Archive for the ‘Climate Change’ Category

Do you really want to know if global warming is real?

January 28, 2017

About a year ago, I thought that Climate Change Deniers had lost the argument.

I thought that we were all moving on to answering more interesting questions, such as what to do about it.

But it seems I was wrong. It seems that in this post-truth world, climate change deniers are uninterested in reality – preferring instead alternative facts.

I am left speechless in the face of this kind of intellectual dishonesty.

Actually I am only almost speechless. I intend to continue trying to empower people by fighting this kind deception.

Rather than trying to woo people over to my view, my aim is simply to offer people the chance to come to their own informed opinion.

See for yourself

As part of my FREE University of Chicago Course on Global Warming, I have been using some astonishing FREE software. And its FREE!

1

The ‘Time Series Browser’ allows one to browse a 7000 station subset of our historical temperature records from meteorological stations around the world.

  • The data are the local station temperatures averaged over 1 month, 1 year or 1 decade. Whichever you choose you can also download this data into a spreadsheet to have fun with on your own!
  • One can select sets of data based on a variety of criteria – such as country, latitude band, altitude, or type of geographical location – desert, maritime, tropical etc. Or you can simply pick a single station – maybe the one nearest you.

Already this is enormously empowering: this is the pretty much the same data set that leading climate scientists have used.

For this article I randomly chose a set of stations with latitudes between 20°N and 50°N.

7

The bold dots on the map show the station locations, and the grey dots (merging into a continuous fill in parts) are the available locations that I could have chosen.

The data from the selected stations is shown below.  Notice the scale on the left hand side runs from -10 °C to + 30 °C.

2

In this form it is not obvious if the data is warming or cooling: And notice that only a few data sets span the full time range.

So how do we discover if there are trends in the data?

The first step

Once you have selected a set of stations one can see that some stations are warm and others cool. In order to be able to compare these data fairly, we subtract off the average value of each data set between 1900 and 1950.

This is called normalisation and allows us to look in detail at changes from the 1900-1950 average independent of whether the station was in a warm place or a cold place.

3

Notice that the scale on the left-hand side is now just ± 3.5 °C.

The second step

One can then average all the data together. This is has the effect of reducing the fluctuations in the data.

One can then fit a trend-line to see if there is a recent warming or cooling trend.

5

For this particular set of stations its pretty clear that since 1970, there is a warming trend. The software tells me it is approximately 0.31 ± 0.09 °C per decade.

What I have found is that for any reasonably diverse set of stations a warming trend always emerges. I haven’t investigated this thoroughly, but the trend actually seems to emerge quite clearly above the fluctuations.

But you can check that for yourself if you want!

Is it a cheat? No!

You can check the maths of the software by downloading the data and checking it for yourself.

Maybe the data is fixed? You download the source data yourself – it comes from the US Global Historical Climatology Network-Monthly (GHCN-M) temperature data-set.

But accessing the raw data is quite hard work. If you are a newbie, it will probably take you days to figure out how to do it.

There is more!

This ability to browse, normalise, average and fit trends to data is cool. But – at the risk of sounding like a shopping channel advertorial – there is more!

It can also access the calculations of eleven different climate models.

For the particular set of stations that you have selected, the software will select the climate model predictions (a) including the effect of human climate change and (b) without including human-induced climate change.

For my data selection I chose to compare the data with the predictions of the CCSM4 Climate model. The results are shown below

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You can judge for yourself whether you think the trend in the observed data is consistent with the idea of human-induced climate change.

For the particular set of stations I chose, it seems the CCSM4 climate model can only explain the data by including the effect of human-induced climate change.

But Michael: this is just too much like hard work!

Yes and no. This analysis is conceptually challenging. But it is not crazily difficult. For example:

  • Schoolchildren could do this with help from a teacher.
  • Friends could do it as a group and ask each other for help.
  • University students could do this.
  • Scout groups could do it collectively.

It isn’t easy, but ultimately, if you really want to know for yourself, it will take some work. But then you will know.

So why not have a go?  The software is described in more detail here, and you can view a video explaining how to use the software here.

[January 28th 2017: Weight this morning 71.2 kg: Anxiety: Sick to my stomach: never felt worse]

5.What was all that about?

January 3, 2017

duty_calls

Interviewer: So Michael, why did you write the last four articles (1,2,3,4) on the transmission of infrared radiation through the atmosphere: that stuff is already well known?

Me: I know, but I was irritated by a friend of a friend who wrote an “exposé” of why carbon dioxide can’t cause global warming.

Interviewer: Curious. Were they an expert in Climate Science? Or had they made a study of radiative transfer through the atmosphere?

Me: Neither. I think they were an electrical engineer.

Interviewer: An electrical engineer? Why did they think that their assessment outweighed the view of the large number of experts who had studied this intensively over the last century or so?

Me: I think it is an example of the Dunning-Kruger effect in which people who don’t know about a subject fail to appreciate how little they know. We are all affected by it at times.

Interviewer: OK, So you wrote all this just to set them straight?

Me: Yes, and hopefully to help others who are curious about radiative transfer. It is complicated.

Interviewer: And how do you feel about it now?

Me: Numb and Tired. But OK. I like one or two of the graphs I have created, and I enjoyed learning how to make animated GIFs. I have also learned quite a bit about MODTRAN.

Interviewer: But…

Me: But the articles took literally weeks to prepare and I still don’t feel satisfied with them. However now, if I see anyone else write stuff like this:

The bottom line is that once Carbon Dioxide reaches a concentration that makes the atmosphere completely opaque in the band where it resonates,  further increases in the concentration cannot result in any additional blocking

I will know exactly where to send them. And so will you.

