Memorandum submitted by the Climatic Research
Unit, University of East Anglia, Norwich
1. The Climatic Research Unit (CRU) has
been in existence for 28 years. It receives funding from several
sources (eg UK government departments, EU, US Department of Energy,
UK Research Councils, Industry/Business and organizations with
charitable status) and is partially supported by the University
of East Anglia, through the School of Environmental Sciences.
Over this time, it has built up an excellent reputation for work
in the Climate Change field. It is most well-known for its studies
on instrumental climate (jointly producing with the Hadley Centre
of the Meteorological Office the time series of hemispheric/global
temperatures used by IPCC), paleoclimate (past estimates of temperature
for the last few millennia) and projections of future climate
(again joint work with the Hadley Centre). CRU is the dissemination
point for all climate model data from the Hadley Centre (funded
by DETR, Department of Environment, Transport and the Regions,
through the Climate Impacts Link project), adding value/details
to future scenario integrations of Hadley Centre models. This
includes validating the models against observational fields. As
an academic institution, CRU does not have a position on this,
or any other matter. The views expressed here are the synthesis
of individual members who have worked in this area.
2. This memorandum will address the five
specific questions, referring back as appropriate to the terms
Q1. What other reasonable explanations, other
than increasing concentrations of CO2 in the atmosphere,
are you aware of for the upward trend in earth temperatures? Has
your organization conducted any assessment of these alternatives
and if so, with what conclusions?
3. First, CO2 is not the only
human-produced greenhouse gas. There are also CH4, N2O and CFCs,
often referred to collectively as greenhouse gases. CO2
alone is only about 60 per cent of the problem. Aerosol emissions
(eg sulphates, soot, and some other particulates) are also considered
as part of the problem. Aerosols have an inverse effect (ie should
lead to cooling) but their use is being reduced on other pollution
grounds (eg they are the root cause of acid rain). The question
is taken, therefore, to refer to "Anthropogenic emissions
or activities, which alter the radiative balance within the atmosphere",
or the loose media phrase "global warming", ie not-natural.
4. There are only two possible natural factors
that could potentially affect global scale temperature changes,
on the annual-to-century timescales (ie similar to that of anthropogenic
activities). These are variations in solar output and the effects
of large explosive volcanic eruptions.
5. It has been shown that large explosive
volcanic eruptions (particularly those in the tropics and subtropics,
30ºN-30ºS), over the past century, have caused short-term
climate change. Mt Pinatubo in the Philippines, for example, erupted
in June 1991, and caused a global average cooling during 1992
and 1993 (mainly from May to September, ie northern summers) of
about 0.3ºC (see, eg, Kelly et al, 1996). Larger eruptions
in earlier centuries may have caused greater reductions in temperature.
The number of volcanic events over the last 600 years is relatively
few (-20 in total, see Briffa et al, 1998).
Impacts might become larger if volcanoes erupted
together compounding effects, but there is no evidence of this
happening, except in the late 17th century and the 1810s. The
only significant eruptions this century occurred in 1902, 1912,
1963, 1982 and 1991.
6. Global temperatures also vary on timescales
of three to five years as a result of changes in the tropical
Pacific Ocean (El Niño/La Niña events). El Niño
events cause warmer years globally and La Niña cooler ones.
Changes in the frequency/severity of these events have occurred
over the last 150 years, but not to an extent to cause any change
in global scale climate on decadal and longer timescales.
7. It is known that the Sun's output varies
on many timescales, but we have only recently begun to realise
exactly how by monitoring the Sun above the atmosphere using instrumentation
on satellites. Ground based measures of solar output are available
for several centuries but they are influenced by the atmosphere.
Despite this, several estimates of past variations in solar output
have been made which extend back several centuries. Variations
in solar output have been considered as being important by scientists
since the 18th century. The possibility that solar variability
might account for all or part of the global warming trend has
been examined by Kelly and Wigley (1990, 1992) in a series of
studies that have assessed the relative contribution of solar
forcing of climate, based on sunspot numbers and solar cycle length
and anthropogenic activities. The overall conclusion of this work
is that although there is evidence that solar variability may
affect global temperature on these timescales, the effect is markedly
less than that resulting from anthropogenic activities. In other
words, these authors and all in CRU would conclude that anthropogenic
activity is the most plausible explanation for the bulk of the
observed warming trend.
Q2. What critical appraisal of climate change
models has your organisation performed and with what result?
8. First, there is no such thing as a climate
change model. Climate models solve the equations of physics (mass,
energy, momentum) and the climate model run in the UK by the Hadley
Centre is essentially the same computer code that produces each
day's weather forecasts. The models are run in (control) present
mode and then the models atmospheric composition is altered to
produce a perturbed (scenario) integration. The change produced
by the model is the difference between the perturbed and control
integrations. We have extensively evaluated the performance of
the control runs of General Circulation Models (GCMs) over at
least the last 10 years in projects funded by DETR. The results
of this work have obviously gone to DETR as annual and project
reports and also as publications to the peer-review literature
(see, eg, Hulme et al, 1993; Airey and Hulme, 1995, Osborn
et al, 1999). The basic conclusions of these studies are:
GCMs have improved over the last
10 years (as have weather forecasts);
the Hadley Centre model is considered
by most atmospheric scientists to be one of the best two in the
world at the moment (the other is at the Max Planck Institute
for Meteorology, Hamburg, Germany). The USA has diversified its
effort into a number of centres and has fallen behind. If research
there was more co-ordinated, it ought to improve; and
the latest two Hadley Centre models
(HadCM2 and HadCM3) do very well at simulating the climate over
the UK and Europe, reproducing features and interrelationships
between surface climate (temperature and precipitation patterns)
and the circulation that occur in the real world (see references
Q3. How much agreement is there between scientists
internationally regarding explanations for climate change?
