Deserts
When astronauts peer down on Planet Earth, the one environment they all notice are the deserts, which make up a staggering 30 per cent of the land's surface. From space they look empty and lifeless. A closer look reveals a very different picture.
Deserts are united by their lack of rain yet they are the most varied of our planet's ecosystems.
Mongolia's Gobi Desert is home to wild Bactrian camels, one of the rarest mammals on the planet, that survive by eating snow in lieu of water.
In Atacama, Chile, in the driest desert in the world guanacos survive by licking the dew off cactus spines.
Changes are rare in deserts but they play a crucial part in their story. Planet Earth is remarkable for having captured some of these key moments of change, from Saharan sandstorms nearly a mile high to desert rivers that run for a single day.
In the USA, the brief blooming of Death Valley triggers a plague of desert locusts 65 kilometres wide and 160 kilometres long, two spectacles that might only occur once in 30 years.
The highlight of the programme is a unique aerial voyage over the dunes and rocky escarpments of the Namibian deserts. From this aerial perspective it is possible for the first time to follow some very un-desert like animals.
Elephants embark on a long and desperate trek for food, and most amazingly of all, desert lions are searching the wilderness for wandering bands of oryx.
Planet Earth unravels the secrets behind desert survival and for the first time on such a scale, reveals the ephemeral nature of this dynamic environment.
Producer - Huw Cordey
Snow in the Gobi - Gobi Desert, Mongolia
When I was at university, the Gobi desert was an analogy for being single. So if you weren't in a relationship, you were 'in the Gobi'.
In our consciousness the Gobi desert was a scorched wasteland of sand and rock; the sort of place where encountering any kind of life at all seemed utterly unlikely.
Nearly 20 years later - and well into married life - the Gobi loomed large again. I couldn't resist phoning my relationship starved university friend to ask for some advice, but it was I who told him about the possibility of snow and the mind numbingly low temperatures.
The Gobi was not, after all, a place of unrelenting heat. In the summer the daily temperature exceeds 40 degrees but in mid-winter there are few places colder.
The Gobi has good wildlife too. It was home to the last truly wild Bactrian camels although seeing them wouldn't be easy. The area was vast, there weren't many of them, and their senses were so acute that they were known to run from humans at a distance of four kilometres.
Then there was the 1500 kilometre journey from Ulan Batar. Ulan Batar, Mongolia's capital, is the only capital in the world where the average yearly temperature is less than zero degrees.
In mid-winter the locals fantasize about it being just zero degrees. I could see their point. Coming out of the city's international airport the dry cold made the moisture in our nostrils freeze. We all laughed nervously knowing we would be camping in these conditions. Astonishingly we were entering a place as large as Holland and we were to be the only people in it.
The first night of camping was a shock. There was no snow but the temperature dropped down to minus 25 degrees.
We had our first camel sighting early on making me think that the challenges had been overestimated but getting close was a different matter.
The camels were spots in my binoculars and any attempt to reduce the distance made them run. Then one morning we woke to find a Siberian wind had dumped several inches of snow over the Gobi's distinctive black gravel plains and rolling hills.
In the distance we spotted a line of wild camels, padding across a vast snowy plain with a backdrop of snowy mountains.
Camels and snow - the sight was sublimely surreal. Oblivious to our presence they gradually got closer - close enough for me to appreciate that superior look worn by all camels.
But these definitely had something to be proud about. They were some of the last surviving members of their species and they had conquered the Gobi.
Huw Cordey
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