My name is Paul Valdes. I'm going to lecture to you on the science of climate change.
And this is a really important lecture.
It's a subject that will affect all of your lives, for better of worse.
You might believe it or you might not, but it will have an impact on your life.
It's also a very unusual subject, because climate change science is incredibly public.
Everybody knows something about climate change. Everybody has a view about climate change.
Yet very few people have been educated in it. Very few people fully appreciate the science behind climate change.
What I'm aiming to do in this lecture today is to review the evidence for the science.
What we know and don't know and what we have to do about it.
This lecture, I would argue, is incredibly important. Really important for you, because for better or for worse climate change will affect all your lives.
The best-case scenario will mean that you're a little but poorer because you have to pay more money for energy.
In the worse case, if you end up working in Africa, for example, it might be life threatening.
So it's really important that you understand a little bit about the science of climate change and where we're coming from.
It's also an incredibly public science. It's really unusual; a taxi driver will have a view on climate change, a shopkeeper will have a view.
My other science colleagues, in Chemistry and elsewhere, will have a view on climate change.
You don't normally have that. Nobody has a view on whether the Higgs Boson exists, or whether black holes exist. But for climate everybody has a view.
But I would argue that most of us do not know about climate. You do not feel climate, you feel weather.
The definition of climate is the 30 year average of weather. None of you are old enough to have experienced climate.
I'm 50 years old. I've been around long enough to know a little bit about climate.
When I think back 30, 40 years, what do I remember? I remember the extreme events.
I remember the incredibly dry summer of '76, of the incredibly cold winter in '81 or '82. I don't remember the average.
I would argue that none of us actually has any perception of what climate change really is, but we all have a view about it.
Can I ask a question? Who believes in the reality of human induced climate change?
OK, quite a lot of you. And who is sceptical about climate change? OK, a real minority this time, 2 or 3 of you.
The general public would actually be a little bit more negative about climate change.
Surveys in the UK suggest that it's only about 70% of people believe in the reality of climate change. Go to the US and you're down at more like 50%.
But it was a trick question in a way. I don't ‘believe' in climate change. Belief is a word that you don't use in science.
What I will show you today if that the vast balance of evidence supports the idea of man made climate change.
Moreover, that there are no observations which completely contradict climate change. Some certainly challenge it.
Moreover that there is no alternative theory that explains as many of the observations. I want to argue that's all I can do as a scientist.
So forget about that word belief, think about the evidence. Think about what we really know and what we really don't know.
That's the aim of my lecture today.
Similarly I would argue that all of you, as scientists, should have had your hands up, when I asked the question ‘are you sceptical?'
All scientists should be sceptical. Because the whole point of science – I can't prove the theory of climate change, you can't prove most theories.
You can disprove them, by challenging them, by really providing testable ideas.
That's what we should all be doing. That's what I do as a climate change scientist, is I continually test and challenge the science that I know.
So that's what I want to cover today.
I always feel a little bit of an imposter when I give this Big Science talk.
You've heard in other lectures about the wonders of quantum science and probably quantum computer and all that modern stuff.
In practice what I am going to talk about was known to the Victorians. This is not new science.
The person who is credited as the real visionary in climate change science was a Swedish chemist, Svante Arrenius.
He realised that at the start of the industrial revolution people were burning a lot of fossil fuel, particularly at that time coal.
He realised that was producing carbon dioxide that that would warm the planet.
Moreover he did a calculation and reckoned that if you doubled the amount of carbon dioxide in the atmosphere it would lead to about a 5-degree warming.
That is uncannily close to what we think today. He knew, right back in the late 1800s, about as much as we know.
This is not rocket science. It's not new science, but it is big and important science.
A lot of what you read about climate change is talking about has climate change already happened? How much has it warmed? And all that sort of thing.
Most scientists working in climate change don't start from the observations, they start from the same point that Svante Arrenius did.
I'm going to explore the subject by basically updating his argument. Why he was worried about climate change right back in those early times.
The first part of his argument was about burning fossil fuels and saying that would lead to carbon dioxide increase.
What I'm showing you here; the curve on the right is from 1970 to 2005, the increases in carbon dioxide that have been observed.
The red curve is from Muana Loa in Hawaii, where observations have been regularly done.
The last month the CO2 concentrations were up at 394 ppmv, compared to pre-industrial values which were more like 280.
