Feynman Diagrams are Maths not Physics

April 13, 2014
A Feynman Diagram such as the one shown above is a succinct way of summarising a mathematical calculation. However, even though it looks like 'cartoon' representation of the physics, it does not describe the physical process.

A Feynman Diagram such as the one shown above is a succinct way of summarising a mathematical calculation. However, even though it looks like a ‘cartoon’ representation of the physics, it does not describe the physical process.

After giving a talk to A level physics teachers the other weekend, I stayed around to listen to a presentation about radioactivity: it really is a pleasure listening to other people teaching!

From my disinterested perch at the back of the class I was surprised to find that the process of beta decay was described by means of a Feynman Diagram.

I was then even more surprised when teachers asked detailed questions about which type of ‘vector boson’ was involved. I began to wonder how this could make any sense to ‘A’ level students. Do they really know what a ‘boson’ is? Or a ‘vector boson’?

And an e-mail today from an AS level student asking me about these diagrams crystallised my misgivings: I realised that teaching and examining this kind of thing as physics is potentially quite misleading.

At the heart of the matter is the fact that Feynman diagrams represent an ingenious way of describing a calculation: they do not describe the physics underlying the process. You can read an excellent article about their history here.

Let me explain:

  • The diagram at the head of the page describes the way that the electrical interaction of two electrons – their mutual repulsion – is calculated in an advanced theory called quantum electrodynamics (QED). The lines and vertices each have a precise mathematical interpretation.
  • QED describes the repulsion between the electrons in terms of the exchange of an infinite number of ‘virtual photons’. The diagram above summarises the way the exchange of a single ‘virtual photon’ - the wiggly line in the middle – is calculated.

Now QED is an astounding theory. It has been checked thoroughly and there is an astonishing correspondence between the results of its calculations and physical reality. In other words it is in some sense ‘correct’.

But nonetheless there are two problems when using these diagrams in schools.

  • Firstly I underlined the word ‘infinite’ in the bullet point above because when you see that word you can be sure you are in the realm of maths, not physics. This is because there are no infinite quantities in physics.
  • The second problem is that it involves the concept of a ‘virtual photon’. Despite 35 years of exposure to this concept – I haven’t a clue what it means physically. I suspect strongly that its role is calculational rather than physical.[I searched for a comprehensible 'link' but there are none! Try this as a typical example.]

Some people might argue that because ‘virtual photons’ are part of the way QED works, then the accuracy of QED is in itself evidence that virtual photons ‘exist’. To these people I have a one word rebuttal: ‘Epicycles‘: just because a calculational technique improves predictions does not mean that there is a physical counterpart to the ‘calculational entities’.

Now why does any of this matter?

It matters because this stuff is being taught for all the wrong reasons. It is being taught , I guess, because it looks like  a cool cartoon, and also requires no numerical skills. We are asking students to simply imitate the marks made on blackboards by other physicists.This is bad.

Further, its inclusion has caused the exclusion of a really interesting feature of beta decay that students could appreciate directly.

Instead of electrons being emitted in the same way as alpha particles are - with a single characteristic energy and momentum, electrons emitted in beta decays have a wide range of energies, from a maximum characteristic value, all the way down to zero.

In the early days of nuclear physics this spectrum was puzzling because it seemed as though beta decay did not conserve energy or momentum. ‘A’ level students can readily appreciate both these conservation laws, and the potential significance of them being broken.

And the resolution of the apparent breakdown of the conservation laws was that there was a third particle involved – a particle with almost no mass called a neutrino. And the existence of this particle – not to be directly detected for 25 years after its existence was hypothesised – was based on the law of conservation of momentum.

So these diagrams look like physics, but they are not. And IMHO they don’t belong in an ‘A’ level physics syllabus.

 

Who is going to die in 2048?

April 9, 2014
Age Standardised UK Mortality

Graph showing Age-Standardised UK Mortality per 100,000 of population per year. In 2010 mortality was around 1100 per 100,000, so for the UK population of 60 million we would expect around 660,000 deaths per year. However if the trend continues, no one will die in 2048!

While investigating causes of death in the United Kingdom, I came across the data above. The graph shows that the age-standardised mortality in the UK has been falling since at least 1980 – and shows no signs of stopping.

Indeed, if the trend continues, then sometime around the 14th March 2048, mortality will reach zero and no one will die in the UK!

Now of course, although this data is real and correct, the trend can’t possibly continue indefinitely. But the data is nonetheless fascinating for at least three reasons.

