Introduction

Climate System

Causes of Climate Change

Empirical Study of Climate

Climate Modelling

Palaeoclimatic Change

Contemporary Climate Change

Epilogue
Appendix
References

6.5.3. DF-DC relationships

The change in net radiative flux (Wm^-2) at the tropopause, DF, associated with a particular greenhouse gas, is usually expressed as some function of the change in atmospheric concentration of that gas. Direct-effect DF-DC relationships are calculated using detailed radiative-convective models (chapter 4). The form of the DF-DC relationship depends primarily on the existing gas concentration, as explained in section 6.5.1. For low/moderate/high concentrations, the form is well approximated by a linear/square-root/logarithmic dependence of DF on concentration. For example, the DF-DC relationship for CO2 is given by:

DF = 6.3 ln (C/C₀) [Equation 19]

where C₀ is the initial CO2 concentration, C is the final concentration and ln is the natural logarithm (Wigley, 1987; Hansen et al., 1988). This relationship is valid for concentrations up to 1000ppmv. Alternatively, the DF-DC relationship for CFC-12 is given by:

DF = 0.22 (X-X₀) [Equation 20]

where X₀ is the initial CFC-12 concentration and X is the final concentration (Hansen et al., 1988). The relationship holds for X less than 2ppbv (2000pptv).

Nevertheless, it should be appreciated that such relationships are empirical in nature and are therefore subject to uncertainties. First, there are uncertainties in the basic spectroscopic data for many gases. Second, uncertainties arise through details in the radiative-convective modelling. Third, the assumptions used to model DF-DC relationships are subject to uncertainties, for example the assumed vertical profile of concentration, temperature and moisture changes, and the indirect effects on radiative forcing due to chemical interactions.

Greenhouse Effect

Enhanced G-Effect

Greenhouse Gases
 -Carbon Dioxide
  ·Sources
  ·Sinks
  ·Carbon Cycle
  ·Concentrations
  ·Equilibrium
 -Methane
  ·Sources
  ·Sinks
  ·Concentrations
 -Nitrous Oxide
  ·Sources
  ·Sinks
  ·Concentrations
 -Halocarbons
  ·Sources
  ·Sinks
  ·Concentrations
 -Ozone
 -Other Gases
 -Lifetimes
 -Summary

Greenhouse Forcing
 -Forcing Factors
 -GWPs
 -ΔF-ΔC
 -1765 to 1990
 -Ozone

Aerosols
 -Sources & Sinks
 -Forcing
  ·Direct
  ·Indirect
 -Total Forcing

Climate Variations
 -Surface Temp.
 -Precipitation
 -Other
  ·Stratosphere
  ·Cryosphere
  ·Atmos. Circulation
  ·Cloudiness

Detection
 -Modelling
 -Attribution
  ·Latitudes.
  ·Stratosphere
  ·Precipitation
  ·Sea Level
  ·Fingerprints
 -When?

Future Climate
 -GCM Simulations
 -Feedbacks
  ·Water Vapour
  ·Clouds
  ·Ice Albedo
  ·G-house Gases
 -21st Century

Impacts
 -Agriculture
 -Forestry
 -Ecosystems
 -Water Resources
 -Oceans/Coasts
 -Human & Health

Responses
 -Stabilising
 -FCCC
 -Kyoto Protocol
 -UK Programme
  ·Energy Demand
  ·Energy Supply
 -Evaluation