2010-10-01 18:28:38Is there a reconstruction of net radiative forcing over the past 1000 years or so?
John Cook


I'm working on an article and it would help to have a graph of net radiative forcing. Eg - GISS have a good graph of forcing over the past century or so but I'm wondering if anyone knows if there are similar reconstructions going back the last 1000 years. Well, I'm sure there are but is there any downloadable data?

I could build my own half-arsed version reconstructing CO2 forcing from the proxy data on CO2 levels and reconstruct solar forcing from TSI reconstructions. But would be good to get a proper one done by a professional.

2010-10-01 19:03:02Not clear what you mean


When we talk about radiative forcing nowadays, we mean a change from the radiation balance due to an influence which is outside normal atmospheric dynamics:

- Additional CO2

- Sulfates

- Volcanic eruptions

- Fires

Further, there is a time frame attached to these external influences: a starting period and an ending period. This is important, because if you add a permanent perturbation to the system, the temperature structure of the atmosphere adjusts until the radiation budget balances out again. 

Example: Take the pre-industrial Earth, and then add a dollop of 100% extra CO2. (In this thought experiment, forget about the carbon feedbacks that would add more CO2 and other greenhouse gases.) This gives us a 2X in CO2, resulting in the 3.7 Watts/m2 radiative forcing.

However, over time, as the Earth heats up in response to this forcing, the forcing itself goes away. The forcing was due to the fact that the temperature profile of the atmosphere was not in appropriate relationship with the outward flux of IR radiation, but the heating effect changes the temperature profile until the amount of radiant power emitted once again matches the solar power absorbed. From that point on, there is a new steady state and the radiative forcing is zero.

So when you talk about RF over time, what is your starting point in time? If you're focused on CO2, is your baseline a planet with no CO2? Or a non-zero reference value? And by the way, you should also take into consideration variations in solar power over the period, since that will affect the power input.


2010-10-01 19:38:00This is what I mean
John Cook


Just found this in Hegerl et al 2006. Now just need to find it in data form.


Incidentally, got an email from one of the co-authors of that paper, Tom Crowley, yesterday. He gave me a dressing down for using the word 'devastating' in that blog post about the "Climate Scientists Respond to Monckton" document. I need to be more neutral :-)

2010-10-01 22:03:16

Really, John?  Was Crowley was objecting to the sentence "The result is thorough, methodical and devastating"?  That doesn't seem like our most egregious departure from neutrality.
2010-10-01 22:12:19comment
Robert Way

hey john,

Check here for some forcing data I think? ||


Did you ask him about writing a post? haha
2010-10-01 22:14:30comment
Robert Way

See crowley (2000) on the list of data... there's a 1000 year forcing reconstruction...
2010-10-01 23:28:44Thanks Robert, that link is exactly what I was after
John Cook


Ned, well, maybe "dressing down" was a tad of an over-dramatisation. It was more a suggestion and he's a class act, a real gentleman. But yeah, I think it was the "thorough, methodical and devastating" bit.

Robert, actually, yes, I asked him about writing a post a few hours ago. We'd established a dialogue, I happened to be reading his paper in preparation for an upcoming blog post, it seemed like serendipity. Just got a response a few minutes ago. He said he'd think about it. I think I'm going to hear that phrase a lot over the next few weeks :-)

2010-10-02 01:55:39nice figure
Dana Nuccitelli
That's a pretty impressive looking figure, with GHG and aerosols just going off the charts over the past century.  Talk about hockey sticks!
2010-10-02 02:20:48
Mark Richardson

One problem we should be cautious about is that albedo changes sound pretty difficult to gather reliable data on for the past. Things like changing land use (dominance of one plant type over another, for example?) might have a significant influence.

 And Spencer's "internal forcing" does sound possible, although the sheer coincidence of Milankovitch cycles and other palaeoclimate evidence suggests that it's not the bullet in the brain of ~3 C climate sensitivity he's looking for.

2010-10-02 15:09:50
Chris Colose


Longer than 1,000 years, but you might find this useful


2010-10-02 16:56:01Thanks for the link Chris
John Cook


Forgot about that paper. Striking is Figure 2:


2010-10-02 17:54:49

Note that the figure displays Rate of Change of Forcing.