• Weather and climate have the inherent characteristic of change. Weather refers to the day-to-day state of the atmosphere, characterised by meteorological variables like rainfall, temperature, wind etc. Climate refers to the normal long term average conditions of weather variables over a specified period, like month, season or year and may also provide information on the frequency and intensity of extreme events and other statistical properties of weather elements. Both weather and climate vary over a wide range of spatial and temporal scales. Weather is variable due to the dynamic nature of atmospheric disturbances. Earth’s climate is fundamentally controlled by its orbital parameters, the chemical composition of the atmosphere and feedbacks within these components of the climate system. Climate varies because of latitudinal and altitudinal temperature gradients, nearness to sea, presence of mountains, forests and deserts, etc.

Major Global Environmental Issues 

• Increased human activity, urbanization, industrialization have led to rapid deterioration of the environment. This has severely affected the life supporting system. The developmental discrepancies in different regions of the world pose a serious threat to our common global environment. Consequently, we are confronted with complex environmental issues deserving attention. The important global environmental issues are: green house effect and global warming; biodiversity loss; desertification; depletion of ozone layer; acid rain; oil spills and dumping of hazardous wastes.

Green House Effect and Global Warming

Fig: Solar radiations strike the earth. Some of these radiations are reflected back by the atmosphere into the space, but some pass through the atmosphere towards earth. About half of these are absorbed by the atmosphere and heat the air. The rest reaches the earth’s surface. The earth’s surface now heats up and gives off longer wavelength, lower energy (infra red or heat) radiations. These infra-red radiations pass back up into the atmosphere. Instead of being radiated 100 percent back into the space, much of it is absorbed by the atmosphere and are redirected back to the earth’s surface. the temperature near the earth’s surface as well as that of the atmosphere then rises. 

• The temperature surrounding the earth has been rising during the recent past. This is due to the ‘green house effect’. A green house is a glass chamber in which plants are grown to provide them warmth by trapping sun light. Sunlight (a form of energy) passes through the glass and it gets absorbed inside releasing heat radiations unlike sunlight, heat radiation cannot escape through glass the heat generated there from, cannot escape out of the glass chamber. Thus, even on a cold winter day, the inside of a green house can become quite warm to support plant growth. The phenomenon of heat build up inside a glass chamber from the absorption of solar radiation is called green house effect.

Global warming and green-house effect 

• The green-house effect is a natural phenomenon and has been occurring for millions of years on the earth. Life on the earth has been possible because of this natural green house effect which is due to water vapour and small particles of  water present in the atmosphere. Together, these produce more than 95 percent of total green-house warming. Average global temperatures are maintained at about 15°C due to natural green house effect. Without this phenomenon, average global temperatures might have been around –17°C and at such low temperature life would not be able to exist.

What Is Climate Change? 

• Climate change refers to long-term shifts in temperatures and weather patterns. These shifts may be natural, such as through variations in the solar cycle. But since the 1800s, human activities have been the main driver of climate change, primarily due to burning fossil fuels like coal, oil and gas. 
• Burning fossil fuels generates greenhouse gas emissions that act like a blanket wrapped around the Earth, trapping the sun’s heat and raising temperatures.
• As a result, the Earth is now about 1.1°C warmer than it was in the late 1800s. The last decade (2011-2020) was the warmest on record. 
• The consequences of climate change now include, among others, intense droughts, water scarcity, severe fires, rising sea levels, flooding, melting polar ice, catastrophic storms and declining biodiversity.

Causes of Climate Change

• Generating power - Generating electricity and heat by burning fossil fuels causes a large chunk of global emissions. Most electricity is still generated by burning coal, oil, or gas, which produces carbon dioxide and nitrous oxide – powerful greenhouse gases that blanket the Earth and trap the sun’s heat. 
• Manufacturing goods - Manufacturing and industry produce emissions, mostly from burning fossil fuels to produce energy. Mining and other industrial processes also release gases, as does the construction industry. The manufacturing industry is one of the largest contributors to greenhouse gas emissions worldwide. 
• Cutting down forests - Cutting down forests to create farms or pastures, or for other reasons, causes emissions, since trees, when they are cut, release the carbon they have been storing. Since forests absorb carbon dioxide, destroying them also limits nature’s ability to keep emissions out of the atmosphere. Deforestation, together with agriculture and other land use changes, is responsible for roughly a quarter of global greenhouse gas emissions. 
• Using transportation - Most cars, trucks, ships, and planes run on fossil fuels. That makes transportation a major contributor of greenhouse gases, especially carbon-dioxide emissions. Road vehicles account for the largest part, due to the combustion of petroleum-based products, like gasoline, in internal combustion engines. But emissions from ships and planes continue to grow. 
• Producing food - Producing food causes emissions of carbon dioxide, methane, and other greenhouse gases in various ways, including through deforestation and clearing of land for agriculture and grazing, digestion by cows and sheep, the production and use of fertilizers and manure for growing crops, and the use of energy to run farm equipment or fishing boats, usually with fossil fuels. 
• Powering buildings - Globally, residential and commercial buildings consume over half of all electricity. As they continue to draw on coal, oil, and natural gas for heating and cooling, they emit significant quantities of greenhouse gas emissions.

