Volcanoes

Volcanic aerosol loading

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

Aerosol lifetime

Sulfate particles typically have atmospheric lifetimes of about 2 years.

Sulfate particles grow slowly from SO2 and Water vapor

Last 50 years

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.

Pinatubo

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.

Troposphere and Stratospheric Response

Cool surface temperature and warm stratospheric temperatures are typical after a significant eruption.

Solar

Solar irradiance variations

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

120 years

Some models of past solar luminosity suggest that the solar luminosity increased

from 1880 to 1950 and has remained fairly constant since.

400 years of solar activity

Some scientists suggest than the little ice age (1400-1800) was link to a weak sun at that time.

ENSOENSOEl Niño Southern OscillationComplete El Niño La Niña cycle

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

SOI (1978 -1998)SOI (1978 -1998)

Greenhouse gas increses

Stratospheric ozone loss.

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 and to increase over the past 100 years. Surface cooling from these aerosols have offest warming expected from greenhouse gases

Estimated Sulfur Emissions

Cooling to offset warming

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

Model response w/o ENSO

-0.4

0

0.4

0.8

1.2

1950 1960 1970 1980 1990 2000 2010 2020

Year

DT

(K)

Equivalent CO2 forcing used IPCC scenario C

300

350

400

450

1960 1980 2000 2020 2040

Year

CO

2 (p

pm)

B(14.1%)C (12.6%)

E (9.8%)

Three different IPCC emission scenarios

Future projections

-0.8

-0.4

0

0.4

0.8

1.2

1.6

1950 1960 1970 1980 1990 2000 2010 2020

Year

T

(K

)

Jones et al

Model

.17 K/decade

0.3 K/decade

+/-0.12 K/decade

+/-0.03 K/decade

Because stratospheric ozone losses will no longer help control warming expected 2000-2020 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.

Conclusions