The apparently simple question like the one in the title of this essay is in fact almost impossible to answer unless it is specified further. Even then, it has been argued that that it implies a quantity — average global temperature — that is both mathematically and thermodynamically impossible to calculate. Interested readers should go to the link to explore further, but a short-cut is that it is as sensible as referring to the ‘average exchange rate’ of all currencies in the world today, or the average of all the telephone numbers in the telephone directory.
Perhaps a prior question is: what is the optimum temperature for human beings and human societies? The assumption underlying the notion of ‘catastrophic’ anthropogenic global warming, after all, is that we are moving away from some kind of optimum towards something dangerous. What is that optimum? It can’t be the period before the Industrial revolution, because that was icily unpleasant, as Judith Curry and others have pointed out. Given the contribution that more carbon dioxide makes to the lives of plants, and therefore animals, I can’t see why another degree or so would be other than beneficial.
But, as I have said before, if one wants to talk about the global warming or ‘climate change’ issue, there is no help for it: one has to use the data that we have. And they are not much help, either, because another prior question is: ‘Warming or not — from when to when?’. Over the last half-million years? The graph looks like this.
The present is to the right. On this ice-core evidence (Antarctic) previous interglacials were warmer. You don’t like that — too long ago? What about the time since our own interglacial began? The graph looks like this.
Yes, more ice cores, from one place. Alas, that’s all we really have. You’ll notice that the modern period is of much the same warmth as some earlier periods, but not as much as that of the Holocene Optimum. So are we warming? On the evidence of that graph, we seem to go through warm and cold periods, and maybe the long-term trend is a cooling one. Don’t like that? Let’s get to our own present and recent past. Here’s a graph I used a little time ago. It doesn’t go quite to the present.
My grandparents, whom I remember quite well, were born in the 1880s, so this whole period is relevant to me. What I take from this graph is more warm and cool phases, though of shorter duration that in the previous graph. There were rising warmth periods, of about the same duration and trend, from 1910 to 1940, and from about 1975 to 2000. There were cooling periods from 1880 to 1910, and from 1940 to 1975. There has been a relatively flat period from 2000 to the present, though this graph only shows the first part of it.
What are we to make of all this? Let’s leave carbon dioxide out of it for a moment. The three graphs show that the planet goes through phases of warming and cooling. There are long phases, medium phases and short phases. We seem to be in a short cooling or static phase at the moment, compared to earlier periods. This period will get cooler or warmer in due course. There are many candidate explanations for why all this happens and has happened, and we can leave them out for the the moment, too.
But what seems almost indisputable to me is that there hasn’t been some kind of special ‘right’ climate for humans. Our species has had to cope with more and less warmth, as we do at the moment. We haven’t had to deal with a really cold period since the 17th and early 18th centuries, but we will be much better prepared for the next one. If we go into a new warming phase, we’ll cope with that too. Eight years ago, in my ‘Cool Look’ address to the Australian Planning Institute, I said I was prepared to accept the IPCC’s estimated average increase in temperature over the 20th century of 0.60 plus or minus 0.20C. I still am. Is it a problem? Not on the evidence of the graphs.
Is it unprecedented? That was the next issue — the orthodox position is that the warming of our period is unprecedented in human history (and must therefore be our fault). I repeat here a little of what I wrote then.
By 10,000 years ago the first small permanent settlements began to appear, as people assembled and domesticated animals, learned how to plant crops, and abandoned being hunter-gatherers. There were then, according to some estimates, about a million of our ancestors. It seems to me to be no coincidence at all that global temperatures had begun to level out. The evidence for these temperatures is based on Greenland and Antarctic ice-core data, and I need to say at once that what happened in Greenland or the South Polar regions may not have happened anywhere else. Average temperatures seem to have remained within a narrow band of about two to three degrees Celsius ever since, save on a few occasions, such as the Mediaeval Warm Period, when English monasteries grew grapes and made wine, and the later ‘Little Ice Age’, when the Thames froze in 1683 and a Frost Fair continued for two months on the ice. On the evidence, present average temperatures are similar to those in the first century AD.
On the face of it, there is nothing especially unprecedented about the 20th century temperature rise, given its ‘agreed’ size. Shifts up and down of that magnitude and more seem to have occurred in the past, and will presumably occur in the future. Climate change is not new, and occurs for reasons that can have nothing to do with us. Orbital changes, sunspots, volcanic eruptions and meteorites have effects on the earth’s climate, and these causes are external to us. We simply have to put up with the changes and adapt what we do to them. Whatever warming that is happening now, and whatever contribution we humans are making to it, have to be seen in that context.
Eight years have passed, a great deal more research has been done, and the science is still not at all settled. I’ll stick to what I wrote then.
Next: Are we causing the warming?
Further reading: I wrote an essay on what had happened since 2008 six years later, and you can see that here. The website has lots of pieces about warming and measurement, because it remains a central intellectual interest for me. My basic position is that what we have as data is just awful, and no basis for making public policy. But elected governments, responding to insistent cries of approaching doom from the Greens and their sympathisers, desperately search for data, any data, that would allow them to make good policy. I don’t believe such data exist, and that governments should do nothing. Alas, that is not a position that governments like at all — they will be accused of indolence or worse. So we have to discuss the data we have. Hence this essay, and others like it.