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Source BBC www.bbc.com/news/science-envir…

One of the biggest icebergs ever recorded has just broken away from Antarctica.

The giant block is estimated to cover an area of roughly 6,000 sq km; that's about a quarter the size of Wales.

An US satellite observed the berg on Wednesday while passing over a region known as the Larsen C Ice Shelf.

Scientists were expecting it. They'd been following the development of a large crack in Larsen's ice for more than a decade.

The rift's propagation had accelerated since 2014, making an imminent calving ever more likely.

The more than 200m-thick tabular berg will not move very far, very fast in the short term. But it will need to be monitored. Currents and
winds might eventually push it north of the Antarctic where it could become a hazard to shipping.

An infrared sensor on the American space agency's Aqua satellite spied clear water in the rift between the shelf and the berg on Wednesday. The water is warmer relative to the surrounding ice and air - both of which are sub-zero.

"The rift was barely visible in these data in recent weeks, but the signature is so clear now that it must have opened considerably along its whole length," explained Prof Adrian Luckman, whose Project Midas at Swansea University has followed the berg's evolution most closely.

The event was confirmed by other spacecraft such as Europe's Sentinel-1 satellite-radar system.

How does it compare with past bergs?

The new Larsen berg is probably in the top 10 biggest ever recorded.

The largest observed in the satellite era was an object called B-15. It came away from the Ross Ice Shelf in 2000 and measured some
11,000 sq km. Six years later, fragments of this super-berg still persisted and passed by New Zealand.

In 1956, it was reported that a US Navy icebreaker had encountered an object of roughly 32,000 sq km. That is bigger than Belgium. Unfortunately, there were no satellites at the time to follow up and verify the observation.

It has been known also for the Larsen C Ice Shelf itself to spawn bigger bergs. An object measuring some 9,000 sq km came away in 1986. Many of Larsen's progeny can get wound up in a gyre in the Weddell sea or can be despatched north on currents into the Southern Ocean, and even into the South Atlantic.

A good number of bergs from this sector can end up being caught on the shallow continental shelf around the British overseas territory of South Georgia where they gradually wither away.

What is the significance of the calving?

In and of itself, probably very little. The Larsen C shelf is a mass of floating ice formed by glaciers that have flowed down off the eastern side of the Antarctic Peninsula into the ocean. On entering the water, their buoyant fronts lift up and join together to make a single protrusion.

The calving of bergs at the forward edge of the shelf is a very natural behaviour. The shelf likes to maintain an equilibrium and the ejection of bergs is one way it balances the accumulation of mass from snowfall and the input of more ice from the feeding glaciers on land.

That said, scientists think Larsen C is now at its smallest extent since the end of the last ice age some 11,700 years ago, and about 10 other shelves further to the north along the Peninsula have either collapsed or greatly retreated in recent decades.

The two nearby, smaller shelves, Larsen A and Larsen B, disintegrated around the turn of the century; and a warming climate very probably had a role in their demise.

But Larsen C today does not look like its siblings. Prof Helen Fricker, from the Scripps Institution of Oceanography, told BBC News: "The signs we saw at Larsen A and B - we're not seeing yet. The thinning we saw for Larsen A and B - we're not seeing. And we're not seeing any evidence for large volumes of surface meltwater on the order of what you would need to hydro-fracture the ice shelf.

"Most glaciologists are not particularly alarmed by what's going on at Larsen C, yet. It's business as usual."

Researchers will be looking to see how the shelf responds in the coming years, to see how well it maintains a stable configuration, and if its calving rate changes.

There was some keen interest a while back when the crack, which spread across the shelf from a pinning point known as the Gipps Ice Rise, looked as though it might sweep around behind another such anchor called the Bawden Ice Rise. Had that happened, it could have prompted a significant speed-up in the shelf's seaward movement once the berg came off.

As it is, scientists are not now expecting a big change in the speed of the ice.
One fascinating focus for future study will be a strip of "warm", malleable ice that runs east-west through the shelf, reaching the ocean edge about 100km north from the Gipps Ice Rise. This strip is referred to as the Joerg suture zone. There is a large queue of cracks held behind it.