Firstly, in the face of seemingly endless stories telling us all how unhealthy we are – it seems that the trend to lower mortality is continuing unabated, despite the obesity ‘crisis’.

Secondly, although the linear trend in the data is striking, we have no justification for extrapolating the trend into the future. Why? Because its the future! And we don’t know what is going to happen in the future.

And finally, these numbers give us a scale for considering the relative seriousness of different causes of death: that was the reason I looked up the data in the first place.

I read that air pollution causes 30,000 deaths a year in the UK and that seemed a surprisingly large number. From the graph we can estimate that mortality in 2014 is approximately 1000 deaths per 100,000 of population per annum. So that that for the UK population of 60 million, this is about 5% of deaths – which still seems shockingly high, but is a smidgeon closer to believability.

So good news all round: especially if you, like me, are a man. The mortality of men and women is shown separately below.

If the trend continues, then after millennia of ‘excess male mortality’, the mortality of men should fall below that of women in approximately 2027 and reach zero in 2042 – before the women – who will not attain immortality until 2060!

Age Standardised UK Mortality by sex

Graph showing Age-Standardised UK Mortality per 100,000 of population per year for men and women. If trends continue, male mortality will fall below female mortality in 2027 and no men will die at all after 2042!

 UPDATE

Dave asked: Are you sure age standardised mortality means what you think it does? Age standardised mortality might drop to zero. But that is not mortality. If the plot showed mortality that would suggest life expectancy has doubled since 1980, from 50 to nearly 100.

And I replied: The calculation is this:

  • How many people died in a particular year aged (say) 69.
  • This number is then expressed as a fraction of the actual UK population who were aged 69.
  • This is then expressed as an actual number who would have died in a ‘standard population’ called the European Standard Population.

This procedure allows the relative mortality in different countries to be compared

So, if for example, the UK has a high absolute mortality for 69 year-olds, but not many 69 year olds – then this will produce a larger number when ‘age standardised’.

I have obtained one or two sets of actual death data – but I don’t know the equivalent population to divide by to get the absolute mortality per 100,000. However this data shows a similar trend with roughly the same intercept.

What does it mean? I don’t know! I think it means that we are living longer (Is that news?). I was just struck by how straight the line was and how it begged to be extrapolated!

Science Demonstrations: the art of seeing things differently.

April 6, 2014

One of the highlights of the last few weeks was attending the premiere of Demo: The Movie by Alom Shaha and Jonathan Sanderson.

Mingling with the gliterati of the science communication world, the event, the conversations, and the film all helped me to reflect on the purpose of science demonstrations.

To me the purpose of a demonstration is to highlight one aspect of the everyday world, and to allow us to look at it ‘differently’.

This is necessary because for most of us, for most of our lives, the world doesn’t seem mysterious: our world comprises familiar objects that behave in a familiar way.

So famously in 1848 Michael Faraday gave a series of six lectures about an object which must have been extremely familiar to his audience: a candle. And this ground-breaking lecture series is the starting point for Demo:The Movie.

From this point Alom, a teacher, travels from his classroom to San Francisco via the western deserts of the USA performing demonstrations and reflecting on the their role in teaching as he travels.

He concludes that performing a successful science demonstration is an art which incorporates elements of stage magic, understanding of teaching aims and objects, and that most difficult to pronounce word, pedagogy.

For me the most important point made in the film is the profound (and paradoxical) point that demonstrations are different from videos of demonstrations.

This point is made by showing a plastic bottle (which you previously saw Alom fill with air at the top of a mountain) has been crushed when he reaches Death Valley, exactly as viewers probably expected.

But Alom points out that seeing this on video, you have no idea whether this is the same bottle you saw filled earlier. Indeed, you have no idea whether that it was even ‘earlier’.

It is the power of seeing things for yourself which is personally challenging. In terms of my own favourite demonstration, anyone who has ever seen a sausage attracted to a balloon is in some way personally challenged to ask themselves’ What is going on?’.

I can strongly recommend this 30 minute epic to anyone who engages in science communication in any form, but most especially to teachers who might feel inclined to simply show a class a video of something happening instead of performing the demonstration themselves.

And if you want help on performing demonstrations and tips on ‘getting it right’ Jonathan and Alom have created a website Sciencedemo.org which has many videos showing you how not to use videos in class!

Finally, if you love the movie as much as I do, you can check out the bloopers movie/trailer below.

