Climate Change| Class 11 Geography Notes (original) (raw)
Last Updated : 23 Jul, 2025
Climate Change is a state of impact that indicates and calculates the increasing frequency and severity of different natural disasters. Increasing temperature may increase the probability of wildfires which release so many pollutants in the climate.
Let us learn more about climate change in the article!
Climate Change: A Natural and Continuous Process
- The planet Earth has witnessed many variations in climate since the beginning. Geological records show alteration of glacial and inter-glacial periods.
- The geomorphological features, especially in high altitudes and high latitudes, exhibit traces of advances and retreats of glaciers.
- The sediment deposits in glacial lakes also reveal the occurrence of warm and cold periods.
- The rings in the trees provide clues about wet and dry periods. Historical records describe the vagaries in climate. **All these pieces of evidence indicate that climate change is a natural and continuous process.
- India also witnessed alternate wet and dry periods. Archaeological findings show that the Rajasthan desert experienced a wet and cool climate around 8,000 B.C.
- The period 3,000- 1,700 B.C. had higher rainfall. From about 2,000 to 1,700 B.C., this region was the center of the Harappan civilization. Dry conditions accentuated since then.
- In the geological past, the earth was warm some 500-300 million years ago, through the Cambrian, Ordovician, and Silurian periods.
- During the Pleistocene epoch, glacial and inter-glacial periods occurred, the last major peak glacial period was about 18,000 years ago. The present inter-glacial period started 10,000 years ago.
Climate in the recent past
- Variability in climate occurs all the time. The nineties decade of the last century witnessed extreme weather events. The 1990s recorded the warmest temperature of the century and some of the worst floods around the world.
- The worst devastating drought in the Sahel region, south of the Sahara desert, from 1967-1977 is one such variability. During the 1930s, severe drought occurred in the southwestern Great Plains of the United States, described as the Dust Bowl.
- Historical records of crop yield or crop failures, of floods, and migration of people tell about the effects of changing climate.
- Europe witnessed the “Little Ice Age” from 1550 to about 1850. From about 1885-1940 world temperature showed an upward trend. After 1940, the rate of increase in temperature slowed down.
Climate Change: Causes
The causes of climate change are many. They can be grouped into astronomical, terrestrial, and volcanic causes.
Astronomical Causes
The astronomical causes are the changes in solar output associated with sunspot activities. Sunspots are dark and cooler patches on the sun which increase and decrease cyclically.
- According to some meteorologists, when the number of sunspots increases, cooler and wetter weather and greater storminess occur. A decrease in sunspot numbers is associated with warm and drier conditions.
- Another astronomical theory is Millankovitch oscillations, which infer cycles in the variations in the earth’s orbital characteristics around the sun, the wobbling of the earth, and the changes in the earth’s axial tilt.
- All these alter the amount of insolation received from the sun, which in turn, might have a bearing on the climate.
Terrestrial Causes
Terrestrial causes are those that are derived from human activities as opposed to those occurring in the natural environment without human interference :
- The most important anthropogenic effect on the climate is the increasing trend in the concentration of greenhouse gases in the atmosphere which is likely to cause global warming.
- The largest concentration of GHGs in the atmosphere is carbon dioxide. The emission of CO2 comes mainly from fossil fuel combustion (oil, gas, and coal). Forests and oceans are the sinks of carbon dioxide.
- Forests use CO2 in their growth. So, deforestation due to changes in land use, also increases the concentration of Co2. The time taken for atmospheric CO2 to adjust to changes in sources to sinks is 20-50 years.
- It is rising at about 0.5percentt annually. Doubling of concentration of CO2 over the pre-industrial level is used as an index for estimating the changes in climate in climatic models.
- Chlorofluorocarbons (CFCs) are products of human activity. The CFCs that drift into the stratosphere destroy the ozone.
- Large depletion of ozone occurs over Antarctica. The depletion of ozone concentration in the stratosphere is called the ozone hole.
Volcanic Causes
- Volcanism is considered another cause of climate change. Volcanic eruption throws up lots of aerosols into the atmosphere.
- These aerosols remain in the atmosphere for a considerable period reducing the sun’s radiation reaching the Earth’s surface.
- After the recent Pinatoba and El Cion volcanic eruptions, the average temperature of the earth fell to some extent for some years.
Climatic Change: Impacts
The impacts of climate change are :
- Rise in the sea level due to melting of glaciers and ice-caps.
- Thermal expansion of the sea may inundate large parts of the coastal area and islands, leading to social problems.
- The globally averaged annual mean temperature at the end of the 20th century was about 0.6°C above that recorded at the end of the 19th century.
- The seven warmest years during 1856-2000 were recorded in the last decade. The year 1998 was the warmest, probably not only for the 20th century but also for the whole millennium.
**People Also View