miércoles, 11 de diciembre de 2013

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. 

by Michael Le Page
05 December 2013 
Magazine issue 2946. Subscribe and save
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