Given that I’ve written about this before I thought I may as well post this short video of Kevin Trenberth talking about the possibility of an El Niño later this year. According to Kevin Trenberth, it’s not so much if we’ll get an El Niño later this year, but how big it’s going to be.
There’s something I’ve been thinking about that I thought I might mention briefly. There seem to be some who think that because we can associate a particular warming event with – for example – an El Niño event, that somehow this warming is natural and not anthropogenic. It’s as if some think that there must be some kind of anthropogenic surface warming mechanism.
Well, there isn’t really. What we’re doing is increasing the greenhouse gas concentrations in the atmosphere, and this is acting to trap more and more energy in the climate system. We can certainly think of the long-term surface warming trend as being representative of an anthropogenic warming rate, since this might represent how the surface would warm if the system were completely steady and every part of the system warmed at a steady rate. However, the system isn’t completely steady and is clearly highly variable. All of the variability, however, is natural. Anthropogenic influences may well influence this variability, but there isn’t some variability that is anthropogenic and some that’s isn’t.
What I’m really getting at is that the change in radiative forcing is almost entirely anthropogenic and hence that we’re warming is also almost entirely anthropogenic. Just because we can associate some warming with a natural mechanism, doesn’t mean that that warming isn’t anthropogenic. The variability may well mean that sometimes the surface warms faster than the long-term trend, and sometimes slower, but while we still have an energy excess (as we do – more energy coming in than going out) we will continue to warm and it will virtually all be anthropogenic.
Anyway, I don’t know if I’ve quite explained that as clearly as I would have liked, but the post was really just an excuse to post the video showing Kevin Trenberth discussing a possible El Niño event later this year 🙂