 

4. Feedback and Climate Models

January 3, 2017

In the last two articles I have written at great length (sorry) about the way carbon dioxide affects the transmission of infrared light vertically through the atmosphere.

Changes in this transmission are – we think – causing Global Warming.

The physics of the effect on infrared transmission is beyond argument. However this is just one component in the energy flows that constitute Earth’s climate system.

What else do we need to consider before we can conclude that carbon dioxide is causing global warming?

What else do we need to consider?

atmosphericmodelschematic

There is so much! The calculations in the previous articles only considered the transmission of infrared radiation and light up and down a vertical column of air with a variable temperature and pressure.

However in reality:

  • Light transmission does not just take place in one dimension (up and down) but in three dimensions.
  • Illumination from the Sun strikes each part of the Earth at different angles.
  • The infrared radiation from the Earth also takes place at many angles, and from many different heights in the atmosphere.
  • There are clouds which dramatically change atmospheric transmission.
  • The air moves in complicated ways “up and down and round and round”.

Additionally, the energy balance is dynamic – all the above factors change from minute to minute – around the surface of the Earth. And the Earth is not a sphere, and is not uniform and does not move in a circle around the Sun. And the Sun’s output varies from year to year.

In order to calculate the long-term averages of temperature and rainfall that determine the climate, we need to take into account all – or as many as possible – of the above effects.

There will be a cascade effects caused by increased  atmospheric carbon dioxide – such as changes in the location or timing of cloud formation. Additionally changes in the Earth’s surface temperature will affect the temperature of the atmosphere.

These changes may either ameliorate or exacerbate the initial effects of increased carbon dioxide concentrations.

In the end one ends up with a complex General Circulation Model of the entire Climate of the Earth – such as that illustrated above. The MODTRAN code – or something similar – is incorporated as one element of all the extant general circulation models.

If it’s all so complicated…why are scientists so sure of themselves?

There are, I think, two or possibly three reasons.

The first concerns calculations of the future effect of increasing carbon dioxide concentrations.

Simple calculations made more than 100 years ago agree pretty well with the results of most recent complicated calculations.

This indicates that the simple calculation has captured the essence of the problem.

Secondly, there is broad agreement with experimental observations – the Earth’s surface really is warming (Data Analysis 1 and Data Analysis 2). You can download the raw data from land stations here.

The third reason – which is really just a different way of thinking about the previous two reasons – is that given its effect on infrared transmission, it would be truly astonishing if adding carbon dioxide to the atmosphere did not affect the climate at all!

Once one admits to this point it becomes a question of asking what the effect will be? And every calculation I have ever seen predicts warming. If anyone has found something different, I would love to hear about it.

What about the saturation of the carbon dioxide bands?

A friend of a friend wrote an analysis in which he argued that increased concentrations of carbon dioxide could not cause global warming because:

The bottom line is that once Carbon Dioxide reaches a concentration that makes the atmosphere completely opaque in the band where it resonates,  further increases in the concentration cannot result in any additional blocking.

He was imagining that the ‘band’ where carbon dioxide molecules resonate is fixed. He was wrong.

For the individual molecules, the frequencies at which they vibrate are fixed. And the width of their ‘natural’ absorption line is fixed by the local temperature and pressure.

But transmission through the atmosphere is complicated, and the width of the band that absorbs radiation just keeps growing in width as the concentration increases.

Additionally the height in the atmosphere at which the absorption takes place gets lower – and hence warmer – and re-radiates more radiation back down to Earth.

That’s all for this article:

Here we looked at how the MODTRAN calculations fit into more complex models of global climate.

The next (and final) article is about the conclusions we can draw from these calculations.

3. Light transmission through the atmosphere

January 3, 2017

co2_band_formation

In part 2 I looked at transmission of infrared light through a gas containing a molecule which absorbs infrared light at one particular frequency.

We saw that at higher concentrations, the absorption at specific frequencies broadened until entire bands of frequencies were ‘blocked’.

We saw that the width of the ‘blocked bands’ continued to increase with increasing concentration.

Here we look at how that insight can be applied to transmission of infrared light through Earth’s atmosphere.

This is even more complicated.

  • We are mainly interested in transmission of infrared light from the Earth’s surface out through the atmosphere and into space, but the atmosphere is not at a uniform temperature or pressure.
  • When absorbing gases are present, the air is not just a ‘conduit’ through which infra-red light passes – the air becomes a source of infrared radiation.
  • We are mainly interested in the effect of carbon dioxide – but there are several other infrared ‘active’ gases in the atmosphere.
  • Gases are not the only thing in the atmosphere: there is liquid water and particulates.

So it’s complicated: Here are a few more details.

1. Density.

If the carbon dioxide is distributed in a fixed proportion to the amount of oxygen and nitrogen through the atmosphere, then it will have more effect where the atmosphere is most dense: i.e. lower down in the atmosphere.

And density is affected by both temperature and pressure.

Since carbon dioxide molecules absorb 100% of the infrared light with wavelengths around 15 micrometres, as we saw in the previous article, increasing the concentration of carbon dioxide increases the range of wavelengths that are ‘blocked’. This is illustrated in the figure at the head of the article.

Increasing the concentration of carbon dioxide also changes the height in the atmosphere at which absorption takes place.

2. Re-radiation.

Once absorbed by a carbon dioxide molecule, the infrared light does not just disappear.

It increases the amplitude of vibration of the molecule and when the molecule collides with neighbouring molecules it shares that energy with them, warming the gas around it.

A short while later the molecule can then re-radiate light with the same frequency. However the brightness with which the gas ‘glows’ relates to its local temperature.

