Friday, December 4, 2009

Climate Variability and Climate change

    The distinction between Climate variability and Climate change inevitably has a degree of arbitrariness and depends on the time frame considered

We can call the natural reversible semi periodic variations which are embedded in the mean state of Climate as Climate variability.

Climate variability is different from seasonal variability which complete its cycle within the period of one year.

some of the examples of climate variabilities are

Indian Ocean Dipole (2 to 3 year)
El-Nino Southern Oscillation (2 to 7 years)
Solar Cycle (about 11 years)
Atlantic Multidecadal Oscillation(AMO) (60 to70 year)
Precession(axis orientation) variation (23000 years)
Obliquity (axis tilt angle) variation (41000 years)
Eccentricity (Ellipticity of orbit ) variation (100000 years)

Mechanisms to which Climate is sensitive

1. Milankovich cycle (Astronomical cycle) are importent in the long term beyond centuaries

2. The solar constant variation is less than 0.1% definitely in the last 25 years, probably in the last century and possibly in the last million years.

3. Green house gases have experienced long term natural and recent anthropogenic changes. The warming effect of green house gases and cooling effect of sulphite aerosols explains the recent warming trend.

4. Deep Ocean Circulation changes can cause climate changes which require mere decades to significantly alter land and sea surface temperature. This has occurred in relatively recent past  of about 10000 years ago and may be possible if triggered by greenhouse warming.

5. The coupled ocean atmosphere system oscillates and produce inter annual and decadal variations in climate, which are predictable in some extend

6. Cloud radiation interaction is another important factor which have strong influence on climate. But no past data is available for the pre satellite era.

7. Land surface changes also have influence on climate but most of them are local and irreversible. One of the major example is the influence of Himalayas orography and Asian monsoon