This book contains a collection of essays and articles by John Scales Avery discussing the severe problems and challenges which the world faces during the 21st century. Human civilization and the biosphere are threatened by catastrophic climate change. Unless rapid steps are taken to replace fossil fuels by 100% renewable energy, we risk passing a tipping point beyond which uncontrollable feedback loops could produce a 6th extinction event comparable to those observed in the geological record.Another serious threat to human civilization and the biosphere is the danger of a catastrophic thermonuclear war. Over a long period of time there is an ever-increasing risk that such a war will occur by accident or miscalculation.Thirdly, there is threat of an extremely serious and widespread famine, produced by the climate change, rapidly-growing populations, and the end of the fossil fuel era. We must urgently address all three challenges.