List of Tables
Chapter 2 Review of Literature
2.6 Climate change projection
Projections of future climate change are typically based on assumptions about future GHGs and aerosols into the atmosphere (Nakicenovic and Swart 2000). Future emissions will be influenced by the evolution of the global population, socioeconomic development, and technological advances (Lee Quere et al. 2009). The interaction of these complex and dynamic factors results in considerable uncertainty about the future trajectory of emissions (Moss et al. 2010; Thomson et al. 2011). The present climate projections exhibit large uncertainties arising among others from assumptions on greenhouse gas emissions,
incomplete climate models and the downscaling of climate projections (IPCC 2007a).
Uncertainty has for many years been recognized by IPCC as crucial (IPCC 2007b), and it will receive even more attention in the forthcoming Fifth Assessment Report (AR5) (Yohe and Oppenheimer 2011). A goal of the AR5 is to apply “a common framework with associated calibrated uncertainty language that can be used to characterize findings of the assessment process” (Mastrandrea et al. 2011). According to an AR5 uncertainty guidance note, the degree of certainty of a key finding should be characterised qualitatively in terms of the confidence in the validity of a finding and the degree of agreement as well as in quantified measures of uncertainty (Mastrandrea et al. 2011).
Increasing trends of greenhouse gases in the earth’s atmosphere could accelerate in the future as a consequence of which the best estimates of increase in average global surface temperature is likely to be in the range from 1.8° to 4.0°C (IPCC 2007a). The mean annual increase in temperature by the end of this century is projected to be around 3.8°C in Tibetan plateau, 3.3°C in South Asia and 2.5°C in South East Asia (IPCC 2007a). For Indian region under south Asia, the IPCC has projected 0.5–1.2°C rise in temperature by 2020, 0.88–3.16°C by 2050, and 1.56–5.44°C by 2080 depending on the pace in future development scenario. Globally, average precipitation is projected to increase, with great deviances at regional scale (Meehl et al. 2007). Although the solar radiation received at the surface will be variable geographically, on average, it is expected to decrease by about 1%
(Hume & Cattle 1990).
It is virtually certain that increases in the frequency and magnitude of warm daily temperature extremes and decreases in cold extremes will occur through the 21st century at the global scale (Seneviratne et al. 2012). It is likely that the frequency of heavy precipitation or the proportion of total rainfall from heavy rainfalls will increase in the 21st century over many areas of the globe. This is particularly the case in the high latitudes and tropical regions and in winter in the northern mid–latitudes. Heavy rainfalls associated with tropical cyclones are likely to increase with continued warming induced by enhanced GHGs concentrations (Seneviratne et al. 2012).
Downscaled projections using the Hadley Centre Regional Model (HadRM2) indicated future increases in extreme daily maximum and minimum temperatures throughout South
Asia due to increase in greenhouse gas concentrations (Kumar et al. 2003). For the Indian subcontinent, Lal et al. (2001) projected mean warming between 1.0°C–1.4°C and 2.23°C–
2.87°C in India by 2020s and 2050s, respectively. Comparatively, increase in temperature was projected to be more in winter season than in summer. During winter, the surface mean air temperature could rise by 3.0°C in northern and central parts while it would rise by 2.0°C in southern parts by 2050. In case of rainfall, an increase of 7% to 10% in annual rainfall is projected over the sub-continent by the year 2080 (Lal et al. 2001). However, the study suggested a fall in rainfall by 5% to 25% in winter while it would be 10% to 15%
increase in summer monsoon rainfall over the country by 2080s. It was also reported that the date of onset of summer monsoon over India could become more variable in future.
The study of Rupa Kumar et al. (2003) revealed marked increase in both rainfall and temperature into the 21st century, particularly conspicuous after the 2040s in India. The study also showed a general increase in minimum temperature up to 4°C all over the country, which may however exceed over the southern peninsula, northeast India and also some parts of Punjab, Haryana and Bihar. The study indicated an overall decrease in number of rainy days over major parts of the country. However, number of rainy days is likely to increase by 5–10 days in the foot hills of Himalayas and northeast India. Kumar et al. (2011) projected a decrease in dry season precipitation and an increase during the rest of the year including the monsoon season.
Results from high-resolution Regional Climate Model (PRECIS), indicate that the night temperatures increase faster than the day temperatures, with the implication that cold extremes are very likely to be less severe towards the end of 21st century (Rupa Kumar et al. 2006; Revadekar et al. 2012). A more recent PRECIS simulations under both A2 and B2 scenarios in India indicated increase in frequency of heavy precipitation events and also enhancement in their intensity towards the end of the 21st century (Revadekar et al. 2012).
In NE India, PRECIS simulations for A1B emission scenario indicates that the projected mean annual rainfall in northeast India will vary from a minimum of 940±149 to 1330±174.5 mm (MoEF 2010). This increase with respect to 1970s (1961–1990) is by 0.3% to 3% with substantial decrease in rainfall in the winter months of January and February with no additional rain projected to be available during the period from March to
May and October to December. In fact, recent data indicated the same pattern. However, monsoon rainfall during June, July and August is likely to increase by 5 mm in 2030’s with reference to 1970’s, a negligible rise indeed. The rise in annual mean temperature in NE region may range from 1.8°C to 2.1°C in 2030s.
Section 2.7 briefly introduces the complex subject of how climate change and variability can affect agricultural productivity.