Examination of Witness (Questions 40 -
WEDNESDAY 15 MARCH 2000
40. And are you satisfied that that sort of
uncertainty is taken into account, when it comes to policy-making?
(Sir John Houghton) Very much so, yes. I say very
much so; sometimes fairly simplistic single numbers are bandied
about, and perhaps simplistic views of what may occur with climate
changes are bandied about, and that is probably inevitable, given
the fact that people like one given number, or to use a given
piece of evidence. But if you take the range of material that
comes out of bodies of that kind you will find all the uncertainties
represented within those bodies.
41. The IPCC has concluded that the influence
of human actions, especially emissions of carbon dioxide, is likely
to be by far the most dominant factor determining climate change
during this century. To what extent is the IPCC still involved
in assessments of other factors and exploring other possible alternative
explanations, not either this or that but the contributions that
could be made by other factors that could contribute to climate
change, such as some of the things we have mentioned already?
(Sir John Houghton) Yes; each time we go through an
assessment we look at all the factors, we look particularly at
those factors that are likely to have changed in their scientific
understanding, or changed for other reasons, during that period
between assessments, and weigh them against what might occur from
greenhouse gases. And the process of the assessment is not just
looking at the effect of carbon dioxide and methane, and so on,
but it is also looking at the sun and volcanoes and dust and particles
and changes in land use, and all sorts of things, and we are constantly
looking at possible other reasons for climate change which may
make a contribution. So we are continually reviewing the whole
42. And what sort of proportionate effect are
they likely to have, compared with carbon dioxide?
(Sir John Houghton) The range, I suppose, is 5, 10
per cent, these other contributions, the likely range; there are
some areas of substantial uncertainty where the contribution might
be greater, up to perhaps 30 per cent, that sort of number.
43. What areas are those?
(Sir John Houghton) That is to do with clouds again,
and the impact of particles on clouds, in particular, it is called
an indirect effect of particles on clouds.
44. A point of clarification, Sir John. When
you talk about clouds, clearly you do not mean clouds that appear
on a Monday and are not there on a Tuesday, you are talking about
the build-up of clouds due to some effect from earth that is making
clouds denser, or more frequent, or more prevalent; when you keep
on talking about how clouds can effect climate change, can you
just give us an idea what you mean by that?
(Sir John Houghton) Let me just give you an example,
which we have spent a lot of time on, actually, in recent months,
in our current assessment, and that is that there is a wide range
of particles that enter the atmosphere from burning of forests,
from sulphur dioxide, creating sulphate particles, and so on.
Those particles have not only an influence of their own on the
amount of sunlight reaching the earth's surface, because they
directly reflect some of that sunlight away, or absorb some of
it, they also act as nuclei for the condensation of droplets in
clouds. Now, if you have a lot more particles in a cloud, instead
of getting a small number of large droplets you get a large number
of little droplets, and the properties of the cloud, the reflectivity
of a cloud, the way it interacts with the energy flows, depends
on the average size of a drop and the number of drops, and so
45. And that could be very different in the
21st century from what it was in the 19th century?
(Sir John Houghton) And that could change quite a
lot, particularly in more industrial parts of the world, depending
on the influence of these particles. So that is a possible reason
for climate change. The largest estimates that people have produced
are actually quite large, maybe 40 per cent, even up to 40 per
cent of possible global greenhouse warming; we do not think those
big numbers probably are justified, but some people are putting
up numbers of that kind. On the other hand, it can be very small.
So there is a wide range of uncertainty there, and this is represented
in our current document.
Chairman: That is very helpful.
46. But there was climate change before the
last 200 years when carbon dioxide has been building up, and quite
substantial fluctuations in climate. How do you filter that out
from the effects of carbon dioxide, in your predictions?
(Sir John Houghton) We try to establish what the reasons
for those climate changes in the past have been; the big reasons,
of course, for the ice ages, we know what has triggered those,
and that is a variation in the earth's orbit round the sun. And
we are in a warm, interglacial period at the moment; the next
ice age is due in due course, perhaps in 50,000 years' time, that
is the sort of timescale of the ice ages. So that is a bit beyond
even the timescale of the general political operations. If you
are looking at variations which occur over the period of a century
then there have been variations in the past, we are not entirely
sure of the reason for all of them, volcanic eruptions have been
one, changes in the sun may well have been another. But those
are small compared with what we expect to occur this century because
of the vast increase in carbon dioxide, which is now way outside,
of course, any level it has been probably for millions of years.
47. The impression, Sir John, you are giving
is that when you give advice, or the IPCC gives advice, the predominance
of the advice is, as you have said already, around the greenhouse
effect. To what extent are these other reservations mentioned
(Sir John Houghton) I give a lot of lectures on the
subject, I talk, of course, to a whole range of people, including
industry and others, and I emphasis the uncertainties too. But
what I do say is that, if you are trying to create a likely scenario
for the future and put probabilities on it, the probability of
the climate remaining the same is very small, the probability
of it being somewhere around a range of what the IPCC is talking
about, that is the most likely range, the probability of it being
so large that we are going to get real catastrophic disasters
occurring is also very small.
