Last week the Met Office issued their Final Briefing of the recent storms. The report is good in parts and down right ugly in others. The report says this:
As yet, there is no definitive answer on the possible contribution of climate change [manmade] to the recent storminess, rainfall amounts and the consequent flooding. This is in part due to the highly variable nature of UK weather and climate.
So the official line is that it is not possible to link the storms to manmade global warming and it is good to get that controversial point cleared up. There are two serious omissions from the whole report 1) heavy snow fall in Scotland is not mentioned once and 2) the role of flood management in causing flooding is not mentioned. And exceptional high tides that are discussed in the main report are omitted from the summary. Including these data in the synopsis drives thinking about these storms quite firmly away from manmade towards natural causes (and vice versa). The main manmade contribution is locally inept flood management.
This post is based around the report summary where each paragraph is dissected and compared with reality and the main report. The Met Office summary in blockquotes below, my commentary in normal text.
Figure 1 Map from the Met Office showing rainfall distribution in December 2013 and January 2014. Scotland was exceptionally wet in December which is mentioned only once. Parts of England were dry in December as was northern Scotland in January. These short time scale regional variations are normally put down to weather.
This winter the UK has been affected very severely by an exceptional run of winter storms, culminating in serious coastal damage and widespread, persistent flooding.
In fact it is mainly southern England and NE Scotland that has been affected according to the Met Office map (Figure 1). Northern Scotland has been much drier than what we consider to be normal.
This period of weather has been part of major perturbations to the Pacific and North Atlantic jet streams driven, in part, by persistent rainfall over Indonesia and the tropical West Pacific.
It is beyond my understanding how they can attribute rainfall to reconfiguring the Pacific jet stream. Surely it is a change in the jet stream track that has caused persistent rainfall in Indonesia? The main report says this:
“La Nina corresponds to the cold phase of El Nino Southern Oscillation (ENSO) cycle in which sea surface temperatures along the Peruvian coast and across the equatorial East Pacific are colder than normal; concurrently sea surface temperatures in the West Pacific tend to be warmer than normal. This change in the pattern of sea surface temperatures drives more rainfall and active weather systems over the warm waters of the West Pacific and Indonesian seas, and the global effects are felt as far as the UK through teleconnections involving changes in planetary waves and hence the position of the jet stream.”
The North Atlantic jet stream has also been unusually strong; this can be linked to exceptional wind patterns in the stratosphere with a very intense polar vortex.
I’m happy to see that my “amateur” explanation given in this post is generally supported by the Met Office interpretation of events.
This paper documents the record-breaking weather and flooding, considers the potential drivers and discusses whether climate change contributed to the severity of the weather and its impacts.
The Met Office have had to torture data to create records to discuss. It is true that the storminess, rainfall and flooding in South England are all at the high end of the natural spectrum but none of it is actually exceptional or unprecedented. Much of the flooding appears linked to poor management of flood defences or river engineering designed to protect one area (upstream of Windsor) making the flooding worse downstream.
Although no individual storm can be regarded as exceptional, the clustering and persistence of the storms is highly unusual. December and January were exceptionally wet. For England and Wales this was one of, if not the most, exceptional periods of winter rainfall in at least 248 years. The two-month total (December + January) of 372.2mm for the southeast and central southern England region is the wettest any 2-month period in the series from 1910.
The regional statistics I have to hand has 5 regions for England and Wales: 1) South East England, 2) South West England and Wales, 3) Central England, 4) North West England and Wales, 5) North East England. Central Southern England is not one of them. Worryingly, Wales is listed twice. Furthermore adding December to January combined with a vague geographic definition makes it virtually impossible to quickly verify this statistic.
I’m really unsure where the Met Office are going with this. A small part of the UK (southern England) was uncommonly wet for a short period of time and this seems to warrant a special report and investigation. Why are they not looking into why Scotland was uncommonly wet in December 2013? And why northern Scotland was hit by drought in January 2014! Regional variations in precipitation over short time scales are normal and natural! It is called weather.
During January and into February the tracks of the storms fell at a relatively low latitude, giving severe gales along the south and west coasts and pushing the bulk of the ocean wave energy toward the southwest of Ireland and England. Peak wave periods were exceptionally long; each wave carried a lot of energy and was able to inflict significant damage on coastal infrastructure.