Some of this re-radiation is downward – warming the Earth’s surface – and giving rise to a ‘greenhouse’ effect.

And some of this re-radiation is upward – eventually escaping into space and cooling the Earth.

3. Other things.

Carbon dioxide is not only the infrared active gas in the atmosphere. There is also methane, ozone and, very significantly, water vapour.

There is also condensed water – clouds.

And then there are particulates – dust and fine particles.

All of these affect transmission of light through the atmosphere to some extent.

For an accurate calculation – all these effects have to be considered.

MODTRAN

Fortunately, the calculation of transmission through the atmosphere has been honed extensively – most notably by the kind people at the  US Air Force.

However the code is available for anyone to calculate atmospheric transmission.

David Archer and the University of Chicago kindly host a particularly friendly front end for the code.

modtran-web-interface

Aside from just clicking around, it is possible to download the results of the calculations and that is how I plotted the graphs at the head of the page.

To get that data I removed all the other greenhouse gases from the atmosphere (including water), and varied only the concentration of carbon dioxide.

Notice that the absorption lines grow into bands that continue to broaden as we add more and more  carbon dioxide. This is exactly what we saw in the simple model in the second article.

This shows that the transmission through the atmosphere is still being affected by additional carbon dioxide, and these bands have not ‘saturated’.

Asking a question

MODTRAN can answer some interesting questions.

Assuming that the Earth’s surface is at a temperature of 15 °C, we can ask MODTRAN to calculate how much infrared light leaves the top of the atmosphere (100 km altitude) as we add more carbon dioxide. The result of these calculations are shown below:

toa-radiative-power

The first thing to notice is the qualitative similarity between this graph – the result of complex and realistic calculations – with the simple spreadsheet model I showed in the second article.

The second thing to notice is that the calculations indicate that increasing the concentration of carbon dioxide in the atmosphere reduces the amount of radiation which escapes at the top of the atmosphere. And that it will continue to do so even as the concentration of carbon dioxide increases well beyond its current 400 parts per million (ppm).

Where does that absorbed radiation go? The graph below shows the results of another calculation. It imagines being on the ground and asks how much infrared light is re-radiated back to the Earth’s surface as the concentration of carbon dioxide increases.

downward-flux-graph

The graph shows that matching the decline in infrared radiation leaving the top of the atmosphere, there is a matching increase in radiation falling back down to Earth.

Importantly, both these effects still depend on the concentration of carbon dioxide in the atmosphere even as the concentration grows past 400 ppm.

Over the longer term, this increase in downward radiation will increase the temperature of the Earth’s surface above the assumed 15 °C. This process will continue until the outgoing radiation leaving the top of the atmosphere is balanced with the incoming solar radiation.

That’s all for this article:

In this article we saw that transmission of infrared light through the atmosphere is complicated.

Fortunately MODTRAN software can cope with many of these complexities.

The conclusions of our calculations with MODTRAN are similar to conclusions we came to in the previous article.

Increasing the concentration of a molecule such as carbon dioxide which absorbs at a single frequency will continue to reduce transmission through the atmosphere indefinitely: there is no limit to the amount of absorption.

The next article is about the conclusions we can draw from these calculations.

2: Light transmission through a gas

January 3, 2017

In the first article I showed experimental data on the spectrum of light travelling through the atmosphere.

We saw that some frequencies of light are ‘blocked’ from travelling through the atmosphere.

Sometimes this ‘blocking’ occurs at specific frequencies, and sometimes at ranges of frequencies – known as ‘blocked bands’.

In this article, we will consider how both single frequency absorption and blocked bands arise.

Air and Light

Air is composed mainly of nitrogen, oxygen, and argon molecules. The frequencies at which these molecules naturally vibrate are very high, typically greater than 400 terahertz. High frequencies like this correspond to light in the visible or ultraviolet part of the spectrum.

Larger molecules – ones composed of more than two atoms – can vibrate more easily.

They are – in a very rough sense – ‘floppier’ and have lower natural frequencies of vibration, typically a few tens’s of terahertz.

Frequencies in that range correspond to light in the infrared part of the spectrum.

The animation below shows qualitatively the relative frequencies of a vibrational mode of an N2 molecule and a bending mode of a CO2 molecule.

co2-animation

When light travels through a gas containing molecules that can vibrate at the same frequency as the light wave, the molecules begin to vibrate and absorb some of the energy of the light wave.

The molecules then collide with other atoms and molecules and share their energy – warming the gas around them. The light has been absorbed by the gas.

But this absorption only happens close to the specific frequencies at which the molecules vibrate naturally.

The effect of a single frequency of vibration

The figure below shows the effect of the presence of a low concentration  of a molecule that can absorb light at a specific frequency.

absorption1

The figure describes how ‘white’ light – in which all frequencies are present with equal intensity – travels through a non-absorbing gas with a low concentration of molecules which absorb at one specific frequency.

Light with a frequency – represented by a colour: yellow, orange or red – which just matches the vibrational frequency of the molecule is absorbed strongly and doesn’t make it far through the gas.

But light with frequencies on either side of this vibrational frequency is absorbed less strongly. So the percentage of light transmitted has a dip in it at the frequency of molecular vibration.

If we increase the concentration of the absorbing molecule, something really interesting happens.

absorption2

The light at the central vibrational frequency is absorbed even more rapidly. But since it is already 100% absorbed – it doesn’t affect the overall transmission at this frequency. However it does affect where the light is absorbed.

But the additional concentration of absorbing molecules now absorbs strongly on either side of the main absorption frequency.