 

 

Eeee-lec-tricity

April 5, 2014

The inimitable Tom Glazer and Dottie Evans sing about electricity

What with finishing the 19th presentation of Protons for Breakfast, and giving three weekend training sessions to teachers, I have found myself over the last few weeks with no time to think. And no time to think means no time to blog. :-(

But now, with the course over and arrival of the lighter evenings I feel freed to think again – and write!

This presentation of Protons for Breakfast was the busiest yet, and I am grateful to my colleague Dale Partridge for evidence that our work is finally leaking into mainstream consciousness.

One of our main aims is to change people’s appreciation of electricity. And indeed we aim to change not just how they think about electricity, but how they pronounce it.

As anyone who has attended the course knows, electricity is pronounced: eeeeeee-lec- tricity, a bit like this:


And it surely can’t be a coincidence that the latest hit by the The Pierces adopts a distinctly similar pronunciation.


Admittedly, the pronunciation by The Pierces lacks the bright, upbeat tone of Tom Glazer, but it is not bad for youngsters.

[UPDATE: My colleague Roberto Gavioso brought this interesting pronunciation by Captain Beefheart  from the 1960s to my attention


It is a little darker than the Pierces, but is clearly influenced by Glazer’s seminal work. The fact that it was not a hit at the time is surely because Protons for Breakfast had not yet influenced the zeitgeist. END OF UPDATE]

Now I am just going to flip back through my notes for the last 6 weeks and remind myself of all the topics I meant to write about.

Happy Listening. The Pierces song is below but the important part is about 1 minute and 10 seconds in. I haven’t listened to the song all the way through, but it doesn’t appear to be about physics at all!

 

Some things to look forward to…

March 1, 2014

Swansea lagoon visitors centre

Swansea lagoon visitors centre. Picture from BBC News.

‘News’ is frequently an abbreviation for ‘Bad News’. There seems to be no end of stories about ‘things’ getting worse.

And so it is something of relief to hear of people providing solutions to our problems. Here are few things which have recently inspired me with hope.

  • Meeting some teachers today.
  • The Swansea Lagoon Project in Swansea.
  • The Solana and Ivanpah Solar Thermal Power projects in the western USA.

Teachers: Today, Saturday March 1st, I got up early and drove to Birmingham to give a talk to a group of eight physics teachers at a training day.

They were a friendly and positive bunch – but what inspired me was not their subject knowledge (which was actually excellent) but their looks. To my 54 year-old male eyes these people didn’t look like what I expected physics teachers to look like.

From this gender-balanced group there was short and tall, thin and chubby, and a range of ethnicities. They were united only in an interest in Physics and in teaching it well.

As I reflected on the long drive home, it seemed as though these people were part of the solution to a long-standing problem in physics education, and I felt honoured to be able help a little.

The Swansea Lagoon Project (BBC Story) may or not get built, but I loved the design flair in their visitors centre (main picture above), and modesty of the project.

This is not the Severn barrage which would block the entire Severn estuary and which would be able to supply 5% of UK electricity demand to the detriment of nobody but a few wading birds.

This is a much more modest lagoon off the coast of Swansea which would not even harm the birds! Its lower cost makes it much more likely to actually get built, and the technology is scalable – multiple projects could be developed one by one – something which also makes it much more investment friendly.

Map of the Swansea tidal lagoon

Map of the Swansea tidal lagoon

Two solar thermal projects in the US have recently begun operating.

  • The Ivanpah plant consists of an astonishing 170,000 parabolic mirrors each of which tracks the Sun to focus light onto a furnace at the top of gigantic tower. This heats steam which drives a turbine to generate electricity.
  • The Solana plant in Arizona is similar, but distinctly different. One difference is that it uses cheaper parabolic troughs to heat a synthetic oil which runs along a tube at their focus. But this plant can also generate electricity after dark! This astonishing engineering ‘trick’ involves storing the thermal energy in gigantic vats of molten salt. The heat can then be used to generate electricity after the Sun has gone down, allowing the generation of electricity at its time of peak demand.

These plants have been heavily subsidised. But they show that this technology is practical and I am sure the next generation of plants will be cheaper to build and operate.

However the LA times reports today that solar thermal plants are already obsolete – even as they open! – because the falling cost of silicon photovoltaic plants is making them uneconomic. That may be true – but photovoltaics definitely don’t work in the dark!

The future is not obvious. But when I see the diversity of people teaching physics and wanting to do it better. And when I see the range of emerging options for sustainable energy generation I feel able to hope that even if I don’t recognise it immediately, the future will arrive all by itself – and that it will not be all bad.

