Indigenous Earth System Model, First From India, Contributed To UN Climate Change Body’s Latest Assessment Report

A climate change assessment made by Indian researchers using an indigenous Earth system model (ESM) featured in the latest assessment report of the Intergovernmental Panel on Climate Change (IPCC), the Minister for Earth Sciences, Kiren Rijiju, revealed in a written reply in the Lok Sabha on 13 December.

The IPCC is the United Nations (UN) body for assessing the science related to climate change. The panel prepares comprehensive reports assessing the state of knowledge of climate change. The reports are published every six to seven years and are key reference materials for making major policy decisions on climate change mitigation.

The IITM-ESM, the first Earth system model from India, was developed at the Centre for Climate Change Research, Indian Institute of Tropical Meteorology (IITM). It was built with the goal of detection, attribution, and projection of changes in the South Asian monsoon.

ESMs incorporate the physical processes of the climate system, as well as the interactions between the climate system and other Earth system components, such as the biosphere and the carbon cycle.

“ESMs are useful for enhancing our fundamental understanding of the climate system, its multi-scale variability, global and regional climatic phenomena and making projections of future climate change,” write the lead authors of a 2021 paper, R Krishnan and P Swapna, explaining the IITM Earth system model. Krishnan is currently the director of IITM, Pune.

“The underlying philosophy behind the IITM ESM,” they write, “is based on developing a global modeling framework to address the science of climate change, including detection, attribution and future projections of global climate, with special emphasis on the South Asian monsoon.”

Apart from the IPCC assessment report, the IITM-ESM has been used in the Coupled Model Intercomparison Project Phase 6 (CMIP6) experiments, which are coordinated by the World Climate Research Programme (WCRP) and form the basis of the climate projections in the IPCC assessment reports.

Since the IPCC reports predominantly offer a global outlook on climate change, an assessment of regional climate change aspects warrant localised studies. There is, for instance, a wide variation and uncertainty in twentieth-century simulations and future projections of the South Asian monsoon rainfall based on the IPCC models.

The Indian assessment report prepared using the IITM-ESM model — the first national climate change assessment report of the Ministry of Earth Sciences — discusses the influence of human-induced global climate change on the Indian subcontinent.

The open-access book, titled ‘Assessment of Climate Change over the Indian Region’ and released in 2020, presents regional climate change projections based on the climate models used in the previous IPCC assessment report (AR5), as well as climate change modelling studies using the IITM-ESM and CORDEX South Asia datasets.

Climate change effects over the Indian subcontinent involve intricate physical processes, thanks to the significant influence of the Indian monsoon, distinctive high-elevation geographical features like the Himalayas, the Western Ghats, and the Tibetan Plateau, and the adjoining Indian Ocean, Arabian Sea, and Bay of Bengal.

“The ENSO-monsoon teleconnections, a present weakness in many of the climate models, is realistically represented in IITM ESM,” IITM says. “ENSO” is short for El Niño–Southern Oscillation, a major factor for climate variability globally.

The Pune-based institute’s model was developed in 2014 by transforming a state-of-the-art seasonal prediction model, the Climate Forecast System version 2 (CFSv2), into a model suitable for long-term climate.

"While the CFSv2 model has been skillful in predicting the Indian summer monsoon (ISM) on seasonal time scales, a century-long simulation with it shows biases in the ocean mixed layer, resulting in a 1.5°C cold bias in the global mean surface air temperature, a cold bias in the sea surface temperature (SST), and a cooler-than-observed troposphere. These biases limit the utility of CFSv2 to study climate change issues," a 2015 paper explained.

The model's development was based on a formal agreement signed in 2011 by India’s Ministry of Earth Sciences and the United States’ National Oceanic and Atmospheric Administration (NOAA). The two parties had decided to collaborate on the implementation of the National Centers for Environmental Prediction (NCEP) weather and seasonal prediction system in India.

Since its creation, the IITM-ESM model has undergone at least two iterations, achieving several significant improvements that enable, among other things, long-term climate change predictions.

Long-term climate studies are essential to making reliable future projections of global and regional climate, and particularly of the Indian monsoon rainfall, with more than one-fifth of the world’s population dependent on monsoon. The IITM-ESM model fulfils that long-term critical need for India.

A next-generation IITM-ESM is already in the works. It is set to include interactive aerosols and chemistry and improved physical processes, and also the use of the atmospheric-only component of the model to generate very high-resolution climate change simulations and future projections. The new features would be added to the model over the next few years.