GLOBAL WARMING

1. Context

2. The difference in Temperature rise

• Temperature rises over land is much higher than over oceans. Overland the annual mean temperatures have risen by as much as 1.59 degree Celsius since preindustrial times, according to the latest report of the Intergovernmental Panel on Climate Change.
• Oceans, in contrast, have warmed by about 0.88 degree Celsius. The warming trends over the Indian region are very different.
• An assessment of climate change over the Indian subcontinent, published by the Ministry of Earth Sciences in 2020, said annual mean temperatures had risen by 0.7 degree Celsius from 1900.
• This is significantly lower than the 1.59 degree Celsius rise for land temperatures across the world. It could give the impression that the problem of climate change in India was not as acute as in other parts of the world. But that is not entirely accurate. 

3. Why is warming over India is lower?

• The relatively lower rise in temperatures over India is not a surprise. Also, India is not a special case. The increase in temperatures is known to be more prominent in the higher altitudes, near the polar regions, than near the equator.
• This is attributable to a complex set of atmospheric phenomena, including heat transfers from the tropics to the poles through prevailing systems of air circulation. India happens to be in the tropical region, quite close to the equator.
• A substantial part of the difference between the temperature rise over India and that over the entire world can be explained by understanding what the different numbers represent. 
• The planet as a whole has warmed by 1.1 degree Celsius compared with preindustrial times.
• But, as mentioned earlier, this is just the average. Different regions have seen very different levels of warming.
• The polar regions, particularly the Arctic, have seen significantly greater warming. The IPCC report says the Arctic region has warmed at least twice as much as the world average.
• Its current annual mean temperatures are about 2 degrees Celsius higher than pre-industrial times. Some other studies suggest the Arctic could be warming even faster.
• Again, this happens because of a variety of reasons, including the processes mentioned earlier. Another prominent cause is what is known as the albedo effect, or how much sunlight a surface reflects. The ice cover in the Arctic is melting, because of which more land or water is getting exposed to the Sun.
• Ice traps the least amount of heat and reflects most of the solar radiation when compared with land or water.
• More recent research suggests that the higher warming in the polar region could be attributed to a host of factors, including the albedo effect, changes in clouds, water vapour, and atmospheric temperatures.
• The warming in the polar regions accounts for a substantial part of the 1.1-degree Celsius temperature rise over the entire globe. 

4. Higher warming over land than oceans

• However, the 0.7 degree Celsius temperature rise over India has to be compared with the warming seen over land areas, not the entire planet.
• As mentioned, land areas have become warmer by 1.59 degree Celsius. Land areas tend to get heated faster and by a larger amount, than oceans.
• Daily and seasonal variations in heating over land and oceans are usually explained in terms of their different heat capacities. Oceans have a higher capacity to cool themselves down through the process of evaporation.
• The warmer water evaporates, leaving the rest of the ocean relatively cooler. However, longer-term enhanced heating trends over land have to be attributed to other, more complicated, physical processes involving land-ocean-atmospheric interactions.

5. Impact of Aerosols

• Aerosols refer to all kinds of particles suspended in the atmosphere. These particles have the potential to affect the local temperature in multiple ways.
• Many of these scatter sunlight back, so that lesser heat is absorbed by the land. Aerosols also affect cloud formation.
• Clouds, in turn, have an impact on how much sunlight is reflected or absorbed.
  Aerosol concentration in the Indian region is quite high, due to natural as well as man-made reasons.
• Due to its location in the tropics and the arid climate, India is no stranger to dust. But it also happens to be experiencing heavy pollution right now.
• Emissions from vehicles, industries, construction, and other activities add a lot of aerosols to the Indian region. A reduction in warming could be an unintended but positive side effect.

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