Why did the world choose 1.5°C as a climate guardrail?
In short: In 2015, 195 nations agreed to a specific number: 1.5°C. But this wasn't an arbitrary choice. It was a hard-won shift from a previous 2°C goal, driven by the urgent needs of vulnerable nations and a scientific understanding of irreversible climate tipping points.
The journey to 1.5°C began with the 1992 United Nations Framework Convention on Climate Change, which aimed to stabilize greenhouse gases to avoid 'dangerous' human interference. By the 1990s and early 2000s, scientists and policymakers identified 2°C above pre-industrial levels as a viable target to prevent the most severe, irreversible effects of warming. This 2°C goal was formally adopted at COP16 in Cancun.
The shift toward a stricter 1.5°C limit was largely catalyzed by the Alliance of Small Island States (AOSIS). Their research highlighted that a 2°C increase would lead to catastrophic sea-level rise and extreme temperatures for coastal and island communities. This evidence prompted an expert-led assessment under the UNFCCC, which concluded that the 2°C 'guardrail' was insufficient to protect the most vulnerable regions. Consequently, the 2015 Paris Agreement adopted the more ambitious 1.5°C target.
To measure this, scientists use the 'pre-industrial' period—generally defined as 1850 to 1900—because it is the earliest era with consistent global temperature records and predates significant human fossil fuel use. During this time, the global average temperature hovered around 13.5°C. While warming has already reached 1.25°C, the goal is not to stop all warming instantly, but to prevent the 'inexorable slide' into climate chaos that occurs as we move further past these critical thresholds.
Every tenth of a degree matters because it influences the frequency and intensity of extreme weather, such as the record-breaking heat and wildfires seen in 2023. While passing 1.5°C does not mean immediate catastrophe, every year of delay increases the eventual cost of climate mitigation for future generations.
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Sources
- Summary by Intellect · source: Why 1.5°C Matters
- Also: Explained: The 1.5 C climate benchmark
- Also: What's in a number? The meaning of the 1.5-C climate threshold
- Also: Why 1.5°C?
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