There’s a recent post on Watts Up With That (WUWT) about a new paper by Syun-Ichi Akasofu. The paper, which has now been accepted, apparently lead to the resignation of one of the editors (Chris Brierley). One of the reasons I was interested in this post is that I’m sure I’ve come across Syun-Ichi Akasofu before. I can’t remember if I’ve met him or am just aware of his work. Either way, he is clearly a scientist who has had a fantastic career and has excellent credentials.
So, does this recent paper reflect Syun-Ichi Akasofu’s excellent credentials? Sadly, I would say no. The abstract of the paper says
The rise in global average temperature over the last century has halted since roughly the year 2000, despite the fact that the release of CO2 into the atmosphere is still increasing. It is suggested here that this interruption has been caused by the suspension of the near linear (+ 0.5oC/100 years or 0.05oC/10 years) temperature increase over the last two centuries, due to recovery from the Little Ice Age, by a superposed multi-decadal oscillation of a 0.2oC amplitude and a 50-60 year period, which reached its positive peak in about the year 2000—a halting similar to those that occurred around 1880 and 1940. Because both the near linear change and the multi-decadal oscillation are likely to be natural changes (the recovery from the Little Ice Age (LIA) and an oscillation related to the Pacific Decadal Oscillation (PDO), respectively), they must be carefully subtracted from temperature data before estimating the effects of CO2.
The paper also includes the following figure which shows the supposed linear recovery from the LIA and the multi-decadal oscillations that produce, at times, surface warming slowdowns. So does this really make sense? No, I think it does not. I suspect most who read this post would agree, but I’ll write my thoughts anyway.
One issue with the idea suggested by Akasofu is that systems don’t simply recover magically. Some process has to act to return the system to equilibrium. You can’t simply ignore the physics associated with the supposed recovery. The other immediate problem is that Akasofu is claiming that the linear warming trend (which is the recovery from the LIA) and the multi-decadal oscillations must be removed before estimating the effects of CO2. Well, as far as I can tell this would leave a flat temperature trend which would lead one to conclude that CO2 has no effect. This is clearly wrong and even Anthony Watts calls those who think CO2 has no effect dragon slayers.
We can go a bit further though. Could it be that the linear trend is simply a recover from the LIA? If so, what could be causing this? There seem to be two options. One is that prior to the LIA some process drove surface temperatures 1oC below equilibrium, and we are now simply recovering back to equilibrium. The other is that it is simply the Sun. Prior to the LIA, the Sun was getting fainter and hence the world got cooler, now the Sun is getting brighter and we’re getting warmer. Neither of these possibilities really works and I’ll explain why below.
Let’s consider the possibility that we’re simply recovering back to equilibrium. The land and atmosphere have a total mass of about 1019 kg. The specific heat capacity is 1000 J kg-1 K-1. That means it takes 1022J to increase the temperature by 1oC. Currently our energy imbalance is about 1022J per year. If we want a recovery of 1oC to take longer than 100 years, the land and atmosphere must be absorbing less than 1% of the energy excess per year (the rest going into the oceans). Given that the heat capacity of the ocean is about 100 times greater than that of the land and atmosphere, this may seem reasonable. The problem is that at the end of the LIA, the energy imbalance would have been 10 times greater than it is today (because the surface temperature was 1oC lower). So, for the process to take more than 100 years, the land atmosphere must have been absorbing a tiny fraction of the excess energy. Given that land makes up 30% of the Earth’s surface and the atmosphere surrounds the planet, this seems remarkably inefficient and hence highly unlikely.
What about the Sun? The flux we’re getting from the Sun has increased by a couple of tenths of a Watt per square metre since the LIA. Alone, this should increase surface temperatures by about 0.1oC. To produce a 1oC increase therefore requires a very large amplification. This is problematic since it would then suggest that our climate is very sensitive to small changes in Solar flux. Paleo-climatological research suggests that this is not the case. Our climate is thought to be remarkably stable. Also, what would provide such a large amplification? As far as I can tell, if you want such an amplification to be “stable” then you need it to be a lot of small effects rather than one big effect (you want the amplifications to be similar to or smaller than the driver). If it’s one big effect then it would seem hard to reverse if the small driver (changes in solar flux) were to reverse. Also, the Solar flux has been dropping since the late 1960s, so why are we still warming if this is the driver? So, no it can’t really be the Sun.
All of the above also ignores that we don’t need some magical recovery from the LIA to explain the warming we’ve experienced since the mid- to late-1800s. We have CO2. We can quantify it’s radiative forcing. It’s quite substantial. It explains some of the warming during the first half of the 20th century of most of the warming in the second half of the 20th century. Ignoring the well understood influence of atmospheric CO2 in favour of some as yet unexplained recovery from the LIA just seems remarkably unscientific. It seems a little sad that someone of Syun-Ichi Akasofu’s credentials would not recognise this.