UK brought low by Arctic high

The weather outside is frightful... Image: NASA

The picture above, taken by NASA’s Terra satellite on the 7^th January, shows the completely snow-bound state of the UK. This winter, temperatures have regularly fallen below -10^oC in some parts of the country, and heavy snow has closed roads, schools and businesses. But why is this year so much colder than usual?

Globally, it isn’t. While the UK, parts of North America and China are suffering in the cold, other parts of the world, including the Mediterranean and Siberia, are experiencing unseasonal warmth. The cause of this confusing weather is an area of unusually high atmospheric pressure over the Arctic, which is driving colder air southwards towards northern Europe.

The changes in air pressure over the Arctic are known as the Arctic Oscillation (or AO, for short). It swings between positive (low pressure) and negative (high pressure). This year, the AO has become very ‘negative’, resulting in the freezing conditions some of us are shivering through at the moment.

One thing this cold weather doesn’t affect, however, is the reality of our changing global climate. Regional weather variations like this do not discredit the long-term climatic warming trend scientists from around the world have observed: the blame for which lies squarely with man’s increasing CO₂ emissions.

Turtles tagged for their own protection

Researchers from the UK and Gabon have attached satellite tags to two leatherback turtles, called Darwinia and Noelle, which live in the South Atlantic off the coast of Gabon, in Africa. This area is an important breeding ground for the leatherbacks but is also under pressure from industrial fishing and oil exploitation.

Noelle the leatherback - easy to find in a game of hide-and-seek. Image: Dr Matthew Witt, University of Exeter

Although leatherbacks are the most widespread marine turtle they are listed as critically endangered by the IUCN, so understanding where the turtles go will help researchers carry out vital conservation work to protect them. Ultimately, the researchers hope the government of Gabon will extend existing marine protected areas – nature reserves of the sea – to protect the areas of greatest importance to the leatherback turtles from increasing industrial activity.

The data from the satellite tags is being made available to the public on the website www.seaturtle.org. You can all follow the journey made by Darwinia and Noelle over the coming weeks here.

Leatherback turtles (Dermochelys coriacea) are the largest living turtle and the fourth largest living reptile, reaching up to 2.7 metres wide, from flipper to flipper. Their most distinguishing feature is their leathery ‘shell’, which replaces the think bony coverings most turtles are famous for. Leatherbacks prey on jellyfish, and they’ve been known to cross oceans in search of their slippery prey.

Witness the death of a sea

The Aral Sea is dying. Between 2006 and 2009 one of the remaining areas of the rapidly-evaporating sea lost up to 80% of its water.  This dramatic new animated image, composed of pictures taken by the European Space Agency’s Envisat satellite, shows the true extent of the loss (the image may take a few seconds to load).

The greenish blue water can be seen retreating, leaving behind a salt-covered desert – the Aral Karakum. Image credit: ESA

The Aral Sea used to be the fourth largest inland sea in the world, so how has this occurred? Receiving only around ten centimetres of rainfall a year, the water level in the Aral Sea was maintained by two rivers, the Syr Darya and the Amu Darya. The Soviet Union diverted these rivers to irrigate water-intensive crops such as cotton and rice, reducing the flow of water reaching the Aral Sea itself to a trickle. Insufficient water reached the sea to replace that lost by evaporation and the resulting environmental destruction was inevitable.

The environmental tragedy of the Aral Sea is only one side of the story. The human tragedy caused by the loss of the sea is immense: as the water evaporated it left behind large amounts of salt and other minerals. These have turned the remaining water into a toxic pool, destroying the previously-abundant fish stocks that used to support a thriving fishing fleet.

The retreating water has also left behind 40,000 square kilometres of salt-covered desert – the Aral Karakum. In the hot, windy climate this dries out and is blown hundreds of kilometres, causing health problems for the people living downwind and stirring up so much dust that the local climate is altered.

A small ray of hope remains for one small part of the sea: using money from a World Bank loan, Kazakhstan hopes to save the small, isolated, northern region of the Aral Sea. The doomed southern sections are expected to dry out completely by 2020.