So we have had more that 100 ppmv increase to date and it's increasing at around about the rate of 2.5 ppm per year.
Last year, when I gave this lecture, it was around slightly over 2 ppmv less.
People at the time, when that Manua Loa came along, if you were sceptical you said ‘well maybe it's volcanic activity that's doing these emissions'.
That has been shown to be rubbish. Partly because the observations show that volcanic emissions of CO2 are about a hundredth of the human values.
But it also is shown by this curve, which shows the oxygen concentration in the atmosphere.
If you think about it; when a volcano emits CO2 it actually emits CO2. It's taking it from the carbonate rocks and emitting directly CO2.
Whereas when we burn fossil fuels we are taking carbon and oxygen to produce that CO2.
So if you're burning CO2 you'd expect the opportune concentrations in the atmosphere to decrease and low and behold the observations show this,
consistent with the idea that it is burning fossil fuel that is causing that rise.
Don't worry, the changes are minute and we're not going to run out of oxygen, but it proves that burning fossil fuel is a very important source.
Other people then came along and said; ‘well it's not human-induced change, it's because of, for instance, biology'.
Plants absorb CO2 in summer when they are growing, them emit CO2 in winter when they are decaying.
So maybe this is all biological processes that cause the CO2 rise.
That we were able to disprove because this curve here is showing you the carbon isotopes of the CO2.
It transpires that the carbon isotope ratio from fossil fuels if very different from CO2 in plants.
So again you can say it must be burning of fossil fuels that's doing it.
The final bit of the argument – of course there's lots of arguments and I'm just illustrating the huge body of evidence that supports the theory that we're changing the CO2.
The final thing is this curve here. The black curve is showing the amount of carbon dioxide that we emit based on simply calculating how much carbon we're burning.
How much coal and how much oil and what have you. Oil companies, coal companies, keep a record of how much that are producing so you can do a simple arithmetic sum.
And is transpires, if you do the calculation, that we're actually emitted about twice the amount that sits in the atmosphere.
In fact we've already been saved by mother earth. In practice half of our emissions have actually been absorbed by the ocean and plants.
There's a lot of concern at the moment whether those processes are saturating and so that saviour is beginning to break down.
There's lots of other evidence; for instance qualitative evidence. It's no the core of the argument,
but qualitative evidence that it's carbon dioxide that's causing the change comes from the ice core records.
This is very different graph. The blue curve is showing carbon dioxide, the orange curve so showing methane.
800,000 years ago, to, effectively this curve is showing the pre-industrial.
What you can see is that the carbon dioxide does change, and that's just natural processes.
Let's superimpose on that the pre-industrial. So that's where we are now. You don't have to be a rocket scientist to feel that that looks a bit different. That's not part of the natural cycles.
Even more scary is projections for the end of this century.
So this is where we think we will be at the end of this century if we just carry on. What I've referred to as ‘business as usual'.
Basically saying we carry on our activities without really making much of an attempt to reduce our dependence on fossil fuels.
We will end up with four times the concentrations of pre-industrial times.
We will have carbon dioxide concentrations that we haven't seen in the world for many tens of millions of years.
So very dramatic changes. And the bottom line is that there is very little doubt that the changes we are seeing are man made.
So that bit of the curve has to be human. So the next part of the story is to think about how does that change the planet.
To do that we've got to spend a bit of time thinking about the basic energetics. A simple model of how the climate works.
A very simple model is to say the atmosphere and climate is warmed by energy from the sun.
The energy is principally in the visible part of the spectrum, shown here. That's because the sun is obviously very, very hot.
The energy going out from the planet is in the infrared part of the spectrum and that's the way that the planet cools.
If you are in equilibrium then the energy coming in equals the energy going out.
If there's an imbalance then you either cool or you warm depending on that balance.
When you look at it in detail you find that every gas in the atmosphere has a different frequency that it absorbs in.
It's classical physics. Some gasses don't do anything.
One of the classics is that people say that CO2 is of such low concentrations how could it be so important?
The answer to that is quite simple. 99% of our atmosphere is nitrogen, oxygen and argon, and that's completely transparent to both visible and infrared radiation.
It doesn't do anything. You could remove it and it wouldn't change the energy balance.
Most of that goes out the window. It's actually a crucial 1% of our atmosphere that actually makes a difference.