"Calving of the iceberg is not likely itself to make the existing cracks at the Joerg Peninsula suture zone more likely to jump across this boundary," observed Chris Borstad, from the University Centre in Svalbard (UNIS).
"At this stage we really don't know whether there is some larger-scale process that might be weakening this zone, like ocean melting at the base of the shelf, or whether the current rift was just a random or episodic event that was bound to happen at some point.
"We know that rifts like this periodically propagate and cause large tabular icebergs to break from ice shelves, even in the absence of any climate-driven changes.

"I am working with a number of colleagues to design field experiments on Larsen C to answer this specific question (by measuring the properties of the Joerg suture zone directly). But until we get down there and take some more measurements we can only speculate."

Source BBC www.bbc.com/news/science-envir…

Global wildlife populations have fallen by 58% since 1970, a report says.

The Living Planet assessment, by the Zoological Society of London (ZSL) and WWF, suggests that if the trend continues that decline could reach two-thirds among vertebrates by 2020.

The figures suggest that animals living in lakes, rivers and wetlands are suffering the biggest losses.

Human activity, including habitat loss, wildlife trade, pollution and climate change contributed to the declines.

Dr Mike Barrett. head of science and policy at WWF, said: "It's pretty clear under 'business as usual' we will see continued declines in these wildlife populations. But I think now we've reached a point where there isn't really any excuse to let this carry on.

"We know what the causes are and we know the scale of the impact that humans are having on nature and on wildlife populations - it really is now down to us to act."

However the methodology of the report has been criticised.

The Living Planet Report is published every two years and aims to provide an assessment of the state of the world's wildlife.

This analysis looked at 3,700 different species of birds, fish, mammals, amphibians and reptiles - about 6% of the total number of vertebrate species in the world.

The team collected data from peer-reviewed studies, government statistics and surveys collated by conservation groups and NGOs.

Any species with population data going back to 1970, with two or more time points (to show trends) was included in the study.
The researchers then analysed how the population sizes had changed over time.

Some of this information was weighted to take into account the groups of animals that had a great deal of data (there are many records on Arctic and near Arctic birds, for example) or very little data (tropical amphibians, for example). The report authors said this was to make sure a surplus of information about declines in some animals did not skew the overall picture.

The last report, published in 2014, estimated that the world's wildlife populations had halved over the last 40 years.

This assessment suggests that the trend has continued: since 1970, populations have declined by an average of 58%.
Dr Barrett said some groups of animals had fared worse than others.

"We do see particularly strong declines in the freshwater environment - for freshwater species alone, the decline stands at 81% since 1970. This is related to the way water is used and taken out of fresh water systems, and also the fragmentation of freshwater systems through dam building, for example."

It also highlighted other species, such as African elephants , which have suffered huge declines in recent years with the increase in poaching, and sharks, which are threatened by overfishing.

The researchers conclude that vertebrate populations are declining by an average of 2% each year, and warn that if nothing is done, wildlife populations could fall by 67% (below 1970 levels) by the end of the decade.

Dr Robin Freeman, head of ZSL's Indicators & Assessments Unit, said: "But that's assuming things continue as we expect. If pressures - overexploitation, illegal wildlife trade, for example - increase or worsen, then that trend may be worse.

"But one of the things I think is most important about these stats, these trends are declines in the number of animals in wildlife populations - they are not extinctions. By and large they are not vanishing, and that presents us with an opportunity to do something about it."

However, Living Planet reports have drawn some criticisms.

Stuart Pimm, professor of conservation ecology at Duke University in the United States, said that while wildlife was in decline, there were too many gaps in the data to boil population loss down to a single figure.

"There are some numbers [in the report] that are sensible, but there are some numbers that are very, very sketchy," he told BBC News.
"For example, if you look at where the data comes from, not surprisingly, it is massively skewed towards western Europe.

"When you go elsewhere, not only do the data become far fewer, but in practice they become much, much sketchier... there is almost nothing from South America, from tropical Africa, there is not much from the tropics, period. Any time you are trying to mix stuff like that, it is is very very hard to know what the numbers mean.

"They're trying to pull this stuff in a blender and spew out a single number.... It's flawed."

But Dr Freeman said the team had taken the best data possible from around the world.

"It's completely true that in some regions and in some groups, like tropical amphibians for example, we do have a lack of data. But that's
because there is a lack of data.
"We're confident that the method we are using is the best method to present an overall estimate of population decline.

"It's entirely possible that species that aren't being monitored as effectively may be doing much worse - but I'd be very surprised if they were doing much better than we observed. "