age. This is Historical Time.
Both these faces appeal, but they deceive us.
In the 1700s, the philosopher Immanuel Kant saw space and time as elements of a systematic mental framework, structuring our experiences. Spatial measurements tell us how far apart objects are, and temporal measurements show how far apart events occur. This eventually intersected Charles Darwin’s idea that many abilities of organisms emerge from evolution by natural selection. Then it follows that time and space are the concepts we and other animals evolved to make the best use of the natural world. In this sense, they emerged from the primordial world where our minds evolved.
But that was not enough. Modern science reveals that time is supple, changeable, and even enigmatic. Further, we stand in a small slice of it, anchored in a moving moment that is an infinitesimal wedge compared with what has gone before, or will come after us. Our telescopes tell us of immensities of space, but other sciences – geology, biology, cosmology – speak of even grander scales of time.
Space and time are so familiar that we forget that they underlie the entire intricate and beautiful structure of scientific theory and philosophy. Perhaps it is not surprising that our first powerful theories built on assumed bedrock, metaphysical intuitions, came to be questioned only later. Clocks in Newton’s universe ran everywhere the same. He invoked ‘absolute, true and mathematical time’ saying that it ‘of itself, and from its own nature, flows equably without relation to anything external, and by another name is called duration’. Of the immense expanse of past time Newton had no true idea, for he took as gospel the Genesis story. Space was similarly absolute. Newton avoided the colossal scale of space by supposing that God had fixed up the cosmos so that gravity, the force he was the first to quantify, had not made it collapse – at least, so far.
This view held up well until the nineteenth century. By then even atheist scientists had faith in a lawlike order of nature – not from philosophy, but because it worked. Though this assumption springs from an essentially theological worldview, it gave useful predictions without a god attached. Still, few saw the full implications of regarding time as a subject of study, not belief.
The first collision between religious views and the study of the far past, which we now call Deep Time, came with the newborn science of geology. In 1830, the geologist Charles Lyell proposed that the features of Earth perpetually changed, eroding and re-forming continuously, at a roughly constant rate. This challenged traditional views of a static Earth with rare, intermittent catastrophes. In the eighteenth and nineteenth centuries the vast depth of the eras before humans arose became apparent, through development in geology and evolution’s grand perspective. These still had to be licensed by physics, the more secure and quantitative science which sets the stage for the events and processes probed by the other sciences.
When William Smith and Sir Charles Lyell first recognised that rock strata represented successive long eras, they could estimate timescales only very imprecisely, since rates of geologic change varied greatly. Even these early attempts got the sciences into trouble. Creationists, reasoning from the Bible, had been proposing dates of around six or seven thousand years for the age of the Earth based on the Bible. Early geologists suggested millions of years for geologic periods, with some even suggesting a virtually infinite age for the Earth. Geologists and palaeontologists constructed geologic history based on the relative positions of different strata and fossils, estimating the timescales based on studying rates of various kinds of weathering, erosion, sedimentation and lithification. The ages of assorted rock strata and the age of the Earth were hotly debated. In 1862, the physicist William Thomson, whose authority endured – as Lord Kelvin and President of the Royal Society – until the end of the century, set the age of Earth at between 24 million and 400 million years. He assumed that Earth began as a completely molten ball of rock, then calculated how long it took to cool to its present temperature. He did not know of the ongoing heat source from radioactive decay.
Physicists had more prestige, but even then, geologists doubted such a short age for Earth. Biologists could accept that Earth might have a finite age, but even 100 million years seemed much too short for evolution to have yielded such complex plenty. Charles Darwin argued that even 400 million years did not seem long enough.
Until the discovery of radioactivity in 1896, and the development of its geological applications through radiometric dating during the first half of the twentieth century (pioneered by geologists), there were no precise absolute datings of rocks.
Radioactivity introduced another measuring clock. Geologists quickly realised this upset the assumptions used befor
e. They re-examined their estimates. This moved the age into the billions (thousands of millions) of years, sweeping away Archbishop Ussher’s biblically inspired dating of Creation to 4004 BC.
Much public ferment paralleled this scientific research and its clash with religion. But by the early twentieth century, opinion settled on an Earth older than a billion years.
Physics, meanwhile, was making hash of the simple view of time that underlay the other sciences. Geology, biology and astronomy would have been happy with Newtonian time, giving them a simple marker of change. The physicists, though, worried about more basic matters.
RELATIVE TIME
In physics, time is, like length, mass and charge, a fundamental quantity – intuitive, given by our basic perceptions. Newton used this view, holding that ‘I do not define time, space, place and motion, as being well known to all’ – i.e., obvious. But Einstein showed that it was not.
Nineteenth-century physicists felt that space was the most basic and irreducible of all things. It persisted while time changed, and points made up space – infinitesimal grains close-packed. Einstein’s fundamental insight was that space and time, which appear so different to us, are in fact linked. He argued this using gedanken (thought) experiments involving rulers and clocks. These were not just instruments to Einstein; he took them to generate space and time, since they represent it.
He took two basic assumptions. First, the speed of light seems the same to everyone in the universe, whether moving or sunk deep in a gravitational well. This may strike us as odd, but an earlier experiment had found it to be so. Not that Einstein cared; his intuition led him to the conclusion. He proved it valid by using the even deeper second assumption: that the laws of physics had to treat all states of motion on the same footing.
