I was a little surprised by some of the views expressed in the comments on my previous post. I had assumed that it was fairly obvious that the term “global warming” should really be used to refer to the overall increase in energy in the climate system and not just to the warming of the surface. It is clear, however, that the scientific literature still uses the term “global warming” when referring to surface warming. It’s also clear that some seem happy with this definition (although are more than willing to acknowledge that it should then be clearly distinguished from overall warming and that it can create confusion). Some have suggested that maybe we need a new term, such as “global heating”, to refer to the overall accumulation of energy in the climate system.
In some sense, if we can clearly define the terminology then it shouldn’t matter what terms we use to define surface warming and overall warming. The problem I can see is it is not immediately obvious that the term “global warming” should refer only to surface warming. This would, typically, need to be made clear when the term is used. Also if we use “global heating” to refer to overall warming, I can see people assuming that “global warming” and “global heating” are simply two terms for the same thing. Personally, I would think that the term “global surface warming” would be a sensible option. Admittedly, I’m simply an anonymous blogger and so really shouldn’t be taken seriously. Also, there is historical precedent to consider. Scientists understand the current terminology and so there should be some kind of consensus about changes to existing terminology. I will also add that there is a scientific argument that could be made for using “global warming” when referring to surface warming. The ultimate consequence of anthropogenic global warming is that surface temperatures will rise so as to reduce/remove the energy imbalance. Hence, one could argue that associating “global warming” with surface warming is fundamentally correct.
However, another factor is that it is clear that some do use “global warming” when referring to overall warming and this, in my opinion, further adds to the confusion. What prompted me to write this was the video interview between Peter Sinclair (who runs the Climate Denial Crock of the Week site) and Kevin Trenberth (a climate scientist at the National Centre for Atmospheric Research). The original is here, but I also include it below. In the video, Kevin Trenberth says
The first thing is that global warming is occurring. It’s related to the build-up of carbon dioxide and other greenhouse gases, heat trapping gases in the atmosphere. It really produces an energy imbalance at the top-of-the-atmosphere. More heat is coming in than is going out.
Now, here, it seems that Kevin Trenberth is using the term “global warming” to refer to the build-up of energy in the climate system and not to surface warming alone (admittedly he says “related to” so one could argue that it could still be consistent with surface warming, but that’s not obvious from what’s been said). So I realise that “global warming” has often been used to refer to surface warming, but it does seem that it has also been used when referring to overall warming. In some sense I find this quite remarkable. One of the fundamental terms associated with one of the most important issues that we face today, has not been defined sufficiently clearly so as to avoid confusion. To be clear, I think I understand why this is and I’m not trying to criticise anyone for this. Some of the data is reasonably new (ocean heat content) and so in the past it made sense to associate “global warming” with surface warming given that the surface temperature dataset covered a longer period than other datasets, and was more robust than other datasets. Also, most paleo-climatological reconstructions are only associated with surface temperatures (I think).
So, I don’t really know what to make of this. Maybe some think this isn’t really an issue, but given how so much in this debate is mis-represented, I would tend to disagree. Carefully defining terminology may be advisable but I can then see some claiming that scientists are now changing terminology so as to make things seem worse than they actually are (i.e., they’re cheating and can’t be trusted). Probably the best is to simply be very clear about what the various terms mean and what aspect of the climate system is being discussed. Then again, what do I know? 🙂