A guest post by David Smith (author of “Tiny Tim Storms” on Climate Audit)
The oceans have great capacity to store heat, much greater than the soil and rock of land. We see this often. For instance, daily sea breezes are the result of the different warming rates of the ocean and land. On a seasonal scale, oceans cool more slowly than land in winter and warm more slowly than land in summer – that’s one reason why beaches are popular getaways in July and August.
It seems reasonable that the same principles should apply in a world which is warming due to the greenhouse effect. Land should respond quickly to greenhouse warming while the seas should lag. It also seems reasonable that, on decadal scales, this difference in warming rates should be visible in the global temperature record by now if AGW is driving the climate.
If, on the other hand, the recent warming involves other significant factors, such as changes in ocean behavior in combination with greenhouse warming, then the differential warming pattern might be murky and mixed.
So, what does the record show? Below is RSS satellite-derived data for the lower troposphere, broken into three regions: the tropics, northern extratropical and southern extratropical. The lines represent the spread between land and ocean temperature anomaly in each region – the smaller the spread, the lower the point on the line. (The three lines are scaled so as to separate them on the graph.)
The small scale may make examination difficult so I’ll summarize. The tropics have shown a decrease (tropical land is warming more slowly than the tropical ocean). That surprises me and is not consistent with my understanding of AGW behavior. The southern extratropics is about breakeven and is, in any case, probably hard to measure due to the limited Southern Hemisphere land.
What about the north? Well, over the three decades of the record the differential trend is upwards. Northern Hemisphere (20N-82.5N) land has warmed faster than the Northern hemisphere oceans. Here is a closeup:
What catches my eye is the odd pattern of flat/ quick increase/flat in the Northern extratropics.
Breaking the graph into two subsets gives this for 1979-1997:
This shows basically flat behavior for 19 years.
And here is 1998-to-today:
This suggests that the Northern extratropical differential is flat-to-declining over the last decade.
Before any howls begin let me state that I clearly am playing with start and end points. I make no claim (or suggestion) that greenhouse warming isn’t the driver behind global warming over the last three decades. I simply don’t know. (Also, I am a “lukewarmer” who thinks that the world is warmer than it would otherwise be due to anthropogenic gases (but doubts that the impact will be extreme)).
What I do suggest is that the patterns are curious. They are not what I expected to find. The patterns open the door wider for the idea that warming since the 1970s has included both natural and anthropogenic factors.
What I’d like is to learn how these patterns fit into the AGW hypothesis. Also, do the GCMs (which reportedly do a good job of replicating recent climate change) show these patterns. The ideal outcome would be to learn what happened in the Northern atmosphere to create these patterns.
As always, I may be making fundamental errors in my simple analysis. If you see such mistakes then please post.