Climate slowdown: The world won't stop warming

Warming has not peaked. Instead, it looks as if the sea is taking the strain (Image: Sesse Lind/Link Image/Gallerystock)

Editorial: "Is it time to stop worrying about global warming?"
"Global warming on pause". "Why has global warming stalled?" "Has global warming stopped?"

IF YOU have been reading the papers of late, you may be under the impression that global warming isn't proceeding as expected.

While most mainstream media have been careful to point out that the apparent lack of recent warming is probably just a temporary hiatus, a few outlets have suggested there is more to it than that. "The climate may be heating up less in response to greenhouse-gas emissions than was once thought," one magazine claimed.

What is going on? Has global warming really slowed or stopped in recent years? If so, why? And does this mean the world won't warm as ...

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What is Argo?
Argo is a global array of 3,000 free-drifting profiling floats that measures the temperature and salinity of the upper 2000 m of the ocean. This allows, for the first time, continuous monitoring of thetemperature, salinity, and velocity of the upper ocean, with all databeing relayed and made publicly available within hours aftercollection.

Positions of the floats that have delivered data within the last 30 days (AIC, updated daily):

 

Why do we need Argo?

We are increasingly concerned about global change and its regional impacts. Sea level is rising at an accelerating rate of 3 mm/year, Arctic sea ice cover is shrinking and high latitude areas are warming rapidly. Extreme weather events cause loss of life and enormous burdens on the insurance industry. Globally, 8 of the 10 warmest years since 1860, when instrumental records began, were in the past decade.

These effects are caused by a mixture of long-term climate change and natural variability. Their impacts are in some cases beneficial (lengthened growing seasons, opening of Arctic shipping routes) and in others adverse (increased coastal flooding, severe droughts, more extreme and frequent heat waves and weather events such as severe tropical cyclones).

Understanding (and eventually predicting) changes in both the atmosphere and ocean are needed to guide international actions, to optimize governments' policies and to shape industrial strategies. To make those predictions we need improved models of climate and of the entire earth system (including socio-economic factors).

Lack of sustained observations of the atmosphere, oceans and land have hindered the development and validation of climate models. An example comes from a recent analysis which concluded that the currents transporting heat northwards in the Atlantic and influencing western European climate had weakened by 30% in the past decade. This result had to be based on just five research measurements spread over 40 years. Was this change part of a trend that might lead to a major change in the Atlantic circulation, or due to natural variability that will reverse in the future, or is it an artifact of the limited observations?

In 1999, to combat this lack of data, an innovative step was taken by scientists to greatly improve the collection of observations inside the ocean through increased sampling of old and new quantities and increased coverage in terms of time and area.

That step was Argo.

Where is Argo now?
Argo deployments began in 2000 and by November 2007 the array is 100% complete. Today's tally offloats is shown in the figure above. While the Argo array is currently complete at 3000 floats, to be maintained at that level, national commitments need to provide about 800 floats per year. Additionally, Argo continues to work toward global ocean coverage. Frequently, even with the 3000 float target achieved, more floats are needed because some areas of the ocean are over populated while others have gaps that need to be filled with additional floats.

Besides float deployment, Argo has workedhard to develop two separate data streams: real time and delayed mode. A real time data delivery and qualitycontrol system has been established that delivers 90% of profiles to users via two global data centers within 24 hours. A delayed mode quality control system (DMQC) has been established and 60% of all eligible profiles have had DMQC applied.

Float reliability has improved each year and the float lifetime has been extended. Argo has developed a large user community in universities, government labs and meteorological/climateanalysis/forecasting centers. The need for global Argo observations will continue indefinitely into the future, though the technologies and design of the array will evolve as better instruments are built, models are improved, and more is learned about ocean variability.

Who Collaborates with Argo?
Argo is a major contributor to the WCRP's Climate Variability and Predictability Experiment (CLIVAR) project and tothe Global Ocean Data Assimilation Experiment (GODAE). The Argo array is part of the Global Climate Observing System/Global Ocean Observing System GCOS/GOOS).

Current Status of Argo

The broad-scale global array of temperature/salinity profiling floats, known as Argo, has already grown to be a major component of the ocean observing system. Argo is a standard to which other developing ocean observing systems can look to. For example, Argo offers ideas on various topics such as how to collaborate internationally, how to develop a data management system and how to change the way scientists think about collecting data. Deployments began in 2000 and continue today at the rate of about 800 per year. 

The latest picture of the Argo array.

Brief History of Argo 
The name Argo was chosen to emphasize the strong complementary relationship of the global float array with the Jason satellite altimeter mission. In Greek mythology Jason sailed in a ship called "Argo" to capture the golden fleece.

An Argo float being deployed from a research ship.

