All posts by Stephen Stretton

How to get to Zero Carbon

How to get to Zero Carbon.pdf

I outline a vision of how a nation state such as the UK can get to a near-zero carbon energy system in 20-30 years. I will argue that we need to get to zero carbon if we are to stabilise the atmosphere’s greenhouse gas concentrations and the oceans’ acidity – if we are to stop turning up the heat in the global saucepan. I will argue how we can get to near-zero carbon in the UK and other developed and developing countries, if we make some difficult choices over our future energy supply. Over the next 20 years, the UK will need to construct of the order of 150GW (annual average rate of electricity generation) low-carbon electricity capacity from nuclear and renewable sources, and from fossil fuels using carbon capture and storage sources; plus an international power grid. I will show what we need to do in terms of policy to make this a reality. Proposed policy includes a global contractual minimum carbon price (or equivalent in terms of electricity) for new energy investment (with higher prices paid for those who invest most rapidly), and an upstream carbon tax (with border-tax adjustment) for a nation-state such as the UK or a larger coalition of nations serious about tackling climate change. In other words, I demonstrate how a bright future can be a plausible evolution of existing political structures. I will show how action on a national and supra-national level is feasible. Finally, I suggest that individual and collective awareness-raising about policy solutions can lead to a plausible route to a safe and secure future.

Back to basics

Back to basics (pdf), by Stephen Stretton and Daniel O’Neil.

In the clamour of contention and controversy surrounding the climate change debate, sometimes it makes sense to return to first principles. I was reminded of this sharply during a conversation with a professor of solar energy technology, when he stated bluntly that speculation on solutions is worthless unless we have come up with a concise definition of the problem we are trying to solve. I hope in this initial column to humbly attempt to lay out the problem we face with the hope of looking at possible solutions, and the debates surrounding them, in later columns.

The UK Energy Crisis

What do we need to do to solve the simultaneous energy and climate crises?

What do we mean by the energy crisis?

There are various energy crises (high prices, unstable suppliers, resource depletion(?)). One possibly serious energy crisis is the potential shortage of electricity generation capacity.

For example, by 2015, the UK might have only 80% of the generating capacity that it needs.

What are the reasons behind this ’energy gap’?

Firstly there is a closing of existing capacity: both of old nuclear power stations coming to the end of their lives and of dirty coal power stations being closed down due to EU regulations: see this report p11-13.

Secondly, there is large uncertainty in the market.

Uncertainty leads to:

a) returns need to be higher or else investment won’t take place [1]

b) investment may be delayed, especially if a delay will lead to the resolution of uncertainty [2]

The problem now is that there is severe uncertainty over the future of the energy in this country. The government has assuaged some of the regulatory uncertainty by making strategic statements about the future of nuclear, renewable and fossil fuel energy. But there remains great financial uncertainty.

Each power source has uncertainties:

a) Gas: the fuel is now expensive, making this source uneconomic if such prices were to be maintained

b) Nuclear: nobody has built a nuclear power station in the UK since Sizewell: there are considerable price escalation and legal risks. A power station can be built in 7 years but with all the regulatory and public opinion hurdles new power is unlikely to come on stream before 2020. The government was 5 years too late in its decision.

c) Renewables: the Renewables Obligation, unlike the German system of ‘feed-in tarrifs’ provides a highly uncertain return

d) Carbon Capture and Storage (coal or gas): again we don’t know the exact cost until the plant has been built. Any plants built by 2015 would be ‘demonstration’ plants.

e) Coal. The dirtiest energy source of them all. The price of energy in the form of coal is a lot lower than the price of energy in the form of natural gas or oil. However, is the European Emissions Trading Scheme carbon price sufficient to control the price?

In this sitution, gas is ruled out as too expensive. renewables may happen if they can get through planning, nuclear is too late for 2015 but could make a significant impact from 2020 onwards. We are stuck between the rock of our climate change ambitions and a hard place of the investment response of low-carbon electricity to current ambitions. What we need is strong incentives for investment and in particular strong incentives for low carbon electricity. My next post will explain how this can be done.


