Its not the Sun, silly! Or is it?


After a small abstract thread on twitter (Dutch), there were a lot of questions involving my analysis. Questions from self proclaimed "climate sceptics" that in reality are climate deniers. But alright, its good ask questions, it is what science is about! So today I'm going to write a more technical analysis of why the Sun is or isn't an important factor in anthropogenic global warming. 

I hope you enjoy this writing, and keep in mind that this is for educational purposes and does not sum the entire field of solar physics and geophysics!  

What is the solar constant?

I scream the term alot on twitter, "SOLAR FUCKING CONSTANT!" A constant is an unchanging value, but how did scientists determine this constant? And is it really a constant?

Well the solar constant is to be valued at 1361w/m² (Lean J. et al. 1998) and of course it varies over an 11-year cycle time due of the amount of sunspots. Nevertheless so called "dark" and "bright" spots rule each other out. So if we were to average a solar cycle we notice the TSI is a constant, and this gives physicist a great value to work with in further calculations. 

I know this can cause some controversy, technically it is NOT a constant. Its not a constant value but if we wanted to do any calculations using TSI it is better to use a constant value. This is what physicist do, we average things out without affecting the outcome of our calculation. Remember that mathematicians don't do this nevertheless their results would be similar to ours, if not exactly the same. Yet obviously, if you want to calculate the impact of TSI on our planet today, you'll need to use the value measured today, in climate science however where global temperatures matter over a significant amount of time (30-years normal or since the start of the industrial ages) this is of no relevance and we can use the solar constant at 1361w/m².

(Click for full image)

fig. 1: TSI measured by SORCE since the start of mission. 

The decadal impact of TSI variation on global climate.

So looking at the solar cycles, amount of active bright sunspots and TSI we can obviously see the correlation. The more sunspots, the higher TSI will be. This variance is determined to be +0.2K on a solar maximum and -0.2K on a solar minimum (fig.2). Now if we were to compare this to the observed temperature trend (fig.3)  there is no correlation to be found. 


Figure 2. Surface temperature compared to TSI variance.

Figure 3. 11 year solar cycles (SSN) and global temperatures by TSI variance (GT) compared to observed temperature trend (GSAT). 

Aegre fero, but not really.

So we can conclude, I WAS WRONG! The sun is not an absolute constant. There is variation in TSI and it does have some impact on global temperatures. However these small decadal variations cannot explain the current trend in warming observed. Thus it's not the Sun and the odds that the Sun has ever changed the global climate is extraordinary small. Therefore I was right in my thread, we can use the solar constant if we want to calculate climatological average temperatures. 

There is still a lot to be discussed on this topic, such as how much cosmic rays affect these variables these would only give us a better insight in variables and might or might not narrow the contribution of humans by a really tiny bit. One thing is for sure, we are the ones causing global warming, the amount of "cosmic rays" and "sun" needed to rule out our contribution to the radiative balance of our planet is a lot more! 



My regards,

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