Carbon dioxide is not such a small player within that 1%.
We can understand this very classical physics and we can observe the fact that carbon dioxide and other gasses absorb infrared radiation, stop the planet cooling, and the only way that the planet can regain balance is to warm up.
You're putting a blanket on the planet and that warms up the climate.
You can calculate it from classical physics, you can observe it in a laboratory, you can observe is from satellite.
So again we're very, very confident that that's a real effect.
You can go one step further and you can calculate how much of a change in the energy balance of the earth an increase, like a doubling in CO2, will make.
You can do through that calculation, very classical physics, and it comes up with a number of 4 watts per square metre.
The average energy imbalance caused by doubling carbon dioxide.
You can argue a little bit. I could accept an argument that it might be 3.5 or 4.5, but it's not 0.4 and its not 40.
So we know that carbon dioxide is going to change the energy balance of the planet by about 4 watts per square metre.
Is that a big number of a small number?
How does that compare? Does anybody know, what's the net amount of energy that we receive from the sun, when you average it out over the whole planet and over the whole year?
Let's focus on the net energy, because some energy from the sun bounces straight back to space and doesn't warm the climate.
So how much energy do you think goes to warming the climate, any ideas?
What numbers are we talking about? 10 watts per square metre, 200, 2000? Any ideas?
A kilowatt per metre squared?
A bit on the high side. Once you average it out over the whole planet and over the whole year you actually come out with about a quarter of that.
So the sort of number of energy we get from the sun is about 240 watts per square metre.
So 4 watts per square metre is about 2% of the energy from the sun.
It's really difficult to argue scientifically with that. The next bit is where the fun begins.
The next bit says; how does that energy balance change the actual climate? You can make a number of different assumptions.
One assumption is that the only way the planet cools is by emission of infrared radiation and if that happens then a thing called the Stefan-Boltzman equation applies
and for a 2% change in the energy balance you would expect a 0.5% change in the temperature.
That temperature has to be the only meaningful scientific temperature, ie Kelvin. So it's 0.5% change in the temperature of the planet, in terms of Kelvin, works out at about 1.5 degrees.
If alternatively, as Arrenius did, you say it's a linear thing. You increase the energy by 2% then you increase the temperature by 2% then you get up at about 5.5 degrees of warming for a doubling of CO2.
And the heart of the real scientific debate is whether we're nearer the 1.5 or we're nearer the 5.
How do we progress the subject?
The way we progress the subject is that we develop more detailed models to try and represent all of the different physics that are going into the climate system.
And that's really my core expertise. What I do a lot is computer modelling of climate. My first degree was in mathematical physics.
The models try and start from the first principles of the science, the hard physics that applies to the climate system.
Basically solving Newton's laws of equations as it applies to a fluid domain.
We're solving the laws of thermodynamics. We're including, increasing these days, how chemistry and biology evolve with the climate system.
We do not put in ‘oh doubling CO2 means it warms', we put in just those radiative properties of the line absorption strengths of CO2 and compare that to all the other sort of things and do that calculation.
Unfortunately we can't do that precisely. To give you an idea of the sort of equation set that we solve these days.
Before you even put it into the computer the equation set that we solve now is about the same size as this book.
Closely typed equations – no words – simply a set of equations. Phenomenal amounts of calculation that do on but we still have to make lots of approximations.
Models are just that. Models are not reality, they are models of the real world.
I've included the quote of George Box here; ‘all models are wrong, but some are useful.'
The real big debate that we have in the climate change community is ‘are climate models good enough for the business or are we missing something?'
That's the challenge that we have at the moment.
Now note, I've got almost half way through my lecture and I haven't talked once about observations of change.
What's actually really happening? But I am going to start to do that now.
Really one of the ways that you might get an idea if a climate model works is ‘does it reproduce the observations that have been made so far?'
So we need to think a little but about what we know about how climate is changing.
This is an updated version, which came out recently, in the past few months. What I'm showing you is the observed temperature changes.
It goes from 1800 to the present day. And there's different curves because there are different estimates of climate change from different research groups.
You'd think that one curve is really easy to calculate. It turns out it's a phenomenal effort to calculate.
The reason for that is that there have been huge changes in the way that you collect the data; the instruments that were used.
Think back to 1850 and the instruments that you were using to record temperature were very different to today.
