Note 1: References

1. Extract from Summary for Policymakers, the Third Assessment Report of Working Group I of the Intergovernmental Panel on Climate Change (IPCC)
1-1. Model calculations of the concentrations of the non-CO₂ greenhouse gases by 2100 vary considerably across the SRES illustrative emission scenarios, with CH₄ changing by between -190 and +1,970 ppb (present concentration 1,760 ppb), N₂O changing by between +38 and +144 ppb (present concentration 316 ppb), total tropospheric O₃ changing by between -12 and +62%, and a wide range of changes in concentrations of HFCs, PFCs and SF₆, all relative to the year 2000. In some scenarios, total tropospheric O₃ would become as important a radiative forcing agent as CH₄ and, over much of the Northern Hemisphere, would threaten the attainment of current air quality targets.ⁱ

1-2. The total amount of O₃ in the troposphere is estimated to have increased by 36% since 1750, due primarily to anthropogenic emissions of several O₃-forming gases.ⁱⁱ This corresponds to a positive radiative forcing of 0.35 Wm^-2. O₃ forcing varies considerably by region and responds much more quickly to changes in emissionsⁱⁱⁱ than the long-lived greenhouse gases, such as CO₂.

2. Explanation of Terminology
2-1. Radiative Forcing
Radiative forcing is the perturbation to the balance of the energy budget expressed as the amount of radiation per unit area at the tropopause. This is caused by factors such as incoming solar radiation, atmospheric greenhouse gas concentrations, and cloud quantity. The concept of radiative forcing can be used to quantitatively compare the contribution of these factors to climate change. Radiative forcing is also used as a gauge for expressing the extent of the greenhouse effect.

2-2. SRES
Special Report on Emission Scenarios (from the IPCC)

3. Stratospheric Ozone and Tropospheric Ozone
Approximately 90% of global ozone is found in the stratosphere, and the remaining 10% exists in the troposphere. Therefore, to prevent the increased ultraviolet radiation at the Earth's surface resulting from a 10% reduction in stratospheric ozone, for example, tropospheric ozone would have to be increased by almost 100% (double) if it were to compensate for the loss. Doubling tropospheric ozone would have detrimental effects such as causing further damage to vegetation, adversely impacting human health, and worsening the greenhouse effect. Therefore, it is unrealistic to think that an increase in tropospheric ozone will compensate for stratospheric ozone depletion. The environmental impact of higher tropospheric ozone levels is expected to become an increasingly serious problem.

ⁱ The average hourly value in Japan is 60 ppb.
ⁱⁱ Ozone is formed by photochemical reactions in the atmosphere of nitrogen oxides, hydrocarbons, and carbon monoxide.
ⁱⁱⁱ The life of ozone is 1 to 2 weeks in summer, and 1 to 2 months in winter.