This article argues, from first principles of thermodynamics and mathematics, that global mean surface temperature (GMST) is physically meaningless. The brief description that follows reproduces the opening paragraphs of the paper verbatim.“The very concept of objective truth is fading out of the world. Lies will pass into history.” — George Orwell, Looking Back on the Spanish War (1943) ABSTRACT Trillions of dollars are being spent ostensibly to avert a threatened global climate disaster. According to the UN Intergovernmental Panel on Climate Change (IPCC), the global mean surface temperature (GMST) must not increase more than a stated amount above the pre-industrial baseline (1850–1900) to prevent irreversible catastrophe. However, the GMST does not have a precise regulatory definition, and is in fact physically meaningless based on fundamental principles of thermodynamics. Nevertheless, all IPCC climate models are tuned to reproduce historical GMST trends. This represents what Orwell presciently described: the systematic replacement of objective truth with politically convenient fiction. Introduction The UN Intergovernmental Panel on Climate Change (IPCC) has assessed the risks of global warming at 1.5°C or 2°C above pre-industrial levels as critical thresholds that some have characterized as the most important numbers in the world. According to the IPCC assessments, global mean surface temperature (GMST) must not increase more than these amounts above the pre-industrial baseline (1850–1900) to prevent irreversible catastrophes from global warming. This target was formally adopted by 196 nations in the Paris Agreement of 2015. However, the mathematical and physical foundation underlying this entire framework does not exist, demonstrating that the concept of global temperature is not merely imprecise or approximate—it is mathematically and physically meaningless.