This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.

Objection:

Climate science can’t even fully explain why the climate did what it did in the past. How can they then claim they know what is going on today?

Answer:

There are two requirements for understanding what happened at a particular climate change in geological history. One is an internally consistent theory based on physical principles and the other is sufficient data to determine the physical properties involved.

It is very hard, in some cases impossible, to gather sufficient data about every aspect of the climate system for periods of time or events in the distant past, and especially to do so at a temporal resolution adequate for a full and nuanced explanation. The record in the ice cores is extraordinarily rich in variety and detail of the data it preserves but it only goes back as far as the age of the ice sheets, actually even less as there is melting from the bottom even as there is accumulation at the top. Past that time, about a million years ago in the Antarctic, the records must come from ocean sediment, rock layers, fossils and other imaginative sources. These are harder to decipher and are much coarser in temporal resolution. The spatial extent of samples is often far from sufficient to get global information.

In contrast, today we are closely monitoring everything we can think of and have a much greater chance of making quality reconstructions of the very recent past for those factors we did not think of until now. We know how the sun is behaving. We know when and how hard the volcanoes are erupting. We know the levels of ozone, CO2, CH4, NO2 etc to an extremely high degree of precision and on a month to month basis across the globe. We know where the continents are, how the oceans are flowing and the size of the ice sheets.

Consequently, our understanding of what is going on today is truly leaps and bounds ahead of any other point in the past and there is no surprise at all that we can speak with much greater confidence about today than we can about yesterday. The real test that the past can provide is some new and exciting data that can not be explained by the current theories, every scientist’s Holy Grail. This happens frequently in the finer details of climate theory, but the basics only become more and more certain the more and more data we can recover.

So far, although we are far from that elusive Perfect Understanding ™ for the reasons described above, there is also no known climate change in the Earth’s past that provides a solid contradiction of the theories that underpin Anthropogenic Global Warming.

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.

“No Past, No Present” was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.