Today, 3.5 billion people are alive because of a single chemical process. The Haber-Bosch process takes nitrogen from the air and makes ammonia, from which synthetic fertilizers allow farmers to feed our massive population. Ammonia is a source of highly reactive nitrogen, suitable not just for fertilizer, but also as an ingredient in bomb making and thousands of other applications.

We make around 100 million tonnes of ammonia annually - and spread most of it on our fields. But this is a very inefficient way to use what amounts to 1-2% of the planet's energy needs. Only around 20% of fertilizer made ends up in our food.

Professor Andrea Sella explores some of the alternative ways we might make fertilizer. Vegetables such as peas and beans, allow certain cells in their roots to become infected by a specific type of bacteria. In return, these bacteria provide them with their own fertilizer. Could we infect the plants we want to grow for food – such as cereals – in a similar way to cut down the climatic and environmental impact of Haber-Bosch?

Are you a lark or an owl? Are you at your best in the morning or the evening? Linda Geddes meets the scientists who are exploring the differences between larks and owls. At the University of Surrey's Sleep Research Centre she talks to its director, professor Derk-Jan Dijk, and finds out her own chronotype by filling in a questionnaire.

Linda discovers why we have circadian rhythms and why they do not all run at the same rate. Dr Louis Ptacek from the University of California, San Francisco, explains his investigation of the genes of families whose members get up very early in the morning and of those who get up very late.

She finds out why our sleep patterns change as we age – teenagers really are not good at getting up in the morning. Professor Mary Carskadon from Brown University explains that although some schools have experimented with a later start there is no plan to put this into universal practice.

Linda talks to Professor Til Roenneberg from Ludwig-Maximilians-University Munich about his concept of social jetlag. And she hears about research trying to reduce the exhaustion often suffered by shift workers. Dr Steve Lockley of Harvard University tells her about using blue light to improve the wellbeing of people with medical conditions.

Geoengineering is a controversial approach to dealing with climate change. Gaia Vince explores the process of putting chemicals in the stratosphere to stop solar energy reaching the earth.

When volcanoes erupt they put sulphur in the stratosphere. The particles reflect solar rays back into space and the planet cools down. Scientists are suggesting that it could be possible to put sulphur into the stratosphere using specialised aircraft or a very long pipe. But if this was implemented there could be impacts on rainfall and the ozone layer.

Another idea is to spray seawater to whiten clouds that would reflect more energy away from the earth.

Gaia Vince talks to the researchers who are considering solar radiation management. She also hears from social scientists who are finding out what the public think about the idea and who are asking who should make decisions about implementing this way of cooling the planet.

(Photo: The ocean with the sun rising in the horizon)

The Australasian Antarctic Expedition has been retracing the steps of the first expedition to East Antarctica, a century ago. Its leader was Douglas Mawson, one of the great figures of the heroic age of exploration of the frozen continent.

Alok Jha and Andrew Luck-Baker continue to follow the scientists on the ongoing Australasian Antarctic Expedition 2013. They go out on fieldwork trips with the researchers studying how the wildlife that lives in this inhospitable environment is responding to climate change. Zoologist Tracy Rogers searches for leopard seals with underwater microphones. From a safe distance she takes a small sample from a Weddell seal to find out what it’s been eating. Ornithologist Kerry-Jayne Wilson discovers that an iconic breeding colony of Adelie penguins at Cape Denison, the rocky area where Douglas Mawson built his expedition hut, has depleted numbers as the fast ice has grown.

Producer: Andrew Luck-Baker

Image: Ice-blocked bow of the Shokalskiy and expedition doctor Andrew Peacock

Alok Jha and Andrew Luck-Baker continue to follow the scientists on the ongoing Australasian Antarctic Expedition 2013. Ice, the oceans and climate change are the themes this week as one of the expedition scientists makes a troubling finding. Moored in Commonwealth Bay in East Antarctic, the expedition’s oceanographer Erik van Sibble discovers a stunning difference in the nature of the water beneath the sea ice. Although it is a preliminary finding, the consequences for the motions of the world’s oceans and climate change could be dramatic.

With thanks to AAE volunteer scientist Terry Gostlow for sound recording assistance.

Join the scientists of the Australasian Antarctic Expedition 2013, as they go about their experiments and seek adventure at the windiest place on earth.This location was named the Land of Blizzard by Douglas Mawson, the Antarctic pioneer who was the first to explore this remote and desolate place 100 years ago.

Between 1911 and 1914, Douglas Mawson explored a fiercely harsh part of Antarctica while the more celebrated Scott and Amundsen raced to the South Pole, elsewhere on the frozen continent. Mawson’s expedition was dedicated to scientific study in the early Heroic Age of Antarctic Exploration but his journey was fraught with horror and danger.

Quentin Cooper takes a look at the new materials that can mend themselves. Researchers are currently developing bacteria in concrete which, once awakened, excrete lime to fill any cracks. In South America you can choose a car paint that heals its own scratches. And there are even gold atoms which can migrate to mend tiny breaks in jet turbine blades.

Engineers normally design things so the likelihood of breaking is minimised. But by embracing the inevitability of breakage, a new class of materials which can mend cracks and fissures before you can see them may extend the lives of our cars, engines, buildings and aeroplanes far beyond current capability.

(Image: Presenter, Quentin Cooper, BBC Copyright)

We like to think that we are in control of our lives, of what we do, think and feel. But, as Geoff Watts discovers, scientists are now revealing that this is just an illusion. A simple magic trick reveals just how limited our conscious awareness of the world is, and how easy it is to fool us.

So if our conscious brain can cope with so little, what is responsible for the rest? Science is starting to reveal the crucial role of a silent partner inside our heads, that we are completely unaware of – our unconscious.

In this programme, Geoff enlists the help of, not just brain scientists but, a conjuror and a musician to reveal the pivotal role the unconscious plays in pretty much everything we do, think and feel. This new-found knowledge is enabling scientists to harness its powers for both medical and military benefit.

The human gut has around 100 trillion bacterial cells from up to 1,000 different species. Every person's microbiota (the body's bacterial make-up) is different as a result of the effects of diet and lifestyle, and the childhood source of bacteria. What is it about the microbes in our guts that can have such an impact on our lives?

Scientists are learning more and more about the importance of these bacteria, as well as the viruses, fungi and other microbes that live in our gastrointestinal tracts. Without them, our digestion, immune system and overall health would be compromised.

Adam Hart talks to researchers who are discovering how important a balanced and robust gut microflora is for our health. And he asks how this can be maintained and what happens when things go wrong.

(Image: Gut Microbiota Copyright: Getty Images)