In the Dark Future

In a recent episode of The Infinite Monkey Cage, The End of the Universe, one of the panel (Brian Greene) made a comment about a future state in which no other galaxies would be visible.  He suggested that, at that time, it would not be possible to work out that the universe is expanding.

I think that he’s wrong about this.

Prior to the work of Hubble, we did not know about other galaxies, for all we knew, the universe consisted only of the Milky Way Galaxy.  If there was nothing to be seen outside of our galaxy, the background would just be a tiny bit darker than it is already and it would be entirely possible to naïvely think that the universe consisted of nothing more that we can see.  Amateur astronomers and galaxologists could argue about whether space outside the Milky Way extended infinitely or if there were some sort of closed border that our spaceships would eventually bump into if we were so bold as to travel outside the galaxy (the only observable galaxy, hence the term galaxologist, rather than cosmologist).

I say amateur here because I believe that there are at least two ways that professional physicists could work out that the universe is not limited to galaxy, that it is expanding and that there is no border that extra-galactic spaceships would bump into (and that the universe is not necessarily infinitely large).

Hubble not only discovered galaxies outside our own, he also worked out that the further a galaxy was away from us, the more red-shifted it was.  There is consistent relationship between the distance of a galaxy and its rate of recession, expressed in the Hubble constant, H_o.  From this observation, it can be worked out that the universe is expanding.

In the far future, all other galaxies will be so far from us that they will be receding at greater than the speed of light and no more light from them will ever reach us.

Note that distant galaxies will not be travelling away from us at greater than the speed of light – that is not physically possible.  All that will be happening is that the totality of space between them and us will be expanding greater than the speed of light.  It is conjectured that there is already a part of the universe that is receding from us at greater than the speed of light – which would be the case if the radius of the observable universe is greater than 13.7 billion light years.  An object that is 13.7 billion light years away from us would be receding at the speed of light, so anything further way than that would be receding at a greater rate.

Note that the observable universe is estimated to have a (comoving) radius about three times greater than 13.7 billion light years.

How can we see objects that are receding at greater than the speed of light?  It gets a bit tangled here due to the notion of simultaneity, and the question of whether it is possible to point to a universal “now”.  Generally, physicists are reluctant to suggest that there is a meaningful “now” that links us here on Earth and observers in a location that is more than 13.7 billion light years away, but if we are fast and loose with the facts and pretend that there is such a meaningful "now", then we could say that no light emitted from those distant observers “now” will ever reach us and no light emitted by us will ever reach them.  (We could more accurately say that we are outside of each other’s light cone and nothing either group does will affect the other – so we are not currently, and cannot ever in the future be, causally linked.)

That said, light emitted from such distant locations in the past can reach us, and it does.  It’s very much red-shifted, from the visible spectrum into microwave spectrum, in which we can see the cosmic microwave background – remnants of the big bang (although it’s not really from the big bang per se, but rather from about 370,000 years later, just after the photon epoch, at the beginning of the somewhat counterintuitively named “dark ages”).

Note that a location that was, at the time, 370,000 light years away from us, “now” looks as if it were 13.7 billion light years away from us (on the erroneous assumption of a static universe).  It’s just that the expansion of the universe has meant that it took about 13.7 billion years for the radiation to reach us.

In the dark future, when our galaxy is the only thing visible to the naked eye, there will still be a cosmic background of some sort (although precisely which spectrum it is in will have changed).  If physicists think to check, there will be evidence of something out there beyond the galaxy, and the fact that we can’t see what caused it now may well give them enough evidence to postulate that the universe used to be smaller and motivate them to work out that the universe is still expanding.

If Hubble had not already provided an explanatory framework, the existence of a cosmic microwave background, whenever it was discovered, would have required some explanation.

There was also Einstein’s “greatest blunder”.  He was convinced that the universe was static, despite the fact that his equations were telling him that the universe was unstable and would either expand or contract.  This led him to introduce a cosmological constant that balanced the books and made the universe static.

Einstein conceded that this was an error when Hubble showed that the universe was expanding, but the point is that there is evidence of the universe expanding in the equations and some fiddling is required to make the universe appear static.  A future analogue of Einstein may not be so wedded to a static universe or a later tinkerer may question the introduction of an arbitrary cosmological constant and voila, you have evidence of expansion.