Together the Argo and Jason data sets will be assimilated into computer models developed by project GODAE (Global Ocean Data Assimilation Experiment) that will allow a test of our ability to forecast ocean climate. For the first time, the physical state of the upper ocean is being systematically measured and the data assimilated in near real-time into computer models. Argo builds on other upper-ocean ocean observing networks, extending their coverage in space an time, their depth range and accuracy, and enhancing them through the addition of salinity and velocity measurements. Argo is not confined to major shipping routes which can vary with season as the other upper-ocean observing networks are. Instead, the global array of 3,000 floats will be distributed roughly every 3 degrees (300km).

Argo's Objectives
It will provide a quantitative description of the changing state of the upper ocean and the patterns of ocean climate variability from months to decades, including heat and freshwater storage and transport.

The data will enhance the value of the Jason altimeter through measurement of subsurface temperature, salinity, and velocity, with sufficient coverage and resolution to permit interpretation of altimetric sea surface height variability.

Argo data will be used for initializing ocean and coupled ocean-atmosphere forecast models, for data assimilation and for model testing.

A primary focus of Argo is to document seasonal to decadal climate variability and to aid our understanding of its predictability. A wide range of applications for high-quality global ocean analyses is anticipated.

An Argo profile from the subtropical North Pacific
(20.25N 121.4W, May 15 2004).
This shows interleaving in the salinity data.

Argo Design and Data 

The design of the Argo network is based on experience from the present observing system, on recent knowledge of variability from the TOPEX/Poseidon altimeter, and on the requirements for climate and high-resolution ocean models.

The final array of 3000 floats will provide 100,000 temperature/salinity (T/S) profiles and velocity measurements per year distributed over the global oceans at an average 3-degree spacing. Floats will cycle to 2000m depth devery 10 days, with 4-5 year lifetimes for individual instruments. All data collected by Argo floats are publically available in near real-time via the Global Data Assembly Centers (GDACs) in Brest, France and Monterey, California after an automated quality control (QC), and in scientifically quality controlled form, delayed mode data, via the GDACs within six months of collection.  Argo Data and How to Get It

argo.avi is a float animation that explains the purpose and method of Argo. 

ORIGINAL: ARGO - UCSD

by Michael Le Page
05 December 2013 
Magazine issue 2946. Subscribe and save
For similar stories, visit the Climate Change Topic Guide

Submerged Forests off the coast of Wales: a Climate Change Snapshot

ORIGINAL: SkepticalScience
by John Mason

7 April 2012 

Sea-level rise over the past 10,000 years is recorded in Cardigan Bay, off the western seaboard of Wales, UK. Peat-beds complete with the remains of trees are today exposed over low tide along several of the Bay's beaches. Incredibly, a new exposure of peat has recently yielded human footprints, made some 3000 years or more ago by the people who witnessed the final stages of the drowning of the land.

The deglaciation that followed the Last Glacial Maximum, twenty thousand years ago, was accompanied by a global sea-level rise that averaged out at some 120 metres. Around the British Isles, there are many areas covered by shallow seas, 10-20 metres in depth, and Cardigan Bay, off the west-facing coast of Wales, is one of them. Sailing due west from the local coastal ports such as Aberystwyth and Aberdyfi, it is a good ten nautical miles before the 20m submarine contour is reached. The sea-bed is a sandy table-land, divided by several great ridges of gravel and boulders - the Sarnau (Welsh for Roads) - that mark the lateral moraines of the valley-glaciers that flowed out westward to join the Irish Sea Ice-Sheet.

above: view across Cardigan Bay to the Snowdonia mountains, with one of the Sarnau, Sarn Cynfelyn, in the foreground. It extends out beneath the sea as a steep-sided reef for over six nautical miles. Photo: author.

The process of post-glacial sea-level rise has been well-charted, and with respect to this corner of the world, the inundation of the land to form much of Cardigan Bay was within the last 10,000 years. We have additional local evidence for this timescale: peat samples, dredged from the seabed not far from Aberystwyth, at a depth of 18.5 metres, yielded a radiocarbon date of 8740 +/- 100 years before present (Haynes et al, 1977). It should be noted in passing that this part of the UK is regarded as having been essentially neutral with respect to post-glacial isostatic rebound: to the north, where the main ice-sheets were formerly located, the land rose whilst to the south, which was mostly ice-free, the land sank.

above: the post-glacial rise in sea-level, adapted from Fleming et al (1998), with dates relevant to this article annotated in red.

8740 years: let's just place that date in context. The Younger Dryas had come and gone (12,900-11,800 years BP), and the Mesolithic was about halfway through. The people who lived in the region were gradually turning from full-time hunter-gatherers to the combination of these with agriculture, something which by the Neolithic was developing various degrees of sophistication. By then, the rate of sea-level rise had slowed, but it continued to advance throughout the Neolithic and the following Bronze Age, and there is impressive evidence from that process right here on the Welsh coast.

above: timeline annotated with the period during which Cardigan Bay was inundated.

