Discussion > Are Geological Paleo-Climate Records Relevant to The Climate Debate?
With reference to flood records there are proxies such as varved sediments. The Lake Amersee record has a flood record going back 450 years that shows flood frequencies to be significantly greater during the little ice age. See Czymzik et al, 2010, Water Resources Research, vol 46. doi:10.1029/2009WR008360
Paul Dennis
Paul,
My view is that flooding is a tricky issue, because it's not a direct climatological consequence of a warmer world; it's a potential consequence of changes to precipitation. As I understand it, an emergent property of climate models is that relative humidity remains constant. If this does occur, then we'd expect the water vapour content of the atmophere to increase at about 7%/K and precipitation to increase at 2%/K. However, one expectation is that more precipitation will ocur in what are currently heavy precipitation events, so we'd expect an increase in the intensity and frequency of extreme precipitation events. This could lead to increased flooding, but that's a much more complex issue.
There are, however, a couple of things to bear in mind. One way that there could be little change in precipitation is if RH increases with warming. However, given that water vapour is a greenhouse gas, this would imply higher climate sensitivity. Alternatively, relative humidity reduces as we warm. This would suggest that climate sensivity is on the lower side, but would suggest an even greater increase in precipitation, with potential implications for flooding.
...and Then There's Physics
aTTP:
Do we have records that go back more than 250 years?Well, according to Dame Julia Slingo we do. Do you not trust her? Mind you, it may surprise you, but the printed and written word gives us records and accounts going even further back! Isn’t that amazing! This is how we know so much about, say, the Great Fire of London, or the Great Storm of 1703. Isn’t it truly amazing that people actually sat down and wrote about events as they happened? Thanks to what so many have written in centuries past in that they can give us a lot more data than counting tree rings of a couple of dozen trees – amazing!
Radical Rodent
RR,
That doesn't necessarily follow from what you quoted. I will add that I was called a git here for apparently being patronising ;-)
...and Then There's Physics
aTTP,
I agree. Flooding is a very tricky issue. Not least because it is affected so much by land use changes, modern building etc. that all impact on storage in the unsaturated zone etc. Long rainfall records and proxies for rainfall amount would be very useful here. Having said that flooding events, at least as recorded at Lake Amerssee seem to be greatest during the little ice age.
Setting aside climate models one might rationalise this as being the result of increased temperature gradients between the source regions for water vapour and the sites of precipitation. The distribution of net evaporation-precipitation peaks strongly in the tropics where evaporation from the ocean dominates. I'm not sure how much the tropics are warming but possibly less than high latitude regions. Therefore one might expect the flux towards these regions to decrease somewhat due to a lowered temperature gradient. Interestingly, in the paper I referenced the authors ascribe the changes to solar effects on precipitation.
In the absence of good quality data I'm not impressed by generalisations from climate models such as a 7%/K increase in water vapour and 2%/K increase in precipitation, particularly when describing regional patterns. It is too easy to say 'is consistent with' etc. which really isn't strong evidence. Are there any models run for say the little ice age that show how the intensity and frequency of intense precipitation events might vary? I don't know.
I think we both agree that absent good quality data we might go round debating this for a long long time. Hence my call for support for very high quality monitoring and proxy studies. I would say that as I'm an isotope geochemist!
Paul Dennis
In the absence of good quality data I'm not impressed by generalisations from climate models such as a 7%/K increase in water vapour and 2%/K increase in precipitation
Sure, but that wasn't quite what I was getting at. If RH remains constant, then this is what we would expect (on average). However, if RH goes down then we would expect an increase in precipitation and a less sensitive climate. If RH goes up we'd expect a decrease in precipitation and a more sensitive climate. I don't think there is a physically plausible scenario where you can have both (again, on average).
...and Then There's Physics
Oh, and when I said "increase" and "decrease" above, I meant relative to RH remaining constant.
...and Then There's Physics
aTTP: well, according to the BBC: 'Dame Julia said the UK had seen the "most exceptional period of rainfall in 248 years."' In saying that, she is implying that there are records over the 248 years, such that she can declare with such confidence, "most exceptional period of rainfall in 248 years". (Okay, so the original was rounded up to 250…meh…) What other conclusions could be drawn from the statement: "most exceptional period of rainfall in 248 years"?
Then there was the Great Storm of 1703. Over 300 years ago, but also when temperatures are accepted as being noticeably cooler than recently; if this warming is going to cause catastrophic weather events (except that most of what is being described as “catastrophic weather events” can only really be blamed on… well… weather), what could these catastrophic weather events be caused by?