Finally, once it is understood that light is speed limited, it is possible to go through the process of amending the Galilean transforms and reach Special Relativity that way.  Once you have that, it becomes clear that space and time are mutable and someone like myself can reach the conclusion that the universe might be expanding (like I did quite a long time ago) and not be persuaded to abandon that line of thinking (like I was for a while) because of the odd notion of a universe expanding the way it does. 

Mathematics tells us that the universe is expanding and while observation makes universal expansion simpler to comprehend, that first-hand observation isn’t strictly necessary. 

The Very Model of Climate Change Concern

A friend of mine, JP, started all of this when writing:

If you were to ask me 2 years ago what my key understandings were about climate change, I would have said the following:

Sea ice is rapidly shrinking (summer arctic sea ice to be gone by 2015)

Sea levels are rising and accelerating

Polar bear populations are under stress (have increased in the last 20 years)

The levels of glacial retreat around the world are unprecedented (similar retreats have been seen in the last century)

97% of scientists agree that global warming is real and an urgent problem

Any scientist who is skeptical about the claims made about climate change is a "denier" and is funded by oil/resource companies

We are seeing an increase in extreme weather events (they are actually getting less common)

Climate models are accurate in their predictions 

Every one of those things is either totally false, or a largely exaggerated claim.

This is the eighth in a series based on my response, which itself was split over a few emails.  The first was Ice Extent Challenge (in which I provided a little more context about JP) and was followed by Sea Levels Rising, Polar Bears and Climate Change, Glacial Retreat, A Worry of Climate Change Scientists, Denying Denialism and Weathering a Storm of Climate Denial.  Some of the issues may also be touched on in a series of articles on the nature of climate denialism.  Please also note the caveat.

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JP’s Claim: The statement “Climate models are accurate in their predictions” is either totally false or largely exaggerated

Note that JP is most familiar with statistical modelling.  JP has modelled demand on a supply chain and it’s amazingly accurate.  Based on statistical data from previous years, and possibly a whole suite of data that I am not aware of, JP can get very close to current demand.  It’s brilliant stuff.  However, it should also be noted that climate models are not, repeat NOT, and – just to make this perfectly clear – climate models are NOT statistical models.  They are models of physical processes.

I’ve long been of the opinion that models are never entirely accurate, no matter what sort of model they are, and that the only completely accurate model of the universe is … the universe.  This applies also to systems that are smaller than the universe, even though processing power necessary to do the modelling decreases significantly as you approach more human-sized scales.

You don’t need to take my word for it, you can just consider the three body problem.  Start with two bodies in otherwise empty space that are acting on each other gravitationally, say a star and a planet.  They will orbit the centre of their combined mass with a speed and separation that is inversely proportional to their relative mass (the heavier body will have a smaller separation from the centre of the combined mass than the lighter one, they will share the orbital period and thus the lighter one will have a higher speed having a greater distance to cover – with something as massive as a star compared to a planet, ).

Then consider three bodies, specifically two stars and a planet – like Tatooine:

Note that the planet orbits the pair of stars, since it’s the light one of the three-some.  This is not solvable analytically, it can only be solved numerically, meaning that you have to plug the figures in an run the problem (like at the link).  Now in the second program window, if you fiddle with the code to make one of the stars more than twice as heavy as the other, something strange happens (at a factor of 2.2):

At higher values, the binary stars lose the planet entirely (pretty much immediately at a factor of 3).

Now imagine trying to predict where the planet in the image above will be after 50 years.  It’s easy enough to run the simple program and find out, but you have some issues that are going to affect your results.  How accurate is your value of G?  How accurate are your masses?  How accurate were your initial conditions (speed and direction)?

Your inaccuracy in any of these figures are going to affect your results and that’s when you are assuming a spherical cow.  The bodies in question are not perfect point masses, they are two balls of gas and … a planet, which might be a third, smaller ball of gas or a conglomeration of rocks – and we are assuming only one single rock in the system.

The upshot of this is that we can predict with great accuracy where the planets in our solar system will be in the short term, but have no idea where they will be in 100 million years – and it’s not that we just haven’t worked it out yet but rather that, at that longer scale, the solar system is chaotic.