Eventually, the absorption here becomes so strong that the absorption is 100% even for frequencies that differ significantly from the main vibrational frequency.

This leads eventually to bands of frequencies that are 100% absorbed.

Band Width

Importantly, as the concentration of the absorbing molecule increases – the width of the blocked band increases.

This increase in absorption band width isn’t a property of an individual molecule – each of which just absorbs at frequencies centred around a particular frequency.

The formation of the band – and its width – is a property of a column of gas containing many absorbing molecules

This can be modelled quite easily and the output of a spreadsheet model is animated below as a function of the concentration.

In each frame of the animation, the concentration increases by a factor 2.7 – so that the concentration range covered in the seven frames is 387 (~2.7 to the power 6).

single-line-absorption

The figure shown in percent on each frame of the animation is the fraction of light in the range from 212 to 228 terahertz which has been absorbed.

Please note that the line-widths and frequencies in the model are arbitrary and approximate. However the qualitative behaviour is universal and independent of the particular mathematics I have used.

  • As the concentration of an absorbing gas increases, the transmission at the central absorbing frequency eventually reaches zero.
  • As the concentration increases further, the absorption increase at frequencies on either side of the central frequency.
  • This eventually forms a range of blocked frequencies – and the width of this blocked range continues to increase with increasing concentration.

The fraction of light transmitted is plotted below.absorption-graph-from-single-line

Once again I would like to emphasise that the graph qualitatively characterises the absorption from a single absorption frequency as a function of concentration.

Significantly, the amount of light transmitted continues to fall even after the transmission at the central frequency reaches zero.

And notice that this broadening of the absorption bands is a property of the transmission of light through a column of gas. It is not caused by line-broadening by individual molecules.

That’s all for this article:

The story so far is that when one looks up through the atmosphere, we see ‘blocked bands’ at a range of frequencies.

In the infrared region of the spectrum, these bands arise from particular modes of vibration of specific molecules which occur at specific frequencies.

In this article we saw that even when the transmission through a gas was saturated, increasing the concentration of the absorbing molecule still reduced transmission through the gas.

This is because the width of the ‘blocked band’ is not a property of the individual absorbing molecules: it arises from transmission of light through a column of gas.

The next article is about how this effect works in Earth’s atmosphere.

1. Light transmission through the atmosphere

January 3, 2017

illustration

Light through a gas

Visible light travels through most gases almost unperturbed.

And broadly speaking, the Earth’s atmosphere is transparent to visible light.

However  if one looks in detail at the way sunlight travels through the Earth’s atmosphere, one can see some remarkable features.

The figure above is a high-resolution spectrum of sunlight. The spectrum would be about 40 times as wide as the figure above but has been ‘folded back’ on itself many times

Light

You may be familiar with the fact that light is a wave in the electric field.

  • When the wave vibrates with a frequency of approximately 430 terahertz it has a wavelength of approximately 0.7 thousandths of millimetre, and it elicits the sensation of red in our eyes.
  • When the wave vibrates with a frequency of approximately 750 terahertz it has a wavelength of approximately 0.4 thousandths of millimetre, and it elicits the sensation of blue in our eyes.

You are probably familiar with the basic features of the spectrum as it sweeps from light which elicits the sensation of ‘red‘ in our brain, to light which elicits the sensation of ‘blue‘.

But this Figure also  shows many dark lines in the spectrum. If we looked at the Sun with filters at these specific frequencies – we would see no light at all! The atmosphere would be opaque!

What has happened is that light with a very specific frequency (and hence wavelength) has been absorbed by vibrations of electrons within specific types of atoms.

Some of these atoms were in the outer layers of the Sun, and some are in our atmosphere.

Infrared Sunlight

Electrical waves exist with lower frequencies that elicit no sensation of colour or brightness in our eyes: this light is called ‘infrared’.

If we look at sunlight coming through the atmosphere at infrared frequencies, the spectrum is even more complex than in the visible region of the spectrum.

The graph below shows data acquired by my colleague Tom Gardiner. It shows the brightness of sunlight coming through the atmosphere at frequencies 10 times lower than visible light.

The brightness is plotted versus the wavelength of the light rather than the frequency because for historical reasons, that is a more common way to present the data.The wavelengths vary between 4 thousandths of a millimetre and 5 thousandths of a millimetre (4 to 5 micrometres).

slide1

There are two remarkable things about this spectrum:

  • the complexity of the spectrum – there are hundreds of peaks and troughs –
  • and the occurrence of a range of wavelengths between about 4.18 and 4.45 micrometres in which the sunlight is completely blocked!

The next two figures show the green region and the orange region in detail.

slide2slide3

If one looks at even lower frequencies (longer wavelengths), one sees the same two features – millions of sharp lines and entire ‘blocked bands’ – repeated again and again.

For example, the image  below is a modified extract from this amazing image (which I don’t have permission to reproduce) and shows details of transmission of sunlight through the atmosphere at frequencies of around 20 terahertz and wavelengths around 15 micrometres.

This particular range of blocked infrared light is caused by carbon dioxide molecules in the atmosphere. At this range of frequencies the carbon dioxide molecule can bend easily.

Amazingly, this simple ‘bendability’ of the molecule plays a significant role in determining the surface temperature of the Earth.

slide4

That’s all for this article:

The story so far is that when one looks up through the atmosphere, there are certain frequencies at which light is blocked.

This blocking sometimes occurs at specific frequencies, and sometimes as ranges of blocked transmission – known as ‘blocked bands’.

For historical and technical reasons, people usually specify the wavelength of the blocked light rather than its frequency.

The next article is about the link between specific blocked frequencies and blocked bands.

When will the North Pole become the North Pool?

