Humanity

Some threats for humanity come from humanity itself. The scenario that has been explored most is a nuclear war or another weapon with similar possibilities. It is difficult to predict whether it would exterminate humanity, but very certainly could alter civilization, in particular if there was a nuclear winter.
Another category of disasters are unforeseen consequences of technology.
It has been suggested that learning computers that rapidly become superintelligent may take unforeseen actions or that robots would out-compete humanity.Because of its exceptional scheduling and organisational capability and the range of novel technologies it could develop, it is possible that the first Earth superintelligence to emerge could rapidly become very, very powerful. Quite possibly, it would be matchless and unrivalled: conceivably it would be able to bring about almost any possible outcome, and be able to foil virtually any attempt that threatened to prevent it achieving its desires.It could eliminate, wiping out if it chose, any other challenging rival intellects, alternatively it might manipulate or persuade them to change their behaviour towards its own interests, or it may merely obstruct their attempts at interference.
Biotechnology could lead to the creation of a pandemic, Nanotechnology could lead to grey goo in which out-of-control self-replicating robots consume all living matter on Earth while building more of themselves - in both cases, either deliberately or by accident.It has also been suggested that physical scientists might accidentally create a device that could destroy the earth and the solar system.Another kind of accident is the Ice-9 Type Transition, in which our planet including everything on it becomes a strange matter planet in a chain reaction. Some do not view this as a credible scenario.
It has been suggested that runaway global warming might cause the climate on Earth to become like Venus, which would make it uninhabitable. In less extreme scenarios it could cause the end of civilization.According to a UN climate report, the Himalayan glaciers that are the sources of Asia's biggest rivers - Ganges, Indus, Brahmaputra, Yangtze, Mekong, Salween and Yellow - could disappear by 2035 as temperatures rise.Approximately 2.4 billion people live in the drainage basin of the Himalayan rivers.India, China, Pakistan, Bangladesh, Nepal and Myanmar could experience floods followed by droughts in coming decades. In India alone, the Ganges provides water for drinking and farming for more than 500 million people.The west coast of North America, which gets much of its water from glaciers in mountain ranges such as the Rocky Mountains, Cascade Mountains and Sierra Nevada, also would be affected.According to the California Department of Water Resources, if more water supplies are not found by 2020, California residents will face a water shortfall nearly as great as the amount consumed today. Directly linked to observed increases in the intensity and frequency of natural disasters, global warming and climate change are now considered key drivers behind rising global humanitarian and emergency relief needs. According to the UN’s Office for the Coordination of Humanitarian Affairs (OCHA), climate disasters are on the rise. Around 70 percent of disasters are now climate related – up from around 50 percent from two decades ago.These disasters take a heavier human toll and come with a higher price tag.In the last decade, 2.4 billion people were affected by climate related disasters, compared to 1.7 billion in the previous decade and the cost of responding to disasters has risen tenfold between 1992 and 2008.Destructive sudden heavy rains, intense tropical storms, repeated flooding and droughts are likely to increase, as will the vulnerability of local communities in the absence of strong concerted action.
Approximately 40% of the world's agricultural land is seriously degraded. In Africa, if current trends of soil degradation continue, the continent might be able to feed just 25% of its population by 2025, according to UNU's Ghana-based Institute for Natural Resources in Africa.
James Lovelock, creator of the Gaia hypothesis, in his book The Revenge of Gaia (2006), has suggested that the elimination of rain forests, and the falling planetary biodiversity is removing the homeostatic negative feedback mechanisms that maintain climate stability by reducing the effects of greenhouse gas emissions (particularly carbon dioxide). With the heating of the oceans, the extension of the thermocline layer into Arctic and Antarctic waters is preventing the overturning and nutrient enrichment necessary for algal blooms of phytoplankton on which the ecosystems of these areas depend. With the loss of phytoplankton and tropical rain forests, two of the main carbon dioxide sinks for reducing global warming, he suggests a runaway positive feedback effect could cause tropical deserts to cover most of the world's tropical regions, and the disappearance of polar ice caps, posing a serious challenge to global civilization.Using scenario analysis, the Global Scenario Group (GSG), a coalition of international scientists convened by Paul Raskin, developed a series of possible futures for the world as it enters a Planetary Phase of Civilization. One scenario involves the complete breakdown of civilization as the effects of climate change become more pronounced, competition for scarce resources increases, and the rift between the poor and the wealthy widens. The GSG’s other scenarios, such as Policy Reform, Eco-Communalism, and Great Transition avoid this societal collapse and eventually result in environmental and social sustainability. They claim the outcome is dependent on human choiceand the possible formation of a global citizens movement which could influence the trajectory of global development.