Now consider a model involving 10⁴⁴ gas molecules (the atmosphere), interacting with 10 million cubic kilometres of water (admittedly only the top layer of it, so more than 350 million square kilometres times the average significant depth, whatever that is) and just under 150 million square kilometres of land surface which is covered variously by deserts, forests, ice, mountains, lakes, grasslands and, relatively recently, cities and towns.  Then factor in the vagaries of the sun, which has its own cycles which do affect us (for example with solar minima, grand or otherwise) and all the different products that end up in the atmosphere (CO2, methane, aerosols, water, etc).

Climate models don’t even bother trying to be accurate.  Instead, they do what is call parametrisation, breaking the planet up into gridboxes – the size of which vary depending on the precise application (and the computing power available).  The smallest gridboxes are usually in the range of about 5km, with clouds sometimes being modelled at 1km – and this is way too coarse for most clouds.

Even at the finest parametrisation used today, there will still be inaccuracies inherent in the model.  These are expected and discussed with an eye to minimising them (see “Are Climate Change models getting better?” which starts on page 824 at the linked document).  In part because the models are never perfect, the IPCC and climate scientists in general talk about trends and projections rather than predictions.  The trend observable in all the models across the standard scenarios (RCPs 2.6, 4.5, 6.0 and 8.5) is that the more you increase the amount of CO2 in the system, the more the temperature rises.

Again, you don’t need to take my word for this.  The outputs of the models are freely available (admittedly they take some time to figure out).

I compared the results against the temperature measurements available from NASA and NOAA which, without a model overlay, looks something like this:

Once I converted to absolute (rather than anomaly) values and corrected for an oddity in starting temperatures, the HADGEM2-ES model results look like this:

Be very careful about just accepting this though.  I don’t understand the starting temperature oddity, but basically not all models had the same temperatures at the beginning of the run, or the same date for the beginning of the run.  I fixed for that and used this model as an example because, without that correction, the results were offset by about 0.2 degree (noting that I used an RCP8.5 run).  The corrections I made did not change the trend, they just shifted the entire yellow line up a bit.  Additionally, I don’t know precisely what was fed into the model.  They seem to have included some volcanoes (which pump aerosols into the atmosphere and push down the temperature for a short period) and anthropogenic aerosol production seems to be accounted for, but this is just guesswork on my part.

With those caveats in mind, this is what the results look like from a raft of models (note that HADGEM is not in this one, so the yellow line represents output from a different model):

There’s a range of about a degree between the models, and about four of them are consistently higher than the measurement (although, prior to my adjustment, they were all below so perhaps I’ve messed it up somehow – and that messing up could be contributing to the spread as well) … but note that the overall trend is precisely the same.  Over the period 1880-2020, there is a rise in temperature of about a degree – which is consistent with the measurements.

Therefore, noting that the models are not expected to be wholly accurate, indicating temperature rise in pretty much precisely what we have experienced, and that they provide projections rather than predictions, JP is simply wrong when claiming the climate change models predictions projections are inaccurate.  They are a lot more accurate than one might have predicted.

Ignoring the Climate

So far, I’ve looked at three approaches used by climate denialists:  to blankly deny that anything is happening to the climate, to distract from the topic and to minimise the effects and/or evidence.  The fourth that I have identified is to ignore, to ignore the whole topic (which is more of a denier tactic than a denialist one) or to ignore selectively (in other words to cherry-pick).

Ignorance is a key element of the other three approaches, but I think it’s worth bringing it out as a separate approach in itself – because cherry-picking is such an important part of the denialist effort.  (I did mention cherry-picking in On Climate Denialism - Deny Deny Deny! and Misdirection and Misinterpreting the Climate and Climate Emergency? What Climate Emergency? and, well, quite a few earlier articles on climate change).

First, consider the denier.  Note that a denier is not a denialist – where I have defined a denialist as “someone who has taken the time to review at least some of the available climate change data and, for whatever reason, rejects enough of it reach a position that climate change is not real, or is not anthropogenic, or is not as serious as it’s being made out to be” and a denier is “an ignorant person who just denies the existence of climate change (to some extent) based on information taken on face value that was originally sourced from a climate denialist”.

There’s a certain amount of synergy among denialists, they take information from each other so they could be called deniers to the extent that they don’t check each other’s work.

