The world’s oceans have absorbed more than 90 percent of global warming since the mid-20th century, making accurate measurements of deep ocean temperatures vital to predicting how much global temperatures and sea levels are going to rise.
In 1999, a group of 30 countries launched the Argo program as the first global, subsurface ocean observing system.
It will improve on the earlier patchwork of observations dating as far back as Britain’s HMS Challenger in 1873, which dropped a weighted thermometer overboard on a hemp line 8mm thick.
The Argo floats are rather more sophisticated with an inflatable chamber and a pump that changes the buoyancy of the float by changing its volume. It can sink from the surface to a depth of 2,000m and then resurface, measuring temperatures and salinity as it goes.
The data so far confirm a warming trend in the oceans over the past century.
Significantly, two recent publications suggest that the deep oceans have warmed particularly quickly in the past decade.
That is important because it may help explain a recent lull in surface warming and so confirm that greenhouse gas emissions are still warming the Earth as much as previously predicted.
SUBMERSIBLE
There is consistent evidence that the world is absorbing more heat than it radiates back into space, mostly because of man-made greenhouse gases, which absorb infra-red radiation and prevent it from leaking back into space.
Measuring changes in ocean temperatures over time will help quantify that energy imbalance.
Argo data can also add detail to the expected impact on world temperatures from greenhouse gas emissions by helping unpick contributions from other sources such as volcanoes, solar cycles and other man-made pollution.
The initial goal of the Argo program was to obtain more than 100,000 profile observations per year, each from zero to 2000m in depth, from 3,300 floats spaced evenly across the globe.
The 30 countries achieved the 3000-float array in late 2007 and have maintained that number since then, according to the recent “State of the climate in 2012,” published in the Bulletin of the American Meteorological Society.
Each profile of ocean temperature and salinity is recorded in a 10-day cycle and subsequently transmitted via satellite.
There are some caveats regarding the results derived so far.
Argo is a recent dataset and so may not be able to distinguish longer natural cycles of ocean warming. And there are difficulties comparing observations before and after the Argo data because of differences in sampling method, instrument and geographical distribution.
In addition, there were initial problems with reliability of the Argo data, which meant accurate conclusions could only be drawn from 2005, and some instrument errors may remain undetected.
The Argo data still can help resolve the issue of a lull in the past decade of warming at the Earth’s surface, where measurements are taken using land-based weather stations, satellites and ocean buoys.
According to those surface temperatures, 11 of the 12 hottest years in the past 150 have been since 2000, NASA data show, illustrating a clear warming trend.
However, the warming trend on land has slowed in the past decade, while warming of the sea surface has stalled.
Warming also seems to have slowed in the ocean to depths of about 700m.
OBSERVED WARMING
The two recent papers based on Argo data found that ocean heat content had risen most rapidly in depths below 700m in the past decade.
One study ran the Argo and other historical data through models, which simulate ocean systems in a technique called reanalysis.
“The deep ocean has continued to warm, while the upper 300m OHC [ocean heat content] appears to have stabilized,” said the authors of the paper “Distinctive climate signals in reanalysis of global ocean heat content.”
DYNAMIC SYSTEMS
Reanalysis is often used to estimate values in complex, dynamic systems and inherently depends on the accuracy of the underlying model and the consistency of the observational data.
By necessity, the technique combines “inaccurate and incomplete observations with imperfect models, using methods and procedures that are technically and scientifically complex,” according to the US National Center for Atmospheric Research’s Climate Data Guide.
Its strength is that it allows scientists to combine millions of observations in a single, coherent model which can be continually improved and updated.
The reanalysis study supported another paper that used raw observations alone and found that the rate of increase in heat content was slowing only to depths of about 700m.
“Leveling is not as pronounced in our ocean heat content to 2,000m estimates, indicating that heat is being stored in the 700m to 2,000m layer,” it said.
Such studies are at the forefront of analysis of this new trove of data and may well prove right.
The implication is that emissions are indeed warming the planet as much as scientists had thought, and the heat will eventually return to the surface. However, it could take another decade of observations to be sure the oceans partly account for the recent slowdown in warming.
Gerard Wynn is a Reuters market analyst. The views expressed are his own.
Congressman Mike Gallagher (R-WI) and Congressman Raja Krishnamoorthi (D-IL) led a bipartisan delegation to Taiwan in late February. During their various meetings with Taiwan’s leaders, this delegation never missed an opportunity to emphasize the strength of their cross-party consensus on issues relating to Taiwan and China. Gallagher and Krishnamoorthi are leaders of the House Select Committee on the Chinese Communist Party. Their instruction upon taking the reins of the committee was to preserve China issues as a last bastion of bipartisanship in an otherwise deeply divided Washington. They have largely upheld their pledge. But in doing so, they have performed the
It is well known that Chinese President Xi Jinping’s (習近平) ambition is to rejuvenate the Chinese nation by unification of Taiwan, either peacefully or by force. The peaceful option has virtually gone out of the window with the last presidential elections in Taiwan. Taiwanese, especially the youth, are resolved not to be part of China. With time, this resolve has grown politically stronger. It leaves China with reunification by force as the default option. Everyone tells me how and when mighty China would invade and overpower tiny Taiwan. However, I have rarely been told that Taiwan could be defended to
It should have been Maestro’s night. It is hard to envision a film more Oscar-friendly than Bradley Cooper’s exploration of the life and loves of famed conductor and composer Leonard Bernstein. It was a prestige biopic, a longtime route to acting trophies and more (see Darkest Hour, Lincoln, and Milk). The film was a music biopic, a subgenre with an even richer history of award-winning films such as Ray, Walk the Line and Bohemian Rhapsody. What is more, it was the passion project of cowriter, producer, director and actor Bradley Cooper. That is the kind of multitasking -for-his-art overachievement that Oscar
Chinese villages are being built in the disputed zone between Bhutan and China. Last month, Chinese settlers, holding photographs of Chinese President Xi Jinping (習近平), moved into their new homes on land that was not Xi’s to give. These residents are part of the Chinese government’s resettlement program, relocating Tibetan families into the territory China claims. China shares land borders with 15 countries and sea borders with eight, and is involved in many disputes. Land disputes include the ones with Bhutan (Doklam plateau), India (Arunachal Pradesh, Aksai Chin) and Nepal (near Dolakha and Solukhumbu districts). Maritime disputes in the South China