We face one of the greatest challenges in the history of humanity, to eliminate the fuels that have driven progress and technology for over a century, while our thirst for energy only grows. The sun is the biggest source of energy in the solar system. It's like a nuclear reactor in the sky, and it provides endless power. If we can harvest just fractions of this, it can power all our consumption. Innovators are searching for new ways to capture more of the sun’s power, and make it available through the night, everywhere.

The extraordinary wildlife, culture and history of this immense, fascinating ocean and its myriad islands are revealed in stunning detail. With its coral reefs, turquoise lagoons and dramatic oceanic atolls, the South Pacific is the archetypal paradise. It is still relatively healthy and teeming with fish, but it is a fragile paradise. International fishing fleets are taking a serious toll on the sharks, albatross and tuna, and there are other insidious threats to these bountiful seas. We look at what is being done to preserve the ocean and its wildlife.

With much of it covered in ice all year round and with no daylight from October to March, the Arctic Ocean is one of the world's most remarkable oceans. Its home to a multitude of unique life forms, all highly adapted to cope with the extreme and seasonal conditions. The impacts of climate change are more strongly felt here than anywhere else in the world.

'The Coldest War': With the polar ice caps shrinking due to global warming, new trade routes are being exposed, along with billions of dollars' worth of natural-resource reserves. The five nations bordering the Arctic are readying themselves to fight for it. The problem is that there's one non-NATO country that already considers itself rightful owner of the region: Russia. With Vladimir Putin's recent military annexation of Crimea, there's a definite possibility its aggressions will boil over, returning the international community to precarious Cold War footing. We will head north to witness NATO forces participating in the largest polar military exercise in history. 'Heroin Warfare': Since the U.S. occupation of Afghanistan, heroin production in the region has skyrocketed, making the country the number-one producer by a large margin. Though Iran, Afghanistan's neighbor, is an ultraconservative country, Afghan heroin flowing across the border has actually caused Iran to have the worst heroin use problem in the world. Suroosh Alvi gets a rare look inside Iran to meet the suffering heroin addicts, and see how the country is coping with the illegal drug trade.

Every day our planet faces cataclysmic events that threaten our very existence. Whether from natural or man-made forces, rising from the earth or menacing from space, the world seems beset by more catastrophes than ever. Some believe the signs of the coming Apocalypse are all around us–as outlined in the bible’s most compelling book of prophecies: Revelation". And even the non-religious can’t ignore what appears to be a growing rate of globe-threatening disasters. Are we approaching a biblical “End of Times”? And if so–how will it happen? Will it come from an act of God? Or a colossal misstep of man? Get an uncomfortably close front row seat to some of the most likely apocalyptic scenarios our world faces today–and the history, both scientific and biblical, behind them.

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.