Climate Change- 2 | Environment for UPSC CSE PDF Download

Climate Forcing’s

• Climate “forcings” are factors in the climate system that either increase or decrease the climate system's effects.
• Positive forcings such as excess greenhouse gases warm the earth while negative forcings, such as the effects of most aerosols and volcanic eruptions, actually cool the earth.
• Atmospheric aerosols include volcanic dust, soot from fossil fuels' combustion, particles from burning forests and mineral dust.
• Dark carbon-rich particles such as soot from diesel engines absorb sunlight and warm the atmosphere.
• Conversely, exhaust from high-sulphur coal or oil produce light aerosols that reflect sunlight back to space, producing a cooling effect. Aerosols that form naturally during volcanic eruptions cool the atmosphere. Large volcanic eruptions can eject enough ash into the atmosphere to lower temperature for a year or more until the atmosphere's sulfate particles settle out.

(a) Forcing

• Altering the Energy Balance
  (i) The power of a process to alter the climate is estimated by its “radiative forcing,” the change in the Earth’s energy balance due to that process.
  (ii) Some climate forcings are positive, causing globally averaged warming, and some are negative, causing cooling. Some, such as from increased CO₂ concentration, are well known; others, such as aerosols, are uncertain.
• Natural Forcings
  (i) Natural forcings include changes in the amount of energy emitted by the Sun, prolonged variations in Earth’s orbit, and volcanic eruptions.
  (ii) Since the start of the industrial revolution, the only natural forcing with any long-term significance has been a small increase in solar energy reaching Earth. However, this change is not nearly enough to account for the current warming.
• Human-Induced Forcings
• Human activities can also cause climate forcing. These activities include greenhouse gas and aerosol emissions from burning fossil fuels and the land surface modifications, such as deforestation.
• Human-Generated Greenhouse Gases
• Greenhouse gases are a positive climate forcing; that is, they have a warming effect. Carbon dioxide emitted from fossil fuel burning is presently the largest single climate forcing agent, accounting for more than half of the total positive forcing since 1750.
• Human-Generated Aerosols
  (i) Burning fossil fuels adds aerosols to the atmosphere. Aerosols are tiny particles in the atmosphere composed of many things, including water, ice, ash, mineral dust, or acidic droplets.
  (ii) Aerosols can deflect the Sun’s energy and impact the formation and lifetime of clouds. Aerosols are a negative forcing; that is, they have a cooling effect.
• Causes of Climate Change
• While natural forcings do exist, they are not significant enough to explain the recent global warming. Human activities are very likely responsible for most of the recent warming.

➤ How to estimate the effect of each gas?

Each gas’s effect on climate change depends on three main factors:

• How much of these gases are in the atmosphere?
  (i) Concentration, or abundance, is the amount of a particular gas in the air. Greenhouse gas concentrations are measured in parts per million, parts per billion, and even parts per trillion.
  (ii) One part per million is equivalent to one drop of water diluted into about 13 galloons of liquid (roughly the fuel tank of a compact car).
• How long do they stay in the atmosphere?
  (i) Each of these gases can remain in the atmosphere for different amounts of time, ranging from a few years to thousands of years.
  (ii) All of these gases remain in the atmosphere long enough to become well mixed, meaning that the amount that is measured in the atmosphere is roughly the same all over the world, regardless of the source of the emissions.
• How strongly do they impact global temperatures?
  (i) Some gases are more effective than others at making the planet warmer and “thickening the Earth’s blanket (greenhouse gas)”.
  (ii) For each greenhouse gases, a Global Warming Potential (GWP) has been calculated to reflect how long it remains in the atmosphere, on average, and how strongly it absorbs energy.

➤ Global Warming Potential

• Global warming potential describes the impact of each gas on global warming.
• The two most important characteristics of a GHG in terms of climate impact are how well the gas absorbs energy (preventing it from immediately escaping to space), and how long the gas stays in the atmosphere.
• The Global Warming Potential (GWP) for a gas is a measure of the total energy that a gas absorbs over a particular period of time (usually 100 years), compared to carbon dioxide.
• Gases with a higher GWP absorb more energy, per pound, than gases with a lower GWP, thus contributing more to warming Earth.

➤ GWP & Lifetime of Green House Gases

Carbon dioxide (CO₂) has a GWP of 1 and serves as a baseline for other GWP values.

• The larger the GW P, the more warming the gas causes. For example, methane’s 100-year GWP is 21, which means that methane will cause 21 times as much warming as an equivalent mass of carbon dioxide over a 100-year time period.
• Methane (CH₄) has a GWP more than 20 times higher than CO₂ for a 100-year time scale. CH₄ emitted today lasts for only 12 years in the atmosphere, on average. However, on a pound-for-pound basis, CH₄ absorbs more energy than CO₂, making its GWP higher.
• Nitrous Oxide (N₂O) has a GWP 310 times that of CO₂ for a 100-year timescale. N₂O emitted today remains in the atmosphere for an average of 120 years.
• Chloro fluoro carbons (CFCs), hydro fluoro carbons (HFCs), hydro chloro fluoro carbons (HCFCs), perfluoro carbons (PFCs), and sulfur hexafluoride (SF₆) are called high-GWP gases because, for a given amount of mass, they trap substantially more heat than CO₂.

Receding Glaciers-A Symptom of Global Climate Change

150 years ago there were 147 glaciers in Glacier National park, but today only 37 glaciers remain, and scientists predict that they are likely to melt by the year 2030. Similarly, glaciers all across the Himalayas and Alps are retreating and disappearing every year. There are almost 160,000 glaciers found in Polar Regions and high mountain environments. Therefore, researchers are increasingly using satellite remote sensors to routinely survey our world’s glaciers in a fraction of the time.

(i) Impact of glacial retreat

• The retreat of glaciers in the Andes and the Himalayas will have a potential impact on water supplies.
• Climate change may cause variations in temperature and snowfall, causing changes in the mass balance of a glacier.
• The Himalayas and other mountain chains of central Asia support large regions that are glaciated. These glaciers provide critical water supplies to dry countries such as Mongolia, western China, Pakistan and Afghanistan. The loss of these glaciers would have a tremendous impact on the ecosystem of the region.
• World’s leading scientists predict that global warming may pose serious threat to national and global economy and the environment.
• The poor and low-lying countries will find it difficult to cope with the damages caused by changing climate and rise in sea level