While Dystopian, Cyberpunk, Post-Apocalyptic, and Biopunk books share some thematic similarities, each subgenre has distinct characteristics that set them apart:

1. **Dystopian Fiction**: Dystopian fiction portrays societies characterized by oppressive governments, social control, and often environmental or technological degradation. These worlds are typically bleak and authoritarian, with citizens living under constant surveillance and facing limited freedoms. Dystopian narratives often focus on themes of resistance, rebellion, and the struggle for individuality within oppressive systems. Examples include "1984" by George Orwell and "The Hunger Games" by Suzanne Collins.

2. **Cyberpunk**: Cyberpunk is a subgenre of science fiction that takes place in dystopian futures dominated by advanced technology, artificial intelligence, and cybernetic enhancements. These worlds are often characterized by urban decay, corporate control, and a high-tech, low-life aesthetic. Cyberpunk narratives explore themes of societal inequality, human-machine interface, and the consequences of unchecked technological progress. Examples include "Neuromancer" by William Gibson and "Blade Runner" by Philip K. Dick.

3. **Post-Apocalyptic Fiction**: Post-apocalyptic fiction is set in worlds devastated by catastrophic events such as nuclear war, pandemics, or environmental collapse. These narratives focus on the aftermath of civilization's downfall, with survivors struggling to rebuild society amidst the ruins. Post-apocalyptic settings are often desolate and hostile, with resources scarce and dangers lurking at every turn. Examples include "The Road" by Cormac McCarthy and "The Stand" by Stephen King.

4. **Biopunk**: Biopunk explores the intersection of biology, genetics, and technology, often depicting worlds where advancements in biotechnology have profound social, ethical, and environmental implications. Biopunk narratives may feature bio-engineered organisms, genetic manipulation, or biotechnological dystopias where corporations wield immense power over genetic resources. Themes often include genetic enhancement, bioethics, and the consequences of playing god with life. Examples include "Oryx and Crake" by Margaret Atwood and "The Windup Girl" by Paolo Bacigalupi.

In summary, while all four subgenres share themes of societal upheaval and speculative futures, Dystopian fiction focuses on oppressive regimes and social control, Cyberpunk explores high-tech, low-life worlds dominated by technology, Post-Apocalyptic fiction depicts the aftermath of civilization's collapse, and Biopunk delves into the ethical dilemmas of biotechnological advancements. Each subgenre offers a unique perspective on the human condition and the potential consequences of our actions on society and the environment.

Climate fiction, or Cli-Fi, emerged as a distinct subgenre of science fiction in response to growing concerns about climate change and its impacts on the planet. While the roots of Cli-Fi can be traced back to earlier works that explored environmental themes, the subgenre gained prominence in the late 20th and early 21st centuries as awareness of climate change and its potential consequences increased.

The popularity of Cli-Fi surged in the 2000s as authors began to grapple with the urgent reality of climate change and its implications for the future of humanity and the planet. Prominent authors such as Margaret Atwood, Paolo Bacigalupi, Kim Stanley Robinson, and Barbara Kingsolver have contributed to the rise of Cli-Fi with their thought-provoking novels that explore environmental degradation, ecological collapse, and humanity's role in shaping the fate of the Earth.

Cli-Fi novels often depict near-future scenarios in which the effects of climate change are fully realized, presenting readers with dystopian or speculative worlds shaped by rising sea levels, extreme weather events, resource scarcity, and societal upheaval. By blending scientific speculation with imaginative storytelling, Cli-Fi novels serve as cautionary tales, urging readers to confront the reality of climate change and consider the potential consequences of inaction.

The emergence of Cli-Fi as its own subgenre of science fiction reflects a growing recognition of the critical importance of addressing climate change in literature and popular culture. By focusing on the intersection of science, society, and the environment, Cli-Fi offers a platform for exploring complex environmental issues, raising awareness, and inspiring action to mitigate the impacts of climate change and build a more sustainable future. As climate change continues to shape the world we live in, Cli-Fi stands as a vital genre for exploring the challenges and possibilities of a changing planet.

Determining the most sold science fiction book ever can be challenging due to various factors such as different editions, translations, and sales tracking methods over time. However, some science fiction novels have achieved widespread popularity and high sales figures.

One of the most iconic and widely sold science fiction novels is "Dune" by Frank Herbert. Published in 1965, "Dune" is a epic saga set in a distant future where noble houses vie for control of the desert planet Arrakis, known for its valuable spice melange. "Dune" has sold millions of copies worldwide, translated into numerous languages, and remains a cornerstone of the science fiction genre.

Another highly successful science fiction novel is "The Hitchhiker's Guide to the Galaxy" by Douglas Adams. First published in 1979, this comedic science fiction series follows the misadventures of Arthur Dent, an ordinary human who is swept away on a cosmic journey after Earth is destroyed to make way for a hyperspace bypass. "The Hitchhiker's Guide to the Galaxy" has garnered a massive fanbase and sold millions of copies globally.