Is the amount of solar energy reaching the Earth's outer atmosphere constant?

Answer 1

No, it is not. The sun is constantly changing, sometimes it burns very slightly stronger and releases more solar energy, sometimes less.

Through the last 2000 years, the intensity of solar radiation reaching Earth has varied up or down by around 0.1 - 0.2 per cent.

We have only been able to directly observe the sun's energy for a bit over thirty years now, to go backwards beyond this time requires the use of proxies and less accuracy on an issue that requires very tight controls. Total warming of our planet is considered to be roughly 3 watts/M2. High accuracy is a must. During our limited length of measuring though, total solar energy variation has maintained a very tight window of under 0.1%.

The total energy hitting our outer atmosphere is roughly constant at an average of 1365.4 to 1366.6 watts per meter2. The variance is around 1.2 watts total on average. Interestingly enough though, this does not mean that the impact of our sun's energy hitting and staying with our atmosphere is constant.

Since the dawn of satellites, we are now able to measure the incoming energy with much more precession, including the bands of energy coming in. Some wavelengths pass through our atmosphere (both in and out) with far less resistance and likelihood of absorption. Ultra Violet energy has been demonstrated to vary in far larger proportions than some other wavelengths according to satellite data. . Some changes in bandwidths are quite large: 6% at 200 nm and 2.5% at 250 nm for example. To maintain a steady and consistent power, this means other wavelengths must also vary.

This ultraviolet energy is the primary energy used in the creation of ozone in our upper atmosphere (ozone layer). Additionally, greenhouse gases absorb different wavelengths so when there is an increase in one wavelength, a corresponding decrease must also occur to compensate and conform to the consistent output of the sun we are measuring. Ongoing studies are needed to understand how this affects global warming. The total affect of this issue is still not fully understood according to the 2007 IPCC report. (see link)