The 21st century The 21st century began with the United States as the sole superpower in the absence of the Soviet Union, with China emerging as a potential superpower. The debate over what should be done about fossil fuel pollution and alternative energy raged in the new century after most of the 20th century was marked by rapid industrial expansion. As the Cold War was over and Islamic fundamentalist-related terrorism on the rise, the United States and its allies turned their attention to the Middle East. Digital technology – in its early stages of mainstream use in the 1980s and 1990s – became widely adopted by most of the world, though concerns about stress and anti-sociality from the overuse of mobile phones, the Internet and related technologies remained controversial. Over 1.5 billion people worldwide used the Internet by the end of the first decade and over 4 billion (more than half the world's population) used cell phones. A global financial downturn – triggered by a sub-prime mortgage crisis in the U.S. – resulted in soaring levels of personal and national debt. Alongside this were ever-growing divides between rich and poor. At the same time, citizens were becoming more and more aware of excessive surveillance, privacy intrusion and erosion of civil liberties by governments and the corporations influencing them. A new set of crises would emerge in the 2020s. Climate change was beginning to have a significant impact on worldwide commodities; in particular, food and water supplies. In the Middle East, Africa and elsewhere, growing instability led to a number of resource wars. Perversely, the hunt for fossil fuels continued, with even the Arctic becoming a political and economic battleground as nations sought to claim the last remaining deposits. The 2030s were marked by a rapid, worldwide shift towards clean energy, algae biofuel and other renewable sources – aided by startling breakthroughs in nanotechnology. This was followed by progress in nuclear fusion, though widespread adoption would have to wait until later decades. Despite this, conflict was now brewing around much of the world. Africa, Asia and other regions were suffering mightily due to food shortages and a growing influx of refugees affected by climate change, resource wars and political instability. Exponential advances in computing power – in parallel with genetics, nanotechnology and robotics – continued into the 2040s, leading to what many called the birth of "transhumanism". Ever smaller, more complex and sophisticated devices were becoming implantable and integrated within the human body – able to combat disease, enhance the senses and provide entertainment or communication in ways that simply were not possible before. Geopolitics was undergoing a revolution too, with India now surpassing the U.S. in terms of economic power and even threatening to overtake China in the near future. Mankind began to escape the confines of its crowded home planet with a permanent colony on Mars in the 2050s. Even greater advances in computing power saw AI beginning to play a major role in business and government decisions. Economic growth was now under severe strain, however, due to ecological impacts, resource scarcity, demographic trends, technological unemployment and other factors. By 2060, the world's population had begun to level off and plateau. This was partly a result of declining fertility rates (aided by improvements in education and birth control), but also from significant numbers of deaths caused by deteriorating environmental conditions. Entire nations were now being devastated by the effects of climate change. Despite advances in technology, the fundamental problem remained that humanity was consuming too much, too fast, beyond what the Earth could sustainably provide. Desperate attempts were made to improve carbon capture and geoengineering methods, but the sheer magnitude of this crisis would persist for decades to come. The 2070s saw major growth in the use of fusion power. Accelerated space development also marked this time, with expansion of the lunar colonies and their automated mining operations. By now, a full-scale environmental catastrophe was unfolding on Earth, with sea levels forcing the large-scale evacuation of cities. With continuing advances in AI, the 2080s saw an explosion in scientific discoveries. This helped to slow the rise in global temperatures and pave the way for a more sustainable future in the 22nd century. Transhumanism was now a mainstream phenomenon, the average citizen becoming heavily reliant on brain-computer interfaces and other implantable devices, contributing to a decline in religious adherence. By the 2090s, it became clear that Homo sapiens were no longer the dominant species on the planet. Much of the day-to-day running of world affairs was now handled exclusively by ultra-fast, ultra-intelligent machines, robots and virtual entities.