I would go so far as to say that all deniers ignore the majority of the information out there on climate change.  They don’t go to the reports that the UN’s Intergovernmental Panel on Climate Change (IPCC), they don’t go to NASA, or NOAA, or any local body responsible for monitoring the climate (Australia, United Kingdom, Sweden, Germany, France, South Africa).  They might, however, watch some local equivalent of Fox News or read some local version of the Murdoch press (News Corp) and shape their opinions based on the advice of people who are possibly less ignorant, but who have been particularly selective in what information they have taken on board.

Denialists don’t have the luxury of passively ignoring all the information available to them, instead they need to have an idea of what is out there so that they can actively ignore that which is inconvenient and carefully carve out factoids that support their case.

An example of this relates to the Federation Drought, which was actually a number of droughts that ran into each over around the year 1900, when Australia was in the process of federating into one country rather than remaining as a few colonies of the United Kingdom.

A family member sent me a post to what looks very much like an astroturf group, Farming in Australia for real farmers and supporters. (noting that the full stop is part of the name of the group).  This Facebook group was set up by a(n unsuccessful) right-wing politician who stood for the Shooters, Fishers and Farmers Party.

Now there are two ways to approach something like this.  The first is to track down the origins of the post, which was presented to me like this:

History is a useful unless it's ignored or even overlooked 

‎Bernie Jackson‎ to Farming in Australia for real farmers and supporters.

October 27, 2019

" CLIMATE CHANGE"
During the 7 year period from 1896 to 1903, before the vast land clearing, Industrial Revolution, before the first world war, and the second world war, before the millions of cars were on the road and the vast amount of coal mining to date, and the Green Party, I was looking at this period and here are some of the facts from the period.
. Rainfall for this period was 46% below the previous wet period
.Federation Drought, Heatwaves, Bush Fires and Dust storms, associated with 40% livestock losses in Queensland.
.Livestock numbers in Queensland reduced from 6.5 million to 2.5.million (cattle), and from 19 million to 7 million ( sheep).
.Western New South Wales, impacted by soil erosion, and woody weed infestation (1898-1899).
.Properties in the Western New South Wales were abandoned with collapse in carrying capacity, resulting in the Royal Commission investigating financial stress in the Western Division.
.Sir Sydney Kidman acquired properties, and nearly lost all by 1901, due to severity and wide spread nature of this drought.
.Tropical Cyclone Mahina struck Bathurst Bay ( Cape York) on the 4th March 1899, the surrounding region suffered a massive storm surge from the category 5 system, killing over 400 people - the largest death toll of any national disaster in Australian History.
Reports recorded that grass was ripped from the ground on the islands offshore and that fish and dolphins were left in trees,15 metres above sea level
This all happened before the new catch cry of "GLOBAL WARMING", and "CATASTROPHIC".
The words they use now to frighten the public.
Puppet Palaszczuk should look back at previous records to see what has happened in years gone by, and order an enquiry into the recent fires in National Parks, she would then find it is the incompetence of National Parks management. Instead of making wild statements, GLOBAL WARMING.!
Reference- QUEENSLAND GOVERNMENT
ECOSCIENCES PRECINCT
Web: www.longpaddock.qld.gov.au
I sympathise with the devastation that farmers and public have endured over the past few years. Is this a matter of history repeating it's self.

There is enough idiosyncratic wording and punctuation in the text that it’s not going to be too hard to see where it really came from.  Perhaps it really was written by a Queensland farmer called Bernie Jackson (albeit on 26 October rather than 27 October 2019), but no.  I found that it was written by Rex Berry (according to Colin Boyce on 1 March 2019), by Angelina Nic (on 28 October 2019), by NighthawkNZ (on 27 October 2019), by Stand Up For Australia-Melbourne (on 1 March 2019), by Bernie Delany (on 12 November 2019), by Claude Bedrossian (on 11 November 2019), by Climate Truth (on 21 October 2019), by Cronin Ken (on 18 January 2020).  A snippet of it also appears to have been written by Chet McAteer (on 9 January 2020).  This is the sort of thing that you see when someone has a barrow to push.

I had to dig deep to find that, apparently, Rex Berry was the original source, but it’s been spread wide and thin ever since – with that post being shared more than 19,000 times.  Most of his other posts get one or two shares although another one, about the climate and bushfires did get twenty-six.  It’s not hard to comprehend why some people are tempted to post inflammatory stuff about climate change.

