Wednesday, December 05, 2012

Global warming over the last 16 years

A brief response to a common claim.


Sam Charles Norton said...

Hmmmm - let's adjust the data so that it matches our assumptions! A few comments: why was the plateau (unadjusted data) not predicted by any models; what is the full basis on which 'man-made' and 'non man-made' influences are separated out; why is there no change in trend despite the huge increase in fossil fuel use over the relevant time frame (something like a third of all CO2 emissions in last 17 years?) The point keeps being made because the fundamentals don't get answered.
What do you make of the leaked IPCC reports? I do recommend LaFramboise

byron smith said...

What is the full basis on which anthropogenic and non-anthropogenic influences are separated out? ENSO has good evidence for being a natural cycle extant as far back as reliable records go. Its effects on the global temperature are increasingly well understood and so removing this effect is fairly straightforward statistics.

Similarly, the effects of variation in direct solar radiation are obviously natural. Volcanoes are slightly more complex, because there is some evidence that vulcanism and seismic activity can be affected by shifts in glacial mass balance, which is responding globally to a warmer climate. But the effect is currently thought to be pretty minuscule, so it's probably pretty safe to place these forcings in the non-anthropogenic column as well.

So this exercise isn't attempting to be comprehensive, but it does give a good idea of what the underlying trend is once various well-understood short term natural variations are removed. It is based on a number of published papers that have made these adjustments and I am not aware of any published literature critiquing their methodology.

"why is there no change in trend despite the huge increase in fossil fuel use over the relevant time frame (something like a third of all CO2 emissions in last 17 years?)"

It has been known for decades that there is a multi-decadal lag between emissions and global surface temperature changes due to the thermal inertia of the oceans. Basically, something like 93% of the additional energy goes into the oceans, and they have indeed been rising faster over the last decade or two. The effects are likely to be visible in the atmospheric temp record in coming decades.

There is another factor not included in this short video, over which there is not yet strong scientific agreement, which is the cooling effect of short-lived anthropogenic aerosol particles from coal burning and wood fires (which have also increased significantly in the last 17 years).

The leaked IPCC reports are drafts and so I have not put much effort into looking into them too much.

byron smith said...

A longer answer is available at the site suggested at the end of the video.

Sam Charles Norton said...

OK, that longer answer is useful, but... a) still no explanation as to why plateau wasn't predicted; b) I think the differentiation of natural and anthropogenic is much more complicated than the vid makes it out to be; c) there is still disagreement about how far the oceans have been warming, and therefore whether or not they have absorbed '93%' of the anthropogenic effect. So I'm still 'hmmmm'!

byron smith said...

"why was the plateau (unadjusted data) not predicted by any models"

It was. Look at the individual model runs (rather than the aggregated averages) and you'll find that they all contain periods of faster or slower warming. And it's not a plateau. Temps are still rising, the trend is still positive. Any short period in a dataset with that level of noise is unlikely to be statistically significant unless you take longer periods.

byron smith said...

CP: Nine charts showing continuing warming.

byron smith said...

(a) See answer above.

(b) You mean that a two minute video failed to dot every "i" and cross every "t"? But I'm curious as to how you think it was deficient in this regard.

(c) Whether it is 93%, 90% or 96%, find me a single reputable source that denies the oceans have been taking the lion's share of the energy imbalance over the last few decades.

byron smith said...

Why don't climate models predict short term cooling periods? They do.

Make sure you listen carefully to what Mojib Latif says. He precisely predicts exactly how the media will misrepresent his talk. And then, cue media misrepresentations.