You are currently browsing the daily archive for May 13, 2007.

Two papers, one published in April and the other still at the discussion stage, caught my eye.

To a scientist in the subject, these may not seem important or novel; I don’t know. They have stuck in my mind though, so perhaps someone can offer some enlightenment.

The first: Objectively analysed air-sea heat fluxes for the Global Ice-free Oceans (1981-2005), by Yu and Weller, of the Woods Hole Oceanographic Institute, (WHOI) appeared last month in the Bulletin of the American Meteorological Society (BAMS).

It is about the air-sea heat flux, how much heat has been transferred between the two mediums in the period since 1981.

The abstract says:


A 25-yr (1981–2005) time series of daily latent and sensible heat fluxes over the global ice-free oceans has been produced by synthesizing surface meteorology obtained from satellite remote sensing and atmospheric model reanalyses outputs. The project, named Objectively Analyzed Air–Sea Fluxes (OAFlux), was developed from an initial study of the Atlantic Ocean that demonstrated that such data synthesis improves daily flux estimates over the basin scale. This paper introduces the 25-yr heat flux analysis and documents variability of the global ocean heat flux fields on seasonal, interannual, decadal, and longer time scales suggested by the new dataset.

The study showed that, among all the climate signals investigated, the most striking is a long-term increase in latent heat flux that dominates the data record. The globally averaged latent heat flux increased by roughly 9 W m−2 between the low in 1981 and the peak in 2002, which amounted to about a 10% increase in the mean value over the 25-yr period. Positive linear trends appeared on a global scale, and were most significant over the tropical Indian and western Pacific warm pool and the boundary current regions. The increase in latent heat flux was in concert with the rise of sea surface temperature, suggesting a response of the atmosphere to oceanic forcing.

The second; The origin of the 1500-year climate cycles in Holocene North Atlantic records, Debret et. al. , Climates of the Past Discussions, March 2007,

deals with the causes of climate change. This is in an open access journal, so you can click on the link at the bottom and read the entire paper. The bit that caught my eye was:

These results reveal that the mysteriously regular 1,500-year climate cycles are linked with the oceanic circulation and not with variations in solar output as previously argued (Bond et al., 2001). In this light, previously studied marine sediment (Bianchi and McCave, 1999; Giraudeau et al., 2000), ice core (O’Brien et al., 1995) and dust records (Jackson et al., 2005) can be seen to contain the evidence of combined forcing mechanisms, whose relative influences varied during the course of the Holocene. Circum-Atlantic climate records cannot be explained by solar forcing, but require changes in ocean circulation, as suggested previously (Broecker et al., 2001; McManus et al., 1999).

What is it about these which made them stand out? I hardly know myself, but have put some thought into the question.

The first paper can been interpreted as supporting the argument that the oceans have warmed over the past 25 years or so. The paper suggest a 10% increase between 1981 and 2002. This would seem to match expectations of climate modellers reasonably well, though perhaps it is a bit higher than might be expected. But why does the warming ‘peak’ in 2002? What has happened since then to alter the picture?

It finally occurred to me that I was thinking about the Lyman & Willis paper, which has been much discussed on the blogs, about the first output of the ARGO measuring buoys, and the absence of warming in the upper ocean between 2003-2005. Put together, the two papers’ results (taking the L&W revision into account) seem to complement and support each other. So what, if anything, happened in 2002-2003 to reduce both the heat flux and the oceanic warming signals? Is this evidence of a climate ‘event’ five years ago which was somehow significant? What does it tell us about what to expect for the future? More on these questions at the end.

The second point about this paper is that it is pointing to an atmospheric response to oceanic warming; this would seem to match reasonably well with the AGW hypothesis, in the sense that ocean warming is to be expected, but leaves a question as to how the extra energy in the system might be transferred to the atmosphere, and the global average surface temperatures.

I originally liked the second paper because it struck me as an elegant piece of work. Debret et. al. have used wavelet analysis to separate out two forcings, solar and ocean circulation, in the climate record and allocate cyclical events to them. The attribution of the 1500-year cycle to ocean circulation changes is the important bit here.

I may have read the graphics/paper wrongly, but it looks to me that we are most of the way up the curve on a cyclical ocean warming phase. This would suggest that at least some of the recent warming (since 1910), can be attributed to natural cycles of climate change, rather than human-induced forcing via the atmosphere. No surprises there. But here is the rub: there may be a conflicting climate ‘moment’ due in the coming years, when we would expect the ocean cycle to turn and begin its ‘cooling’ phase, but the addition of WMGHGs has placed a new component of heat addition into the system; what happens then?

I am loath to talk of ‘tipping points’; the term smacks of alarmism and ‘doomsday’ scenarios, but my thoughts are now running along the lines of ‘key moments’ in the global climate system. A ‘key moment’ is a short period (less than a decade?), during which the climate system ‘hops’ into a subtly different regime. The nearest analogy might be quantum theory; rather than seeing the climate system as a purely linear progression, there may be some mileage in the notion that it also experiences ‘quantum jumps’, as it were. These would not be of the magnitude of an apocalyptic one-off ‘inversion’ or ‘crisis point’ (taken from catastrophe theory), but more discrete ‘steps’ in the progression of the global climate.

Was 2002-2003 a ‘quantum moment’ in the climate system? If we are approaching the end of a warming cycle of ocean circulation, when is the ‘step’ shift down, towards a new regime, due? Will the human element of climate forcing disrupt the cycles? If so, what will the consequences of this be?

On this occasion in particular, the contribution of someone who knows what they are talking about would be most helpful.

Be loved.


Blog Stats

  • 64,787 hits
May 2007
« Apr   Jun »