Another approach, the one I actually took with my relative, is to address the content of such a post.  It’s worth a reminder that I am talking about how selectively ignoring facts and evidence is a key element to being a denialist.  Much of what Rex wrote is true enough. 

The Federation Drought did happen.  Having followed a particularly wet spell, that drought was perfect for contributing to bushfires (a lot of growth followed by an extended drying out period, leaving plenty of readily ignitable fuel) – and there were some major bushfires in 1896 and 1898 which denialists are keen to point out, while skilfully ignoring that in 2019 (but not in in the 1890s) we had aerial support, modern firefighting ground vehicles, radio communications and a regime of fuel reduction.

There was a Category 5 cyclone in 1899, Mahina, although dolphins 15m up in trees appears to be a bit of an exaggeration (or misremembering of dolphins being found on 15m cliffs).

Rex argument pivots on the reader being ignorant with respect to a number of key facts: no-one is denying that Australia has experienced droughts regularly in the past, Mahina was a one in two to three hundred year storm (more on Mahina in a moment), climate scientists have not categorically stated that there is a direct link between climate change and drought frequency and severity in Australia and climate scientists have instead indicated that storms may in fact decrease in number, although they are expected to increase in intensity.

As I responded to the person who sent me Rex Berry’s work:

No-one is suggesting that intense storms haven’t happened in the past.  The fact that there was one in 1899 is immaterial.  The question is more about what is happening in general with storms over the past 100 years or so.  I have, coincidentally, been researching storms and the following is salient:

if we look at Cat 4 hurricanes (in the Atlantic), we see:

Which does seem to have a distinct trend to it.  If we did something similar with Cat 5s, it would look like this:

Which again appears to have something like a trend to it.

and:

In IPCC report AR5 Part A, there is reference to Severe Storms:

Severe storms such as tropical and extratropical cyclones (ETCs) can generate storm surges over coastal seas. The severity of these depends on the storm track, regional bathymetry, nearshore hydrodynamics, and the contribution from waves. Globally there is low confidence regarding changes in tropical cyclone activity over the 20th century owing to changes in observational capabilities, although it is virtually certain that there has been an increase in the frequency and intensity of the strongest tropical cyclones in the North Atlantic since the 1970s (WGI AR5 Section 2.6). In the future, it is likely that the frequency of tropical cyclones globally will either decrease or remain unchanged, but there will be a likely increase in global mean tropical cyclone precipitation rates and maximum wind speed (WGI AR5 Section 14.6).

Note that there was a prediction that the number of storms will (likely) decrease.  What we see, however, is the number of storms remaining about the same, but the strength of them increasing on average, leading to a greater number of higher rated storms.  The Atlantic has a higher concentration of storms than other basins (this might be why Magellan gave the Pacific its name, ie the [relatively] calm ocean) and there are twice as many cyclones/hurricanes in the Northern hemisphere than the south (probably due to the Northern being the warmer hemisphere). 

Additionally, the Atlantic is much smaller than the Pacific, which means that storms that are generated there are more likely to make landfall at full strength and that is a key also to the newsworthiness of Mahina.  Mahina made landfall at Cape York while at Cat-5 level (note that of Pacific storms, which are by definition North Pacific Storms, only 18 have reached Cat-5 since 1959 and none of them made landfall – no-one cares too much about a super storm that only happens at sea [well, seafarers and fishermen, perhaps].  It’s entirely possible that no-one would remember today Mahina if it got to Cat-5 out in the middle of the Coral Sea and made a less intense landfall). 

There’s another question though, why was that cyclone particularly bad?

It was because two factors combined to make it so:

It wasn’t just one storm, it was two.  Therefore, it was a bit of an outlier (a 1:200 to 1:300 year event) and should not be taken as indicative.  If we start seeing storms like this every second year, then we ought to start worrying.