Radical Rodent
RR,
I don't know the answer. I'm simply pointing out that what Julia Slingo said does not immediately imply that we have a longer record. It could be that that is the length of the reliable record. I don't think it follows that the record has to be longer than 248 years.
What I will add, though, is that the expectation is not necessarily that we will see events that we've never seen before. The expectation is that we will see an increase in the frequency and intensity of these events. Of course, we might see an event that that has never occured before in any record, but that we can find evidence for events in the past that match extreme events today is not some kind of evidence against AGW.
...and Then There's Physics
aTTP,
it's not immediately intuitive to me what the effects would be. As far as the water cycle is concerned we're actually talking about comparatively small changes in temperature and temperature gradients as well as possible RH. Moreover, RH changes might be different in different regions. The effect this has on precipitation, at least to me is not clear and I'm not sure it is to anyone else beyond statements such as 'is consistent with'.
I certainly wasn't arguing for both increased climate sensitivity and precipitation!
Paul Dennis
I certainly wasn't arguing for both increased climate sensitivity and precipitation!
I realise. My point was quite simply that increased RH means reduced evaporation, and vice versa. The main climatological consequence of warming is precipitation (not flooding). As I understand it, the only way we could see little change in overall precipitation as we warm is if RH increases. That's all I was really getting at. Of course, there could be regional variations, etc.
...and Then There's Physics
Floods are obviously associated with storms and there is much evidence that storminess was greater in the LIA than at present. Evidence comes from weather reports at the time (commonly associated with shipwrecks) and in the form of surviving physical evidence like increased sand transport on land (eg Brecklands) or on the coast. Lamb, for example, believed wind speeds were much higher then than at present.
Much of the evidence is detailed in Brian Fagan's fine book The Little Ice Age.
Alan Kendall
aTTP says....."the rate at which it has warmed has probably been faster than at any other time during the Holocene."
the data to support that speculation are very tenuous - similar rates of increase have probably occurred several times earlier in the Holocene.
For example:-
50 year mean temperatures over central England rose about 1.25ºC between 775 and 650 ybp ( Lamb 1966a)
Chinese temperatures rose 2ºC between 850 and 1150 AD ( Hsieh 1976)
New Zealand cave temperatures rose 1ºC between 1350 and 1450 AD.
Temperature rises comparable or faster than the rise in the last 150 years have occurred at least five times since the 10.3 ky event. The rise following the cold nadirs of the 10.3, 9.3 and 8.2 ky events was almost certainly larger and faster than that which has occurred in the last 150 years . Indeed most cooling events recorded in the NORTHGRIP dO18 data are followed by rapid temperature rises.
Spectator
Paul Dennis
I suggested a polynomial because a variety of lines of evidence, from monastery and estate records through freezing of ponds and the River Thames suggest a cooling trend through the 2nd millennium in Western Europe, followed by warming as the Industrial Revolution gathered pace in the latter 1800s.
A linear regression would not detect a pattern of cooling followed by warming, A 1st order polynomial might.The CET is very noisy data, so it may be difficult to distinguish a possible LIA from the noise.
I was reading a short précis of Richard Alley's 2000 paper and was struck by one omission. How big are the 95% confidence limits on his temperatures? Is the GISP2 data good enough to reliably distinguish the +/- 0.5C variations of the "Minoan Warm Period" and "Roman Warm Period" from the longer term cooling trend?
Entropic man
Radical Rodent, interesting that you should link to the Great Storm of 1703. One of the Royal Navy heroes to survive that was Sir Cloudesley Shovell, one of history's more preposterous names. The 1707 Scilly Naval Disaster, saw Shovell smash 4 mighty ships into the Scilly Isles, with much loss of life, including his own.
The Fleet Wreck was partially due to bad weather for a few days, compounding navigational errors, until they made landfall at night, where no land was supposed to be.
This led the Admiralty and Houses of Parliament to launch a competition for someone to build an accurate Marine Chronometer, very belatedly won by John Harrison, of 'Longitude' fame, along with 'Only Fools and Horses'.
The Beaufort Scale, a method of assessing the wind's force by observation was devised in 1805, but not introduced as a 'standardised' measurement until 1830. Whether this was due to more stormy weather during the LIA, or about Britain ruling the waves by defining how unruly they were, I don't know.
Charting of the seas and oceans of the World by the Royal Navy was carried out in about this time (mid third of the 1800s) and I presume that with knowledge of 'trade winds' gathered over centuries, some patterns of world weather and circulation were formed.
Charted depths of water on many charts of the world are still using the depths recorded 150 years ago. Tectonics have shifted a bit since then, but charts are not normally updated until after the first ship has bumped into the 'error'.
golf charlie
aTTP (Mar 28, 2016 at 3:56 PM):
I don't know the answer.Is this a first?
