Monday, October 23, 2006

All climate is global.....

A theme of those that disrespect the IPCC and global climate models is that all climate is local and that the models are useless for discussing local events. Now come Kumar, Rajagopalan, Hoerling, Bates and Cane in Science, 314 (2006) 115 to show that indeed, local climate is global, or more accurately global effects on local climate can be controlling.

The monsoon is the controlling climate phenominon on the Indian subcontinent. From the abstract:

The 132-year historical rainfall record reveals that severe droughts in India have always been accompanied by El Niño events. Yet El Niño events have not always produced severe droughts. We show that El Niño events with the warmest sea surface temperature (SST) anomalies in the central equatorial Pacific are more effective in focusing drought-producing subsidence over India than events with the warmest SSTs in the eastern equatorial Pacific. The physical basis for such different impacts is established using atmospheric general circulation model experiments forced with idealized tropical Pacific warmings.
Changes in El Nino driven by global climate change will change the monsoon and thus the lives of everyone everywhere on the Indian subcontinent.

Isaih Berlin, a rather overrated mid-twentieth century philosopher, talked of two kinds of thinkers, the fox and the hedgehog. The fox knows many small things, the hedgehog only one big one. To abuse this political simile, greenhouse gas concentration is one big thing that moves the entire climate system in one direction. Local effects are many small things that move the system, in one direction and then the other. For local effects to overcome the push from the global greenhouse gas forcing all the local effects must go in one direction, but how likely is that? The central limit theorem is a good guide. Any sum of many small randomly distributed forcings will tend towards zero. Even if the local forcings are controlling locally (whatever that may mean), when you average them over the globe, the net effect will tend to zero if the local forcings are randomly distributed.


Fergus Brown said...

In one sense, your comment here is self-evident, in the sense that the larger system will always tend to overwhelm the smaller, but here are two thoughts to consider:

Firstly, this doesn't take into accounts the significance of local or regional conditions as feedback mechanisms. Given the number of times we are assailed by reports that x 'here' implies y 'there' in the media (often misguidedly), it is important to distinguish between circumstances such as the Indian monsoon and El Nino events, and discussions about, for example, the impact of Atlantic SST on Caribbean/US hurricanes, or the impact of wildfires in one area or another. The cryosphere is a good example of a distant (for most of us) system which has a huge impact on both global and local climate.

The second consideration has more to do with realpolitik. Decision makers often 'talk the talk' when it comes to helping those outside their own specific zone of influence, but they need, by and large, to focus on local impacts and local interests to engage their electorate in active processes, rather than simply sit and watch the world go to ****.

This is why, to me, those such as RP Sr. have an important role to play. Though parochialism is always a danger of regional or local focus, it allows us to understand why the global issue is also a local one, thus contributing to the inclination to act amongst the otherwise inert masses and their ineffectual leaders.

As I am a first-timer, I will say that I like your work and your comments on other sites, as well as your 'tone'. Keep up the good work,

EliRabett said...

Why, thank you very much Fergus. Eli has always believed that it is important to state the obvious early and often, as a) it tends to get lost in many complex discussions and b) half the class is surfing YouTube at any time.

We did have a post that commented on the tension between the local and immediate and the global. Look down towards the bottom. Actualy it was the IPCC's point, not mine, but I will take whatever credit I can get, and if I can tear it loose I will claim it.

J. S. - (Wacki) said...

Eli, I must admit I'm a big fan of your writing style. Just curious, do you talk about yourself in the third person in real life as well?