9. The most comprehensive assessment of
explanations for climate change are given in the reports of the
Intergovernmental Panel on Climate Change (IPCC) in 1990 and 1995.
Most of the world's leading scientists are involved in contributing
to the reports and most would agree with the main conclusions.
The large majority of atmospheric scientists would accept IPCC's
most quoted conclusion that "The balance of evidence suggests
a discernible human influence on global climate". There will
be differences of opinion on some of the details but all atmospheric
scientists would accept that IPCC provides the concensus view.
IPCC and climate scientists both accept there are knowns and unknowns,
with respect to the causes of climate change, but there are no
great schisms within the community regarding what the important
mechanisms are. This concensus has been there since CRU began
in the 1970s and predates IPCC.
Q4. To what extent are the fruits of your
research fed into Government machinery and by what means? Do you
think that the Government is made sufficiently aware of alternative
explanations? By what means does this occur?
10. The results of our research reach the
government macinery in a number of ways: through direct contact
with politicians (ministers and MPs), through contract reports
to departments such as DETR (informing also our contract officers
when important papers will appear in journals like Nature and
Science), through collaboration with government scientists
(eg the Hadley Centre of the Met. Office and NERC Research Institutes),
through publications in the scientific literature, and through
media. We also inform other departments, such as MAFF and DoH,
and advise the UK Climate Impacts Programme (funded by DETR).
Over the last few years we have occasionally been consulted by
DETR concerning statements made by ministers in the House and
elsewhere. In our view, the government is totally briefed on our
research results regarding the causes of climate change, validation
of GCMs, and observed changes in a global and UK climate. We always
emphasise areas of uncertainty, although these are often missed
by the media who like things to be black and white.
11. Our belief is that there are no credible
alternative explanations (ie the 0.6ºC increase in global
temperatures during the 20th century cannot be explained without
including a major component from anthropogenic emissions to the
atmosphere). We hear, occasionally, of alternatives (all in the
grey literature or on web pages). In the climate area, as in all
science, credibility is measured by publication in an appropriate
peer-review journal. As climatologists we intuitively rank journals,
depending on our knowledge of how easy/difficult it is to get
articles published (ie how rigorous the journal's reviewing policy
is). CRU would rank the following journals; Nature, Science,
J. Climate, J. Geophysical Research, Climate Dynamics, the
International Journal of Climatology and Geophysical
Research Letters in the premier league. We mention this, as
any alternative explanations should appear in these sort of journals
for them to have any credence. Anyone can publish a book or set
up a web page to expound their views. This is not what we understand
as scientific publication. If alternative explanations were published
in these journals we would be the first to be informing departments
Q5. How important is the International (sic)
Panel of Climate Change in co-ordinating research on climate change
and disseminating findings (sic)?
12. The IPCC does not co-ordinate research
into climate change. Its role is to review existing research and
to advise the international community on the current state of
scientific and technical understanding. In this respect, IPCC
makes authoritative statements but only based on material published
in the peer-reviewed scientific literature. In this way it plays
a crucial role in disseminating research findings by reaching
a concensus judgement of all the published literature on the subject.
13. The IPCC does not fund any scientific
research. In the UK, the Technical Support Unit for Working Group
1, funds scientists involved in writing drafts of chapters to
attend co-ordination meetings, where the lead authors get together.
The IPCC's recommendations regarding the current issues in climate
(eg what we need to know more about to reduce uncertainties) does
influence funding in indirect ways, but only alongside a host
of other factors.
15 February 2000
These references are those specifically referred
to in this memorandum. CRU has written several hundred scientific
papers. Of the names on these papers, CA Senior and SFB Tett work
at the Hadley Centre and FH Schweingruber at the Swiss National
Institute of Forest, Snow and Landscape research. All others are
or were members of CRU at the time the papers were published.
Airey, M and Hulme, M, 1995: Evaluating climate
model simulations of precipitation: methods, problems and performance.
Prog Phys Geog 19, 427-448.
Briffa, KR, Jones, PD, Schweingruber, FH and
Osborn, TJ, 1998: Influence of volcanic eruptions on Northern
Hemisphere summer temperatures over 600 years. Nature 393,
Hulme, M, Briffa, KR, Jones, PD, and Senior,
CA, 1993: Validation of GCM control simulations using indices
of daily airflow types over the British Isles. Climate Dynamics
Kelly, PM and Wigley, TML, 1990: The influence
of solar forcing trends on global mean temperature since 1861.
Nature 347, 460-462.
Kelly, PM and Wigley, TML, 1992: Solar cycle
length variations, greenhouse forcing and global climate. Nature
Kelly, PM, Pengqun, J and Jones P D, 1996: The
spatial response of the climate system to explosive volcanic eruptions.
Int J Climatol 16, 537-550.
Osborn, TJ, Briffa, KR, Tett, SFB, Jones, PD
and Trigo, RM, 1999: Evaluation of the North Atlantic Oscillation
as simulated by a coupled climate model. Climate Dynamics