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Sunspots are regions on the solar surface that appear dark because they are cooler than the surrounding photosphere , since they are cooler , a reduction would lead to warmer temperature on earth.
"Intuitively one may assume the that total solar irradiance would decrease as the number of (optically dark) sunspots increased. However direct satellite measurements of irradiance have shown just the opposite to be the case. This means that more sunspots deliver more energy to the atmosphere, so that global temperatures should rise"
Sunspots are areas of lower surface temperature. They are formed due to magnetic flux which hinders convection and thus reduces temperature.
However, the relation between the number of sunspots and irradiation is a bit more complex. This is because most coronal mass ejections occur around areas of intense magnetic activity. So while sunspots are definitely cooler than the surroundings, the areas surrounding the sunspots do become hotter in most cases; and lead to increased solar events.
This is true to some extent because as depicted in the graph above, the variance in Sun's irradiance is less when compared to the corresponding variance in the number of sunspots.
So what NCERT says is also correct and what the source you cited in the first comment says is also correct, both due to the reasons I mentioned above. The former is true because a decrease in sunspots means a uniformly hotter sun and the latter is true because it increases the frequency of CMEs and other solar events which will affect the Earth's temperature.
TL;DR = an increase or decrease in sunspots leads to a directly corresponding change in solar irradiance, but to a lesser magnitude.
This is what I could infer from what I read online. Hope it's helpful.
This golmol answer is beneficial for mains. But prelims me increase ya decrease choose krna hoga.
@DrkingSchultz ...But if sunspots leads to Increase in insolation then how can less sunspots lead to warm and dry temperature? Shouldn't it be the opposite?
Going by what @narinderkareer said and point mentioned in Bold letters in Your comment. .. Ncert kaise correct ho Sakti hai?
There is no 'one' acceptable theory on sunspots, therefore dont indulge too much into this. Ncert also 'only' talks about 'probability' of a relationship between sunspots and insolation.
And UPSC does not ask questions where answer can be contested.
The notion of a rigorously constant amount of solar radiation reaching the earth was upset recently by a team of scientists at the National Center for Atmospheric Research (NCAR). John Eddy, Ronald Gilliland, and Douglas Hoyt of NCAR's High Altitude Observatory report that sunspots, which speckle the sun's surface in a fluctuating 11-year cycle, diminish the amount of sunlight reaching the earth. Their conclusion, which may radically affect global climate modeling, is based on data gathered from the Solar Maximum Mission (SMM) satellite and their own solar blocking model.
Data collected by the SMM satellite reveal that only a small fraction of the energy blocked by sunspots is balanced by immediate, enhanced emissions from bright areas on the sun. Moreover, solar energy can remain trapped in the sunspots, which have an average diameter of 9000 km, for years. Blocked radiative energy can be stored in the lower convective zone of the sun and have a ‘relaxation-time scale’ of 100,000 years, during which time it may slowly seep out. Fluctuating solar output affects the accuracy of global climate models that forecast long-term effects on the world's weather: Weather and climate are determined by the circulation patterns of the oceans and air, which are driven by solar energy coupled with the rotational inertia of the spinning planet.
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Comments
Yes that's what NCERT says but found this online
"Intuitively one may assume the that total solar irradiance would decrease as the number of (optically dark) sunspots increased. However direct satellite measurements of irradiance have shown just the opposite to be the case. This means that more sunspots deliver more energy to the atmosphere, so that global temperatures should rise"
Graphs in the link show direct relationship between insolation and number of sunspots.
Thanks for quoting the source.. ..Yes thats what I was saying. ..many online sources contradict NCERT
@DrKingSchultz .....King What's your take on this?
Shouldn't it be the opposite?
Going by what @narinderkareer said and point mentioned in Bold letters in Your comment. ..
Ncert kaise correct ho Sakti hai?
And UPSC does not ask questions where answer can be contested.
The notion of a rigorously constant amount of solar radiation reaching the earth was upset recently by a team of scientists at the National Center for Atmospheric Research (NCAR). John Eddy, Ronald Gilliland, and Douglas Hoyt of NCAR's High Altitude Observatory report that sunspots, which speckle the sun's surface in a fluctuating 11-year cycle, diminish the amount of sunlight reaching the earth. Their conclusion, which may radically affect global climate modeling, is based on data gathered from the Solar Maximum Mission (SMM) satellite and their own solar blocking model.
Data collected by the SMM satellite reveal that only a small fraction of the energy blocked by sunspots is balanced by immediate, enhanced emissions from bright areas on the sun. Moreover, solar energy can remain trapped in the sunspots, which have an average diameter of 9000 km, for years. Blocked radiative energy can be stored in the lower convective zone of the sun and have a ‘relaxation-time scale’ of 100,000 years, during which time it may slowly seep out. Fluctuating solar output affects the accuracy of global climate models that forecast long-term effects on the world's weather: Weather and climate are determined by the circulation patterns of the oceans and air, which are driven by solar energy coupled with the rotational inertia of the spinning planet.
http://onlinelibrary.wiley.com/doi/10.1029/EO064i012p00114-03/abstract
this link says the opposite
http://www-das.uwyo.edu/~geerts/cwx/notes/chap02/sunspots.html
...lets go with ncert