Cosmic rays are elementary particles like proton, electron, photons, muons, etc. which are generated in deep space by energetic processes like normal fusion reactions, degenerate collapses into white dwarfs and neutron stars, or total gravitational collapses. Actually some cosmic rays have so much energy (a photon with 10^20 eV) that nobody can explain how they could have been generated.
Nevertheless, the charged cosmic rays can be deflected by magnetic fields and that is just what solar flares which are sourced by sunspots are, unusual alignments of magnetic field lines which look like dark spots on the sun’s surface. So if there are sunspots, there are strong magnetic fields extending out from the surface of the sun deflecting those cosmic rays passing close to the sun. It just so happens that such a situation results in a decrease in the number of cosmic rays hitting the earth’s atmosphere.
When cosmic rays impact aerosols, tiny bits of matter floating in the atmosphere, collections of molecules, they knock off electrons causing the aerosol to generate an electric field which attracts water molecules in the neighborhood . Water molecules are permanently polarized even though they are neutral. Therefore many can be attracted to a single aerosol and form the nucleus for a water droplet. Many droplets make a cloud and the cloud blocks the sun, keeping the sun’s energy from reaching the ground. So sunspots mean less cosmic rays and less clouds. On the other hand fewer sunspots mean more cosmic rays and more clouds.
This idea is not just a theory. There are measurements of cosmic ray flux and cloud cover and sunspots versus cosmic ray flux showing the modulation of clouds with sunspots. There are also preliminary results from an experiment at CERN called the CLOUD experiment which is consistent with high energy particles causing water droplets. They haven’t published final results yet.
In the years from 1950 t0 2000, the amount of CO2 in the atmosphere has increased due to the burning of carbon based fuels. At the same time there has been an unusual increase in solar activity. See Wikepedia “Solar Cycle”where it says “Overall level of solar activity in the second half of the 20th century is the highest in 10,000 years.” Since CO2 infrared absorption is only increasing logarithmically at present concentrations, it seems that most of the warming over the last 50 years has been from natural causes like ocean current oscillations, cosmic rays, and a small amount of visible light energy modulation.
Don’t be confused by the wordplay on “global warming”. CO2 does absorb maybe 25% of the infrared emitted by the hot earth which is absorbed (mostly by water.). And the temperatures have been a wee bit higher the last fifty years (less than .4 degrees Celsius over the average of the last 100+ years). But there are distinct disagreements as to what the future will bring. Attempts at modeling a climate system which theoretically can’t be modeled due to its nonlinearities and feedback have not been successful in explaining past situations but of course we don’t know what will really happen in 100 years until 100 years goes by. The mechanics of climate dynamics depends sensitively on the feedback of the energy trapped by the greenhouse gases, dominated by water vapor ( like in the clouds generated by cosmic rays – cloud thermodynamics is too hard for present models and computers and cosmic rays are specifically ignored – not included at all.). Just as there is not a consensus on the importance of CO2 in the energy balance in the atmosphere, there is a deeper uncertainty about whether its contribution is positive or negative – causes the average temperature to increase or decrease.
There has been a pause in the recovery of average global temperature from the Little Ice Age and a hesitation to depend on average temperature as a relevant parameter for the problem of climate change. For the last 15 years the average temperature, not matter which average you use, has not increased even though it is between zero and 0.4 degrees above the average for the last 100 years. The models, on the other hand, have predicted a lockstep monotonic increase in the global average with the CO2 fraction of the atmosphere. Therefore the models are now in significant disagreement with reality, not only in the present value of the global temperature, but in the way that the temperature has increased.
When an event like an El N¡ño occurs (a spontaneous rearrangement of ocean currents), the temperature response is smooth and noise free, a response curve any scientist can admire. The variations in global temp as the temperature has increased over the last 50 years by 1/2 degree Celsius are large and not just measurement fluctuations. The CO2 increases have been smooth, the temp changes have been much greater than the average change and in both directions. You could say that the average of these large changes has nevertheless increased over the last 100 years, but I think the fluctuations represent physics, an El Niño here, a La Niña there, the overlay of the 11 year sunspot cycle, variations of the sunspot cycle width, etc. – natural variations not forced by CO2. Once I get the knack of efficiently adding graphics, I will repost some signs of what I feel are conclusive in forming an opinion that CO2 is not a pollutant (not a major players as far as global warming goes.), it is beneficial in major ways, and the calculations of climate science are woefully short of the amount of physics needed to calculate the temperature average over the next 100 years. Such a calculation is after all one of the hardest calculations ever attempted in science. In fact, it is theoretically impossible given the limitations of knowledge of the weather today. That is to say, we don’t have enough data at any one time to provide the starting data for our models, regardless of whether they are capable of projecting the future correctly or not. Most of our major computer advances have been partially driven by the desire to calculate the weather.