Memorandum by Professor Sir David King,
Chief Scientific Adviser to the UK Government
CURRENT UNDERSTANDING OF CLIMATE CHANGE SCIENCE
1. I welcome the Committee's interest in
the critical issue of climate change. In my capacity as the Government's
Chief Scientific Adviser my own involvement in the subject is
well known and has been wide-ranging. This has included:
Presenting climate change science
and raising the awareness of climate change amongst the public,
industry, Parliament and Governments worldwide.
Focusing on the action required,
including: (i) the energy innovation needed to achieve a radical
shift to a low carbon economy, (ii) the establishment of the
UK Energy Research Centre, (iii) UK participation in the International
Thermonuclear Experimental Reactor (fusion) project, and (iv) steps
to improve the energy performance of the built environment.
Focusing on actions required to meet
the impacts of global warming: particularly through the Foresight
Flood and Coastal Defences Project, set up with the Environment
Minister Elliot Morley, as stakeholder Minister.
Providing support to Defra, FCO and
No 10 on international action, as well as through the network
of international Science and Technology Attaches and the Global
Science and Innovation Forum.
2. The science of climate change is a mature
subject. The French mathematician Fourier in 1827 put forward
the greenhouse gas concept: our atmosphere absorbs heat that would
otherwise radiate out into space. This manifests itself in two
important ways. Firstly the Earth's average surface temperature
is kept at about 15ºC by this blanket effect of the atmosphere
that surrounds it. Without the greenhouse effect, life on this
planet would not exist as we know it, as the average temperature
would be -18ºC. Secondly, night-time temperatures would otherwise
be much lower than they are without the blanketing effect provided
by the greenhouse gases. Fourier's work was followed in 1860 by
the discovery by the British scientist Tyndall that the major
constituents in our atmosphere, nitrogen and oxygen, do not absorb
heat (infrared radiation from the earth), and that the greenhouse
effect is due to the minority gases in our atmosphere, especially
water vapour, carbon dioxide and methane: the greenhouse gases.
3. On this basis the Swedish Nobel prizewinner
Arrhenuis did the first global warming calculation in 1896. He
said: If the human population should burn so much fossil fuel
that the carbon dioxide level in the atmosphere should double,
what would the temperature rise be? His calculation yielded an
average global increase of 5ºC. This is a very large increase:
for example, the difference in temperature between an ice age
and a warm period is about 5ºC to 8ºC.
4. More recent calculations of the global
temperature increase that results from a doubling of carbon dioxide
levels yielded a temperature range of 1.5-4.5ºC and research
from the Hadley Centre proposed a temperature range for doubled
CO2 of 2.4-5.4ºC, but these results, and other recent research,
do not rule out the possibility of even greater temperature change,
suggesting that the scale of climate change could be quite different
from previous assumptions.
5. Carbon dioxide levels in the atmosphere,
and water isotopes serving as a proxy for global temperatures,
are encapsulated in ice layers in the Antarctic and on Greenland.
The latest data from ice cores show that over the past 750,000
years the Earth has been through eight cycles of ice ages and
warm periods. In each of the ice ages the carbon dioxide levels
were at around 210 parts per million in the atmosphere. In each
of the warm periods the carbon dioxide levels rose to 260-280
ppm. Temperature changes were 5 to 8ºC. The correlation bears
out the greenhouse model described above.
6. Carbon dioxide levels in the atmosphere
have been accurately recorded at the Mauna Loa Observatory, Hawaii,
since 1959. They are now rising at a rate of approximately 2ppm
per annum, and are approaching 379ppm, 40 per cent above the pre-industrial
levels of our current warm period and also all previous warm periods.
