Climate Scientists are agreed that global warming is a serious
problem that must be addressed urgently. Polls show that only
about 60% of ordinary people are convinced that global warming
is man made.
This paper aims to present the essential case for action on global
warming in a way that ordinary people can understand.
1. The Earth's Temperature
The temperature of Planet Earth is maintained by two sources,
heat from the sun, and a tiny amount of heat from the Earth's
2. The Greenhouse Effect
Without the atmosphere, Earth would be 33°C colder than it
is because the sun's heat is retained by the gases in the atmosphere,
which act as a kind of duvet.
3. Life on Earth
Life is adapted to a narrow global temperature range, which we
alter at our peril.
The atmosphere is a system that is so complex that it can only
be studied by computer models which can make the various factors
interact. All these models show that we face serious problems.
Six factors affect the Earth's surface temperature
a. the distance from earth to sun, which varies very slowly
b. sunspot activity, which has a cycle of about 11 years
c. Albedo - the reflectivity of the earth's surface - mainly clouds
d. aerosols and soot, mainly from volcanoes, which can cool the
atmosphere by throwing dust into the air. Industrial soot plays
a part here
e. greenhouse gases, which trap the sun's heat
f. Ocean currents, notably El Nino and La Nina
6. Greenhouse gases
The main greenhouse gases are:
---------------------% of greenhouse effect
Water - - - - - - -- - 36-72
Carbon Dioxide- - - - 9-25
Methane - - - - - --- - 4-9
Nitrous Oxide - ---- - 1-3
Ozone - - - - - --- - - 3-7
CFCs - - - - - - - - -~1
Water vapour is the main warming factor. It is not directly produced
by human activity, but it does become more powerful in a warmer
atmosphere. Its effect is difficult to predict, because vapour
also produces clouds, which have a cooling effect.
Water vapour has a short residence time in the atmosphere - about
10 days, compared to decades or centuries for CO2, and decades
for methane. This means that if the atmosphere is cooler, water
vapour condenses, and falls as precipitation. If the atmosphere
warms, more water vapour can be held, and its greenhouse effect
In short, water vapour is a passive component of the greenhouse
effect, acting as a feedback to amplify whatever else is going
7. Changes caused by human activity
Since the industrial revolution:
CO2 has increased by 38%,
CH4 by 150%, and
NO by 15%
These are the "anthropogenic" (man-made) changes
in the atmosphere. Together, they increase the greenhouse effect
by about 15%, which may not seem a lot, but taken year on year,
on a delicately balanced system, and with tipping points (see
below), this is a very significant increase.
8. Correlation and Causation
There is a correlation between CO2 and average global temperature.
The graphs below show average earth temperature, and CO2 levels.
This is the temperature since 1860.
This graph is of temperatures for the past 1000 years. It shows
a striking upswing since we began burning fossil fuels.
As you can see, there is a good match between the graphs of CO2
Since CO2 is known to trap heat, it is reasonable to accept
that our CO2 is causing the increase in temperature that
we observe. Indeed, there is no other explanation for present
temperatures. If we take man-made gases out of the equation, the
simply do not match.
Causation in science is not something that can be "proven",
because proof is something that happens in mathematics and logic,
not in science. Scientific "proof" is a common misconception.
The best status that a scientific theory can achieve is "not-yet-disproven",
and the assertion that CO2 and other greenhouse gas changes are
causing the climatic change that we are witnessing is certainly
in this state.
9. Tipping Points
The increase in global temperature can trigger several positive
feedback loops, or "tipping points":
a. Methane releases from permafrost
b. Less reflection of heat from lost snow
c. More water vapour held by warmer air
d. More forest fires from drier forests
These tipping points make it urgent that we act now to reduce
We cannot wait for the sceptics to be convinced. Some sceptics
are academics, and are quite capable of arguing a point for the
rest of their lives.
Most sceptics are politicians, journalists and non academics who
are simply in denial, because the economic changes that we need
to make are incompatible with their lifestyle and their political
For reasonable people, the balance of evidence is sufficient,
and when the majority of the scientific community is in agreement,
then a scientific view can be regarded as established, and politicians
are well advised to act on it, as they are doing in Copenhagen.
10 The politians' choice - Costs and Benefits
In the end, this is not an academic debate, because we and
our children are part of the experiment. The consensus among scientists
(with a few exceptions, as is always the case in science) is that
we should decarbonise our economy as a matter of urgency.
Academics can debate endlessly, but politicians have to make
a choice. Every choice involves a degree of uncertainty. So let
us look at the results of the choice.
Say we decarbonise our economy, and it turns out (unlikely as
that may be) that scientists' view is wrong?
· We will have created hundreds of thousands of jobs in
insulation and renewable energy manufacturing and taken thousands
out of fuel poverty.
· We will also have reduced the shock of Peak Oil and Peak
Gas, (the unavoidable dwindling of supply in future) and reduced
the acidification of the oceans.
· We will have addressed our energy security problems.
· We will increase prosperity in hot countries through
solar energy, and therefore reduced immigration.
Say on the other hand, we go the way of the denialists and skeptics,
and it turns out, as expected, that they are wrong?
· We will have problems with energy security,
· Peak Oil,
· Peak Gas,
· acidified oceans,
· acid rain,
· fuel poverty,
· civil unrest
· massive, catastrophic climate disruption from droughts,
floods, crop failures, disease, and war, and finally
· massive migration caused by environmental collapse.
Any sensible decision maker will put our money into decarbonising
the global economy.
We, the people must accept, support and the necessary changes.
24 November 2009