CB part 2: It's The Sun Wot Did It

Apologies for taking last week off, I was in New York City. It felt rather trivial to write a climate change blog in the glaring neon light of Times Square, where any energy saving attempt seems like trying to spit out the sun. Speaking of which, today I will be covering another common climate myth, to wit:

The Idea
All of our energy comes from the Sun. If something changes, then why look any further than the source? It's pretty obvious that changes in the brightness of our home star would effect the temperature of the Earth. So even if global warming is happening, it's not humans. How dare scientists suggest it might be us. For their arrogance they should be transported to the hottest desert on Earth to KNEEL BEFORE THE MIGHTY HELIOS UNTIL BURNED TO DUST.

I'm paraphrasing here, slightly. But if you'd like to see an example, I'll choose foxnews this week. I've been picking on British newspapers a lot recently so I'll mix it up a bit.

Why it's bollocks
Well it is, and it isn't. Unlike the last one of these, where I discussed the whole "no warming for 15 years" phenomenon (which is just bad statistics), there's an actual hypothesis here, which can be tested to see if it's correct or not. The statement: "Changes in the temperature of the Sun have changed the temperature of the Earth" is something science can actually answer, unlike "but people grew wine in Greenland during the medieval warm period." That's an argument I won't be covering in this blog, because it's just an anecdote and you can't do anything with that except shrug and point to the vast quantities of proxy data collected to examine past climate.

Anyway, I digress. There are two questions when it comes to solar activity, both of which have been answered by climate scientists many times previously (which is good, because otherwise I'd have to do the research myself and this blog would take like 10000 hours and I'm kinda hungry). First, is solar activity currently increasing? Second, are we in a particularly high period of solar activity historically? The first one is easy, because we can point satellites at the sun and measure the solar energy it's kicking out in Watts per metre squared. Here's the graph. Thanks NASA.

As we can see, there is an approximate 11 year cycle in solar activity, ranging between 1365 and 1367 W/m2. The overall trend is shown as the red dotted line from 1985-2010, a whopping -0.012% per decade. From this Foster and Rahmstorf (2011) calculated a temperature trend of -0.014 to -0.023 °C/yr. So there goes the first idea. We aren't done yet though, because it's possible over a longer time period solar activity is much higher that it used to be. We need to answer the second question I referred to earlier.

This is much tricker, because we don't have a time machine or a 1000 year old satellite record. Handily, 17th century astronomers like Thomas Harriot and Galileo have come to our rescue by observing sunspots, dark patches on the surface of the Sun caused by high magnetic activity. Turns out there is a very clear link between number of sunspots and the amount of solar radiation the Earth receives. Thanks long dead folks who spend their days staring at the sun until they went insane. We owe you one.

Lean et al (1995) looked at the sunspot record and found a surface warming of around 0.5 degrees since 1700 due to increased solar activity. So it is fair to say the current climate is warmer than it was 300 years ago because of the sun. However, they also point out that of the 0.36 degrees of warming from 1970-1995 solar forcing accounted for around 0.11 degrees, leaving two thirds of the problem unaccounted for. Since then, solar forcing has decreased but the surface has continued to warm.

That should be it for the theory of solar forcing then, especially since the last paper I referenced was published in 1995. Surely the media wouldn't continue to lazily publish stories about already answered questions though would it? What? Oh. Right.