Picky I know, but the industrial revolution is more commonly said to have started in 1760 (at least the First Industrial Revolution), with coal production rising significantly in the 1790s (to feed steam engines).  I think the author may be referring to the second industrial revolution, also known as the Technological Revolution which was, in part, dependent on the introduction of fossil fuels on a major scale, with petroleum taking off in the 1850s.  I know Australia tends to be behind on some things, Queensland doubly so (with waking up to the climate change related issues being one of those things), but I don’t know how this guy can think that 1903 was before the industrial revolution.  The first railway in Queensland opened in 1865 and the steam train was a product of the industrial revolution.  They didn’t use donkeys to pull the trains:

That is definitely a steam locomotive, although initially wood or coke was the fuel.  The locomotives began being converted for coal burning after an edict by the Commissioner for Queensland Railways in December 1870.

Other than that, the author appears to have dug up the Federation Drought, which we already know about, and tried to present it as something new.  We have droughts in Australia.  Note that the link between climate change and drought is nuanced.  Warmer air holds more water, which could mean that some areas which are currently particularly drought prone will become wetter (more tropical), while other areas, further south and nearer the coasts, will become drier and more prone to drought.  The AR5 findings were:

·       Low confidence in an observed global-scale trend in drought or dryness (lack of rainfall) since the 1950s, due to lack of direct observations, methodological uncertainties and choice and geographical inconsistencies in the trends;

·       High confidence that the frequency and intensity of drought since 1950 have likely increased in the Mediterranean and West Africa (although 1970s Sahel drought dominates the trend) and likely decreased in central North America and northwest Australia;

·       Low confidence in attributing changes in drought over global land areas since the mid20th century to human influence owing to observational uncertainties and difficulties in distinguishing decadal-scale variability in drought from long-term trends;

·       High confidence for droughts during the last millennium of greater magnitude and longer duration than those observed since the beginning of the 20th century in many regions.

In other words, increased drought in Australia is not a climate change prediction.  So, the fact that we had a long drought a hundred and twenty years ago, give or take, is immaterial.  (Note: the possibility of human drivers on drought is raised as an emerging area of research – it’s not a claim that humans caused the droughts now or in the past.)

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I have great confidence that Rex Barry was entirely ignorant of most of that and that it was that ignorance that enabled him to put together a post that gave him his fifteen minutes in the spotlight.

More well-established denialists, such as Tony Heller, Joanne Nova and Anthony Watts (basically anything where he writes about “the pause”), are unlikely to be so comprehensively ignorant and instead they aggressively cherry pick, even the more scientifically inclined collaborators have been shown to cherry pick.  Note that the fact that these people are masters of cherry picking does not stop them from accusing others of cherry picking, in fact it’s one of their favourite accusations.

Weathering a Storm of Climate Denial

A friend of mine, JP, started all of this when writing:

If you were to ask me 2 years ago what my key understandings were about climate change, I would have said the following:

Sea ice is rapidly shrinking (summer arctic sea ice to be gone by 2015)

Sea levels are rising and accelerating

Polar bear populations are under stress (have increased in the last 20 years)

The levels of glacial retreat around the world are unprecedented (similar retreats have been seen in the last century)

97% of scientists agree that global warming is real and an urgent problem

Any scientist who is skeptical about the claims made about climate change is a "denier" and is funded by oil/resource companies

We are seeing an increase in extreme weather events (they are actually getting less common)

Climate models are accurate in their predictions 

Every one of those things is either totally false, or a largely exaggerated claim.

This is the seventh in a series based on my response, which itself was split over a few emails.  The first was Ice Extent Challenge (in which I provided a little more context about JP) and was followed by Sea Levels Rising, Polar Bears and Climate Change, Glacial Retreat, A Worry of Climate Change Scientists and Denying Denialism.  Some of the issues may also be touched on in a series of articles on the nature of climate denialism.  Please also note the caveat.

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JP’s Claim: The statement “We are seeing an increase in extreme weather events” is either totally false or largely exaggerated and “they are actually getting less common”

There are two factors here which need to be extracted – the frequency of extreme weather events and the severity of extreme weather events.  JP’s parenthetical codicil seems to indicate that it’s a question of frequency while, from my reading, it’s more about severity.

Then there is the question of timing.  Is it merely about historical records, about which you think there would be little controversy?  Or is it about the projections produced by climate modelling?

If it’s related to climate modelling, then we must consider both the accuracy of the models and the accuracy of the data.  It’s quite possible that models, especially earlier models, have been inaccurate in their projection of extreme weather events – underlying assumptions may have been wrong, our understanding of the physics may have been immature, parameterisation may have been too coarse and the data input to the models is unlikely to have been absolutely correct (for instance there will be rounding of datapoints).