Protons for Breakfast 19 is about to begin…

February 23, 2014

PfB Logo

The nineteenth presentation of Protons for Breakfast is imminent, and so a cascade of preparatory activity has begun.

  • I have read through and responded to ‘questions’ and ‘reasons for attending’ from the 130 people who have signed up.
  • I have revised the PowerPoint files for Week 1 – somehow still finding things to improve.
  • The NPL security staff have been notified
  • The facilities team have been asked to makes sure the air conditioning stays active late on the relevant evening.
  • And the biscuits have been ordered by the catering team.

So I guess that is about that. What can possibly go wrong?

There were a couple of amusing reasons for attending:

  • Accompanying Grandmother
  • Made to come by parent.

And quite a few insightful questions. Several people wanted to know either when we would have ‘proof’ that Global Warming had an anthropogenic origin, or when we would pass ‘the point of no return’, or why people weren’t ‘more concerned’. But a lot of questions were simple puzzles:

  • How do we know there are more stars in the Universe than grains of sand upon the beaches of the Earth?
  • Why do we feel colder when the wind blows?
  • Why does hot water freeze faster than cold water?
  • What is a HD Picture?
  • How do quantum computers work?
  • Can protons become neutrons?
  • Why do our stomachs ‘rumble’?
  • Will the universe ever be totally dark when all energy has been lost?

And many more. I love the diversity of these questions.

Having run these sessions for 10 years now I am constantly surprised at how each group has its own personality.

And I am very much looking forward to getting to know this group and the individuals within it.

By the way, while the course is on, the frequency of blog articles generally declines – sorry: it’s just all I can do.

Happy Birthday Ludwig Boltzmann

February 20, 2014
Happy Birthday Ludwig Boltzmann.

Happy Birthday Ludwig Boltzmann. My colleagues at NPL ate a ceremonial cake.

Last week I spoke with Ludwig Boltzmann’s great grandson: it was an honour and a pleasure.

Gerhard Fasol had e-mailed me to ask for details about plans to re-define the SI units of temperature (the degree Celsius and the kelvin) in terms of the Boltzmann constant.

Gerhard has a fairly impressive scientific CV in his own right, but of course his great grandfather’s legacy stands above his achievements and most other scientists. If there was a Premier league of scientists, he would be in it.

Boltzmann’s essentially took the ‘idea’ that atoms really existed, and turned the ‘idea’ into a detailed theory of matter with quantitative predictions and brilliant insights.

His ideas were not immediately accepted, which in retrospect makes his achievements all the greater. His motto was apparently

Say what is true;
Write the way that it is clear.
And advocate it until it is your opinion!

Physics has several ways of acknowledging the achievements of its ‘stars’. Their name can be used for an Equation, or a unit of measurement, or a fundamental physical constant. These honours are the scientific equivalent of having one’s paw-print set into the walk of fame.

And Boltzmann has a constant, k or kB, according to fashion, describing the link between temperature and energy. Scientists use this constant every day making his memory immortal, and raising his image to an almost mystical level

So speaking with his real great grandson was something of a shock! It reminded me that even ‘great’ people are people too, and I was happy to celebrate his birthday (he would have been 170) with my team today.

And we were very fortunate that Tesco had a suitable cake in store – what are the chances of that?

Flooding and Climate Change: What have we learned?

February 17, 2014
The River Thames in flood last weekend. As I write, the water level has called by around 20 centimetres.

The River Thames in flood last weekend. As I write, the water level has fallen by around 20 centimetres. What lessons have we learned?

As the flood waters slowly recede, can I be the first to congratulate the Environment Agency?

We have just experienced the worst sequence of weather events for a few decades or a few centuries. And almost nobody was hurt, and only a few thousand houses were flooded. That has to be a pretty good result.

Although these events cannot in any way be linked to Climate Change, there is still a lesson to be learned in that regard: and that is that we are vulnerable.

If the future climate changed so that such weather was more normal – then we would be have to adapt and there would be real costs (financial and otherwise) involved. And if the weather changed more dramatically, then the consequences could easily be more significant.

Now you may think that following Julia Slingo’s comments to the media that there is a link toClimate Change. So I read the Met Office’s 27 page media briefing on ‘the recent storms’ with interest. It reads like a police report of a pub brawl. But instead of:

  • A hit B because B said’s A’s girlfriend was sleeping with C.
  • C screamed and hit A who then attacked D who fell over and hit the bar.