December 16, 2016

arctic_ssi_201612_chart

It is a sad fact, but it is likely that within my lifetime it will become possible to sail to the North Pole. I am 56.

Tragically it is also true that there is absolutely nothing that you or I can do about it.

In fact, even in the unlikely event that humanity en masse decided it wanted to prevent this liquefaction, there would be literally nothing we could do to stop it.

The carbon dioxide we have already put in the atmosphere will warm the Earth’s surface for a few decades yet even if we stopped all emissions right now.

Causation

The particular line of causation between carbon dioxide emissions and warming of the arctic is long, and difficult to pin down.

Similarly it is difficult to determine if a bull in a china shop broke a particular vase, or whether it was a shop helper trying to escape.

Nonetheless, in both cases the ultimate cause is undeniable.

What does the figure show?

The animation at the head of the page, stolen from NASA’s Earth Observatory, is particularly striking and clear.

The animation shows data from 1979 to this past November 2016 showing the extent of sea ice versus the month of year.

Initially the data is stable: each year is the same. But since the year 2000, we have seen reductions in the amount of sea ice which remains frozen over the summer.

In 2012, an additional one million square kilometres – four times the area of England Scotland and Wales combined – melted.

The summer of 2016 showed the second largest melt ever.

The animation highlights the fact that the Arctic has been so warm this autumn, that Sea Ice is forming at an unprecedentedly slow rate.

The Arctic Sea Ice extent for November 2016 is about one million square kilometres less than what we might expect it to be at this time of year.

My Concern 

Downloading the data from the US National Snow and Ice Data Centre, I produced my own graph of exactly the same data used in the animation.

The graph below lacks the drama of the animated version at the head of the article. But it shows some things more clearly.

sea-ice-december-2016-graph

This static graph shows that the minimum ice extent used to be stable at around 7 ± 1 million square kilometres. The minimum value in 2012 was around half that.

The animated graph at the head of the article highlights the fact that the autumn freeze (dotted blue circle) is slower than usual – something which is not clear in the static graph.

My concern is that if this winter’s freeze is ‘weak’, then the ice formed will be thin, and then next summer’s melt is likely to be especially strong.

And that raises a big question at the very heart of our culture.

When the North Pole becomes the North Pool, where will Santa live?

 

Global Warming Trends

December 3, 2016

 

The anomaly in the Earth's temperature based only on thermometers in meteorological stations and excluding the oceans which cover about 70% of the Earth's surface. The Daily Mail only draw your attention to a small fraction of the data - and they include monthly fluctuations which disguise the clear warming trend.The anomaly in the Earth’s temperature based only on thermometers in meteorological stations and excluding the oceans which cover about 70% of the Earth’s surface. The Daily Mail only draw your attention to a small fraction of the data – and they include monthly fluctuations which disguise the clear warming trend.

Why do I ever even look at the Daily Mail website?

The other day I came across this pernicious article purporting to describe a plummeting of global temperatures above the land surfaces of the Earth. The article states:

Global average temperatures over land have plummeted by more than 1C since the middle of this year – their biggest and steepest fall on record. [P.S. by 1C they mean 1 °C not 1 coulomb]

The news comes amid mounting evidence that the recent run of world record high temperatures is about to end.

Some scientists, including Dr Gavin Schmidt, head of Nasa’s climate division, have claimed that the recent highs were mainly the result of long-term global warming.

Others have argued that the records were caused by El Nino, a complex natural phenomenon that takes place every few years, and has nothing to do with greenhouse gas emissions by humans. The new fall in temperatures suggests they were right.

It is accompanied by a misleading graphic:

Graphic from the Daily Mail website. Notice their graph only runs from 1997 and includes large fluctuations due to sub-annual changes. It describes only the changes in temperature above the land surfaces of the Earth.

Graphic from the Daily Mail website. Notice their graph only runs from 1997 and includes large fluctuations due to sub-annual changes. It describes only the changes in temperature above the land surfaces of the Earth.

The article is nonsense from start to finish, but I just thought I would show you how to get at the data for yourself so you can make up your own mind.

Decide for yourself

This excellent NASA web page allows you plot various graphs of temperature data, and change the degree of smoothing applied to the raw data. I invite you to try it out for yourself.

This NASA web page has excellent links and descriptions

You can choose to include land stations only, or combine land and ocean data. Remember that the land surface of the Earth represents less than 30% of our planet’s surface, and so the most relevant measure of global warming involves both land and ocean data.

As well as generating graphs, you can use the website to download data and then graph the data in Excel™ as I have done for the graph at the top of the page.

I don’t fully understand where the data in the Daily Mail graphic comes from. They appear to have picked only recent data and included monthly data rather than annual averages to increase the noise and de-emphasise the obvious trend in the data.

The background colouration in the Daily Mail graphic implies that the high temperatures are all associated with the El Nino conditions. This is not correct. As the graphic below (from skeptical science) shows, years with and without an El Nino are all showing a warming trend.

An animated file showing global surface temperatures in El Nino years, La Nina years, and neutral years. The graphic is from sceptical science.

An animated file showing global surface temperatures in El Nino years, La Nina years, and neutral years.

For the technically-minded reader, this article from Victor Venema may help.

The Trend 

What struck me as shocking was what happened when I set the smoothing of the data to 20 years – so that the trend represented a trend in climate rather than annual or multi-annual fluctuations.

In the figure below I show the data for the land and ocean mean temperature anomaly and the red line shows the smoothing with a 20-year running average. Since 1980 – which was 36 years ago – the data is essentially a straight line.