In IPCC report AR5 Part A, there is reference to Severe Storms:

Severe storms such as tropical and extratropical cyclones (ETCs) can generate storm surges over coastal seas. The severity of these depends on the storm track, regional bathymetry, nearshore hydrodynamics, and the contribution from waves. Globally there is low confidence regarding changes in tropical cyclone activity over the 20th century owing to changes in observational capabilities, although it is virtually certain that there has been an increase in the frequency and intensity of the strongest tropical cyclones in the North Atlantic since the 1970s (WGI AR5 Section 2.6). In the future, it is likely that the frequency of tropical cyclones globally will either decrease or remain unchanged, but there will be a likely increase in global mean tropical cyclone precipitation rates and maximum wind speed (WGI AR5 Section 14.6).

Note that this IPCC report is a key reference document with respect to climate change.  It basically collates evidence from 9200 peer-reviewed studies and concludes that climate change is happening, that climate change is due to human activity and that the effects of climate change (both current and future) are worth worrying about.  Per Wikipedia, the principal findings were:

General

·        Warming of the atmosphere and ocean system is unequivocal. Many of the associated impacts such as sea level change (among other metrics) have occurred since 1950 at rates unprecedented in the historical record.

·        There is a clear human influence on the climate

·        It is extremely likely that human influence has been the dominant cause of observed warming since 1950, with the level of confidence having increased since the fourth report.

·        IPCC pointed out that the longer we wait to reduce our emissions, the more expensive it will become.

Historical climate metrics

·        It is likely (with medium confidence) that 1983–2013 was the warmest 30-year period for 1,400 years.

·        It is virtually certain the upper ocean warmed from 1971 to 2010. This ocean warming accounts, with high confidence, for 90% of the energy accumulation between 1971 and 2010.

·       It can be said with high confidence that the Greenland and Antarctic ice sheets have been losing mass in the last two decades and that Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent.

·        There is high confidence that the sea level rise since the middle of the 19th century has been larger than the mean sea level rise of the prior two millennia.

·        Concentration of greenhouse gases in the atmosphere has increased to levels unprecedented on earth in 800,000 years.

·        Total radiative forcing of the earth system, relative to 1750, is positive and the most significant driver is the increase in CO
2's atmospheric concentration.

Models

AR5 relies on the Coupled Model Intercomparison Project Phase 5 (CMIP5), an international effort among the climate modeling community to coordinate climate change experiments. Most of the CMIP5 and Earth System Model (ESM) simulations for AR5 WRI were performed with prescribed CO2 concentrations reaching 421 ppm (RCP2.6), 538 ppm (RCP4.5), 670 ppm (RCP6.0), and 936 ppm (RCP 8.5) by the year 2100. (IPCC AR5 WGI, page 22).

·        Climate models have improved since the prior report.

·        Model results, along with observations, provide confidence in the magnitude of global warming in response to past and future forcing.

Projections

·        Further warming will continue if emissions of greenhouse gases continue.

·        The global surface temperature increase by the end of the 21st century is likely to exceed 1.5 °C relative to the 1850 to 1900 period for most scenarios, and is likely to exceed 2.0 °C for many scenarios

·        The global water cycle will change, with increases in disparity between wet and dry regions, as well as wet and dry seasons, with some regional exceptions.

·        The oceans will continue to warm, with heat extending to the deep ocean, affecting circulation patterns.

·        Decreases are very likely in Arctic sea ice cover, Northern Hemisphere spring snow cover, and global glacier volume

·        Global mean sea level will continue to rise at a rate very likely to exceed the rate of the past four decades

·        Changes in climate will cause an increase in the rate of CO2 production. Increased uptake by the oceans will increase the acidification of the oceans.

·        Future surface temperatures will be largely determined by cumulative CO2, which means climate change will continue even if CO2 emissions are stopped.

The summary also detailed the range of forecasts for warming, and climate impacts with different emission scenarios. Compared to the previous report, the lower bounds for the sensitivity of the climate system to emissions were slightly lowered, though the projections for global mean temperature rise (compared to pre-industrial levels) by 2100 exceeded 1.5 °C in all scenarios.