48. That was not what I was getting at. I accept
that those changes will happen. My question is about the origins
of them, the sources of them, and you are touching on other issues,
variations in cloud, variations in sun activity, volcanic eruptions.
To what extent are those being brought in as factors when governments
are being advised on these issues?
(Sir John Houghton) If we are discussing with government
scientists then we raise all these points and show diagrams, and
so on, which illustrate what we are saying.
49. They are brought in?
(Sir John Houghton) Because they are bound to ask
questions about it, because, of course, some of them are raised
so regularly in the media; but in any case we would do that, yes.
50. Would I be right in concluding, from our
session today, that it is your feeling that most of the scientific
objection to the consensus is actually from vested interests within
the oil/coal lobby, rather than from scientists?
(Sir John Houghton) Yes.
51. What is your view of the green groups in
this debate, thinking of Greenpeace, Friends of the Earth; have
they been generally responsible, or have they exaggerated the
argument for their own purposes?
(Sir John Houghton) They vary from one green group
to another, but some of the green groups are really very responsible.
They do tend to emphasise, of course, the larger effects. On the
other hand, some green groups have produced documents which are
really exaggerations, with unjustified statements, saying, for
instance, a statement like Hurricane Mitch is the result of global
warming; it is not a statement which can be justified scientifically.
52. What about the media? Have the media given
the idea, say, that the Mozambique floods are due to global warming;
you have got much better television, more of it, these days, and
they have tended to say that there are more incidents of extreme
weather now than perhaps five or ten years ago, and, again, they
tend to attribute that to global warming?
(Sir John Houghton) There is a tendency on the part
of the media, in some of their programmes, to overemphasise, or
to overillustrate the effects. We are going to get more stories,
for instance, with global warming, of a kind that we are not sure
about, we are not sure about more hurricanes, for instance, or
more typhoons. We are sure that some sorts of storms have gone
up in frequency in recent years, which is probably due to global
warming, but we would be much more cautious in the statements
we would make than the statements that sometimes come out from
the media. On the other hand, of course, there are some media
productions that also say, well, this is all rubbish, because
they are relying on some of the lobby groups.
53. Moving on now. The conference in Edinburgh,
a couple of weeks ago, on genetically-modified foods, chaired
by Professor Krebs, came to the decision, I think, that there
should be an international body set up, perhaps modelled on the
IPCC, to consider this whole area of GM foods. Do you think that
that is a good model?
(Sir John Houghton) I am with the IPCC and I tend
to see its advantages, I suppose; but this is a good model. And
one reason for that is, if I can just give a bit of history of
the IPCC again and my involvement with it, when we began, in 1988,
we had our first meeting of scientists on the issue, there were,
I suppose, a significant number of scientists, good scientists,
there, who said: "We don't know enough to say anything, let's
keep quiet; we can't get involved in this sort of political stuff,
you see, because we don't know enough to argue that." So
we had a big discussion on that issue, should scientists be saying
things, trying to make very responsible statements, or should
scientists keep quiet; and the result of that discussion was that
virtually all of them said, in the end, of course: "We've
got to say what we know, and in order to say what we know we have
got to discuss what we know so that we can have a debate about
it". And I think what is a bit unique about the IPCC, it
was helped, of course, by the international nature of the science
in which we are involved anyway, there were international bodies
dealing with meteorology and oceanography, and the like, which
were there, so scientists were used to talking to their international
counterparts, and so on; but what I think is fairly unique is
that scientists have taken the trouble to try to debate amongst
themselves what we know and what we do not know, because they
feel responsible, and because there is a mechanism whereby the
assessment can be carried out. Now in other areas of science,
which are equally politically important, I do not think scientists
worldwide have got together in the same way to argue about it
and take the time and the trouble to try to come up with really
good statements. And, I think, if we had not done what we have
done, in the IPCC, we would be in a much more uncertain scene
as far as climate change is concerned, just because people had
not really thought about it hard enough.
54. If we bring your model to the GM foods scenario,
there is some difference, as I had understood, as to whether the
new bodyif there was this international GM bodyshould
be accountable to the OECD or to the World Trade Organisation;
or, in your own case, you are a United Nations organisation. Do
you thinkit is certainly my own viewthat it is the
UN umbrella that is fairest for GM foods as well; what would be
(Sir John Houghton) The parentage of the IPCC is one
UN environmental body, the UNEP, and the World Meteorological
Organisation, which is a UN technical support agency, so it is
strongly scientifically based because both of those bodies are
strongly scientific in their ethos. I could imagine there being
some difficulty with a body like the World Trade Organisation
being its parent, because the influence might be such that it
might not be entirely neutral. If there were scientific bodies
who could, bodies like FAO, for instance, would be very interested
in the GM business, and I do not know whether they could be a
possible parent. Though, having said all that, I also reflect
on my experience with the aviation report, which the IPCC has
recently done, which was partially parented by ICAO, the international
body that joins the airline industries together, and that actually
was no problem, they played a sensitive, positive role, and really
wanted a good report which spelled out the science in a sensible
55. It could be horses for courses, could it
not, really, depending on what the topic is?
