Describe net accumulation of GHGs.
Net Accumulation of GHGs refers to the increase in atmospheric concentration of greenhouse gases when total global emissions exceed the rate at which these gases are removed by natural carbon sinks (oceans, forests, soil). This accumulation enhances the greenhouse effect and drives climate change.
Net Accumulation = Total Emissions - Natural Absorption by Sinks
If Emissions > Absorption → Positive Accumulation → Rising Concentrations
| Component | Amount (Gt CO2/year) | Notes |
|---|---|---|
| Emissions from Fossil Fuels | ~36-37 | Coal, oil, gas, cement |
| Emissions from Land Use | ~4-5 | Deforestation, land conversion |
| Total Emissions | ~40-42 | Human-caused emissions |
| Ocean Absorption | ~10-11 | Dissolved CO2, marine organisms |
| Land Sink (Forests) | ~11-12 | Photosynthesis, soil storage |
| Total Absorption | ~21-23 | ~50% of emissions |
| Net Accumulation | ~19-20 | Remains in atmosphere |
Key Point: Earth's natural sinks absorb only about 50% of human CO2 emissions. The remaining 50% (~20 Gt CO2/year) accumulates in the atmosphere, causing concentrations to rise continuously.
| Gas | Pre-Industrial Level | Current Level (2024) | Increase |
|---|---|---|---|
| CO2 | 280 ppm | ~420 ppm | +50% |
| CH4 | 700 ppb | ~1,900 ppb | +170% |
| N2O | 270 ppb | ~335 ppb | +24% |
CO2 has an exceptionally long atmospheric residence time, contributing to persistent accumulation:
Implication: CO2 emitted today will continue affecting climate for hundreds to thousands of years. This creates "carbon debt" - even if emissions stopped today, accumulated CO2 would continue warming the planet.
Stabilizing atmospheric GHG concentrations requires:
Net accumulation of GHGs occurs because human emissions far exceed the absorption capacity of natural carbon sinks. Currently, about half of annual CO2 emissions (~20 Gt) accumulate in the atmosphere each year, raising concentrations from 280 ppm (pre-industrial) to over 420 ppm today. This accumulation, combined with the long atmospheric lifetime of CO2, creates a persistent warming effect that will impact climate for centuries. Achieving climate stabilization requires not just reducing emissions but ultimately reaching net-zero emissions where any remaining emissions are balanced by removal.