THE RIGHT WAY AND THE WRONG WAY TO TEST HYPOTHESES. Although evidence consistent with anthropogenic global warming is sometimes evidence consistent with other hypotheses, polemical amateurs ought tread carefully in interpreting that evidence. A journalist asks a climate scientist a number of loaded and polemical questions (is that a redundancy) and a Northern Illinois colleague fires back.

Ultimately, it's about understanding the processes and mechanisms by which global climate is maintained. It's not about politics or about squabbling over different people's views of temperature records. The scientists involved in the IPCC study are speaking from the analysis of how the climate system works’ and what models of climate process fit with observation.

There certainly was a Little Ice Age’ in the 1400s to 1600s, that resulted in cooling of particular regions of the earth. This affected the northern hemisphere, especially in the Atlantic sector, most significantly. Other parts of the globe registered less cooling, and the cooling at any location was small on the scale of climate change involved past glacial epochs, or compared to the temperature changes likely with greenhouse warming. Global-warming deniers bring up the Little Ice Age constantly as a full explanation of the climate changes over the past few centuries. What is missed here is that it is truly unfortunate that human-driven warming is superimposed on a natural warming cycle. That only increases the potential for adverse results as the natural and the human-caused processes combine. It is ironic that warming deniers make such a case of the Little Ice Age.

And at the same time, researchers face the difficulty of specifying a model capable of disentangling the solar from the anthropogenic effects. There's a lot of multicollinearity in the observations.

There is little doubt that solar activity played a role in the Little Ice Age. But records of solar activity cannot explain the climate change we have experienced over the past 200 years. The topic has been examined in detail, and certainly not ignored or denied by climate scientists.

Left as an open question: how much of that residual is attributable to human activity? Within that human activity, what is the partial effect of increasing CO2 as distinct from the partial effect of cutting (or regrowing) forests or from building permanent settlements?