Solar irradiance

    • Changes in the sun’s energy output would cause the climate to change, since the sun is the fundamental source of energy that drives our climate system.
    • Studies show that solar variability has played a role in past climate changes, a decrease in solar activity is thought to have triggered the Little Ice Age between approximately 1650 and 1850, when Greenland was largely cut off by ice from 1410 to the 1720s and glaciers advanced in the Alps.
    • But several evidences show that current global warming cannot be explained by changes in energy from the sun:
      • Since 1750, the average amount of energy coming from the sun either remained constant or increased slightly.
      • If the warming were caused by a more active sun, then scientists would expect to see warmer temperatures in all layers of the atmosphere. Instead, they have observed a cooling in the upper atmosphere, and a warming at the surface and in the lower parts of the atmosphere. That’s because greenhouse gases are trapping heat in the lower atmosphere.
      • Climate models that include solar irradiance changes can’t reproduce the observed temperature trend over the past century or more without including a rise in greenhouse gases.
    • Sunspot Cycles:
      • The increased sunspot activity (increase in the number of sunspots) causes warming of the earth’s surface and its atmosphere and vice versa.
      • Sunspots are darker and cooler areas in the photosphere of the sun.
Solar cycles have an average duration of about 11 years. Solar maximum and solar minimum refer to periods of maximum and minimum sunspot counts. Cycles span from one minimum to the next. The cyclical variation in sunspot counts, discovered in 1843 by the German astronomer Samuel Heinrich Schwabe, is called “the Sunspot Cycle”

Sunspots are regions where the solar magnetic field is very strong. In visible light, sunspots appear darker than their surroundings because they are a few thousand degrees cooler than their surroundings. Most of the visible surface of the Sun has a temperature of about 5400 degrees C, but in a big sunspot the temperature can drop to about 4000 degrees C. Sunspots come in sizes between about 2500 km and about 50,000 km.


Astronomical Theories

  • The Milankovitch Theory or Milankovitch Oscillations have tried to explain the causes of climate change through change in the eccentricity of earth’s elliptical orbit, obliquity including of the earth’s rotational axis and precession of the equinoxes
  • On the basis of above theory, he tried to explain the advancement and retreat of ice sheets during Pleistocene Ice Age.
  • Atmospheric Dust Hypothesis (mainly volcanic eruptions and dusts)
    • The atmospheric solid particulate matters include dust particles, salt particles, pollen, smoke and soot, volcanic dusts and ashes, etc.
    • Black carbon (BC) is a solid particle or aerosol, not a gas, but it also contributes to warming of the atmosphere.
      • Unlike GHGs, BC can directly absorb incoming and reflected sunlight in addition to absorbing infrared radiation.
      • BC can also be deposited on snow and ice, darkening the surface and thereby increasing the snow’s absorption of sunlight and accelerating melt.
    • Sulfates, organic carbon, and other aerosols can cause cooling by reflecting sunlight.
Black Carbon

  • Black carbon is the sooty black substance emitted from gas and diesel engines, coal-fired power plants, and other sources that burn fossil fuel. It comprises a significant portion of particulate matter or PM, which is an air pollutant.
  • Black carbon is a global environmental problem that has negative implications for both human health and our climate. Inhalation of black carbon is associated with health problems including respiratory and cardiovascular disease, cancer, and even birth defects. Black carbon also contributes to climate change causing changes in patterns of rain and clouds.
  • As black carbon deposits in the Arctic, the particles cover the snow and ice, decreasing the Earth’s ability to reflect the warming rays of the sun, while absorbing heat and hastening melt.


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