So-called Submerged Forests are known from various parts of the world, but the one at Borth, on the Cardigan Bay Coast of Wales, is a particularly fine example. Every winter, after storms have scoured away parts of its extensive sands, large areas of peat appear, littered with fallen tree-trunks and with stumps in growth position. Although it is sometimes referred to as the "Fossil Forest", the wood is not fossilised as such: it looks and feels just like what one might expect waterworn and waterlogged wood to look and feel like. The peat is hard and compact: walking on its surface barely leaves a mark.

above: part of the Submerged Forest at Borth. Photo: author.

The basal peat, upon which the tree-stumps are situated, is around 6,500 years old. Above it, where erosion has not removed it, there lies a layer of bluish-grey clay and, at the south end of the beach, atop the clay is a second, thinner peat. The succession records the transition from forest to salt-marsh, between 6,500 and 3,000 years ago, which is late Mesolithic through to mid Bronze Age. It is thought that, originally, the coastline, with its shingle storm-beach and dunes, was over a kilometre to the west (seawards): during this period, the storm-beach advanced towards the land and its immediate hinterland became salt-marsh: the trees became waterlogged with brackish water and died. The retreat of the coast would likely have continued were it not for the establishment of the fishing-village of Borth and various sea-defences, the most recent of which is just nearing completion. Local people living here are constantly reminded of sea-level rise when they look out across the beach at low tide and see the trees emerging from the waves.

The Submerged Forest has recently been in the news. In February 2012, retired geology lecturer Dr Denis Bates, of Aberystwyth, noticed that a new area of ancient peat had become visible along the southernmost part of the beach. Taking a closer look, he discovered that the peat contained scatters of burnt stone - an archaeological feature typical of Bronze Age sites. Burnt stone consists of sharp, angular fragments of bleached-looking rock produced by heating large pebbles in fires and then immersing them in water: it was the instant cooling that shattered them. Why they did this is not clear: one theory is that it was a means of heating-up the water whilst some archaeologists have connected the practise with sweat-lodges, as in the Native American tradition.

Dr Martin Bates, Denis' son, is an archaeologist based at the University of Wales, Lampeter, and was therefore quickly on hand to undertake a detailed investigation of this find. Despite the peat and clay beds spanning an important period of human activity in the area, they have to date yielded few remains: an Aurochs skeleton was discovered many years ago and a small number of flint and bone implements have been recorded over the years. But when surveying commenced, the site proved to be of even greater interest, as upon the surface of the upper peat layer, and impacting into the clay below, the surveyors discovered footprints. There were the circular depressions made by the hooves of cattle, sheep and goats and, incredibly, human prints. It appears that the adults were foot-clad, but one print was found that belonged to a child aged approximately four years, which showed the impressions of bare toes. I visited the site over low tide a few days ago: standing next to such impressions, my heavy rigger-boots hardly left a mark: back when the prints were made this would have been squelchy marsh that you could go up to your knees in if unlucky.

above: photographed whilst still underwater, a human footprint in now hard and compact peat at the Submerged Forest, Borth. Photo: author.

Interestingly, coastal West Wales has its very own Flood Legend, which goes as follows:

Cantre'r Gwaelod (also known as Cantref Gwaelod or Cantref y Gwaelod) translates into English as the Lowland Hundred. It is the legendary sunken kingdom that is said to have long ago occupied a tract of fertile land in what is now Cardigan Bay. Cantre'r Gwaelod's capital was Caer Wyddno, seat of the ruler Gwyddno Garanhir. The land is usually described as being defended from the sea by a dyke, complete with sluice-gates, managed by one Seithennin, who, it was said, was fond of his drink. One dark and stormy night, the gates were neglected during drunken festivities and as the tide rose, so the sea swept in, ruining the land.

above: lost landscapes? A map of the UK, Ireland and N France ten thousand years ago, at the start of the Mesolithic, when sea levels, though rising, had not yet reached their full post-glacial extent. The brown areas are lands that have since been lost. Redrawn from Lambeck, 1995 (PDF).

Mere folklore, yes, but it is often wondered locally whether the legend recalls stories handed down over many generations, via the oral tradition, of lands that produced good hunting and gathering, but which by the start of the Neolithic had largely been lost to the advancing sea. The generations of people who followed-on from those who left the footprints would certainly have witnessed the environmental changes that led to the loss of the forests described above: they would have walked through what had become salt-marsh beneath dead and dying oaks and pines. They would have seen environmental change as starkly as anyone.

So what is in store for this small corner of the planet in the coming decades? According to Vermeer and Rahmsdorf (2009), the worst-case scenario would be a rise of 190cm by 2100. Using Alex Tingle's handy plotter, this is what a rise of 2m would look like:

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And a rise of 6m, which would occur if parts of both the Greenland and West Antarctica ice-sheets continued to melt, would look like this:

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Borth and Aberdyfi would be overwhelmed and even my hometown some distance inland would be affected: the fertile agricultural lands along the Dyfi flood-plain would be replaced by the relatively poor grazing offered by salt-marsh and another legend of flood would be born. Being rather fond of these places and the communities that live in them, I would personally prefer an outcome that did not involve such inundation. Future generations have just as much right to enjoy them as I do at present. It is such considerations that come to mind when people ask me why I blog.