Warming of climate over the last 24,000 years

Context:

Scientists have reconstructed Earth’s climate since the last ice age, about 24,000 years ago. The study suggests that current temperatures are unprecedented in 24,000 years.

Relevance:

GS-III: Environment and Ecology (Climate Change and its impact, Environmental Pollution and Degradation, Conservation of the Environment)

Dimensions of the Article:

1. About the study on Climate Change
2. Evolution of climate change
3. Causes of Climate Change
4. Global Warming

About the study on Climate Change

• Scientists created maps of global temperature changes for every 200-year interval going back 24,000 years.
• They combined two independent datasets – temperature data from marine sediments and computer simulations of climate – to create a more complete picture of the past.

The study on Climate Change through 24,000 years has three main findings:

1. It verifies that the main drivers of climate change since the last ice age are rising greenhouse gas concentrations and the retreat of the ice sheets.
2. It suggests a general warming trend over the last 10,000 years, settling a decade-long debate in the palaeoclimatology community about whether this period trended warmer or cooler.
3. The magnitude and rate of warming over the last 150 years far surpasses the magnitude and rate of changes over the last 24,000 years.

Evolution of climate change

• India also witnessed alternate wet and dry periods. Archaeological findings show that the Rajasthan desert experienced wet and cool climate around 8,000 B.C.
• The period 3,000- 1,700 B.C. had higher rainfall. From about 2,000-1,700 B.C., this region was the centre of the Harappan civilisation. 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.

Recent examples

• 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 southwestern Great Plains of the United States, described as the dust bowl.

Causes of Climate Change

The causes for climate change are many. They can be grouped into

1. Astronomical – [Sunspot activities and Volcanism]. The astronomical causes are the changes in solar output associated with sunspot activities.
2. Terrestrial causes – [Green House gases, Pollution and aerosols, Ground level ozone]

Sunspots are dark and cooler patches on the sun which increase and decrease in a cyclical manner.

• According to some meteorologists, when the number of sunspots increase, cooler and wetter weather and greater storminess occur.
• A decrease in sunspot numbers is associated with warm and drier conditions

Volcanism is considered as another cause for climate change. Volcanic eruption throws up lots of aerosols into the atmosphere.

• These aerosols remain in the atmosphere for a considerable period of time reducing the sun’s radiation reaching the Earth’s surface
• 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.

Global Warming

• Due to the presence of greenhouse gases, the atmosphere is behaving like a greenhouse.
• The atmosphere also transmits the incoming solar radiation but absorbs the vast majority of long wave radiation emitted upwards by the earth’s surface.
• The gases that absorb long wave radiation are called greenhouse gases.
• The processes that warm the atmosphere are often collectively referred to as the greenhouse effect.

-Source: Indian Express