[1] uncertain cashflows will lead investors to require a higher return in order to compensate for the risk. in otherwords people will invest but only if the price is right.

In otherwords, uncertainty may lead to less investment and the prices of that investment may rise to compensate investors for the extra risk incurred.

The relevant theory of this is known as certainty equivalent. Under certain conditions, an investor’s aversion to risk can be represented by a higher or ’risky’ discount rate. For a full account of the relation between the various ways of representing risk in investment decision see Rothwell and Gomez (2003) “Electricity Economics”, IEEE press, NJ, USA pages 53-74

If governments make investing more risky than it needs to be, then electricity consumers (industry and the public) are likely to have to pick up the bill in higher bills or blackouts.

[2] If investment is irreversible there is a further effect. Real options theory shows that a combination of irreversibility and uncertainty can lead to investments being delayed. See for example Dixit and Pyndyck ’Investment Under Uncertainty, Princeton.

How Sensitive Is The Climate?

Why ‘Fast Feedbacks’ are quite slow and ‘Slow Feedbacks’ might be rather fast.

This paper by Hansen et al. has lots of interesting material on climate sensitivity:
The climate sensitivity is the temperature response of the whole climate to a forcing of greenhouse gases. We know that there are two basic sorts of feedback processes going on in the climate. Firstly we know that as the temperature rises, relative humidity will stay roughly constant and thus absolute humidity will increase. This leads to more water vapour in the air; and water vapour is a strong greenhouse gas. Higher temperatures also has an ambigous (to this author) effect on clouds. The sum of all these atmospheric effects yields the ‘Charney’ definition of the climate sensitivity which is the equilibrium temperature rise from a doubling in CO2 concentrations; assuming that the land albedo and carbon (CO2/Methane) sinks stay constant. (of course they don’t stay constant; we will come to this). This has been argued to be close to 3Celsius (3C) for a doubling of CO2 or 0.75C/(W/m2)*. [*A doubling of CO2 gives an increase in radiative forcing of about 4W/m2, so multiply the C/(W/m2) by 4 to get the temperature change for doubling CO2]

Hansen et al. (1993) calculated the ice age forcing due to surface albedo change

to be 3.5 C/(W/m2). The total surface and atmospheric forcings led Hansen et al. (1993) to infer an equilibrium global climate sensitivity of 3C for doubled CO2 forcing, equivalent to 3/4 +/- 1/4 C/(W/m2). This empirical climate sensitivity corresponds to the Charney (1979) definition of climate sensitivity, in which ‘fast feedback’ processes are allowed to operate, but long-lived atmospheric gases, ice sheet area, land area and vegetation cover are fixed forcings. Fast feedbacks include changes of water vapour, clouds, climate-driven aerosols1, sea ice and snow cover. This empirical result for the ‘Charney’ climate sensitivity agrees well with that obtained by climate models (IPCC 2001). However, the empirical ‘error bar’ is smaller and, unlike the model result, the empirical climate sensitivity certainly incorporates all processes operating in the real world.
This ‘fast feedback’ is not all that fast however… The fast feedbacks being slow: 50% of the climate response happens in 30 years and the rest takes 1000 years. So we see in immediate terms (net of the cooling effect of aerosols) about 50% of the climate change that we are likely to see.

Now to the `slow’ feedbacks, namely the ice-albedo changes from melting ice and carbon dioxide and methane releases. How fast are they? And how serious?