A huge amount of work goes on in producing this record..
What you can see is that in terms of the land temperature you've got a climate change of just over 1 degree, from 1850 to now.
This is only land temperatures. If I showed you ocean the temperatures would be slightly smaller.
Ballpark is about 1 degree change over the past century or so.
Note that the change is not simply a correlation with CO2 rise.
You can see that we had a rapid warming period between the 1900s and 1940s, but the CO2 wasn't particularly doing anything abnormal.
And it transpires when you do the calculations that during that period we had a lot of changes is solar and volcanic activity. So natural causes meant that we had quite a rapid change at that stage.
But when you do the analysis you find that it's impossible to explain this recent rise without invoking the effects of CO2 and other gasses.
That's the temperature rise; we've got about a degree so far.
I thought I'd also point out that there are a lot of miss-publications about climate change. Lots of rubbish that is talked about in the media and in blogs.
Different ways of representing the data. This animation from the website scepticalscience.com is a very nice illustration.
If you go to, for instance, the Daily Mail website, they've got recently an article saying ‘oh climate's cooling, climate change has stopped'.
They are right if they just look at a very short timescale period. If you look at very short periods, this is 5 or 10 years.
Every 5 or 10 years you could draw a line which looks as if climate isn't changing.
But you look at that longer timescale picture and I don't think anybody would argue that, yes climate is warming.
The Daily Mail is right in saying that it's been pretty flat for a bit, but nothing exceptional in the patterns of variability that we have.
All this short-term variability of weather, not particularly predictable, but that longer-term picture is what we're talking about in terms of climate.
So this explains why there are different views on the observational record.
So you can take those observations. And I've focused on temperature but there are observations of changes in rainfall or snow cover and sea ice.
I'm focusing on temperature for simplicity.
And you can run a computer model over the same time period and say, do the observations and the models fit?
That's what I'm showing you in this diagram.
The red curve is the observation data, the grey curve is a model prediction of that same record.
All that's gone into the model is the physics of climate plus the observed changes in CO2, the observed changes in solar activity and observed changes in volcanic activity.
So you put those into the model and you see what it predicts for temperature. And low and behold I would argue that it's a pretty good fit, at least on decadal timescales, to the observed variability.
If I'm honest I don't want to oversell this. The reason why I quoted Peter Stott's work in 2000. He was the first to do that work and his was a genuine test.
They'd never done if before and they didn't really look at the observational record before they ran their model.
These days, I have to confess, people tune to get this answer. So it's not a wonderful test of the models but it shows that they are kind of in the right ballpark at least.
It shows that they're not doing daft things.
So now we move on. I could say a lot about the strengths and weaknesses of models. I do a lot of work testing them, going back many thousands, indeed hundreds of thousands of years to see whether the models reproduce past changes.
We're going to now think about the future. Predicting the future is even tougher than look at the past.
This graph on the right is almost the iconic graph of the IPCC.
Have people heard about the IPCC – the intergovernmental panel on climate change.
They every about 5 years produce a report on the science of climate change. I used to bring along those reports. I've cheated today.
The reason I've cheated, is that that this is the 2007 report but it is 1 of 3 volumes.
It's a review of climate change and it's just the increment, what has changed over the previous 5 years.
If I was to bring the whole set it's the equivalent of about 12 of these volumes.
The last time I tried to do that for a talk I actually broke the axle on my bike, because of the weight.
So just imagine a stack of 12 of those. And they are just reviews. They're not actually doing new science.
But this was one of the big results. A big synthesis of results.
The predictions of global mean temperature change. These are the observations, then it goes into the projections to 2100.
There are a number of different colours and each one of those depends on the way that you think people will respond to climate change.
That problem of how you respond to climate change. Will we ever reduce our emissions? That's something a physical scientist can't answer.
Do you think we'll start to reduce our emissions? Despite all the rhetoric I should say we haven't achieved it yet. We've barely slowed down emissions at all.
We can't answer that question. So all we have to do; they're sometimes called scenarios, sometimes just storylines.
I can't tell you which one of the different coloured curves are the most probable future, because it depends how we behave.
But given a particular storyline I would love to be able to tell you exactly what the climate change will be.
And we don't know that. The uncertainty, in the graph it is shown by this shading.
These are the final temperatures at 2100 for the different types of scenario and the grey bars are alliterating the uncertainty.