In bold is the explanation. The storm track was further south. No mention of tides here in the summary. The main body of the report says this:
“During December widespread high wind speeds were recorded across UK, as a sequence of deep lows tracked across or to the north of the country. The storm on 4th-5th December generated a major North Sea storm surge event, which coincided with one of the highest tides of the year and threatened much of the east coast in a similar manner to the 1953 event. With improved coastal defences built by the environment agency and accurate early warnings several days in advance major damage was avoided. The Environment Agency Thames Barrier was raised to protect London from the largest tide recorded at Southend since it became operational.”
In a series from 1883, flow rates on the River Thames remained exceptionally high for longer than in any previous flood episode. Correspondingly, floodplain inundations were extensive and protracted.
They are really torturing and cherry picking the statistics here since they forget to say in the summary that the peak flow of the Thames at Kingston has been matched or exceeded on 14 prior occasions since 1880, many of these events occurring during the late 19th and early 20th century (Figure 2). There is nothing exceptional about the recent Thames flooding apart from the media coverage and political agenda to justify a failing energy policy.
Figure 2 Maximum flow rate of The Thames at Kingston. The red line marks the peak flow of December 2013 that was matched or exceeded on 14 occasions since 1880. Chart from The Met Office.
The severe weather in the UK coincided with exceptionally cold weather in Canada and the USA. These extreme weather events on both sides of the Atlantic were linked to a persistent pattern of perturbations to the jet stream over the Pacific Ocean and North America. There is a strong association with the stormy weather experienced in the UK during December and January and the up-stream perturbations to the jet stream over North America and the North Pacific.
Agreed, but they forget to say that this is ultimately linked to a cold and active polar vortex, a point made clear in the main body text.
The major changes in the Pacific jet stream were driven by a persistent pattern of enhanced rainfall over Indonesia and the tropical West Pacific associated with higher than normal ocean temperatures in that region.
Since this point is made twice in the summary the authors must consider it to be important. The cause seems to be rooted in Pacific Ocean currents and a latent La Nina condition. 37 years ago in a climatology course at university I learned that global climate was anchored to the Pacific Ocean and so have no major objection to this explanation.
The North Atlantic jet stream has also been unusually strong; this can be linked to an unusually strong westerly phase of the stratospheric Quasi-Biennial Oscillation (QBO), which in turn has driven a very deep polar vortex and strong polar night jet.
As yet, there is no definitive answer on the possible contribution of climate change to the recent storminess, rainfall amounts and the consequent flooding. This is in part due to the highly variable nature of UK weather and climate.
This is good and is effectively all The Met Office needed to say. But on every occasion that climate scientists mention “climate change” it should be qualified by the descriptor “man made” or “natural”. Failure to do this simply lacks rigour.
At this point it should also have been pointed out that much of the flooding was the consequence of neglect or actions by the Environment Agency.
Sea level along the English Channel has already risen by about 12cm in the last 100 years. With the warming we are already committed to over the next few decades, a further 11-16cm of sea level rise is likely by 2030. This equates to 23-27cm (9-101⁄2 inches) of total sea level rise since 1900.
12 cm in 100 years translates to 1.2 mm per year of sea level rise along the English channel over the past 100 years. The Met Office is now suggesting that this is going to accelerate to 13.5 cm (median) in the next 16 years giving a rate of 8.4 mm per year until 2030. This represents an acceleration in the rate of sea level rise of 700% that is forecast to start happening tomorrow! This must surely be total drivel (Figure 3).
The land in northern Britain is still rising following melting of the ice (this process is called isostatic rebound). A compensating flow in the lithospheric mantle results in the land of southern Britain actually sinking at an estimated rate of 5 to 10 cm per century (Figure 3). This results in a change of relative sea level. It is not made clear in the Met Office report if this is accounted for in their 12 cm per century estimate, I suspect not, leaving a very modest 7 cm per century rise in sea level that may be attributed to a change in ocean water volume.