(Sir John Houghton) And who is prepared to do it,
56. Sir John, what importance do you attach
to the climate change models and general circulation models in
predicting and analysing climate change?
(Sir John Houghton) Models are very important; and
they are not the only thing, observations are even more important,
because if you have no observations you cannot actually make any
progress. But if you are going to put the observations and the
data you have together, which come from a very wide range of components
of the climate aspects of it, and so on, and if you are going
to try to understand mechanisms, then you need a framework in
which to generate that understanding, and a model provides that
framework. And the reason we need a framework is because all the
processes we are talking about are non-linear processes, so there
is not a simple proportionality between an increase in this and
an increase in that, it is much more complicated than that. And
when you have many things varying; at the same time you have to
find some way of putting together the forcing factors and the
responses and adding them up, and the model does that for you;
you cannot do it analytically because it is too complicated to
do that, it is not mathematically possible, but you can do it
by using numerical methods to add together the forcing factors
and add together the responses. Because we do know, we have a
very good knowledge of the physical laws and the chemical laws,
and, indeed, the biological ones, which operate in different parts
of the climate system, and in order to add those together you
need to carry it out with a tool, and the model is that tool.
The model can be quite a simple thing, involving an equational
tool, in its very simplest form, or it can be a much more complicated
thing involving many equations and many factors in a much more
57. How accurate are these models, would you
say; is there a way of testing the accuracy of the models, that
you have tested in any way?
(Sir John Houghton) If you make a model of the climate,
the first thing it has to be able to do, of course, is to describe
the current climate rather well, with the current forcing, which
comes from solar radiation, and the like, it has to be able to
produce a response to the diurnal cycle, with a change during
the day, to the annual cycle, that is the change during the year,
through the variations that occur due to things like the El Niño
phenomenon, and the like, or to other factors, volcanic eruptions.
And you can test the model, over different timescales, by testing
how it responds to things that you know about, which have occurred
already or which regularly occur, and get a very good idea of
how that response might be. And, to give you an example of something
which has helped, I think, to give us confidence in models, more
than we had before, in 1991 there was an eruption of a volcano
in Pinatubo, in the Philippines, which put out a lot of dust into
the high atmosphere, which was circulated around the globe, in
a fairly uniform manner, actually, cut out some solar radiation,
a few per cent, the average temperature of the surface and the
lower atmosphere went down by about half a degree, over a two-year
period, and the models produced that response quite well. But
a more stringent test from that was that, as a result of that
volcanic eruption, perturbations of the climate ocurred; there
was an anomaly in the regional pattern of climate change. I do
not know if you remember the years 1992 and 1993 but they were
particularly mild winters in western Europe and particularly cold
winters in the Middle East, there was snow in Jerusalem in both
those years, I think, or very cold in Jerusalem in both those
years. And the climate model in Hamburg attempted to try to simulate
that response, and, in fact, they simulated it reasonably successfully,
not perfectly, by any means, but the major anomalies which occurred
in the regional climate change, as a result of that volcanic eruption,
were reasonably well simulated by the Hamburg model. So that gave
us some confidence in the use of models in simulating climate
change on a global scale.
58. Some people have proposed the fossil data
studies, in measuring the changes in climate change; have you
(Sir John Houghton) Yes. There are some models, a
Hadley Centre model has been used to try to simulate the climate
of about 6,000 years ago, for instance, with some success, at
least as good success as you can test, because the data from that
period is not very good, is not perfect by any means, but at least
some of the features of the climate of that period have been well
simulated, and others have gone further back, actually, to parts
of the last ice age, and the like, in order to test models. So
models have been tested against quite different climates which
have occurred during the ice age, or since the ice age.
59. And are there any reservations in the research
community about these models that we have?
(Sir John Houghton) There is no reservation about
the fact that they are valuable and useful. There is much discussion
about how certain they are and how accurate they are and how you
actually establish that, in terms of the detail of climate change.
Many of the models, of course, we can test models against each
other, and there are, what, 20, 30, 40 elaborate, coupled ocean
atmosphere models worldwide, you can compare the results from
the different models. But then, of course, you would argue, and
quite rightly, that many of those models have the same pedigree,
some of them came from the same sources, or similar sources, they
are all different in some regard, but in other regards they are
very similar; so how good a test is that. And that is a question
we often debate, actually, as to how well tested they can be.
I think, the way our confidence has grown, however, over the last
15 years, since good models have been available, is interesting,
because every time, I think, the models have improved dramatically
in some technical way; there has been more confidence in the results;
it is not obvious that that is going to be the case, actually.