7. Global temperatures have increased by
0.6ºC over the past century. This is in broad agreement with
the theory of the greenhouse effect, and is what Arrhenius predicted
8. Some argue that warming is happening,
but that it is simply part of a natural cycle. They point to the
relative warmth in Europe in the middle ages and the cooler conditions
that occurred in the 17th and 18th centuriesthe so-called
little ice age. There are undoubtedly natural fluctuations but
we are now facing a sustained warming trend that can only be explained
by the rise of greenhouse gases in the atmosphere. The effect
of such warming is seen globally in glaciers, which are in retreat
around the globe. Some have been dated back to the last ice age,
12,000 years ago, and are in retreat for the first time in our
warm period. The latest supporting data was published from the
Chinese Academy of Sciences late last year. A 25 year analysis
of the Chinese glaciers, which correspond to 15 per cent of land-based
ice on earth, based on more than 30,000 aerial photographs and
satellite images, demonstrated the loss of 8,000 km2 of ice cover
in this period. They estimated that the Chinese glaciers will
have disappeared by the end of the century.
9. Impacts of climate change predicted by
the modellers are already occurring: the middle Europe summer
of 2003; high intensity rainfall, hotter summers, etc. Climatologists
are currently focusing their attention on a number of key factors.
(i) What are the extreme events that
we are vulnerable to as global warming continues?
These include: a slowing, or even termination,
of the thermohaline circulation which maintains northern temperatures
about 8ºC higher than they would otherwise be; loss of the
Greenland ice sheet, which would produce global sea level rises
of about 7 metres over a timescale of a thousand years or more;
enhanced retreat of glaciers in some regions; major alterations
to the Indian monsoon and desertification of increased areas of
the African continent.
(ii) Water vapour
As carbon dioxide levels increases all models
show an increase in the temperature of the earth and sea. In turn,
this increases the amount of water vapour in the atmosphere, which
is a greenhouse gas itself and will further raise the temperature.
This is a big positive feedback. However, this water vapour can
form clouds, and the clouds can have opposite effects: they can
act as a blanket, adding to the greenhouse effect, or they can
reflect sunlight back into spaceespecially high white cloudsand
cause cooling. This is very difficult to model.
(iii) Loss of forest
Forests remove carbon dioxide from the atmosphere.
Deforestation due to human activity is a well-known problem. But
sophisticated models now show that decreased rainfall is likely
to accompany global warming in some critical forested areas. These
include the Amazonian tropical rainforests. Reduced rainfall could
lead to dryer conditions and increased numbers of forest fires.
This would increase global warming quite substantially.
(iv) Acidification and warming of the
As the CO2 level in the atmosphere increases,
so does it also increase in the oceans, which raises the ocean
acidity (ie lowers the pH). Effects on coral reefs and plankton
populations have already been noted. The wider impact on marine
life and on the food chain, including the human food chain, is
an area requiring urgent further study.
(v) Global dimming due to aerosols
Careful measurements of solar intensity indicate
a reduction in sunlight over the past four decades. This is attributable
to pollution generated by advanced societies, sulphurous coal
in power stations and cars being the major sources. This cooling
effect could have masked the true extent of global warming. The
clean up process in power stations, car exhausts and other sectors
of industry is reducing the aerosol content of the atmosphere
and this could lead to greater levels of global warming than we
11. These fall into three quite different
(i) Serious scientists who stress the problems
of modelling aerosols and cloud cover. They do not reject the
greenhouse model, the observed increases in carbon dioxide or
the observed increase in global temperature. There are very few
in this category. The best known is the American climatologist
(ii) A second small group of scientists who
appear at every meeting but are not seriously regarded. These
include scientists who argue, without any proper evidence, that
sea levels are not rising at all or that global warming is due
to increased solar activity.
(iii) Finally, there is a very vocal group
of professional lobbyists. Some have had scientific training,
but most have not. They manage to make their voice heard as they
are articulate and clearly well-funded. They fall into the same
category of lobbyists for the tobacco companies who claim that
links between smoking and ill health are still not proven.
12. In summary, it is quite clear that the
balance of international scientific opinion is overwhelmingly
in support of the conclusion that climate change is a real and
present danger, requiring urgent and committed action. It nonetheless
remains a significant issue, in terms of gaining wider political
and public consensus on the need for action, that the arguments
put forward by the sceptics gain publicity and influence far beyond
that which can be justified by the standing of the individuals
concerned, by the validity of their arguments, and by the scientific
credibility of the evidence that they are able to put forward.
24 February 2005