That uncertainty is estimated from the so-called Monte Carlo techniques, where we just run the models a lot with all the uncertainties that we know about and see how much difference it makes to the predictions.
In Donald Rumsfeld's perspective what these uncertainties are. They are an estimate of uncertainties of the known unknowns.
What no scientist can say is whether there are unknown unknowns that we just haven't really thought about.
Again you get into a tremendous debate where some opinion makers say ‘there are lots of unknown unknowns and that means that climate change is not going to be as big as we think it is.'
And I can't say they're wrong, because they are unknown unknowns nobody can. That's when you have to just go back to belief.
I would say that unknown unknowns can work in either direction. Unknown unknowns might reduce these estimates but they might, indeed, increase it.
And I'll show you an example where unknown unknowns did increase it.
If you look at one of these storylines. The B1 scenario, which basically means that we do a hell of a lot, very quickly, to reduce our emissions.
To be honest nobody really believes we will achieve that because we are almost too late for it already.
So we are too late to achieve the B1 scenario. What that says it that typical warming is about 2 degrees centigrade, with an error which is 1.5 to 2.5 degrees. Coming out just from the basic physics of climate.
If, on the other hand, we follow the A2 or the A1 F1 scenario, which I still have a tendency to call business as usual, ie we don't do much about controlling emissions.
Then we're talking about a temperature rise, by the end of this century, of more than four degrees centigrade, with a possibility that it could be beyond six degrees.
That's a global average. If you looked at the regional patterns of temperature change it would mean that in some places you would have 20 degrees temperature rise.
With a six degree global mean. So huge, huge changes being talked about.
Huge uncertainties both in the socio-political changes that we think but also the science that we have.
We can go a bit further. We can also think about regional changes with these big computer models, which predict not just temperature but lots of other things.
What I'm showing you here are estimates of rainfall.
In general when you move away from temperature and into rainfall and other things the uncertainties, unfortunately get higher.
The uncertainties become larger when you think about regional change as well.
Politicians are desperate that we reduce these uncertainties. They want to be able to know what is going to be the climate change, in Bristol, in 2050.
If I'm honest I don't think we can do that yet. We can't say more that just those average, large-scale numbers that we were talking about.
They use it as an excuse for not doing anything. This is me being political. I'm not being a scientist at this stage.
I would argue that that's really weird. Climate models have been shown to be much more accurate that economic models, yet the Chancellor of the Exchequer doesn't say ‘oh I'm not going to do anything because it's all uncertain.'
But they'll do that for climate. There's lots of other socio-political issues that I won't talk about.
I could show you lots of other variables. What I'm showing you here is arctic sea ice predictions.
The grey area is what models were predicting for the evolution of arctic sea ice in September, which is the minimum.
The grey curve is showing you what the models were predicting. The red is showing you what's actually happened.
So these predictions were made in about 1990 and you can see that we've gone way off the predictions.
The real world is changing more dramatically than the models.
This was effectively an unknown unknown in 1990. We think we understand it now. It was a process related to the fact that when sea ice gets thin in behaves differently to when it's thick.
We hadn't incorporated that properly into the models. It's an example of the fact that unknown unknowns can actually make things worse.
I do a lot of work in past climates. The message that comes out of past climates is that is that when the models are wrong they have always been wrong in a conservative sense, they've underestimated change.
So I would argue that unknown unknowns are not reason for complacency. They actually remain reasons of great concern.
I could take loads of time talking about this, but we have to move on.
So I've talked about the climate, but what does that mean for us? What does it mean for society?
Gradually we're getting into more and more uncertain territory.
I started off by saying with carbon it's very, very clear, then climate which is a bit more uncertain. We're now moving into what is the potential impacts of those climate changes on our lives.
One of the big questions that everybody asks is, when does climate change become dangerous? That's what politicians want to know.
And my answer to that is that word is not a scientific word. Dangerous is relative.
If I was driving at 100 miles an hour, that would be dangerous. My wife says it's dangerous when I drive at 30 miles and hour. I'm a lousy driver.
If Lewis Hamilton was doing 100 miles an hour around a racetrack they'd be saying he was slow.
So dangerous is a relative term. It's not something that you can define scientifically. But we try to.
What this cartoon is showing. There are some small things going on; mountain glaciers disappearing which has an impact on water supplies, or coral reefs getting damaged.
