Conference on Climate Change: Shifting Science and Changing Policy
14 October 2011
Phirozeshah Mehta Building , Mumbai University ,
Abstracts of papers to be presented
in session on Monsoon and its impact.
Variability over India:Coupled Climate Model Simulations and Projections
By : Dr. R.H.
The Indian summer monsoon
precipitation and its variability are examined from the outputs of the coupled climate
models assessed as part of the Intergovernmental Panel on Climate Change Fourth
Assessment Report. Out of the 23 models examined only 7 models are able to generate
a realistic 20th century monsoon climate over India. The diverse
nature of model
simulations could introduce uncertainty in future projections. Hence these 7 models
only are selected to examine future projections under the doubling CO2 and other SRES scenarios A1B (medium CO2 forcing), A2 (high forcing) and B1 (low forcing).
Projections reveal a significant
increase in mean monsoon precipitation of 8% and a possible extension of the monsoon
period based on the multi-model ensemble technique. Extreme excess and deficient
monsoons are projected to intensify. The projected increase in precipitation could
be attributed to the projected intensification of the heat low over northwest India,
the trough of low pressure over the Indo-Gangetic plains, and the land-ocean pressure
gradient during the establishment phase of the monsoon. The intensification of these
pressure systems could be attributed to the projected decline in winter/spring snowfall.
Furthermore, a decrease of winter snowfall over western Eurasia is also projected
along with an increase of winter snowfall over Siberia / eastern Eurasia. This projected
dipole snow configuration during winter could imply changes in northern hemisphere
mid-latitude circulation conducive to subsequent summer monsoon precipitation activity.
An increase in precipitable
water of 12-16% is projected over major parts of India. A maximum increase of about
20-24% is found over the Arabian Peninsula, adjoining regions of Pakistan, northwest
India and Nepal. Although the projected summer monsoon circulation appears to weaken,
the projected anomalous flow over the Bay of Bengal (Arabian Sea) could support
oceanic moisture convergence towards the southern parts of India and Sri Lanka (northwest
India and adjoining regions).
The phenomenon of Indian Summer Monsoon must surely be among the
most complex and somewhat illusive dynamical operations of the weather and climate
involving a relatively long list of initial and boundary conditions.
It is indeed a scientific puzzle that computer climate models offerred projection
of Indian monsoon rainfalls covering the full 21st century with apparent ease and
convenient. In this talk, I hope to highlight some unscientific aspects of those
projections including the discussions in IPCC AR4 (2007) report. I wish to challenge
the false perception of computer climate model being a good-enough tool for such
assessment of future rainfalls, even if one narrowly considering only the single aspect
of rising atmospheric CO2.
How Total solar irradiance forcing manifests itself in the inter-decadal variability
of Indian Monsoon: Evidences from the recent past
By: Dr. Rajesh Agnihotri
Numerous paleo-studies have shown that global climate varies either in unison or
delays with contemporaneous solar variability on decadal to centennial scale, even though the mechanism of change in the terrestrial climate through small change in
the Sun’s energy output still remain illusive. While majority of such studies have
come from northern hemisphere especially in the monsoonal domain of South Asia,
recently there are several reports from equatorial Africa and South America, demonstrating
influence of solar cycles on regional climate manifestations such as lake levels,
integrated stream flows/ precipitation patterns. Most of these studies have used
sunspot numbers or group sunspot numbers as a metric or proxy for solar intrinsic
variability to correlate it with regional climatic manifestations, whereas it is
the Total solar irradiance (TSI) which contributes to the net radiative forcing
Earth climate system. Sunspot numbers have thus appear to be a good index of
solar variability for qualitative Sun-climate studies, but for any quantitative
effort it fails due to lack of knowledge of forcing component when Sunspot numbers
reach zero or near zero values during
their cyclic variability. In our recent study, therefore, we introduced a new physical parameter namely temporal derivative of
TSI and shown that the Indian summer monsoon rainfall correlates well with the temporal
derivative of TSI on multi-decadal timescales. This linkage was further tested and
both for the instrumental period (1871-2006) and for the last ~300
years using a speleothem d18O record representing rainfall in southwestern India.
Our analyses also indicated anomalous dry periods of the Indian monsoon are mostly
coincident with negative TSI derivative. Our study thus hitherto demonstrates the
potential of ‘TSI derivative’ as an important indicator of natural monsoon variability
on inter-decadal timescale.