1. Volcanoes
Large volcanic eruptions with high SO2 content can release SO2 into the stratosphere. This SO2 eventually combined with water vapor to make Sulfate aerosols that are good reflectors of solar energy and can stay in the stratosphere for 1 to 2 years.

3. Volcanic aerosol loading
Volcanic eruptions near the equator, large explosive energy, and high in SO2 gas influence (cool ) surface temperatures most.

4. Aerosol lifetime
Sulfate particles typically have atmospheric lifetimes of about 2 years.
Sulfate particles grow slowly from SO2 and Water vapor
Sulfate particles typically have atmospheric lifetimes of about 2 years.

5. Last 50 years
There have been several major eruptions over the past 50 years. The climatic effects of the El Chichon Eruption in 1982 was partially masked by the large El Nino event in 1983.
There have been several major eruptions over the past 50 years. The climatic effects (cooling) of the El Chichon Eruption in 1982 was partially masked by the large El Nino event in 1983.

6. Pinatubo
The large eruption of Mt Pinatubo in June 1991 was one of the most highly recorded eruption ever. Not only did it cool surface temperature and warm stratospheric temperatures but the volcanic aerosol enhance ozone destruction much like the effects of polar stratospheric clouds.
The large eruption of Mt Pinatubo in June 1991 was one of the most highly recorded eruptions ever. Not only did it cool surface temperatures and warm stratospheric temperatures but the volcanic aerosol enhance ozone destruction much like the effects of polar stratospheric clouds.

7. Troposphere and Stratospheric Response
Cool surface temperature and warm stratospheric temperatures are typical after a significant eruption.
Cool surface temperature and warm stratospheric temperatures.

8. Solar

9. Solar irradiance variations
As sunspot numbers increase, solar activity and total luminosity also increase. Solar variability can contribute significantly to the natural climate variability.
As sunspot numbers increase, solar activity and total luminosity also increase. Solar variability can contribute significantly to the natural climate variability.

10. 120 years
Some models of past solar luminosity suggest that the solar luminosity increased from 1880 to 1950 and has remained fairly constant since.
Some models of past solar luminosity suggest that the solar luminosity increased from 1880 to 1950 and has remained fairly constant since.

11. 400 years of solar activity
Some scientists suggest than the little ice age ( ) was link to a weak sun at that time.
Some scientists suggest than the little ice age ( ) was link to a weak sun at that time.

12. ENSO El Niño Southern Oscillation Complete El Niño La Niña cycle
Large exchange of energy from and to the deep ocean can influence the natural fluctuations of Earth’s mean climate.
Large exchange of energy from and to the deep ocean can influence the natural fluctuations of Earth’s gloab mean climate. There is not trend associated with these fluctuations

13. SOI ( )

14. Greenhouse gas increses

15. Stratospheric ozone loss.

16. Tropospheric Sulfate Aerosols
Coal fire power plants, automobiles, and other industrial sources have cause the amount of tropospheric sulfate aerosols to keep step with industrial growth an to increase over the past 100 years.
Coal fire power plants, automobiles, and other industrial sources have cause the amount of tropospheric sulfate aerosols to keep step with industrial growth and to increase over the past 100 years. Surface cooling from these aerosols have offest warming expected from greenhouse gases

17. Estimated Sulfur Emissions

18. Cooling to offset warming
The increase in tropospheric sulfate aerosols has caused surface cooling which has likely offset some of the expected greenhouse warming.
The increase in tropospheric sulfate aerosols has caused surface cooling which has likely offset some of the expected greenhouse warming.

19. Model response w/o ENSO
After 2000:
tropospheric aerosol, Stratospheric Aerosol, Stratospheric Ozone
are all held at 1999 values.
* Solar cycle repeats most recent cycle
* and CO2 concentrations continue to increase.

20. Equivalent CO2 forcing used IPCC scenario C
% change represents 2000 to 2020 % changes for different scenarios.
Scenario C emissions continue to increase at ~1%/yr
Scenario E : emissions are fixed at 2000 levels
Scenario B : emissions increase at ~1.5 % /year

21. Future projections
Expected trend will be larger than 1980 –2000 trend because stratospheric ozone losses will no longer help control warming. Caveats: future forcing from: tropospheric aerosol loading, Volcanic eruptions, ENSO, solar irradiance variations are all highly uncertain.

22. Conclusions
Because stratospheric ozone losses will no longer help control warming expected global mean surface air temperature trend will be larger than it was between 1980 –2000.
Results are not very sensitive to: 1) Assumed future CO2 emission scenario (significant changes in emissions result in small concentration differences over next 20 years) 2) ENSO internal variability (contributes little to trend)
Results are somewhat sensitive to: 1) Future volcanic eruptions (several large eruptions between 2010 and 2020 could reduce trend significantly. Long term trends should not be significantly influence by random volcanic eruptions) 2) future solar irradiance variations
Results are sensitive to: Assumed tropospheric aerosol loading (IPCC has scenarios of increased and decreased aerosol loading over next 20 years) Since particulate matter from combustion have immediate health risks it is expected that developing countries will want to limit future tropospheric aerosol emissions.