In answer to the ‘how fast’, the simple answer is we don’t know. Traditionally, ice-melting has been seen as a slow process. But the old models may not be correct; as was shown by record melt rates in the early 21st century. Paleotological evidence points to times between the ice ages where sea levels have risen metres in a single decade. Hansen suggests that the relative stability of our epoch may have been to do with the fact that there was a zone of comfort between the melting of the great Eurasian and North American icesheets and the melting of Greenland and West Antarctica.
The second question is ‘how much’. One approach is bottom up: you add carbon cycle causation to the greenhouse effect.
If the effect of temperature on radiative forcing is given by s and the effect of radiative forcing on temperature by g, the feedback relation is simply:
DT(with feedback)/DT(without feedback)= 1/(1-g*s). This amounts to 15-78% more warming (Cox and Scheffer 2007):
the feedback of global temperature on atmospheric CO2 will
promote warming by an extra 15–78% on a century-scale.
This estimate may be conservative as we did not account for
synergistic effects of likely temperature moderated increase
in other greenhouse gases.
But as the authors point out, this does not include the effect of everything working together.
What evidence do we have of everything working together?

A cursory inspection of this graph of greenhouse gas forcing shows:
a) A very high correlation (suggesting a strong link between greenhouse gas concentrations and warming)
b) Episodes of very rapid temperature change and ice melt (over the time scale of decades – e.g. the ‘Younger Dryas’ event.
c) a correlation between the two variables of about 3C/(W/m2)
Now the temperature shifts at the poles by about twice the global temperature change, we can imply a correlation of about 1.5C/(W/m2).
This is about double the ‘fast feedback’ 0.75C/(W/m2) predicted byclimate models and would imply a temperature change of six celsius for a doubling in CO2, twice what we have already found. But this is not the same quantity. It’s not clear that the figure found by dividing the standard deviation of the Temperature graph by that of the Forcing graph is the quantity that Hansen asserts it is and that we want. What is going on?
So, following Scheffer and Cox, here is some basic theory of feedback loops…
Let’s assume that Forcing (in W/m2) leads to temperature increases in Celsius (C). Let’s assume both processes are linear:

Forcing –> Temp
\ /
< --

If we denote the initial change in forcing by f (before feedbacks)
and the final change in temperature by T (after feedbacks)
This gives T/f=g+g(sg)+g(sg)*(sg)…= g/(1-s*g)
What about the other direction?

Temp –> Forcing
\ /
< --

Here we observe only the final F and the final T
We see Forcing = (s+gs+gs*gs+…)t

F = t * s / (1-gs)

And T = t(1+gs+gs*gs+…)=t/(1-gs)
So F = s * T
T/F = 1/s

So if we observe T/F = 1.5 this implies that s = 2/3.

So the overall effect all depends on the overall strength of the feedback 1/(1-gs).

So ice core evidence provides us with information about the *strength of the Temperature-CO2 feedback* not on the overall greenhouse effect, including feedbacks.

The information about the gain of the whole system will therefore be gleaned from the size of the equivalent radiative forcing change that started the whole process off. If the huge temperature change and big CO2 increase was the result of a huge temperature forcing, this would imply that the feedback from temperature to CO2 was huge, but that the greenhouse effect was small.

Hansen’s paper provides some very interesting evidence of the magnitude of the forcings from precession, but does not go so far as to come to an estimate of the ‘equivalent’ forcing implied by the Milankovich cycles. It is clear that the forcing on a global sense is small, but as Hansen points out, the effect at the ice age boundary is larger.
My conclusion supports the methodology of Cox and Sheffer over that of Hansen. However, it suggests that it should be easy to extend Cox and Scheffer to include
other greenhouse gases and ice-albedo effects (by using the data that Hansen himself uses).
What is needed is to have a rough estimate of the magnitude of the original ‘equivalent temperature’ forcing (already including *local* ice-albedo feedbacks – since an insolation increase at the polar rim where ice is melting is clearly very effect; but *excluding* global feedbacks) that started the whole process off.
Hansen’s paper hints at it but does not profer an estimate. His guess is probably a bit better than mine. Perhaps he should guess. An approximate answer to the exactly relevant question may be as much use as the exact answer to an approximately relevant question.

