Are Computer Models Reliable – can they be used to predict the future climate?
Government climate change propagands vs actual science
Yes: says the Met Office (link on the Act On CO2 Uk Government website)
Are computer models reliable? (pg 12)
Yes. Computer models are an essential tool in understanding how the climate will respond to changes in greenhouse gas concentrations, and other external effects, such as solar output and volcanoes. Computer models are the only reliable way to predict changes in climate. Their reliability is tested by seeing if they are able to reproduce the past climate, which gives scientists confidence that they can also predict the future. But computer models cannot predict the future exactly. They depend, for example, on assumptions made about the levels of future greenhouse gas emissions.
No: says the IPCC (Chapter 14, 220.127.116.11, Working Group 1, The Scientific Basis)
Third Assessment Report: “In sum, a strategy must recognise what is possible. In climate research and modeling, we should recognize that we are dealing with a coupled nonlinear chaotic system, and therefore that long-term prediction of future climate states is not possible.”
Quite how, (as described above) the climate models predict the unknown effects of an unknown quantity of future volcanic eruptions at unknown locations and unknown power, in the next 90 year is beyond me. I imagine that would be an interesting bit of code to witness, but let us put that aside. No mention of, not exactly, an unequivocal not possible, by the IPCC, recognising the type of problem that no amount of money or faster computers can resolve. This has not changed since 2001.
The Met Office Climate Computer Model, is their weather model. When it is run in ‘climate’ mode, no further inputs/corrections are allowed (as happens as weather forecasting and predictions progress) and it produces scenarios based on the outputs depending on the all the assumptions of natural forcings and varying assumptions of feedback and levels of Co2 emmissions programmed in.
Some ‘climate scientists like to call these scenarios that run 50 – 90 years into the future ‘experiments’ and the output ‘data’
No: said Professor Kelley ( Oxburgh – FOI requests produced these notes – thanks to Bishop Hill)
(i) I take real exception to having simulation runs described as experiments (without at least the qualification of ‘computer’ experiments). It does a disservice to centuries of real experimentation and allows simulations output to be considered as real data. This last is a very serious matter, as it can lead to the idea that real ‘real data’ might be wrong simply because it disagrees with the models! That is turning centuries of science on its head.
The computer models are verified against past climate data including reconstructions, to gain confidence in their ‘projections’ which make Professor Kelleys comment on Briffas work very relevant:
The first sentence of the text refers to climate model experiments, which offends me!
All the computer models do is produce scenarios based on the assumptions and limited understanding of climate programmed into them. They do not do clouds, some of the assumptions are estimates that vary by orders of magitude, we have different scenarios varying from 1.0C to 6.0c, some scarier scenarios of 10 – 12 C for the next century. These assume ‘climate sensitivity’ – ‘feedbacks’ due to CO2 which amplify the simple physics of per doubling of CO2 in the atmosphere of ~1.0C , to increasing temperatures due to positive feedbacks producing the various accelerated global warming scenarios… Yet the order of magnitude of the sensitivity is unknown.
In fact the sign is unknown, it is assumed positive, is could equally be a negative feedback, it is currently uncertain.
I do hope that some scientists somewhere are doing some actual experimentation with observable data to establish this. The fact that the Earth has not experienced this behaviour in the past at point when CO2 were much higher naturally, must demonstrate these assumptions of strong positive feedbacks are wrong.
Up to and throughout this exercise, I have remained puzzled how the real humility of the scientists in this area, as evident in their papers, including all these here, and the talks I have heard them give, is morphed into statements of confidence at the 95% level for public consumption through the IPCC process. This does not happen in other subjects of equal importance to humanity, e.g. energy futures or environmental degradation or resource depletion. I can only think it is the ‘authority’ appropriated by the IPCC itself that is the root cause.
All scientists should be concerned because:
The IPCC Science in Working Group 1 (AR3 and AR4) take a look and see how it translates in government, political and lobby group pronouncements.
Act on Co2 (DECC)