Climate change is the effect caused by a rising concentration of greenhouse gases (GHGs), mainly carbon dioxide emitted in the atmosphere through the burning of fossil fuels. The increased level of carbon dioxide results in changes in the state of the climate that persist for a decade or longer. Since the mid-late 19th century, several changes in climatic variables have been observed. These changes are collectively known as climate change. Another term commonly used for these effects is global warming, due to the direct effect of a rising concentration of GHGs on Earth’s temperature. Scientists report the rise in average temperature as a temperature anomaly. The difference in global surface temperature relative to 1951-1980 average temperatures is shown in the graph below. According to the data, 2016 was the warmest year on record (source).
The scientific visualization of the time series data on a five-year variation of global surface temperatures is shown in the video below from NOAA, NASA.
The rise in global temperature is changing the hydrological cycle of the planet, resulting in changes in weather patterns, such as increased intensity and duration of rainfall and snowfall, and a rise in extreme weather events, e.g., droughts, floods and hurricanes. The rising temperatures are resulting in the warming of oceans, melting of glaciers, and an inexorable rise in sea level. In addition to the effects due to this rise in temperature, the increase in the concentration of carbon dioxide in the atmosphere is causing an increase in oceanic acidity. The major signs of climate change are listed below:
- Ocean warming and acidification: The ocean absorbs excess heat from the air, making it warmer. The ocean also absorbs CO2 from the air. In fact, it absorbs almost 25% of the total CO2 emitted from the burning of fossil fuels. However, due to this excessive absorption of CO2, the water is becoming more acidic. Excess heat and acidity have an adverse impact on the plants and animals living in the ocean.
- Changes in precipitation: Rising temperatures result in increased evaporation. Increased evaporation will result in more storms in some areas and excessive drying over other land areas. The storm-affected regions are likely to experience increases in precipitation, while areas located far from storm tracks are likely to experience less rainfall.
- Changes in snow, ice, and frozen ground: Increases in temperature directly impact the snow, river and lake ice, sea ice, glaciers, and ice caps, ice shelves and ice sheets, as well as frozen ground. The rising surface temperature is causing an overall decline in ice mass.
- Shrinking ice sheets (Land ice): Ice mass measurements by NASA’s satellite show that the Antarctica and Greenland mass is declining at a rate of 127 (+/-39) Gigatons/year and 286 (+/- 21) Gigatons/year, respectively, since 2002.
- Glacier retreat: Glaciers are retreating almost everywhere around the world, including in the Alps, Himalayas, Andes, Rockies, Alaska, and Africa
- Sea level rise: Sea level rise is caused primarily by water from melting ice sheets and glaciers and the expansion of seawater as it warms. Satellite-level observations indicate that the sea height is increasing at a rate of 3.2 mm/year.
- Changes in weather patterns and extreme weather events: Changing climate leads to changes in the frequency, intensity, spatial extent, duration, and timing of weather and climate extremes. Weather and climate extremes are events that occur when the weather or climate variable is above or below a threshold value of the variable. Some of these changes in weather patterns include an increase in the number of warm days and nights, and a decrease in cold days and nights, as well as an increase in the frequency and intensity of daily temperature extremes. Some of the extreme weather events linked to climate change include floods, droughts, hurricanes, and heat waves.
What causes climate change?
The rising concentration of greenhouse gases (GHG) in Earth’s atmosphere is causing climate change. The sun emits solar radiation, which is shortwave radiation such as UV radiation and visible light. The planet’s surface absorbs some of the solar radiation, and the rest is reflected as long-wave radiation, i.e., infrared radiation. Some of the reflected radiation escapes the earth’s surface, while some are absorbed by other gases, such as carbon dioxide and methane. These gases act similarly to a greenhouse and are therefore called greenhouse gases.
The most significant GHG is carbon dioxide. Other GHGs are methane, nitrous oxide, and fluorinated gases – hydrofluorocarbons, perfluorocarbons, etc. The effect of these gases on climate change depends on the amount of gas and their global warming potential (GWP). GWP is calculated to reflect how long a gas remains in the atmosphere, on average, and how strongly it absorbs energy. Gases with a higher GWP absorb more heat and thus contribute more to warming Earth. The concentration of CO2 is higher than any other gas and is the major contributor to the warming of the planet.
The emission of GHGs can be attributed to both natural causes and human activities. There is sufficient scientific evidence that human-induced GHG emissions have caused the observed temperature anomaly in recent decades. The increase and evolution of economic activity since the Industrial Revolution has resulted in perpetually increasing amounts of GHG emissions. These emissions are greater than the amount that can be captured by the earth’s natural carbon cycle. The primary source of human-induced GHG emissions is the burning of fossil fuels, agriculture, and changes in land use patterns. These major causes are briefly explained below:
- Burning of fossil fuels: The burning of fossil fuels, e.g., coal and oil, has increased the concentration of atmospheric carbon dioxide significantly. The contribution of fossil fuels to overall GHG emissions is the largest, in the range of 70- 80% of the total emissions.
- Agriculture: GHG emissions from agriculture come from livestock, such as cows, agricultural soils, and rice production, putting agriculture in the range of 10-15% of the total emissions.
- Changes in land use patterns: The clearing of forests for cultivation, industry, and other human activities have also increased concentrations of greenhouse gases. The share of changes in land use patterns in the total emissions is in the range of 5-10% of the total emissions.
To summarize, the rising concentration of GHGs, mainly caused by carbon dioxide, is driving an increase in the average temperature of the earth’s surface. The primary source of carbon dioxide emission is the burning of fossil fuels for various economic activities. The increase in the planet’s temperature is disturbing natural cycles and causing notable changes in climate and weather variables. These changes are expected to intensify as the level of GHGs continues to rise.