The estimated change in the temperature of the air above the oceans and the land. The red line shows a smoothed version of the annual data with a 20-year window to reflect changes in climate rather than the internal fluctuations of the Earth's complex weather systems. Source: NASA-GISS: see article for detailsThe estimated change in the temperature of the air above the oceans and the land. The red line shows a smoothed version of the annual data with a 20-year window to reflect changes in climate rather than the internal fluctuations of the Earth’s complex weather systems. Notice that since 1980 , the smoothed line is essentially straight with a gradient of approximately 0.017 °C per year. Source: NASA-GISS: see article for details

What if…

Friends, just suppose that NASA had spotted not a global warming trend, but an asteroid headed straight for Earth. Suppose they calculated it would not destroy civilisation, but it would nonetheless be devastating: its tidal disturbance would cause widespread floods

Would we want to know? Well Yes!

Now suppose that the entire world got together in, say, Paris, and developed a plan to deflect the asteroid. The plan would be expensive and risky – costing about 1% of global GDP – but after about 100 years of effort we would be freed from the risk of a collision.

Would we follow the plan? Well Yes!

Friends, Global warming is equivalent in its impact to an asteroid headed to Earth, and the Paris Accord, while inadequate in itself, represents the start of a plan in which the disparate governments of Earth have agreed to slow development (that brings direct benefit to their citizens) in order to tackle this threat.

Please don’t let the Daily Mail deceive you into thinking global warming is not happening: it is. It is happening slowly – 0.017 °C per year  – and the odd year of inaction makes no difference.

But year upon year of inaction condemns us to a fate that is out of our control.

 

Global Warming for Electrical Engineers

November 21, 2016
An electrical analogy to the flux of energy from the surface of the Sun energy as it reaches and then leaves the Earth's surface on its journey into deep space. If these fluxes are not equal then the Earth's surface temperature will change.

An electrical analogy to the flux of energy from the surface of the Sun as it reaches and then leaves the Earth’s surface on its journey into deep space.

I haven’t written much about global warming lately, but I have noticed that the resurgence of the ‘alt-right‘ seems to have emboldened people to express ‘sceptical’ views.

People expressing these views are in general no more or less stupid than anyone else. However, they do fail to understand that their own competence in one area, or the popularity of their views in polls, has no bearing on the correctness or otherwise of their understanding of anthropogenic global warming.

In a recent interaction with a Nameless American, it became clear that despite being able to assemble the facts, this individual was unable to understand the basic process by which the surface temperature of the Earth comes to be what it is. And hence they could not understand why it is rational to expect that increased amounts of carbon dioxide in the atmosphere are affecting the surface temperature of the Earth.

So here, for that Nameless American, is Global Warming for Electrical Engineers: Apologies to everyone else.

Basic Circuit

Figure 1: A simple electrical circuit. The key feature is that the same current flows through both resistors R1 and R2.

Figure 1: A simple electrical circuit. The key feature is that the same current flows through both resistors R1 and R2.

The basic circuit required to understand the way in which the surface temperature of the Earth is established is shown in Figure 1. Two key features of this resistor-divider circuit are that:

  1. The current flow through circuit elements R1 and R2 is the same.
  2. The DC steady state operating point of the circuit is determined just by the resistances and the voltage of the DC power supply

Now the analogy we will make is this:

  • Voltage is analogous to temperature: In the same way that voltage differences drive electrical currents, temperature differences drive energy flows.
  • V0 is like the surface temperature of the Sun
  • V1 is like the surface temperature of the Earth
  • V2 is like the temperature of the deep space – almost absolute zero.

Importantly, the only way to get thermal energy on or off the Earth is by electromagnetic radiation – mainly visible and infrared light.

Notice that the surface temperature of the Earth is determined (in the steady state) by the requirement that the average flux of energy onto the Earth’s surface is the same as the average flux off the Earth’s surface.

This is analogous to the way Kirchoff’s current law is used to establish the steady state DC voltage V1.

Figure 2: We are drawing an analogy between the flow of electrical current through resistors in series and the flow of energy from the Sun onto the Earth's surface and then secondly off the Earth's surface and out into space.

Figure 2: We are drawing an analogy between the flow of electrical current through resistors in series and the flow of energy from the Sun onto the Earth’s surface and then secondly off the Earth’s surface and out into space.

How the analogy works

The surface of the Sun is hotter than the Earth: Radiation travels from the surface of the Sun through space and arrives at the top of the atmosphere.

For the moment let’s forget about the radiation reflected from the cloud tops, and consider only radiation which travels through the atmosphere and reaches the Earth’s surface. We’ll discuss the effect of this assumption in Subtlety #2 below.

The radiation which travels through the atmosphere is mostly visible light – the sunlight which warms the Earth’s surface.

The resistance R1 then determines the amount of heat delivered to the Earth’s surface from the Sun’s Surface. The actual value of R1 is determined by factors such as the distance from the Sun to the Earth.

Now we consider the re-radiation of thermal energy from the Earth’s surface. This is in the form of infrared light. In the same way that warming happens mainly on the ‘day’ side of the Earth, cooling happens mainly on the ‘night’ side of the Earth.

Whereas the atmosphere is mainly transparent to incoming radiation, the atmosphere is mainly opaque to infrared radiation. If we humans could see at the relevant the wavelengths, and looked up at the night sky, we would not see the stars, but just a ‘fog’.

The atmosphere would appear to be totally opaque at these wavelengths: but it is not.

When we shine light into a fog, it is multiply scattered and only a tiny amount of light makes it out the other side of the fog. We can consider the fog as presenting an impedance R2 to the transmission of radiation out to the heat sink of deep space.

