Global impact of climate change on agriculture

Introduction

Since the beginning of Earth's existence 45 billion years ago, the climate has changed naturally at its own rate; yet, due to unintentional human disruptions, it has recently acquired momentum. These alterations could have a negative effect on both human health and the environment, which is essential to our survival. The complex interactions between people and the concentration of greenhouse gases (GHGs), such as CO2, CH4, and N2O, cause global warming and other cascading effects, such as changes in rainfall patterns, glacier melting, sea level rise, etc. The aforementioned complex relationships between atmospheric composition, climate change, and the health of people, plants, and animals must be examined, and potential remedies to the unfavorable changes may be looked for. According to the World Meteorological Organization, Climate is the aggregate of weather condition over a long period of time, the classical period is 30 years.

Climate Change: Climate change is any long-term significant change in the expected patterns of average weather of a specific region over an appropriately significant period of time.

Climate Variability:

The way the climate varies annually above or below a long-term average value is known as climate variability.

Climate Vulnerability:

The degree to which a system is vulnerable to or incapable of handling the negative consequences of climate change, such as climate extremes and variability, is known as vulnerability.

Causes of Climate Change (a) Natural Processes Variation in Earth's Orbital Character

The Earth's orbit around the Sun is shaped by the first cyclical fluctuation, called eccentricity. Over the course of around 100,000 years, the orbit gradually shifts from being elliptical to almost circular and back again. The difference in solar energy received at the top of the atmosphere between Earth's closest (perihelion) and furthest (aphelion) approaches to the Sun increases with orbital eccentricity, or how elliptical the orbit is. The quantity of solar radiation received at the top of the atmosphere varies by around 7% due to the difference in Earth's distance from the Sun between perihelion and aphelion, which is only about 3%. The difference in solar energy received is approximately 20% when this distance is at its highest (9%). Volcanic Eruptions Large, explosive volcanic eruptions have been linked to shortterm climate change, according to climatologists. There have been two major eruptions that have altered the climate in the past century. In April 1982, El Chichon erupted in Mexico, and in June 1991, Mount Pinatubo erupted in the Philippines. Of these two volcanic eruptions, Mount Pinatubo released over 20 million tons of SO2 into the stratosphere and had a bigger impact on Earth's climate. The Pinatubo explosion was thought to be the main cause of the 1992 global average air temperature drop of 0.8 degrees Celsius. According to satellite data, the eruption's sulfur dioxide plume increased the amount of sunlight reflected back into space by the Earth's atmosphere by several percent, causing the planet's surface to cool.

Variation in Solar Output

In just eighteen months, measurements taken by radiometerequipped satellites in the 1980s and 1990s revealed a 0.1 percent drop in the overall quantity of solar energy reaching Earth. The global climate might be impacted if this tendency continued for several decades. For a long time, scientists have also attempted to connect sunspots to climate change. Large magnetic storms known as sunspots appear as colder, black patches on the Sun's surface. Sunspot size and quantity exhibit cyclical patterns, peaking roughly every 11, 90, and 180 years. According to the 11-year cycle, the early 1980s solar energy decline coincides with a time of peak sunspot activity.

a) Anthropogenic Causes

The amount of sunlight reflected back into space (the surface albedo) has changed as a result of changes in land use, such as the clearing of forests to make way for farms. These fluctuations are thought to account for roughly one-fifth of the global climate forcing caused by variations in greenhouse gas emissions. An estimated half of the changes in land use are thought to have happened during the industrial era, primarily as a result of agricultural cropping and grazing fields replacing forests.

Source: NATCOM-2004

Greenhouse Gases Carbon Dioxide (CO2)

With a contribution of 63.54% to the total global radiative forcing, carbon dioxide is the most significant anthropogenic greenhouse gas in the atmosphere. Burning wood and wood products, fossil fuels (coal, oil, and natural gas), and solid waste releases carbon dioxide into the atmosphere. About 50% percentage of carbon dioxide that is emitted into the atmosphere is absorbed by the ocean. Because it can reabsorb long wave radiation from the Earth's surface, it can change the planet's energy balance. Because it affects root and soil respiration, temperature has a significant impact on the evolution of CO2 from soil. It should be noted that the main carbon dioxide sinks are plants, oceans, and atmospheric processes.

