1. Climate and Climate Change: An Overview

This chapter primarily provides an overview on climate and climate change with a general description on climate system its connection with geological phases and sun-earth system as a whole. Archeologists and historians have attributed many episodic changes in human civilization to the climate changes which have also been detected in the data relating to the evolution of geomorphic features in the time span of the geological periods. The first few sections deal with the evolution of science of climate change and its theoretical and observational foundation. Mechanisms taking place through the atmosphere as a result of solar radiation and anthropogenic activities are also described. Solar spectrum and the interactions with earth-atmosphere system are discussed along with the thermal structure of the atmosphere. The role of greenhouse gases (GHGs) is to give rise to the mean surface temperature of earth and its repercussions on Himalayan ecosystem, in particular, demonstrates a dynamic interplay of all forms of weather and climates interacting with a highly fragile mountain ecosystem. Science of climate and climate change has been enriched by a large galaxy of scientists from diverse disciplines coming from many countries and a few of them have been mentioned in the respective section. A holistic picture of global climate emerges out of evolutionary and interactive processes within a complex system consisting of five major components, namely, Atmosphere, Hydrosphere, Lithosphere, Cryosphere, and Biosphere. The climate change due to natural causes, in terms of Milankovitch hypothesis, a very large timescale and a very small timescale such as El-Nino is also discussed. IPCC WG1 report has provided the observed global mean land and ocean surface temperature anomalies from 1850 to 2012 that indicates the increasing trend in the global rise in temperatures as a result of increase in the anthropogenic emission of GHGs. There are a number of governmental and non-governmental organizations working with many initiatives focused on environmental issues, the role of such organization to mitigate various climate-related issues are discussed in the section devoted to it. Climate in India has always been a key factor in the socioeconomic well-being of the country; therefore, there have been a number of Indian national initiatives on climate change in the recent past in concurrence with the international agencies. A section summarizes the climate science in the context of ancient ideas and from historical perspective which gives a detailed account on the chronological development of climate science right from the time of Rigveda with the famous sentence “आदित्यात् जायते वृष्टि: | वृष्टि: धान्यम् तत: प्रजा।” to the modern observational network and the weather forecasting system. The chapter also presents the observations and data for climate change studies taken over 300 Indian stations established by India meteorological department. All-India surface temperature and rainfall anomalies are the highlights of this section. Finally, the relation between climate change and society is presented.