The expectation is that we will see an increase in the frequency and intensity of these events.On what evidence? All the data we have to date is that the warming has caused a decrease in the frequency and intensity of these events; why is there the conviction that this is going to change, and soon?
Radical Rodent
RR,
Is this a first?
Nope, I often don't know the answer to things.
On what evidence? All the data we have to date is that the warming has caused a decrease in the frequency and intensity of these events; why is there the conviction that this is going to change, and soon?
That isn't my point. I'm pointing out that showing that something has happened before is NOT evidence against an increase in the intensity and frequency of such events.
...and Then There's Physics
A linear regression would not detect a pattern of cooling followed by warming, A 1st order polynomial might.The CET is very noisy data, so it may be difficult to distinguish a possible LIA from the noise.
Mar 28, 2016 at 7:03 PM | Unregistered CommenterEntropic man
EM, I think you probably have in mind a second order polynomial (ie a quadratic). A first order polynomial is just a straight line, eg x(t) = a₀ + a₁.t .
However, unless you have reason to think that a parabola is likely to describe how the temperature is changing over the 360 odd years of the data, it does not seem to make much sense to try to fit one.
I tried smoothing the data over a ~41 year window (more or less the equivalent of a 40-year moving average with a bit of additional high frequency attenuation to give a prettier looking curve).
Result here in red. (First and last ~25 years not shown to avoid displaying artifacts from filter transients.)
To work out whether these curves are anything other than what you would get by running white noise (ie uncorrelated random numbers) through a smoothing filter would need a statistical test. But my eye suggests to me that they are probably indistinguishable from smoothed white noise.
Martin A
I'm pointing out that showing that something has happened before is NOT evidence against an increase in the intensity and frequency of such events.You're right, of course, but at the same time you cannot have it both ways.
My understanding of the climate issue has always been that the poles will warm faster than the tropics which will reduce the temperature gradient and in so doing make severe storms less likely rather than more — a situation we are already seeing in the frequency of Cat3+ hurricanes in the North Atlantic, the last to make landfall on the US being Wilma 11 years ago.
There will always be weather events even one in 250 year ones. The history of flooding in the Severn catchment is well documented here and those of us familiar with the River Avon (and several of those involved in its restoration for navigation and subsequent management) will tell you that the recent flooding events have been on the cards for years, citing several aspects of river (mis)management partly due to a refusal to listen to those who know what flood plain is for and partly due to refusal to carry out proper maintenance in the catchment.
Agreed that 2007 was exceptional but there is no need to use the position of the jet stream and an intense low over Biscay and the English Channel as an excuse to bleat "climate change" when Occam's Razor is available!
Mike Jackson
Proof that climate scientists have been wrong before, is NOT evidence against an increase in the intensity and frequency of such events.
golf charlie
Martin A
Thanks for the information on 2nd order polynomials.
Looking at your graphs, I would estimate the 95% confidence limits for your regression lines at +/-2.5C.
I would agree that there is little chance of pulling useful trend information out of CET.Anything between no change and +/-5C would fit within those limits.
Entropic man
Mike Jackson
By eye, there looks to be an increase in named storms, but no real change in the number of hurricanes or major hurricanes.
If the US has not had a hurricane in ten years that suggests
a) that the hurricanes are tending to go elsewhere, perhaps staying offshore.
and/or
b) that the USA has been lucky.
Entropic man
if there i8s a staw to be clutched at, EM will reach for it. I suggest he relabels himself as Ecdysiast Man, always eager to display his lack of credentials.
diogenes
"luck" is one of those quantities that EM will no doubt define with a formula involving made up numbers, like most of the formulae he writes.
diogenes
michael hart,
It's not many years ago (probabaly about one year pre-Climategate) that I decided I needed to read up on what all this Global Warming stuff was about. Failing to find general-reader articles explaining it all at anything deeper than the "CO2 traps heat" level, I had already suddenly realised "This is nothing more than a theory!" (Or hypothesis as EM insists we say.)
Then came Climategate. I downloaded the emails for myself, including Hansen's missing heat "...it's a travesty...". A couple of years more recently, the so-called pause (ie failure of predicted accelerated warming) became embarrasingly undeniable.
Then, at a stroke, climate science (so-called) discovered the ocean. Glad tidings of great joy! Rejoice!
At a stroke, the missing heat issue was resolved (it's hiding in the ocean). Likewise the pause - "the ocean is the true measure of climate change" (© EM - I hope I have remembered his exact words)
The ocean - overnight and uncontradictably - resolved climate science's crises.