I have been engaged in a Twitter discussion with @PiersCorbyn, who claims accurate long-range weather forecasting based on solar activity. His methods are secret, and he sells his forecasts to farmers and others interested in weather. He claims 86% accuracy, based on assessments of some of his forecasts.
Piers Corbyn on Weather
I find Piers interesting as far as his forecasts are concerned. The next step in confirming or refuting his claims should be to assess his full forecast stream for accuracy, in order to avoid potential selection bias in the segments of his forecasts that have been examined.
He cannot claim scientific status for his methods because he keeps them secret. One of the characteristics of real science is that all the methods used must be laid out so that other workers can try to replicate the original results.
So there are two separate issues: his claim to be able to forecast extreme weather events based on solar activity, and his contention that the sun, not CO2, controls the global climate.
This argument is based on a common misconception, a belief that climate scientists give CO2 as the sole determinant of climate. They do not. They factor in solar intensity, particulates from volcanoes and industry, ocean currents, albedo and as many other factors as they can. They are open to including other factors as and when they become credible, and it is quite possible that an influence of cosmic rays (related to troughs in sunspot activity) could be factored in to the models in the future.
Piers Corbyn on Global Climate change
Piers puts his argument against CO2 having an influence on global climate here.
Overall, he is talking about very long time periods, and his graphs squeeze out the last 150 years, thus excluding any real consideration of anthropogenic climate change.
His graphs are sometimes unreadable, often they have no source, and rarely show confidence errors.
Being a Powerpoint presentation, they are not self-explanatory.
But here are his arguments, insofar as they can be gleaned, with answers from the excellent Skeptical Science site.
1 CO2 is a tiny fraction of the atmosphere.
True. Most of the atmosphere is nitrogen (78%) and oxygen (21%), which are not greenhouse gases.
Water vapour contributes 36-72% of the greenhouse effect,
Water vapour has a short residence time in the atmosphere, about 9 days, as opposed to about 5 years for CO2 which is why CO2 has more importance as a greenhouse gas, since it accumulates.
The natural cycle adds and removes CO2 to keep a balance; humans add extra CO2 without removing any.
2 Solar flares cause weather changes
As above, we can have an open mind on this. Weather is distinct from global climate.
3 Piers Corbyn predicts falling temperatures over the next 20 years
Based on his expectation that we are going to move into another solar minimum. I have written before about this possibility, and we should greatly welcome it, as solar cooling might save our sorry asses by offsetting our CO2 warming, and give us a chance to sort out our act.
4 Climategate means all climate science is to be distrusted.
This common point is answered here
5 Earth history going back 500 million years shows no relation between CO2 and temperature
Piers uses this common figure, below. He does not say where it comes from. [Update: in fact is seems to be derived from the work of the excellent H.H. Lamb, one of the earliest true climatologists. It is bizarre that contrarians still use this early work as a reference point.]
The best way to understand Paleoclimatology is by watching this brilliant and entertaining video lecture by Richard Alley. He dives into this whole graph, showing what is happening at every point.
Paleoclimate is very complex, but key is that solar activity was far less in ancient times.
6 CO2 lags temperature
Alley addresses this point at 35:25 in the above link.
It is true that in the warming episodes that followed the Ice Ages, CO2 levels rise after temperature rises.
CO2 and temperature follow each other over the last 400 million years, but CO2 tends to lag behind temperatures by a few centuries. To be honest, there are some rises where CO2 clearly leads, and in most of the upswings CO2 and temperature are far closer than on the downswings, where CO2 fall as a distinct lag.
The Ice Age swings are caused by variations in earth's orbit, which cause slight warming. CO2 release from oceans in response to the initial warming leads to further rises in temperature. In other words, CO2 is acting as a positive feedback in response to solar forcing. The effect of the CO2 is to amplify the temperature swings resulting from solar changes.
In summary, Piers may or may not have an important contribution to add to weather forecasting, but his views on climate change are not convincing.