Methane (CH4):

It is twenty fold more effective as a heattrapping gas than CO2. It is a product of incomplete decomposition caused by a group of bacteria called Methanogens, under anaerobic condition. The main sources of methane are: wetlands, organic decay, termites, natural gas and oil extraction, biomass burning, rice cultivation, cattle and refuse landfills. Agriculture contributes 68% to it. 18.1% of the total radiative force in the world comes from methane. Methane is released when coal, natural gas, and oil are produced and transported. It is also released when organic materials break down.

Nitrous Oxide (N2O):

Nitrous oxide is 298-times more effective than CO2. The main sources include burning fossil fuels and organic materials, applying fertilizer and manure, and cultivating land. It depletes the ozone layer. It makes up 6.24% of the total radiative forcing in the world. It is released during industrial and agricultural processes, as well as when fossil fuels and solid waste are burned.

Water Vapour: More thermal infrared radiation from the Earth can be absorbed by it, warming the atmosphere even more. More water vapor can then be stored in the warmer atmosphere.

Climate Change and Indian Agriculture

Agriculture sector alone represents 23% of India's Gross National Product (GNP), plays a crucial role in the country's development and shall continue to occupy an important place in the national economy. It sustains the livelihood of nearly 70% of the population. It seems obvious that any significant change in climate on a global scale will impact local agriculture and therefore affect the world's food supply. Global climatic changes can affect agriculture through their direct and indirect effects on the crops, soils, livestock and pests.

Impact of Climate Change to Agriculture 1. Impact on Crop Growth Parameters and Yield

CO 2 content continues to rise, most plants will exhibit increased rates of photosynthesis and biomass production. Consequently, this phenomenon should enhance the amount of food, fiber and timber products population. However, some individuals have predicted that the growth-promoting effects of atmospheric CO2 enrichment may be negated by global warming, which could compromise our ability to sustain greater human populations without increasing arable land acreage. We thus turn to the scientific literature to see if plants will continue to exhibit CO2-induced growth increases under conditions of elevated air temperature.

A) Photosynthesis

In C 3 plants, Rubisco is not saturated by the current concentration of CO 2 in the atmosphere. So an increase in its concentration will improve the balance of CO 2 and O 2 at Rubisco site, thus improving the CO 2 -Exchange Rate (CER) of the plant by providing more substrate for photosynthesis (Carbon dioxide fertilization) Prasad et al. (2003) reported that doubling of ambient CO 2 concentration (350 vs. 700 µmol mol-1) enhanced leaf photosynthesis of groundnut by 27% across a range of day-time temperatures (32 to 44 0 C).

B) Water Relations a) Stomatal Conductance

Elevated CO2 causes partial stomatal closure, which reduces the stomatal conductance for the exchange of gases between the internal tissues of plant leaves and the atmosphere approximately by 10% both in C3 and C4 plants (IPCC, 2007). This will increase the stomatal resistance leading to reduced evapotranspiration by 0.9% (Kimball, 2007).

b) Canopy Temperature

Elevated CO2 reduces stomatal conductance, transpirational cooling of the plant leaves is also reduced causing leaf temperature to rise. Hence, rise in canopy temperature.

c) Evaporation or Water Use

With rise in canopy temp., the vapour pressure inside the leaves raises, which tend to increase the leaf transpiration negating some of the reduction due to reduced stomatal conductance.

A Simulation Study in Punjab by Kaur (2010) [4] Shows That • Increase in temp. by 1-2 o C reduced grain yield in wheat by 9.8-18.4%, in rice by 2.8 to 9.6% and by 10.4 to 14.6% from normal in maize; • Increased in CO2 showed counteracting effect on increasing temperature in yield reduction to more extent in wheat (where grain yield increased by 5.6%) as compared to maize (increased by only 2.8%).