Evidence for Climate Change and Related Policy Issues

Science Issues

Why do we think that the observed increased concentrations of CO2 and Methane will warm the earth?
1) Basic physics
2) Water vapour feedbacks from recent measurement of radiative outflow from satellites & Models integrating these observations
3) Observations of the climate warming up already (see below for detailed refs)
4) Observations CO2 of the ice ages (showing evidence for positive feedback as well as a very close link between temperature and CO2 and Methane)

Concentrations of CO2
Concentrations of CO2 went between 180 (ice age) and 280ppm (warm period between ice age). They are now at 388ppm: higher than the last few million years; the sun is also getting stronger over the very long term.

Science of Greenhouse Effect

  • Basic Physics: see this BBC site
  • Undergraduate level Physics: see Archer

Greenhouse gases increase the flow of energy into the Earth. It has been estimated that a concentration of CO2 of 550 parts per million (before industrialization the level was 275 parts per million) would leave to 3.7 Watts extra heat imput per square metre of the Earth’s surface area.

Water vapour
The Stefan Boltzmann law would shows that the heat radiated from the earth’s surface increases by about 3.2 Watts per square metre per degree Celsius rise in temperature. Therefore, the Earth’s temperature would need to rise by about 1.2 degrees Celsius to balance out this rise in temperature.

However, we know that warmer air has a higher absolute level of humidity (in otherwords it contains more water vapour). Water vapour is also a greenhouse gas, and so this traps heat too.

We can estimate that water gives a positive feedack of -1.6 Watts per square metre per degree Celsius rise in temperature.

This should be compared to ‘StefanBoltzmann’ extra heat flow of 3.2W/m2K, giving net effect of 1.6W/m2K

When we include this effect (but assume no other feedbacks), that means that the earth would have to rise in temperature by 2.3 Celsius (not 1.2 Celsius) before the outflow of heat balanced the extra inflow.

So CO2 drives temperature, that increases humidity, and that leads to the water vapour feedback, which can be observed. See this article.

All the evidence is put together with computer models, but we don’t really need computer models to estimate these issues, we can work it out ourselves from science and observations

Evidence of warming

Specific Fingerprints

Observed Impacts

Very many different observations around the world e.g. temperature measurements, rate of glacier melt, species shifts, Artic sea ice, sea surface temperatures, coral reef bleaching, heat waves:

Most of these show some evidence of climate change. People will I’m sure, come to their own conclusions.


There are some arguments about climate change by self-styled ‘sceptics’. Here is an explanation of the more complex issues.

Policy Issues

Uncertainty & Risk?
Of course, there is always discussion and debate, but the fact that there are big risks shouldn’t blind us to doing something to secure ourselves against those risks.

We know that the earth responds to a lag to our behaviours. We already have seen serious effects to climate change (see ‘evidence of warming’ elsewhere in this reply) and the rate of increase of greenhouse gas concentrations is itself accelerating (think of putting the foot down when you see a road traffic accident). Don’t you think it might be good to be a little bit safe rather than sorry?

Kyoto Ineffective??
We need a much stronger treaty that doesn’t only include global targets, but also coordinated taxes.

It has been estimated that the investment required to decarbonize the UK is around £600bn (which would spent mostly on UK resources). The UK consumes 1.7million barrels of oil per day or 620 million barrels per year, with a value (at $80/bbl) of $50billion (£30billion).
We use 91.1 billion cubic metres of gas per year present, worth £11billion (at 35p per therm or 13p/cu m). So we spend more than £40bn per year on fossil fuels; replacing this with renewable and nuclear infrastructure could get a return on our investment of 15 years. Not bad.

Good, strong, climate policies could increase investment in real infrastructure, providing jobs, and making us less dependent on foreign oil!

A Risky Business

By Stephen Stretton.

I was talking about risk last night with a couple of friends. I was asked why climate change is a risk to individuals, nations and the world. Here’s why. The following distribution describes the estimated chance of different warmings if we give up producing CO2 and other greenhouse gases now (actually if we stopped in 2005). You will see that we have a more than evens chance already of melting the greenland ice sheet (7m of sea level rise, enough to reach the shores of Cambridge). Over the next few years we will reach the same chance of destroying the amazon rain forest (it’s even possible that if climate change was compounded by drought, a vast fire might erupt). Big risks.

