The Greenhouse Effect is fundamentally the atmosphere’s selective transmission of solar radiation: short-wave solar radiation penetrates the atmosphere and reaches the surface where it’s absorbed and converted to heat; the long-wave infrared radiation emitted by the surface is absorbed by atmospheric greenhouse gases (CO₂, CH₄, N₂O, H₂O, etc.) and re-emitted, thus retaining heat. Without the natural greenhouse effect, Earth’s average temperature would be approximately -18°C rather than today’s +15°C — the greenhouse effect itself isn’t the problem; the problem is that human activities have rapidly increased atmospheric greenhouse gas concentrations, causing additional Radiative Forcing.
## Key Climate Indicators and Current Status
**Atmospheric CO₂ concentration**: approximately 280ppm pre-industrialization; 2024 measurements have exceeded 420ppm — the highest level in the past 3 million years — with growth rates still accelerating (approximately 2.5-3ppm annually). **Global average temperature**: approximately 1.2°C above the 1850-1900 pre-industrial baseline; the IPCC’s 1.5°C threshold is expected between the 2030s and 2040s. **Arctic amplification**: the Arctic is warming four times faster than the global average; sea ice extent continuously sets historical minimums; permafrost thaw releases methane forming positive feedback loops.
## Carbon Cycle Imbalance
Earth’s carbon cycle was in dynamic equilibrium pre-industrialization: atmospheric carbon entered the terrestrial biosphere through photosynthesis, entered the ocean through plankton, and was slowly released through geological processes like volcanic activity. Human activities emit approximately 36 billion tons of CO₂ annually (fossil fuel combustion dominant; land use change approximately 10-15%); terrestrial ecosystems and oceans each absorb approximately 25-30%, with the remainder accumulating in the atmosphere. The problem is that we have released carbon accumulated over hundreds of millions of years of geological history within decades — a rate exceeding natural carbon sinks’ absorption capacity.
## Climate Tipping Points
Climate tipping points are nonlinear thresholds in the climate system: once crossed, they self-sustain and are difficult to reverse even if external forcing stops. Major tipping points: West Antarctic Ice Sheet collapse (possible trigger at 1.5°C) → global sea level rise of several meters; Greenland Ice Sheet melt (long-term trigger) → additional 7-meter sea level rise; Amazon rainforest drought collapse (approximately 3-4°C trigger) → loss of the world’s largest carbon sink; permafrost methane release (a slow-onset tipping point already occurring); Atlantic Meridional Overturning Circulation (AMOC) weakening. These tipping points have mutual triggering “domino effects” representing the systemic risk most concerning to climate scientists.
See [Heatwaves and Urban Heat Islands](https://sunqi.org/heatwave-urban-heat-island-en/), [Carbon Markets and Carbon Neutrality](https://sunqi.org/carbon-market-neutrality-en/), and the [IPCC Sixth Assessment Report](https://www.ipcc.ch/assessment-report/ar6/).