We have:

  • Excess rain in the tropical Pacific affected stratospheric winds
  • These winds made tropospheric storms across North America move southward drawing air from the warm Atlantic etc. etc.

And then after 26 pages the report concludes

… it is not possible, yet, to give a definitive answer on whether climate change has been a contributor or not. 

So let’s put that particular baby to bed: in 30 years time when we look back we will see whether this event was part of a trend or merely a blip – but at this moment, we just don’t know.

And when in 30 years we look back, what will we say?

  • Will we say ‘Thank you’ to ourselves for considering the  possibility that this could be start of a significant change?
  • Will we be grateful to ourselves for updating our flood defences, and adapting our farming and flooding strategies?
  • Will be glad that the extra money we spent saved lives in the many storms which followed?
  • Or will we regret spending the money because – as things turned out – there were no major floods since.
  • Or will we look back and say ‘Great’ we got away with that – we have had 30 years without flooding?
  • Or will we kick ourselves for not acting when we could have done.

Whatever we want to be thinking in 30 years time, we need to act to achieve it now.

How good are climate models and climate forecasts?

February 12, 2014
Figure 10.1 (b) from the IPCC 5th Assessment Report shows the results of climate calculations ignoring the effect of human-induced climate forcing due mainly to carbon dioxide.

Figure 10.1 (b) from Chapter 10 of the IPCC 5th Assessment Report. The red line shows the results of calculated change in global mean surface temperature ignoring the effect of human-induced climate forcing due mainly to carbon dioxide. The black line shows our observations. We conclude that we cannot understand the Earth;s climate without account for human-induced Climate Change. If only we could go back to the 1960′s and make different choices…

Modelling the interactions of the ocean and atmosphere to predict the future climate of the entire Earth is one of the most breath-taking achievements of modern science. The sheer chutzpah of the endeavour is inspiring.

And much of the debate about the impact of climate change centres on the reliability of these ‘Climate models’. So I read with interest the review of climate models included in Chapter 9 of the 5th Assessment report of the state of the Intergovernmental Panel on Climate Change (IPCC) and enjoyed the presentation at the Royal Meteorological Society meeting last week.

I am not a specialist in this field, but I was impressed by the report, by the talk, and by just how good Climate Models are. The report draws on two ‘Coupled Model Inter-comparison Projects’: CMIP Phase 3 which covers 24 models and CMIP Phase 5 which covers 41 models.

Each model makes predictions for one possible evolution of Earth’s weather and its results are then averaged over time and region to yield Climate estimates.

Each model is fed data on the past state of the climate up until (say) 1900 and then calculations are made in roughly 15-minutes steps to see how the climate evolves as the Earth turns, the Sun shines, Volcanoes erupt, and carbon dioxide levels increase.

We then look back at our actual climate records and see how well each model performed. Of particular interest is the average performance of the models – which represents our collective ‘best estimate’ for what will happen.

What struck me most strongly is that the authors highlight where models get things wrong. This is such an unfashionable writing style one could easily get the sense that none of the climate models are ‘correct’. And of course none of them are perfect. But it is this obsession with error and uncertainty which is a hallmark of a community genuinely concerned with accuracy.

Actually, the models do pretty well. For me the most amazing graph was Figure 9.35 on Page 803. It shows the model’s predictions for the variability of the air temperature above the ocean surface in a particular region of the Pacific Ocean. Most models show a pattern of variability with peaks every 2 to 7 years – similar to the observed variability of El Nino events.

But ‘predicting’ the past is relatively easy because ‘bad’ models can be eliminated.

What about predicting the future? Can we say how reliably the models will predict the future? The authors summarise the state of the art thus (Page 745)

In general, there is no direct means of translating quantitative measures of past performance into confident statements about fidelity of future climate projections.

There has been substantial progress since the AR4 [the 4th Assessment Report in 2007] in the methodology to assess the reliability of a multi-model ensemble, and various approaches to improve the precision of multi-model projections are being explored. However, there is still no universal strategy for weighting the projections from different models based on their historical performance.

The models represent our very best attempt to consider all the physical factors of which we are aware, and to work out what is going to happen. Using multiple models and looking at the extent of agreement and disagreement between them is one way of assessing the likely accuracy of the model predictions.

But the long and the short of this is that ‘we just don’t know’ what will happen in the future.

However this shouldn’t diminish the achievements of understanding that these models embody, even if they prove inaccurate in some predictions. Similarly, it would also be unwise to believe them absolutely, even if they prove accurate.

