What is climate change

• Climate change is a long-term shift in the statistics of the weather (including its averages).
• For example, it could show up as a change in climate normals (expected average values for temperature and precipitation) for a given place and time of year, from one decade to the next.

Why is climate changing?

Natural causes

• Climate change is a normal part of the Earth’s natural variability.
• It is related to interactions among the atmosphere, ocean, and land.
• Variation in Solar energy: It is also related to changes in the amount of solar radiation reaching the earth-As the stream of solar energy reaches earth, the character of the Earth’s orbit and of its rotation plays a major role in causing long-term climate change.
• Volcanic eruptions:
• Explosive volcanic eruptions can inject large quantities of dust and the gas, sulphur dioxide, high into the atmosphere.
• Whereas volcanic debris in the lower atmosphere falls out or is rained out within days, the veil of pollution in the upper atmosphere is above the weather and may remain for several years, gradually spreading to cover much of the globe.
• The volcanic pollution results in a substantial reduction in the stream of solar energy as it passes through the upper layers of the atmosphere, reflecting a significant amount back out to space.

Anthropogenic Causes

• Humans are increasingly influencing the climate and the earth’s temperature.

How?

The Fourth Assessment Report of the Intergovernmental Panel on Climate Change(IPCC) concludes, “that most of the observed increase in the globally averaged temperature since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.”

What are the causes of rising emissions?

• Combustion of fossil fuels (coal, oil and gas) produces carbon dioxide and nitrous oxide.
• Increasing deforestation: Trees help to regulate the climate by absorbing CO₂from the atmosphere. As trees are being recklessly cut, the beneficial effect is lost and the carbon stored in the trees is released into the atmosphere_, adding to the greenhouse effect.
• Increasing livestock farming: Livestock such as cows produce large amount of methane when they digest food.
• Overuse of fertilizers: Fertilisers containing nitrogenproduce nitrous oxide emissions.
• Fluorinated gasesproduce a very strong warming effect, up to 23 000 times greater than CO₂.
• This leads to the  increase in the globally averaged temperature-Global Warming
• The world’s leading climate scientists believe that the human activities are almost certainly the main cause of the warming observed since the middle of the 20^th

Climate is always changing. Why is climate change of concern now?

• Recent estimates of the increase in global average temperature since the end of the last ice age are 4 to 5 °C.
• That change has occurred over a period of about 7,000 years, starting 18,000 years ago.
• The current global average temperature is 0.85ºC higher than it was in the late 19th century.
• CO2 has risen by 40% in just the past 200 years, contributing to human alteration of the planet’s energy budget.
• The scientists consider that an increase of 2°C compared to the temperature in pre-industrial times is as the threshold beyond which there is a much higher risk that dangerous and possibly catastrophic changes in the global environment will occur.