But really a lot of the damage to systems, whether it's food, water or ecosystems, really starts around about 2 degrees centigrade warming.
And the EU has adopted that as their definition of dangerous climate change. They say dangerous climate change is if climate change exceeds 2 degrees centigrade.
It's not a rigorous number. Clearly if it's 1.9 it's not safe if it's 2.1 its dangerous. It's not really sharp definition, but it's a simple way of thinking about it.
If you go back to those previous calculations, including all the uncertainty and all of the risk analysis.
You go through the analysis it transpires that we have a 50-50 chance of stopping a 2 degree rise in temperature.
Only 50-50, when you take into account all of the scientific uncertainty. Let's put it in another context; would you play Russian roulette with 3 bullets in the gun.
Would you fly on a plane when every other plane will crash.
But it's still not good enough. It still doesn't seem to change any of our minds. I should say, my carbon footprint is not wonderful.
But that's the odds we're talking about taking into account a full probabilistic risk analysis.
We're talking about odds of 50-50 that there will be dangerous climate change.
So the scientists are saying that, but it's not happening. Why is it not happening? Again, way beyond my remit.
Talk to the psychologists, talk to the sociologists about why do we not respond. Clearly one of the big things is that it's a long way in the future.
We're talking about 2100. I'll be dead by then. You probably won't be. You'll experience it. A bit like student tuition fees. I had it for free, you have to pay.
I had carbon for free. You'll have to pay something. So what are the options? What can we do about it?
This is very non-scientific. We're going into a very different regime, in terms of politics and policies.
The big issue that we have to think about is the difference between mitigation and adaptation.
Mitigation is all about reducing our emissions. Adaptation is all about coping with the climate change.
I've put it as either or, probably that's the wrong language, it's both at the same time. We are guaranteed to have climate change, even if we did a lot of mitigation quickly.
Economically mitigation works out as by far the cheapest option. It's by far the cheapest thing to do mitigation now that to have to adapt in the future.
Nicholas Stern, who was a former economist at the Bank of England, did a report a few years ago. And came out very clearly that it doesn't really cost us much to mitigate climate change.
I look at it as buying an insurance premium.
We're used to spending a bit of money now. We're a little bit poorer because I insure my car or my house, against the fact that that house might burn down in 50 years time.
Adaptation, much more expensive. But it is for you, not for me. You'll have to pay the cost of that adaptation. I won't, because I'll be dead and gone.
Adaptation for Europe and the UK is all about money, building more flood defences, etc, etc.
For Africa it's not. Africa it's something different. Africa will probably be the worst hit continent in terms of climate change, because it's so marginal, particularly in terms of water resources.
It's also got the least finances to cope with climate change.
Part of the adaptation story has become very much part of the whole development issue.
All the big international conferences on climate change are really part of parcel of the same story.
There's lots of talk about trying to create an adaptation fund that Africa could draw on to pay for climate change. It hasn't been delivered yet.
To give you an idea of the scale of emissions reductions if we go down the mitigation route. This is just for the UK.
The UK has a climate change committee, which is independent of government, which determines what do we need to do in terms of reducing our emissions.
They work on the principle called contraction and convergence, which is based on the principle that we have to reduce our emissions lots as developing countries must be allowed to increase their emissions a little bit.
If you do that analysis for the UK we have to reduce our emissions by 80% by 2050.
And most analysis says that means that climate change will end up being about 3 or 4 degrees.
Even that 80% reduction is well into the dangerous climate change story.
To put it into context, this is where our emissions go; heating, transport, whatever. And this is what we've got to fit into in 2050.
What's amazing is that the climate change committee has also come up with scenarios of how we do it.
It is possible. And the exercise that you're going to do as this part of the course is to come up with you own policy.
What do you think we should do to achieve that 80% reduction? And you can choose to cover the UK with wind farms, or put a few nuclear plants, or import a lot of renewable energy from elsewhere.
You get to choose that policy and there's a very nice website that you'll get to hear about in the tutorials.
It will enable you to come up with your own ideas about how we should try and achieve this target.
Are there any other options?
There's an option that Bristol actually does quite a lot of research on, even though most of us who work in that area think it's bananas.
It's an option called geo-engineering. Geo-engineering is saying let's forget about trying to reduce our emissions and after the event let's do something else to the climate system. To cool the climate.