Figure 3 Map and chart from Roger Andrews. The Newlyn tide gauge record is from SW England. The Met Office forecast rise of 11 to 16 cm by 2030 is indicated. The map shows isostatic rise and fall across Britain with the S coast of England subsiding at 0.4 to 1.2 mm / year.
[note added 24th Feb. It was brought to my attention that Dr Ruth Dixon blogged on the sea level issue on 9th February. The Met Office responded by rewording the report and there is now a second version at large. The rewording is as follows:
Sea level along the English Channel has already risen during the 20th century due to ocean warming and melting of glaciers. With the warming we are already committed to over the next few decades, a further overall 11-16cm of sea level rise is likely by 2030, relative to 1990, of which at least two-thirds will be due to the effects of climate change.
It's a bit better in that it allocates one third of sea level rise to isostasy. But it seems like they just made something up. The "new rate" is 3.4 mm / year, almost 3 times the rate of the last century according to Met Office statistics.]
In the main body of the report the authors do discuss the exceptional Spring tides of early and late January but in the summary instead choose to present drivel on sea levels. Clive Best has estimated that the additional tidal height caused by rare alignments of Earth, Moon and Sun may have added over a meter to the normal Spring tide events. If correct this will have added significantly to coastal flooding and is totally unconnected to manmade global warming.
Recent studies suggest an increase in the intensity of Atlantic storms that take a more southerly track, typical of this winter’s extreme weather. Also the long-term warming of the sub-tropical Atlantic will also act to enhance the amount of moisture being carried by storms that take this more southerly track.
The main body of the report also says this:
“Not only would this act to invigorate storms forming on the jet stream, but the inflow of warm, moist air from the tropics would enhance the moisture being carried by the storm systems and potentially lead to higher rainfall downstream over the UK.”
There is an increasing body of evidence that extreme daily rainfall rates are becoming more intense, and that the rate of increase is consistent with what is expected from fundamental physics. There is no evidence to counter the basic premise that a warmer world will lead to more intense daily and hourly heavy rain events.
The high rainfall in southern England was brought about by a series of fast moving storms. The large amounts of water dumped on South England was down to a flow of storms and there is no need to invoke a larger quantity of water in the atmosphere. This is simply looking for links to non-existent warming.
The same storms also dumped large amounts on snow on Scottish Mountains. It is therefore not at all obvious to me that the air masses were somehow warm as implied.
More research is urgently needed to deliver robust detection of changes in storminess and daily/hourly rain rates. The attribution of these changes to anthropogenic global warming requires climate models of sufficient resolution to capture storms and their associated rainfall. Such models are now becoming available and should be deployed as soon as possible to provide a solid evidence base for future investments in flood and coastal defences.
On reading this I am left wondering what the Met Office has spent all the hundreds of millions of pounds of tax payers money on? This statement does at least specify “anthropogenic global warming” but to have any scientific merit, any future work should first and foremost define the natural process and natural variability and then attribute anthropogenic overprint, if there is any. It is just as important to protect the British population from natural storms as those imagined to be enhanced by global warming.
History of events. The report would have been enhanced with a time-line / history of storm events, with dates, estimated strength and human impact.
Snow. While it was raining in the S of England the same storms brought large amounts of snow to the Scottish mountains. Local press has recently reported that it has snowed every day on The Nevis range for 6o days. I have scanned the report and can find no reference to the word “snow” in it. I think an explanation from the Met Office is required!
Neglect of flood defences. I can see no discussion of the impact of neglect on the Somerset Levels and river engineering on the Thames upon the pattern and extent of flooding.
Tides. High tides are discussed at length in the report but omitted from the summary.
- The main body of the report is substantially better than the summary. The section on “Global Context of Recent UK Weather” is a good read, rooted in climatology.
- The summary is not a faithful summary of the report, omitting some important points made in the main report whilst dangling the possibility of human made climate change at the reader.
- The information on sea levels cannot possibly be correct and is presumably a mistake.
- Data are tortured to create records that do not really matter or exist.
- There are three serious omissions 1) snowfall connected to the storms, 2) tides (omitted from summary) and 3) flood defences role in the flooding.
- The sub-text is frequently searching for links to human made climate change that is quite simply not there.