We know from research and simply everyday experience, that cloud cover can have a significant effect on temperature.
I promised I would get back to our discussion about solar activity and variability of the climate here on Earth. Some people have been asking me how this fits into the weather lessons series I have been trying to follow. While I might be going off on a little bit of a tangent, I think it does fit fairly nicely into our current topic. If you remember back to early summer, we were discussing the energy balance of our atmosphere – how much energy was coming in and then what was happening to that energy once it is in our atmosphere. All we are doing right now is taking a closer look at the energy coming into our atmosphere.
Climate variability (we could call it climate change, but our climate is always changing and I find using the term climate change implies that this change is a recent phenomenon) is often attributed to several physical factors.
Long-term changes in the Earth’s orbit are thought to cause the ice ages. Internal changes in the ocean’s atmospheric circulation pattern can cause changes in our climate (the movie “Day After Tomorrow” partially played on this idea). Volcanic eruptions are known to affect the Earth’s climate for short periods, but prolonged periods of volcanism can also affect climate for an extended period. Finally, we have changes in the sun’s activity that we believe can have either a warming or cooling effect on the Earth.
It was this final point that we touched on last time by looking at the sunspot cycle and comparing it to changes in the temperature of our atmosphere. I finished up that article by mentioning some work done by Henrick Svensmark, senior scientist at the Danish National Space Institute. His work focused on Galactic Cosmic Rays and how they may play a significant role in the variability of the climate here on Earth. While his work is rather new, he has found some interesting correlations. But as he points out, the underlying mechanisms on how Galactic Cosmic Rays affect our climate are not yet established.
Just what are Galactic Cosmic Rays (GCR)? Well, just as our sun gives off energy which bombards our planet, billions of other celestial objects in our galaxy are doing the same
thing. Here on Earth, we are shielded from some of the energy coming off of our sun by the Earth’s magnetic field, but some of this energy still makes it in. The same thing is happening with the GCR. But in this case, our solar system is being protected by the sun’s magnetic field and the solar wind. Just like with the Earth and the sun, some of these GCR do make it though to the Earth, creating an ionization of the atmosphere that we can measure. Interestingly, we have measurements of GCR dating back to the mid-1930s.
OK, so now we know what GCR are – the next question is how can they affect the climate here on Earth? According to Svensmark’s research, there appears to be a fairly strong correlation between the amount of GCR and cloud cover. This is where Svensmark admits that, while there is this strong correlation, the physics behind how or why GCR could affect cloud cover are not really understood. But let’s assume GCR can influence cloud cover; what does that mean for our climate?
We know from research and simply everyday experience, that cloud cover can have a significant effect on temperature. Clouds can help to cool things off (a cloudy summer day for example) and clouds can act to warm us up (a cloudy fall or winter night).
Overall, on Earth, we receive an average of 1,365 W/m2 (watts per square metre) of energy from the sun. It has been estimated that cloud cover cools the planet by about 17 to 35 W/ m2. The sunspot cycle (the period from high to low sunspots) only affects the amount of energy reaching the earth by about one W/ m2, significantly less than cloud cover (which ranges from 17 to 35 W/m2). If there were a change in the amount of cloud cover by about three per cent, this would equate to around 1.5 W/m2. This is more than the change accounted for by the solar cycle or the estimated effect of increased greenhouse gases since 1850 (both of which individually account for approximately one W/ m2). So cloud cover plays a significant role in moderating temperatures here on Earth.
If GCR are found to play a role in the formation of clouds, then our climate variability story has become even more complicated, or maybe it will be simpler to figure out. Only time will tell.