Re: Old News?
Seems it provides a science-based, non-CO2-based explanation for climate changes (besides the Milankovitch cycles).
But there are problems with Milankovitch cycles. Just as there are problems with CO2-driven climate change. It's all about quantifying effects. So the key CO2 one is sensitivity. That's generally X degrees per doubling of CO2. If X is high, more warming, low, less. And it's generally assumed the response is logarithmic.
That's where there's a lot of sensitivity. For a small value of X, CO2's not a problem, ie if X=1.2 we'll keep to the arbitary <2C warming. Then there's comparisons between models using different CO2 sensitivity values and measured temperatures. If the model says we should be 3C warmer, and observations show we're only 0.5C, then sensitivity is too high, or there are negative effects. If those negative effects counter CO2 warming, then there's no problem, and arguably benefits from higher CO2 levels, like the 'greening of the planet'.
Which is where Svensmark's theories, and also Milankovitch cyles come in. We know climate changes naturally. We know that can be extreme, ie an Ice Age, or less extreme, ie a Little Ice Age or Medieval Warming Period. Some try to deny the extent or magnitude, but there's evidence supporting them. CO2 driven climate can't really support natural cooling, especially not to Ice Age levels. Milankovitch cycles struggle with effect exceeding cause, ie a small change in insolation leading to a large change in temperature.
Where I think Svensmark's theory comes in is filling in some of the feedback or forcing gaps. So on it's own, it may not be enough to explain recorded climate changes, but we know there are solar cycles and variability in things that affect or attenuate cosmic rays.. But there are also issues with weak correlation, or effect exceeding cause. But we do know that clouds are notoriously difficult to model, and have a large impact on temperatures.