Studies in Bundhelkhand Region Shows

• Rainfall shows declining trend and shifting of precipitation by over a month. [6] . d) Damage-niche concept by Donald (2009) refer to the suite of factors under which specific weed species are judged troublesome to the production of specific crops.

Impact on

Impact on Soil Productivity

a. The residues of crops under the elevated CO2 concentrations will have higher C: N ratio, and this may reduce their rate of decomposition and nutrient supply. b. Rise in soil temperature will increase N mineralization, but its availability may decrease due to increased gaseous losses through volatilization and denitrification. c. Change in rainfall volume and frequency, and wind may alter the severity, frequency and extent of soil erosion. d. Rise in sea level may lead to salt-water ingression in the coastal lands, turning them less suitable for conventional agriculture.

Impact on Cropping System

a) Studies in Bundhlekhand region shows that sorghum area is decreasing due to uncertainty, erratic and low rainfall for more than 5 years. The area is now shifted to black gram/greengram and sesame in kharif season b) The rainfall shows declining trend and shifting of precipitation by over a month. The shift causes delay in sowing.

Impact on Water Availability

a. Demand for irrigation water would increase with rise in temperature and evapo-transpiration rate. b. Significant increase in runoff is projected in the wet season. c. This additional water in the wet season, on the other hand, may lead to increase in frequency and duration of floods. d. The water balance in different parts of India will be disturbed. e. The quality of groundwater along the coastal track will be affected more due to intrusion of sea waters.

Impact on

Residue Retention Instead of Burning Reduces GHG Emission

Residue retention at the field can be used a mulch which helps in moisture retention as well as prevents soil erosion. It also increases organic matter content of soil when incorporated. Burning of 1 Mg rice straw emits CO2-C: 280 kg, CH4-C: 3 kg, N2O-N: 0.07 kgGWP: 1118 kg CO2 equiv.

One of the preliminary understandings of residue incorporation and retention in rice wheat cropping system can mitigate global warming. A 1118 kg gas of CO2 equivalent produces as well as 10-15 kg of NPK is lost from the soil which can be easily incorporated in soil by adopting these CA based RCTs. Csequestration is the additional advantage in residues incorporation. Burning of crop residue releases the GHG sin the atmosphere. Emissions of GHGs was determined on basis of product of emission factors and crop residues burnt(Based on IPCC Coefficient). The quantity of GHGs(CO2, CH4, N2O) emitted by crop residue burning from Madhya Pradesh itself is about 5676.46 kg/year. In which contribution ofCO2; CH4 and N2O is about 5666.1 kg/year, CH4 is about 10.10kg/year and about 0.26 kg/year respectively. Critical analysis oftable-3 indicates that, carbon dioxide is the most dominant among three gases.

Conclusion

• Increased CO 2 will facilitate fertilization effect.

• Increased temperature increase the production in temperate region whereas decrease in tropical countries.

• Irregular precipitation pattern leads to flood or drought causing shift in cropping system. • Loss of soil productivity and scarcity of irrigation water impacted agriculture production. • Adaption and Mitigation strategies are to be adopted based on the prevailing situation for sustained supply of food for the growing population.

References

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2. Agarwal PK. Climate change: implications for Indian agriculture. Jalvigyan Samakshya. 2007;22:1-22.
3. Hatfield JL. Climate impacts on agriculture: implications on crop production. Agronomy Journal. 2011;103(2).
4. Kaur P. Effect of climate change on agriculture. In: Walia SS, Gosal SS, editors. Contingent crop planning. 2011:8-32.
5. Prajapati RK, Singh SR, Gangwar RK. Effect of climate change on plant disease in Bundelkhand zone leading to change in cropping system. Agriways. 2015;3(2):120-138.
6. Chauhan BS, Ramesh K. Weed regimes in agro-ecosystems in the changing climate scenario: a review. Indian Journal of Agronomy. 2005;60(4):479-484.