Monsters and Such (1959) by MurRay Leinster

'The Mad Planet' by Murray Leinster was the first global warming story ever written. Set hundreds of years in the future, Earth has gone mad, CO2 levels have risen across the globe causing a rise in temperature, and human beings have descended to savagery. The change in climate has wreaked havoc with the environment giving rise to new predators and challenges for man. Burl has spent his entire life one step away from oblivion, he's heard the stories about the former greatness of his race, and yearns for a return to that time.

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