The IPCC report is by no means a climate denial document, but even so, it states that the number of tropical cyclones (including hurricanes and typhoons, which are basically the same thing in a different geographical location) will either decrease or stay the same and it’s only the severity that might increase, with increased global mean windspeed and precipitation rates.  The only quantitative statement I could find on cyclones was this (page 247): “In the tropics, the intensity of cyclones is projected to increase 2 to 11% by 2100, which may increase soil erosion and landslides (Knutson et al., 2010).”  Given the timescale involved, it would be unsurprising if there was little or no indication of an increase in cyclone severity in the recent past.

It should be noted that cyclones have a maximum potential intensity and thus a maximum windspeed (about 100 m/s or 360 km/hr), but so far the top speed measured was 345 km/hr in 2015.  (Prior to that, the record was 305 km/hr in 1980.)

Therefore, even if the ocean is warming and that provides more energy to spin up cyclones, then there’s still going to be an upper limit.   It would be reasonable think though that a warmer ocean would power a storm for a longer period and a greater proportion of storms would reach Cat 5.

There is a problem associated with assessing the number and severity of storms, related to the news cycle.  The whole world will hear about a storm that affects the US for days, but rarely will we hear anything about any storm that wipes out small, remote islands without a large tourist trade.  The Union of Concerned Scientists did however report an increase in hurricane activity in the North Atlantic:

Note that there is a downwards trend for hurricanes that reach the US.  The total number of hurricanes appears to be about even (on average) or perhaps increasing, but only by a little.  The data there says nothing about strength though, or duration of the storms.  The same organisation reports that there does not seem to be an increase in hurricane activity across the world, with about 90 per year, mostly in the Pacific.  NOAA report basically no change in the number of storms and their models predict fewer storms, but these storms would produce more precipitation, they would be more intense and more of them would be Cat 4 or 5.  This is also a bit hard to track, I don’t know if they bother recording a storm if it doesn’t reach land, but I am going to go out on a limb and say that they pretty much all do (reach land that is because a cyclone just keeps getting stronger while over a warm sea and will only lose power if it ends up over land or cooler water).

Looking at the records for the Atlantic, there were 2 Cat 5 in the 1950s,  (6 in the 1930s, but there don’t seem to be records for the 40s), 4 in the 60s, 3 in the 70s, 3 in the 80s, 2 in the 90s, 8 in the 00s, and 6 in the 10s.  They seem to be getting stronger, with 5 out of 6 being at 280km/hr or less in the 30s and 4 out of 5 being 280km/hr or more in the 10s, the most recent being 295km/hr (beaten only by Allen in 1980).  There’s an oddity in that in the past, there is a correlation between pressure and top windspeed, generally the lower the pressure, the faster the wind – but in the 2010s, all of the storms had higher pressures despite the wind being fast (recent slower storms were all quite short lived as a Cat 5, half an hour, three hours and six hours – these were basically ambitious Cat 4 hurricanes that didn’t really have the legs to become a proper Cat 5).

I don’t know whether there is enough data there to make any conclusions.  But if we look at Cat 4 hurricanes (in the Atlantic), we see:

Which does seem to have a distinct trend to it.  If we did something similar with Cat 5s, it would look like this:

Which again appears to have something like a trend to it.

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Going back to JP, it was claimed that the statement “We are seeing an increase in extreme weather events” is either totally false or largely exaggerated and “they are actually getting less common”.

This just does not seem to be true.  There appears to be about the same number of severe storms, cyclone or hurricanes, but there is a distinct increase in the number of both Cat 4 and Cat 5 cyclones.  NOAA reports “that, after adjusting for such an estimated number of missing storms, there remains just a small nominally positive upward trend in tropical storm occurrence from 1878-2006. Statistical tests indicate that this trend is not significantly distinguishable from zero.”   They conclude: “In short, the historical Atlantic hurricane frequency record does not provide compelling evidence for a substantial greenhouse warming-induced long-term increase.”  That would indicate that the increase in Cat 4 and Cat 5 storms is at the expense of less intense storms, or rather those storms that do happen are more likely to be intense.

This, in any rational interpretation, means that we are seeing an increase in number of extreme weather events and, on average, weather events are becoming more extreme – although it is conceded that the number of weather events themselves are not necessarily increasing in number.

Therefore, with regard to weather events, the evidence does not support JP’s claim.