The surface temperature of the Earth is determined in the steady state by the requirement that it is hot enough to ‘drive’ infrared radiation through the impedance R2 and out into space.

  • If the Earth’s surface temperature is ‘too low’, more energy will arrive on the surface of the Earth than leaves and the surface temperature will rise.
  • Similarly, if the Earth’s surface temperature is ‘too high’, more energy will leave the surface of the Earth than arrives and the surface temperature will fall.

Eventually, a steady-state is reached: a dynamic equilibrium. The temperature of the Earth’s surface becomes hot enough, that it glows brightly enough to drive sufficient infrared radiation through the Earth’s atmosphere and out into space.

In our circuit, this is equivalent to the voltage V1 rising until it reaches a value sufficient to drive the operating current  through the resistor R2.

Anthropogenic global warming is caused by an increase in the impedance R2. For a fixed surface temperature, this reduces the amount of radiation which leaves the Earth’s surface and reaches space.

In order to re-establish the equilibrium and drive the requisite energy flux through the atmosphere and out into space, the temperature of Earth’s surface needs to rise

Subtlety #1

The electrical analogy in Figure 1 is ridiculously simple, so let’s make it more complicated and (very slightly) more realistic.

Figure 2: Ra, Rb etc represent transmission through the atmosphere in different wavelength bands.

Figure 2: Ra, Rb etc represent transmission through the atmosphere in different wavelength bands.

Figure 2 replaces a single resistance R2 with an array of parallel resistances each of which radiatively couples the surface of the Earth to the coolness of space. We could imagine that each parallel resistance represents (say) transmission in a different wavelength band.

The important observation is that increasing the impedance any of Ra, Rb etc always increases, the total impedance R2. Since the current through the circuit is fixed, this will cause an increase in the voltage V2.

Considering our Earth analogy, if we decrease the transparency of the atmosphere to infrared light in any waveband, this will increase the overall impedance. Since the flux of radiation onto the Earth is unaffected, this will cause an increase in the surface temperature of the Earth.

Of particular interest is the radiation which leaves the Earth’s surface in wavelength bands that are absorbed by carbon dioxide molecules.

Aside on Subtlety #1: ‘blocked bands’

The conclusion of the previous section is that if we make the atmosphere more opaque in any wavelength band, the surface temperature of the Earth will increase. This conclusion is inescapable. Unless…

…The only time that increasing a number makes no difference to the number’s value is if that number is already infinite.

So global warming sceptics frequently argue that ‘the carbon dioxide bands are blocked‘. They argue that carbon dioxide absorbs infrared light so effectively, that at certain specific wavelengths the atmosphere is (practically) 100% opaque.

Their argument is that increasing the amount of carbon dioxide cannot therefore increase the opacity of the Earth’s atmosphere any further. The problem with this argument is that it is ‘just wrong‘.

[We can see why in various ways, but firstly I feel compelled to note that water vapour is dramatically more effective than carbon dioxide at blocking infrared light, and yet sceptics don’t apply the same argument to water vapour!]

The actual mechanism of transmission of infrared light through the atmosphere is complex: it is illustrated schematically in Figure 3.

At infrared wavelengths the atmosphere looks ‘foggy’. Radiation travels through ‘fog’ in a process involving multiple scatterings – think of car headlights shining into fog: some of the light comes back in the direction towards your headlights and some goes forward and sideways.

 

Figure 3: Illustration of the energy flux onto and off the Earth's surface. On average, roughly 240 W/m^2 of solar energy reaches the Earth;s surface. This is re-radiated as infrared red light at wavelengths at which the atmosphere is opaque. The light is scattered, and some comes back to the Earth, and some makes its way further up the atmosphere. Eventually the light reaches a height - typically 6 km to 10 km - where it can radiate freely into space.

Figure 3: Illustration of the energy flux onto and off the Earth’s surface. On average, roughly 240 W/m^2 of solar energy reaches the Earth;s surface. This is re-radiated as infrared red light at wavelengths at which the atmosphere is opaque. The light is scattered, and some comes back to the Earth, and some makes its way further up the atmosphere. Eventually the light reaches a height – typically 6 km to 10 km – where it can radiate freely into space.

This process of multiple scattering goes on repeatedly until radiation makes it to an elevation of typically 6 km to 10 km above the Earth’s surface at which point the atmosphere is thin enough to allow radiation directly out into space.

Importantly, there are no ‘completely blocked bands’. If there were, our satellites would fly over the Earth at night and find no emission at all at some wavelengths: that is not what is seen.

What is seen is the ‘top of the fog’: the radiation from the highest part of the ‘fog’. Radiation at all wavelengths does eventually make its way through the atmosphere in a process of multiple random scatterings.

Increasing the concentration of carbon dioxide makes the atmosphere less transparent in some wavelength bands and, as we saw in the previous section, that inevitably drives an increase in the temperature of the Earth’s surface.

Calculating the sensitivity of the Earth’s surface temperature to an increase in carbon dioxide concentration is complex, but in fact our estimates have not changed much since Arrhenius’s first estimate in 1896.

Arrhenius calculated that doubling carbon dioxide concentration from the historical value of 280 ppm  to 560 ppm would cause an increase of 4 °C.

Now using supercomputers and complex climate models we estimate this sensitivity to be 3 °C ± 1.5 °C. The robustness of this estimate in the face of the overwhelming additional calculational complexity is testament to the fundamental simplicity of the physics involved.

Subtlety #2

This article is already long enough, but back when I was a few hours younger, I said I would comment on the effect of reflections at the top of the Earth’s atmosphere.

