By James Annan and William Connolley
In this post, we will try to explain a little about chaos theory, and its relevance to our attempts to understand and forecast the climate system. The chaotic nature of atmospheric solutions of the Navier-Stokes equations for fluid flow has great impact on weather forecasting (which we discuss first), but the evidence suggests that it has much less importance for climate prediction.
Guest contribution by James Annan of FRCGC/JAMSTEC.
“The more unpredictable the world, the more we rely on predictions” (Steve Rivkin). The uncertainty of an unknown future imposes costs and risks on us in many areas of life. A cereal-growing farmer risks a big financial loss if the price of grain is low at harvest time, and a livestock farmer may not be able to afford to feed his herd if the price of grain goes up. One way to reduce the risk is to hedge against it in a futures market. The two farmers can enter a forward contract, for one to deliver a set quantity of grain to the other for a fixed price at a future date. And indeed farmers do routinely use futures contracts to reduce their risks.
A while ago, we wrote about Global Dimming – a reduction in downward solar radiation of about 4% or about 7W/m2 from 1961 to 1990 was found at stations worldwide. We said at the time that there were hints of a recovery underway post-1990; now research has been published showing this. From Dimming to Brightening: Decadal Changes in Solar Radiation at Earth’s Surface by Martin Wild et al. (Science 6 May 2005; 308: 847-850; subscription required for link) uses surface measurements; Do Satellites Detect Trends in Surface Solar Radiation? by Pinker et al., Science 2005 308: 850-854 uses satellites; both find a recovery of surface downward radiation since about 1990.
by William Connolley and Eric Steig
The 10th Feb edition of Nature has a nice paper “Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data” by Anders Moberg, DM. Sonechkin, K Holmgren, NM Datsenko, & W Karlin (doi:10.1038/nature03265). This paper takes a novel approach to the problem of reconstructing past temperatures from paleoclimate proxy data. A key result is a reconstruction showing more century-scale variability in mean Northern Hemisphere temperatures than is shown in previous reconstructions. This result will undoubtedly lead to much discussion and further debate over the validity of previous work. The result, though, does not fundamentally change one of the most discussed aspects of that previous work: temperatures since 1990 still appear to be the warmest in the last 2000 years.
The conference last week in Exeter on “Avoiding Dangerous Climate Change” grew out of a speech by UK Prime Minister Tony Blair. He asked “What level of greenhouse gases in the atmosphere is self-evidently too much?” and “What options do we have to avoid such levels?”. The first question is very interesting, but also very difficult. As Roger Pielke has noted the conference organisers actually choose three “key questions”:
It is worth thinking about the difference between the initial aim and the “key questions” chosen. Question 1 is essentially IPCC WGII impacts); question 2 is firmly WGI (how-much-climate-change); question 3 is fairly WG III (mitigation, including technical options). I guess they switched questions 1 and 2 round to avoid making the identification too obvious. The conference steering committee report makes it very clear that they are building on the IPCC TAR foundation.