There are two types of ideas. One type is not quite so crazy, which are all to do with reducing carbon dioxide.
So you pump it out in the first place, and then you try and suck it back in. So-called carbon capture and storage.
Carbon capture is quite viable. It's quite possible to, for instance on a power station, to capture the CO2 you emit.
Storage is a bit more problematic. Where the hell do you put all that CO2.
For a decade we could get away with it. In the UK we could fill up the North Sea oil reservoirs. We could pump the CO2 back in.
That would actually give us about 10 years. What the hell do you do after that. It is viable and I think carbon capture is real and quite good.
But there are other ideas like fertilising the ocean, throwing lots of iron into the ocean, to get the biology in the ocean to soak up the carbon dioxide. Many of those are pretty weird.
It gets even weirder when you say the other part of the story is that we are warmed by the sun, so let's suppose that we increase carbon dioxide but we actually reflect sunlight back and cool the climate that way.
To give you an example of the whacky schemes out there, NASA, for example, have already done quite a lot of studies on the idea of putting a mirror in space to quite literally reflect sunlight.
You can only stop climate change in a particular region. It will still happen globally but you can modify if locally.
So it would be quite possible for a country to put a big mirror in space and for them to do nothing about emissions and have no climate change, but the rest of us get stuffed.
Is that ethically right? Your choice, not mine.
Other schemes that are out there is to mimic a volcano. Amazingly this is something that Earth Sciences in Bristol are actually leading, although he's ethically hugely against it the leader of that project.
The basic idea is that when a volcano goes off it puts a lot of sulphate into the atmosphere and that reflects sunlight and cools climate.
So the idea is let's mimic that process and pump sulphur into the atmosphere. It has to be into the stratosphere. You have to pump it 10 kilometres high.
The current idea is that you have a big balloon and you attach a big hose to the balloon, ten kilometres long. And you pump the sulphate up and then spray it out.
It's a weird world we live in that that's more acceptable than just reducing our emissions.
Very quick summary of climate change. I've tried to emphasise some of the things that we know about and some that we don't know about.
One final thing that I want to comment on is that climate change is part of a much bigger issue; the sustainability of the planet.
I've shown you the exponential rise in carbon dioxide, but along with that you've got to bear in mind that we've got an exponential rise in population.
Lots of people equate one to the other. Probably fair enough to do that in some sense, although it is worth remembering that 98% of all emissions are produced by 1% of the population.
Exponential growth also in terms of water use. The next war will probably be a water resource war.
When it gets too dry, partly exacerbated by climate change, but nonetheless a very serious issue.
Global biodiversity; we are seeing an extinction event which is similar to the mass extinction events in the past.
We're in a new geological era called the anthropocene. The idea is that if, in a million years, somebody came and looked at the planet, they would see something weird happened.
We are leaving a mark which is global and huge.
Most of that biodiversity loss is nothing to do with climate change and is much more to with habitat loss.
Climate change will exacerbate the problem. Climate change keeps exacerbating these sort of problems.
My favourite curve is this one; a curve showing you the global exploitation of the ocean.
What you can see is that we're very close to being near 100% exploitation of the fisheries of the ocean. Not just in the north Atlantic, but globally.
There is nowhere else that we can fish now because we have basically harvested almost the whole planet at the rate that is possible to sustain.
Along with all those changes in the natural systems comes along the fact that we've got a lot wealthier.
No doubt about that. Wealth has been growing exponentially. It does have a bit of a dip in the past year or two.
Whether we've been using that wealth sensibly, you can decide.
I'm basically done. I'm going to finish with my favourite quote on the subject:
"At every level the greatest obstacle to transforming the world is that we lack the clarity and imagination to conceive that it could be different."
I don't think I've changed anything in terms of your imagination but I hope I've given you a little bit of clarity when it comes to climate change.
Thank you very much. And have you got any questions?
I was slightly confused by the carbon dioxide graph and how it mirrors the population graph. The population has multiplied massively as has the CO2.
The amount per person can't have changed that much. We'd have needed a lot more CO2 just to accommodate for all the increasing amount of people.
Do you reckon there be a need to constantly lower the amount of CO2 we're using; fossil fuels or otherwise, until there's a cull of people.
We hope that there won't be a cull of people. Some of the more extreme climate change people might talk about that.
