Asking about the “hiatus” is the wrong question!

Someone made a link to my blog in the comments of this recent article about the congressional science committee reaction to a paper by Karl et al. (2015) in the journal Science which claims that the hiatus never really occurred based on new bias corrections in the data. The corrections primarily dealt with weighting buoy data over ship intake water for ocean temperature measurements. But a quote in this other article by Naomi Oreskes got me thinking that questions about the existence of the “hiatus” are actually bad ones to ask.

Here’s the quote by Dr. Oreskes:

“I hope the scientific community will do a bit of soul searching about how they got pulled into this framework, which was clearly a contrarian construction from the start.”

Labeling the “hiatus” as a contrarian construction is absolutely appropriate. We actually expect hiatuses to occur. Even though models might appear to predict a clean linear increase of global temperature due to averaging of ensemble members, no one would argue that the warming trend will always be noticeable apart from the climate variability in any given decade. The main point I want to make here is that decadal climate variability can be large, and easily comparable to the trend from global warming. This is especially true when several modes of variability add constructively to cool or warm.

And because this variability on decadal scales can be big, we have to recognize that we can’t expect the temperature trend over a decade to refute or confirm the signal of anthropogenic global warming. In other words,

asking whether or not there is/was a hiatus is an ignorant question!

Another paper came out soon after the Karl et al. (2015) paper written by Kevin Trenberth that serves to give a straightforward explanation of the state of understanding about the recent temperature variability. I know Dr. Trenberth has a lot of enemies, but there’s no denying that he knows what he’s talking about.

Trenberth, K. E., 2015: Has there been a hiatus? Science, 349, 691-692.

I really like how this article is written because it’s very clear and concise. He compares the recent “hiatus” to a previous one that happened around 1943 to 1975. He reviews all the recent findings about the role of decadal variability in the global surface temperature (see figure below).

He talks about the role of aerosols in the previous “hiatus” and also discusses various things known to be influencing about 20% of the temperature trend over the last 10-15 years:

  • Small volcanic eruptions (not included in IPCC simulations)
  • Solar output was slightly lower during 2003 to 2009
  • decreased water vapor in the stratosphere after 2000

But above all, there is a maturing consensus that heat has been “going” into the deep ocean, specifically in the Pacific. Saying it this way makes it sound like “heat” is a pesky rodent that we are trying to get out of our house. There are many recent papers that reach this conclusion:

So, just to reiterate, let’s try and take Dr. Oreskes advice and not let questions about the “hiatus” obscure our understanding of the basic science behind global warming by being frank about the long-term nature of the anthropogenic signal. There’s no static rule about how much time is needed to reveal the temperature trend associated with anthropogenic emissions, but we should be in agreement that a decade is definitely too short.

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