Attributing the External Forcings Responsible for Near Surface Air Temperature Changes over India

How the near-surface air temperature (TAS) changes in regional scale is a point of considerable importance to the public. Attribution of the causes of temperature change is vital for making informed adaptation and mitigation policies. Regional scale D&A studies are challenging due to the greater contribution of internal variability, greater uncertainty in regionally important forcings, greater errors in climate models, and more considerable observational uncertainty.

We present results of an investigation into the causes of changes in TAS over Indian region from 1906 to 2005. We use the CRU 3.22 gridded temperature dataset along with the outputs from 7 models in the Coupled Model Intercomparison Project Phase-5 (CMIP5) database that carried out single forcing experiments with, Natural, Anthropogenic, GHG, and Anthropogenic Aerosols forcings as well as pre-industrial (PiControl) simulations for conducting the formal D&A study. Here we compute the model simulated spatial pattern of changes in TAS from the individual forcings - the "fingerprint" - for DJF, MAM, JJA and SON seasons, as well as annual mean over the Indian land area. After estimating the fingerprint patterns, we searched for time-increasing correspondence between the model-predicted TAS fingerprint and the observational data sets, and then to determine whether such correspondence could be due to natural variability alone by estimating the signal to noise ratio. We determine the detection time at which S/N time series exceeds and remains above a designated 1 % (or 5%) significance threshold level. For exploring the sensitivity of results we carried out the analysis with raw and optimized(rotated) fingerprints. Our findings suggest that attribution studies with the seasonal TAS changes provide strong evidence for significant anthropogenic influence on India's climate.