The reality is you're right and that's encapsulated in this principle called contraction and convergence.
It's saying we've got to converge in the sense that everyone in the world should have a right to have a certain amount of carbon emissions.
It's not that Europe and the US can continue emitting lots and other places not so much. That's the convergence idea.
The contraction idea is that everybody as got to contract their emissions to a large extent.
That's why you come out with a huge number like 80% reductions for ourselves, smaller numbers for China of somebody like that.
In fact China has round about now reached the world's average value of emissions that we could like to eventually converge to.
Unfortunately they are passing it in a transient way to meet us, in some senses.
Although you're right in saying there is a strong mirroring of population growth and the CO2 curve, if you actually do the numbers you will find it's more than just taking a figure per person and multiplying it.
There is an additional factor so our per person numbers have been increasing as well as the population.
Just to add onto that. Is it by 2050 that it was an 80% drop. Does that take into account what the population could be by 2050.
That is certainly very much part of the calculations that go into these sort of estimates.
Those things are more imprecise. Current thinking is that the population of the world will plateau around about 10 billion.
That's the sort of number that went into the calculation. Another thing I should add is that what a lot of climate scientists are concerned about.
Is now that 80% is used. Carbon dioxide stays in the atmosphere for about 150 years.
Quite a lot of what we've emitted stays in the atmosphere. So it's much more an accumulative thing rather than an instantaneous value.
Not only do we have to reduce out emissions by 80% by 2050, but we can't leave it to 2049 to do that, we've got to start now to move in that direction.
You say that the climate models – there's quite a lot of uncertainty. If you take into account something like chaos theory is there a limit as to how far you can reasonably predict the future.
And also if you take into account the amount of uncertainty now, maybe it's already trying to predict too far in the future.
A very good question and chaos theory does provide some interesting challenges.
An analogy I like to start with between weather and climate, it's like tossing a coin.
You toss a coin, that's weather, you can never predict whether it's going to be heads of tails. However, if I got all of the room to toss a coin.
You can predict fairly comfortably that 50% is going to be heads, 50% is going to be tails.
That's the same idea between weather and climate; weather has an unpredictable limit, which we're not at yet but they think is 2 or 3 weeks.
In the future we will never be better than 2 or 3 weeks.
Climate has a very different type of chaotic behaviour. We think as long as you average over a long enough time period; again these 30 years.
We think that the details of climate we can do fairly well up until the next century.
However, there are what they call, climate tipping points. In mathematical language they're bifurcations.
Where just a very small change will send us into a completely different state.
It's not like weather where you're just seeing it random, it's we go there or we go there. Not anywhere in between.
There are number of ideas that say climate does have these tipping points and we're rubbish at predicting those.
It is possible that it we get close to one of those tipping points we'll actually plummet into one state or another state.
Very interesting, the UK is very interested in tipping points because if there is a tipping point it would really define what is dangerous climate change.
So we don't know about that. Certainly there are limits to what we can do, but in a slightly different way to weather.
In terms of the natural processes of the earth; heating, cooling. How much of an effect do you think we have had in changing that? Because there have been ice ages and where it gets warmer for millions of years.
A lot of my research is thinking about those natural changes like the ice ages.
In terms of the actual temperature change that we're talking about for the end of this century, the earth has seen that it the past.
If you go back 50 million years you will find climates that are as warm as are being predicted for the end of this century.
The thing that really is different about man-made climate change is the speed of change.
What we're talking about is a 5 degree warming in a century. By comparison in the last ice age, on a global scale, 5 degree took more like 500 years.
Really more like 1,000 years so there's a factor of 10 difference in the speed of that change.
Of course we are moving into a very warm regime. If you look at the last million years climate was either like today or colder than today.
There is no example in the last million years where we are a lot warmer than today.
One final comment on that which is an amazing epitaph for mankind, there have been studies which shows that the impact we're making in terms of CO2 is actually enough to break the ice age cycles.
Ice ages occur about every 100,000 years. You have 90,000 years of cold, 10,000 years of warm.
We think the CO2 changes that we're making are enough to break the natural cycle.
It means that actually even when we stop we won't go back to the natural rhythms for about 30-50,000 years.
Which I think is quite an impressive achievement for mankind to actually break the natural cycles for 30,000 years.
That's what our current thinking is about natural change.
OK, that's it, thank you very much.