We are talking about the future, and we need to remind ourselves of this. The results of climate forecasts can guide us, and it would be bonkers to ignore their guidance. But the real challenge is to make policy choices now in the face of the real uncertainty.

The IPCC 5th Assessment Report: The authors speak

February 9, 2014
A slide from the first talk of the Royal Meteorological Society Event.

A slide from the first talk at the Royal Meteorological Society meeting discussing the 5th Assessment Report of the Intergovernmental Panel on Climate Change. Is it really unequivocal?

Last week I attended my first meeting of the Royal Meteorological Society: it was a Wowser!

Many of UK’s leading climate scientists gave 15 minute précis talks describing the key results from the chapters of the IPCC 5th Assessment report on which they were authors.

  • The slides used in the précis talks and audio recordings of each talk can be found here.
  • The chapters of the IPCC assessment report can be found here.

I went with the aim of getting answers to three questions:

  • How good are climate models?
  • What does the data look like on sea level?
  • Why is Antarctic Sea Ice increasing in extent?

I will cover these questions in future articles, but here I would just like to comment on one of the first slides (reproduced above) stating baldy that there was simply no doubt that the Earth’s climate had warmed.

I found this interesting in the of a light of comment by climate skeptic Judith Curry who quotes another web-site stating that ‘Freezing is the new warming

Or try refuting global warming. Temperatures have stopped warming for more than a decade? That’s just a temporary “pause” in the warming that we just know is going to come roaring back any day now. Antarctic ice is growing? That’s actually caused by the melting of ice, don’t you know. A vicious cold snap that sets record low temperatures? That’s just because the North Pole is actually warming. So if the winter is warm, that’s global warming, but if the winter is cold, that’s global warming, too. If sea ice is disappearing, that’s global warming, but if sea ice is increasing, that’s global warming.

Now we can see what they mean when the warmthers say that global warming is supported by an ironclad scientific consensus. The theory is so irrefutable that it’s unfalsifiable!

Which is to say that it has become a cognitive spaghetti bowl full of ad hoc rationalizations, rather than a genuine scientific hypothesis. 

As the meeting progressed I reflected on the possibility that these scientists – myself included – were involved in some kind of collective delusion. Was that really believable?

I decided not, but I thought it was a question worth asking, and answering clearly. So here is the answer.

There are three key facts which are beyond any reasonable doubt.

  1. The concentration of carbon dioxide in the Earth’s atmosphere is increasing.
    • This has been measured directly for more than 50 years and historical values can be inferred from ice cores in Greenland and in Antarctica.
  2. The reason for this increase is our burning of fossil fuel
    • We can detect the isotopic signature of ‘fossil’ carbon and the reduction in oxygen concentration cause by the combustion.
  3. Carbon dioxide increase the ‘radiative forcing’ on the Earth’s climate system.

What is unknown is precisely what the consequences of the warming will be, or how rapidly they will become apparent. The Earth’s climate system is complex, and it does not repond in a simple way.

To use a mechanical analogy, if one pushed a rigid sphere one could predict how it would respond. But if one pushes a spherical jelly, then it will still move, but there will be many wobbles and its precise trajectory is not easily predictable.

So if we look at Curry’s criticisms one by one:

  • Temperatures have stopped warming for more than a decade?
    • A decade is not a long time in Climate Studies, and this just doesn’t mean anything yet. Many other indicators of climate change have continued to change.
  • Antarctic ice is growing?
    • As I mentioned previously – Antarctic Sea Ice is growing slightly. I don’t know why and when I ask specialists I get answers that seem handwaving. However Arctic Sea is shrinking dramatically, and this is well understood and predicted by climate models.
  •  A vicious cold snap that sets record low temperatures?
    • Curry here talks of North America: globally it has not been particularly cold. But one cold winter is weather not climate.

Predicting the future climate of Earth is almost as hard as predicting the weather, and in fact predictions from the 1980s are shaping up pretty well.

So as time moves on, and our understanding of the basic principles that determine climate improves, this only reinforces our understanding that human-kind’s emissions of carbon dioxide are affecting the Climate. There really is no doubt about it.

I was impressed that at the meeting there was complete openness about which data were well-understood, and which models worked well and which worked not so well. Hearing this open discussion is one of the most convincing signs of a research community that was very much focussed on reality, which is never simple.

==============

Thank you to Variable Variability for the quote from Judith Curry’s site.


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