Effects of Climate Change

Hotter temperatures 

• As greenhouse gas concentrations rise, so does the global surface temperature. The last decade, 2011-2020, is the warmest on record. 
• Higher temperatures increase heat-related illnesses and make working outdoors more difficult. Wildfires start more easily and spread more rapidly when conditions are hotter. Temperatures in the Arctic have warmed at least twice as fast as the global average.

More severe storms 

• Destructive storms have become more intense and more frequent in many regions. As temperatures rise, more moisture evaporates, which exacerbates extreme rainfall and flooding, causing more destructive storms. The frequency and extent of tropical storms is also affected by the warming ocean.

Increased drought

• Climate change is changing water availability, making it scarcer in more regions. Global warming exacerbates water shortages in already water-stressed regions and is leading to an increased risk of agricultural droughts affecting crops, and ecological droughts increasing the vulnerability of ecosystems. 
• Droughts can also stir destructive sand and dust storms that can move billions of tons of sand across continents. Deserts are expanding, reducing land for growing food.

A warming, rising ocean

• The ocean soaks up most of the heat from global warming. As the ocean warms, its volume increases since water expands as it gets warmer. Melting ice sheets also cause sea levels to rise, threatening coastal and island communities.
• In addition, the ocean absorbs carbon dioxide, keeping it from the atmosphere. But more carbon dioxide makes the ocean more acidic, which endangers marine life and coral reefs.

Loss of species 

• Climate change poses risks to the survival of species on land and in the ocean. These risks increase as temperatures climb. Forest fires, extreme weather, and invasive pests and diseases are among many threats related to climate change. Some species will be able to relocate and survive, but others will not.

Not enough food 

• Changes in the climate and increases in extreme weather events are among the reasons behind a global rise in hunger and poor nutrition. Fisheries, crops, and livestock may be destroyed or become less productive. 
• With the ocean becoming more acidic, marine resources that feed billions of people are at risk. 
• Changes in snow and ice cover in many Arctic regions have disrupted food supplies from herding, hunting, and fishing. 
• Heat stress can diminish water and grasslands for grazing, causing declining crop yields and affecting livestock.

More health risks 

• Climate change is the single biggest health threat facing humanity. Climate impacts are already harming health, through air pollution, disease, extreme weather events, forced displacement, pressures on mental health, and increased hunger and poor nutrition in places where people cannot grow or find sufficient food.

Poverty and displacement

• Climate change increases the factors that put and keep people in poverty. Floods may sweep away urban slums, destroying homes and livelihoods. Heat can make it difficult to work in outdoor jobs. Water scarcity may affect crops.

Some Important Green House Gases 

• Carbon dioxide (CO2 ): Carbon dioxide enters the atmosphere through burning fossil fuels (coal, natural gas, and oil), solid waste, trees and other biological materials, and also as a result of certain chemical reactions (e.g., manufacture of cement). Carbon dioxide is removed from the atmosphere (or “sequestered”) when it is absorbed by plants as part of the biological carbon cycle. 
• Methane (CH4 ): Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices, land use and by the decay of organic waste in municipal solid waste landfills. •
• Nitrous oxide (N2 O): Nitrous oxide is emitted during agricultural, land use, and industrial activities; combustion of fossil fuels and solid waste; as well as during treatment of wastewater. 
• Fluorinated gases: Hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride are synthetic, powerful greenhouse gases that are emitted from a variety of household, commercial, and industrial applications and processes. Fluorinated gases (especially hydrofluorocarbons) are sometimes used as substitutes for stratospheric ozonedepleting substances (e.g., chlorofluorocarbons, hydrochlorofluorocarbons, and halons). Fluorinated gases are typically emitted in smaller quantities than other greenhouse gases, but they are potent greenhouse gases. With global warming potentials (GWPs) that typically range from thousands to tens of thousands, they are sometimes referred to as highGWP gases because, for a given amount of mass, they trap substantially more heat than CO2 . 
• Black carbon (BC) is the most strongly light-absorbing component of particulate matter (PM), and is formed by the incomplete combustion of fossil fuels, biofuels, and biomass. BC is emitted directly into the atmosphere in the form of fine particles (PM2.5). BC is the most effective form of PM, by mass, at absorbing solar energy: per unit of mass in the atmosphere, BC can absorb a million times more energy than carbon dioxide (CO2). BC is a major component of “soot”, a complex light-absorbing mixture that also contains some organic carbon (OC).