The sun and climate change
The Sun is a giver of life; it helps keep the planet warm enough for us to survive. It also influences Earth’s climate: We know subtle changes in Earth’s orbit around the Sun are responsible for the comings and goings of the past ice ages. But the warming we’ve seen over the last few decades is too rapid to be linked to changes in Earth’s orbit, and too large to be caused by solar activity.
A common call of those who deny anthropogenic climate change is that the warming of the planet has been caused by the sun. But the facts do not support this hypothesis. The sun does drive life on the planet, is the source of almost all of the energy on planet Earth. But many of those same people cannot correctly explain why we have seasons. Many have the misconception that seasons are caused by the elliptical orbit of the earth around the sun. In earth’s orbit, we are actually closest to the sun in January when the northern hemisphere is in winter. We have seasons because of the tilt of the planet, which causes unequal heating of the planet as it moves through its yearly orbit. The Sun can influence the Earth’s climate, but it isn’t responsible for the warming trend we’ve seen over the past few decades.
One of the “smoking guns” that tells us the Sun is not causing global warming comes from looking at the amount of the Sun’s energy that hits the top of the atmosphere. Since 1978, scientists have been tracking this using sensors on satellites and what they tell us is that there has been no upward trend in the amount of the Sun’s energy reaching Earth.
A second smoking gun is that if the Sun were responsible for global warming, we would expect to see warming throughout all layers of the atmosphere, from the surface all the way up to the upper atmosphere (stratosphere). But what we actually see is warming at the surface and cooling in the stratosphere. This is consistent with the warming being caused by a build-up of heat-trapping gases near the surface of the Earth, and not by the Sun getting hotter.
Some skeptics of human-induced climate change blame global warming on natural variations in the sun’s output due to solar flares, coronal mass ejections, sunspots and/or solar wind. The explosive heat of a solar flare cannot make it all the way to our globe because the atmosphere filters or blocks most of the higher frequency electromagnetic radiation such as gamma and x-rays. But some electromagnetic radiation and energetic particles can get through our protective atmosphere. Solar flares can temporarily alter the upper atmosphere creating disruptions with signal transmission from, say, a GPS satellite to Earth causing it to be off by many yards. Another phenomenon produced by the sun could be even more disruptive. Known as a coronal mass ejection or CME these solar explosions propel bursts of particles and electromagnetic fluctuations into Earth's atmosphere. Those fluctuations could induce electric fluctuations at ground level that could blow out transformers in power grids. A CME's particles can also collide with crucial electronics onboard a satellite and disrupt its systems. But these activities of the sun have been ongoing for millennia. There is no association with mass extinction events and activity of the sun over geologic time.
One needs to understand why the earth has seasons, the electromagnetic spectrum and the workings of our atmosphere to understand the subtle nuances of solar science and anthropogenic climate change. To state that climate change is simply caused by the sun shows a lack of comprehension of the complex processes in the interaction of the sun and earth.