One of the features of my home is a gas-log fireplace. Why is this of any importance to the topic of the global-warming/climate-change debate?
Stick with me a moment or two.
As I was about to say, the heat output, the irradiance of the fireplace isn’t constant. We can easily adjust the heat output with the convenient gas valve on the hearth.
One can experience variable heat another way, by moving closer or farther from the flame. This effect is due to the inverse-square law, you know, physics.
Patience, my friend. I’m about to get to my point.
Solar radiance, like my gas-log fireplace, has natural variable irradiance, that is, a range of heat output that changes.
Like my fireplace, the output of the sun’s broad-spectrum irradiance varies measurably.
“We can easily see from the table that the Total Solar Irradiance (TSI) is the MAIN CONTRIBUTOR of energy to Earth. We are fortunate that visible and IR light, which contribute the majority of energy to Earth, exhibit the smallest relative variation. But, although TSI varies by only a fraction of a percent, it has the greatest magnitude of change (~1.2 W/m2). This may be enough to cause observable changes at Earth.” – NASA: SOLAR IRRADIANCE
Just as you can find your warm spot in front of my fireplace by moving farther or closer, so does the earth-sun relative distance vary with the elliptical orbit about the sun.
A movement of only one or two feet can change the sensation of irradiance from my fireplace. Imagine what happens when the distance between our earth and the sun changes by millions of miles.
At perihelion (closest distance), the distance from the earth to the sun is 91.4 million miles.
At aphelion (farthest distance), the distance from the earth to the sun is 94.5 million miles.
If that small change in distance between you and my fireplace causes such a significant change in the heat you receive, imagine how a 3.1 million miles change in distance affects how much solar irradiance changes on the surface of the earth.
In 2019, the earth was at perihelion with the sun on July 4. In 2020, aphelion will be on January 5.
“The “solar constant” is, in fact, not constant. Recent satellite observations have found that the Total Solar Irradiance (TSI), the amount of solar radiation received at the top of the Earth’s atmosphere, does vary — see the graph for the results from six satellites. “The variations on solar rotational and active region time scales are clearly seen. The large, short-term decreases are caused by the TSI blocking the effect of sunspots in magnetically active regions as they rotate through our view from Earth. The peaks of TSI preceding and following these sunspot “dips” are caused by the faculae of solar active regions whose larger areal extent causes them to be seen first as the region rotates onto our side of the sun and last as they rotate over the opposite solar limb.” [Excerpted from the UARS descriptive text] The TSI provides the energy that determines the Earth’s climate.”NOAA: Total Solar Irradiance
Rest easy, Chicken Little. The daily activities of you and your puny fellow chickens are of no consequence whatsoever with respect to weather, climate changes, or sea level. It is the Total Solar Irradiance from that enormous ‘fireplace in the sky’, the sun, that determines the Earth’s climate.