Committed Warming


The commentary “Stop Worrying Start Panicking?” on this is here:

The other thing I’ve been thinking about is the basic evidence about why the planet is cooking (in particular, how we determine the radiative forcing of different gases). I’ve found this article which appears quite good:

Global Climate Policy: An Agenda For Effective Action

Climate Policy A New Agenda (pdf), by Stephen Stretton


 “Rules must be binding; Violations must be punished; Words must mean something.”

(US President Barack Obama)

The negotiations currently taking place at Copenhagen at the fifteenth Conference of the Parties (COP-15) of the United Nations Framework Convention on Climate Change (UNFCCC) aim at the fundamental objective of the UNFCCC, namely to stabilize atmospheric greenhouse gas concentrations at non-dangerous levels. It is argued that the existing institutional tools at our disposal – international treaties and in particular the Kyoto protocol – are insufficient to achieve this goal. Furthermore, the framework put in place at Kyoto suffers multiple and fundamental flaws which fatally undermine its effectiveness; any new treaty must have a structure which mostly evades these flaws if it is to be effective. Treaties, legal structures, and other institutions more commensurate with the scale of the climate change challenge are suggested to inform discussions around the structure of any future climate agreement. An agenda for effective global action is outlined here:

  1. Strong global institutions – e.g. a world environmental agency – including an agreed framework (such as coordinated carbon taxes) for collective policy, to replace national commitments.

  2. A framework action plan to eliminate carbon emissions sector-by-sector, region-by-region, over the next two to three decades. In particular a plan to develop, transfer and deploy the safe, responsible, and very large-scale use of enhanced energy efficiency, renewable-electric, nuclear, and carbon capture and storage energy technologies; and to encourage responsible land use and agriculture, including the sustainable use of water1.

  3. A significant ($100-$200/tCO2e), sectorally complete, substantially geographically complete, agreed, and guaranteed minimum carbon price, levied upstream at the national level (including embodied carbon from any regions not otherwise carbon-constrained), with revenues used at national discretion. It is possible that a carbon tax may have net economic benefits at the national level if used to replace taxes with higher ‘deadweight’ costs. The removal of fossil fuel subsidies has already been agreed as part of the Kyoto protocol, but has not been fully implemented.

  4. A plan to protect forests and other natural carbon stores.

  5. A plan to keep high carbon fuels in the ground (following Hansen et al. 2008).

  6. An enabling framework for enforceable state-corporation climate contracts (e.g. guaranteeing the carbon price for investors) (Ismer & Neuhoff 2006).

  7. An enabling framework for the use of trade sanctions to enforce state-state climate commitments, such as border tax adjustments (Ismer & Neuhoff 2007).

  8. Unimpeachable monitoring and verification of all commitments.


What is a Carbon Tax?

A carbon tax is a tax on fossil fuels according to the amount of CO2 they would produce on combustion (burning).  It would apply to all fossil fuels, and would be charged at extraction or importation of the fossil fuel. This tax would generally be passed on to consumers in an interim before alternatives are developed; but the revenue generated can also be refunded to taxpayers more generally so that average taxpayers are no worse off.

UK Carbon trading scheme ruled out

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"The government has ruled out a nationwide carbon trading scheme to
reduce emissions, describing the idea as "ahead of its time".&quo=

"Under a 2006 plan, every adult would receive an annual carbon
"allowance", with those not using their allocation selling surplu=
to those using more."

"But a government report said the scheme would cost up to =A32 billion=
set up and seemed like a "big brother" idea."

Stephen J. Stretton

4CMR, 19 Silve=
r Street, Cambridge. CB3 9EP. UK
W: 01223 764 871
M: 07879 625 706
H: 01223 721 316
skype: stephen.=