I may regret writing this post, but here goes anyway. Although some probably disagree, and I don’t always succeed, I do try to maintain a sense of scientific credibility; include caveats, acknowledge uncertainty, recognise that we really can’t “know” anything, etc. It is, however, tempting sometimes to be a bit more forceful and definite, but I’m just a physicist. Although I think I understand the physical science associated with climate change quite well, there are many related aspects with which I only have a passing familiarity; ecology, chemistry and the carbon cycle, economics, policy making, sociology,….. I may not completely avoid discussing these other aspects, but I feel that if I do have a role to play, it’s in trying to explain the physical science as clearly as I can and in a manner consistent with best scientific practice. Others can work out how to influence society and policy makers, or what it is we should be considering doing.
However, sometimes when I read things like this article about the bleaching of the Great Barrier Reef with Ove Hoegh-Guldberg saying
The current bleaching event and this attribution study leads me to believe that my highly controversial predictions in 1999 were actually conservative
or this one about widespread loss of oxygen to become noticeable in 2030s, which says
A reduction in the amount of oxygen dissolved in the oceans due to climate change is already discernible in some parts of the world and should be evident across large regions of the oceans between 2030 and 2040
I think that maybe we really are screwed. Being measured, not over-reacting, sticking to the evidence, is all good and well, but is going to count for very little if – in 20 or 30 years time – we go “shit, why didn’t we do more? Why weren’t we more forceful and insistent?”. To be clear, I’m not suggesting that we should necessarily change how we’re conducting ourselves; it’s clearly a very complex situation with many factors at play. However, that doesn’t alter that climate change is probably irreversible on human timescales and if what we do – or don’t do – turns out to be insufficient to avoid many of the negative impacts, we don’t get to go back and try again.
So, I do sometimes wonder what those who are engaged in this topic (scientists, social scientists, policy wonks, ….) will think if it becomes clear that we’ve done too little, too late. Maybe publicly they’ll say “we might not have done enough, but at least we didn’t step over the bounds of what was regarded as acceptable for people in our position”, but you’d imagine that they might be thinking about why they didn’t do more and didn’t try harder to convince people of the seriousness of this situation. Of course, I hope not; I hope that we either do enough (whatever that might be) or that the impacts are less severe than they might be.
I’ll end with an illustration of why even a physicist might have reason to be really concerned. It seems as though we have benefitted from a climate that has been reasonable stable over the last few thousand years. The reason it’s been reasonably stable is that the external changes have been small, and the response has been roughly linear. For example, you can write the Planck response as
where is the radiation response, and is the change in temperature. As long as any external changes are small, the system can return to quasi-equilibrium through a small change in temperature.
Since starting to emit CO2 into the atmosphere, we’ve warmed by about 1oC and currently have a planetary energy imbalance of 0.6 – 0.8Wm-2. The Planck response is 3.2Wm-2K-1, so the net radiative perturbation is about 4 Wm-2. The total Greenhouse effect is about 120Wm-2, so we’ve perturbed it by a few percent. However, if we carry on as we are, we could produce a perturbation that is 10-20% of the total Greenhouse effect. This is no longer small, and a large perturbation of a non-linear system can produce big, and unexpected, changes.
I guess it’s possible that such changes might be beneficial, but given that we’ve benefitted from stability and are not as able to move as we once were, it seems much more likely that any such changes (were they to happen) would be very difficult to deal with; pushing a non-linear system hard and fast just seems like a bad idea. This is in addition to the expected changes (warming, intensification of the water cycle, increase in intensity and frequency of extreme events,….) that might be problematic by themselves.
I don’t really know what else to say or quite what my point is. I think we’re going to continue to be somewhat hamstrung by how we’re expected to conduct ourselves and by the constraints of the system in which we operate. I really hope that doesn’t mean that we end up looking back with regret at what we could have done, but didn’t.
Update: Elsewhere people are illustrating why I added the caveat at the beginning of the post. They also seem a little confused by my “radiative perturbation” point, and seem to think that it is wrong. An alternative way to think of it is that the Greenhouse Effect is about 33C. We’ve warmed by about 1C, which is then a few percent of the overall Greenhouse Effect. If we were to warm by 3C, it would be about 10%. More than 3C is then more than 10%, etc.