Originally Posted by Going Walkabout
[...]"However, at the National Astronomy Meeting in Wales, Northumbria University professor Valentina Zharkova said fluctuations an 11-year cycle of solar activity the sun goes through would be responsible for a freeze, the like of which has not been experienced since the 1600s.[..]."
While sieving through old posts in this thread I found that one. This one is completely down my alley as my research
field and expertise is determining spots and magnetic activities on exoplanetary host stars.
I met Prof. Valentina Zharkova at a convention in Tenarife. At breakfast one of our group called her the "ice queen" because of the storm of misinformation her paper has caused. She was not amused.
Nowhere in her paper did she mention any form of cooling
. Her paper was about a model for the sun’s magnetic field and sunspots, which predicts a 60% fall in sunspot numbers when extrapolated to the 2030s.
The whole thing started when the PR guy of the Royal Society called her preparing a press release. As he did not understand "solar activities at a minimum" she said something along the line of "you know the Maunder minimum I mentioned in my paper". The overly diligent PR guy made a mini-iceage out of that and released the whole thing without her knowledge.
She regrets having done this every time a Journalist calls asking for information about global cooling
predicted by her.
However, Earth's systems will always reach a state of radiative equilibrium that is
incoming radiative energy from the Sun = outgoing radiation of planet
That means that the planet is in energy balance. If a planet is not in radiative equilibrium the temperature of the planet will increase or decrease.
The amount of incoming radiation depends on the albedo of the planet or in other word the amount of incoming radiation which is not reflected back out in space. The amount of incoming radiation is determined by
where (σT_⊙^4 )(4πR_⊙^2 ) represents the luminosity and a the albedo. Rp is the radius of the planet and D the distance to the star.
Considering the planet as a blackbody any radiation reaching the planet is radiated as heat (Stefan-Boltzman Law) as follows:
where T is temperature. A is the area (=4πR_p^2) as a planet most likely emits radiation spread over the whole surface which is close to a sphere. Therefore the outgoing radiation is
where Teq is ((L_⊙ (1-a))/(16σπD^2 ))^(1/4)
Consequently the planet is in radiative equilibrium when
(σT_⊙^4 )(4πR_⊙^2 )(1-a)((πR_p^2)/(4πD^2 ))=(σT_eq^4 )(4πR_p^2 )
What does that mean for Earth? Assuming the surface of the earth without atmosphere would pretty barren I assume an albedo a=0.12 (similar to the Moon). R_⊙=6.96◊10^8m, T_⊙=5778K, D=1.496◊10^11m. Rearanging the above equations we can determine T_eq by
T_eq=T_⊙ (1-a)^(1/4) (R_⊙/2D)^(1/2)=5778K(1- 0.12)^(1/4) ((6.96◊10^8 m)/(2*1.496◊10^11 m))^(1/2)=269.9K
If we consider Earth’s real albedo of a=0.3 we get an even lower T_eq of 254.9K. The difference to the real measured average temperature on the surface of the earth of ~287K is caused by greenhouse effect of earth’s relatively thick atmosphere. So first of all we should be grateful for the greenhouse gases, because without them Earth would be a frozen ball of ice and we would most likely not exist at all.
You see solar
activity plays a rather minor role. Most of the temperature control happens in the atmosphere. Maybe I'll show you how that works when I have time to prepare something.