This episode explores the nature of the greenhouse effect (discovered by Joseph Fourier and Svante Arrhenius), and the evidence demonstrating the existence of global warming from humanity's influence. Tyson begins by describing the long-term history of the planet Venus; based on readings from the Venera series of probes to the planet, the planet had once had an ocean and an atmosphere, but due to the release of carbon dioxide from volcanic eruptions, the runaway greenhouse effect on Venus caused the surface temperatures to increase and boiled away the oceans. Tyson then notes the delicate nature of the amount of carbon dioxide in the atmosphere can influence Earth's climate due to the greenhouse effect, and that levels of carbon dioxide have been increasing since the start of the 20th century. Evidence has shown this to be from mankind's consumption of oil, coal, and gas instead of from volcanic eruptions due to the isotopic signature of the carbon dioxide. The increase in carbon dioxide has led to an increase in temperatures, in turn leading to positive feedback loops of the melting polar ice caps and dethawing of the permafrost to increase carbon dioxide levels. Tyson then notes that humans have discovered means of harvesting solar power, such as Augustin Mouchot's solar-driven motor in the 19th century, and Frank Shuman's solar-based steam generator in the 1910's. Tyson points out that in both cases, the economics and ease of using cheap coal and oil caused these inventions to be overlooked at the time. Today, solar and wind-power systems would be able to collect enough solar energy from the sun easily. Tyson then compares the motivation for switching to these cleaner forms of energy to the efforts of the Space race and emphasizes that it is not too late for humanity to correct its course.

The Ebola virus is one of the most virulent infections known to science. This special episode of Horizon meets the scientists and doctors from all around the world looking for the cure and hears first-hand accounts of what it is actually like to catch and survive the disease

Academy Award-winning director Alex Gibney (Taxi to the Dark Side) masterfully explores the fall of the disgraced cycling champion following the 2009 Tour de France, making use of his extraordinary access to attain rare interviews with former teammates, alleged doping mastermind Dr. Michele Ferrari, and Armstrong himself. What was Lance Armstrong thinking? For years, after seizing international fame as the cancer survivor who won seven Tour de France titles, he fiercely denied accusations that he used performance-enhancing drugs. He used his power to aggressively litigate journalists and publicly humiliate former friends who claimed otherwise. His deceit finally cracked in January 2013, when he admitted guilt to Oprah Winfrey in a television interview that critics decried for only scratching the surface. Academy Award-winning director Alex Gibney approaches Armstrong with unique and extraordinary access. In 2009, Gibney was commissioned to make a film about Armstrong's return to the Tour de France, four years after the racing champion had declared retirement. That race would later stir up devastating evidence in the case against Armstrong. But Gibney came away from the experience unable to reconcile the discrepancy between doping allegations and Armstrong's emphatic denials. Then, post-Oprah, Gibney went back to Armstrong for new interviews to extract a more detailed account of his double life. In The Armstrong Lie, Gibney masterfully explores the complexities of the case, interweaving the dramatic action of the 2009 Tour de France, when Armstrong found himself unexpectedly competing against his own teammate Alberto Contador. Gibney attains rare interviews with Armstrong's former teammates and alleged doping mastermind Dr. Michele Ferrari. The film also raises troubling questions about the process of doping regulation. Recently, when asked to give advice to documentary filmmakers, Gibney responded with a motto exemplified by this film: "Embrace contradictions."

Travelling from K2 in Pakistan to Ladakh in India. It is a short distance as the crow flies but, due to politics, a huge loop. He passes through the Sikh city of Amritsar, with its Golden Temple, and through Shimla with its Vice Regal Lodge, Gaiety Theatre and cosy half-timbered tea-houses. He then meets the 14th Dalai Lama in Dharamsala, where the Tibetan government is in exile.

This episode tells the story of the Jewish Revolt, which swept through Judea in AD 66 and threatened to destabilise the whole empire. Rome turned to the disgraced General Vespasian and his son Titus to put it down. Filled with spectacular sieges and huge set-piece action, the film pits the discipline and ingenuity of the Roman army against the passion and commitment of the rebels.

In episode two, we discover the golden age of the La Tene Celtic warrior and reveal how their world extended as far as central Turkey. But by the middle of the first century BC, the Celts were under threat from an expanding Roman Empire, and the Gallic warrior Vercingetorix would challenge Julius Caesar in an epic battle that would shape the future of Europe.