Climate change is simultaneously one of the strongest scientific consensuses and the most politically contested global issues. The IPCC’s Sixth Assessment Report (AR6, released 2021–2022) represents the work of thousands of scientists globally and provides the most authoritative foundation for understanding climate change.
## Current Warming Level and Projections
Per IPCC AR6, global average temperature has risen approximately 1.1°C above pre-industrial levels (1850–1900 baseline) as of 2019. Across emissions scenarios:
– **Low-emission scenario (SSP1-1.9, rapid reduction)**: warming held below 1.5°C by century end, though possibly briefly exceeding 1.5°C mid-century before declining (Overshoot).
– **Intermediate scenario (SSP2-4.5)**: approximately 2.7°C by 2100.
– **High-emission scenario (SSP5-8.5)**: approximately 4.4°C by 2100.
## 1.5°C vs. 2°C: The Real Difference
Why 0.5°C matters: climate system nonlinearity means 2°C impacts aren’t linearly greater than 1.5°C — they diverge sharply on key indicators:
– Ice-free Arctic summer: once per century at 1.5°C; once per decade at 2°C.
– Coral reefs: 70–90% degradation at 1.5°C; near-total loss (>99%) at 2°C.
– Sea level rise by 2100: ~0.43m at 1.5°C vs. ~0.46m at 2°C (limited near-term difference; long-term divergence beyond 2100 is much larger).
– Extreme heat: heatwave intensity, frequency, and duration substantially higher at 2°C than 1.5°C.
## Climate Tipping Points
Tipping points are irreversible transitions from one stable climate state to another — once triggered, potentially impossible to reverse even if emissions cease completely. Most-studied tipping points:
– **West Antarctic Ice Sheet collapse**: possibly triggerable at 1.5–2°C; would cause meters of long-term sea level rise.
– **Greenland Ice Sheet melt**: trigger range possibly 1.5–2°C; ~7m long-term sea level rise potential.
– **Amazon Dieback**: the Amazon may transition from rainforest to savanna after losing ~20–25% forest cover (currently ~17–20% lost).
– **Permafrost thaw**: massive methane and CO₂ release creating self-reinforcing warming feedback.
See [Green Finance and Carbon Markets](https://sunqi.org/green-finance-carbon-market-en/), [Carbon Capture Technology](https://sunqi.org/carbon-capture-technology-en/), and the [IPCC AR6 Synthesis Report](https://www.ipcc.ch/report/ar6/syr/).