We can model this by splitting R1 into two series resistances describing transmission from the surface of the Sun to the top of atmosphere (R1a) and subsequent transmission through the atmosphere to the surface of the Earth (R1b). The equivalent circuit diagram is shown in Figure 4.

Figure 4. Modification of the equivalent circuit to describe reflection from the top of the atmosphere.

Figure 4. Modification of the equivalent circuit to describe reflection from the top of the atmosphere.

In this modification, R3 describes the reflection of light from the top of the atmosphere.

  • If there are lots of white cloud tops during the day, then R3 is small: it is small compared with the sum of R1b and R2, But notice that clouds at night don’t affect R3.
  • If very little light is reflected from white cloud tops during the day, then R3 is large compared with the sum of R1b and R2.

In practice, on average the flux of energy from the Sun is 340 watts per square metre at the top of the atmosphere, and about 100 watts per square metre are reflected into space. This indicates that R3 is approximately twice as large as the series sum of R1b and the components of R2.

Clouds

The reason I mention this additional complexity is because of the role of clouds. It is important to look at clouds from both sides, from up and down and from night and day.

The inevitable warming caused by increasing carbon dioxide concentrations will inevitably cause changes in the amount of water vapour in the atmosphere. And these changes can affect the pattern of clouds formed on Earth and give rise to effects which alter R1b – the transmission of visible light between the top of the atmosphere and the surface of the Earth.

Roughly speaking, additional cloudiness during the day could cool the Earth, reducing the warming effect. But additional cloudiness at night will warm the Earth.

On balance the effect is difficult to calculate, but our best estimates result in warming consistent with that observed experimentally.

Conclusions

This article is written for one individual: the Nameless American  who thinks that his cleverness and popularity means that their’gut belief’ that global warming is a hoax is correct. They are, sadly, ‘just wrong’.

I too would love to believe that global warming is a hoax, but it isn’t.

The electrical models I have described could be improved by adding some capacitances to the circuit to allow the dynamics of the changes in temperature to be simulated.

These electrical capacitances, would be analogous to the heat capacity of the top layers of the land and ocean surfaces of the Earth.

But there is not much point: scientists have done this calculation and the results are in. We have already made the measurements, and the results are in also.

The real argument for the ‘alt-right’ is this: if you think the economic benefits of burning unlimited coal and emitting unlimited carbon dioxide outweigh the costs: please make this argument. I disagree with you, but it’s a fair argument.

But don’t attack the science. Our understanding of this process is a collective triumph for humanity.

[November 21st 2016: Weight this morning 73.5 kg: Anxiety: High: off the scale]

 

 

Uncertain Uncertainty and Variable Variability

October 4, 2016
Graph prepared by John Kennedy illustrating the effect of some of the uncertainties. Any one of the blue of the blue lines - or an un-drawn similar line - could be what actually happened. We don't know - but all of them show significant warming.

Graph prepared by John Kennedy illustrating the effect of some (but not all) of the uncertainties in the data. Any one of the blue lines – or an un-drawn similar line – could be what actually happened. We don’t know – that’s the nature of uncertainty. The significant thing is that even considering the confounding factors, all of the estimates show significant warming.

Variable Variability

One of the real pleasures of attending WMO CIMO TECO last week was the chance to meet some of my heroes. And among them I finally met Victor Venema.

Victor is climate scientist whose primary interest is in identifying and removing biases from the instrumental temperature record. He is – in the very best sense of the word – a sceptic.

His blogVariable Variability – is one of my few ‘must reads’.

Uncertain Uncertainty

Victor’s last article drew together many representations of our instrumental temperature record to ask the question: what makes people pay attention to the fact that OUR PLANET’S SURFACE IS WARMING UP!

This shocking fact has gone from being widely denied or ignored to being widely accepted and ignored.

The aim of all the presentations Victor draws together is to fairly communicate the reality of the uncertainty of the conclusions drawn – but also that the warming trend is strong when compared with these uncertainties.

Alternative Reality

But Victor’s page does not (yet!*) contain the beautiful representation at the head of this page.

The animated graph was devised by John Kennedy from the UK’s Met Office and illustrates many of the possible curves – alternate realities – that are consistent with the data.

There are more curves that would be consistent with the data but John wasn’t quite sure how to represent them.

One of the most important ‘uncertain uncertainties’ that John didn’t include is called ‘coverage uncertainty’. It arises from the fact that the instrumental record derives from thermometers that are not optimally positioned around the globe.

When I wrote to him to ask permission to use the graph he said:

The coverage uncertainty has, I suspect, an important low-frequency component. We know HadCRUT4 has a tendency to slightly under-represent Arctic areas, which have been relatively warm these past 10 years. Over time, the balance of land and ocean changes too and we know these warm at different rates. The coverage uncertainty also has a high-frequency component too.

I will get round to writing a blog post about the wiggles at some point, but in the meantime I’m interested in what people think about it. Lots of the animated presentations that I see don’t obviously add anything beyond what the standard static time series graph would show, so one concern I have is, does it add anything to that? Is there any way we can improve the representation of uncertainty in our graphs and other visual aids, particularly where there are more complex error structures that can affect the interpretation?

I love John’s attitude. Critical of his own work and looking for feedback to improve it.

 

Certain Certainties

I think the animation does add something. Each line represents a possible ‘reality’ that is consistent with the data we have.

The animation shows which features persist from one ‘possible reality’ to another.

In general, a year which is hotter than it’s predecessor, stays hotter in all ‘realities’.

Critically, none of the realities consistent with the data reverse or cancel the overall warming trend.

And that makes it essentially certain that the warming trend is real. And that the world really is hotter than it has been for a long, long time.

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*The image is there now!


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