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Unforced Variations: Feb 2016

Filed under: — group @ 1 February 2016

This month’s open thread.

Just so you know, a lot of people have complained that these threads have devolved – particularly when the discussion has turned to differing visions of solutions – and have therefore become much less interesting. Some suggestions last month were for a side thread for that kind of stuff that wouldn’t clog interesting issues of climate science. Other suggestions were for tighter moderation. The third suggestion is that people really just stay within the parameters of what this site has to offer: knowledgeable people on climate science issues and context for the science that’s being discussed elsewhere. For the time being, let’s try the last one, combined with some moderation. The goal is not to censor, but rather to maintain somewhere where the science issues don’t get drowned out by the noise.

How Likely Is The Observed Recent Warmth?

Filed under: — mike @ 25 January 2016

With the official numbers now in 2015 is, by a substantial margin, the new record-holder, the warmest year in recorded history for both the globe and the Northern Hemisphere. The title was sadly short-lived for previous record-holder 2014. And 2016 could be yet warmer if the current global warmth persists through the year.

One might well wonder: just how likely is it that we would be seeing these sort of streaks of record-breaking temperatures if not for human-caused warming of the planet?

Precisely that question was posed by several media organizations a year ago, in the wake of the then-record 2014 temperatures. Various press accounts reported odds anywhere from 1-in-27 million to 1-in-650 million that the observed run of global temperature records (9 of the 10 warmest years and 13 of the 15 warmest years each having had occurred since 2000) might have resulted from chance alone, i.e. without any assistance from human-caused global warming.

My colleagues and I suspected the odds quoted were way too slim. The problem is that each year was treated as though it were statistically independent of neighboring years (i.e. that each year is uncorrelated with the year before it or after it), but that’s just not true. Temperatures don’t vary erratically from one year to the next. Natural variations in temperature wax and wane over a period of several years. More »

Blizzard Jonas and the slowdown of the Gulf Stream System

Filed under: — stefan @ 24 January 2016

Blizzard Jonas on the US east coast has just shattered snowfall records. Both weather forecasters and climate experts have linked the high snowfall amounts to the exceptionally warm sea surface temperatures off the east coast. In this post I will examine a related question: why are sea surface temperatures so high there, as shown in the snapshot from Climate Reanalyzer below?

 

GFS-025deg_NH-SAT1_SST_anom_24_Jan_2016

I will argue that this warmth (as well as the cold blob in the subpolar Atlantic) is partly due to a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), sometimes referred to as the Gulf Stream System, in response to global warming. There are two points to this argument:

More »

2015 Temperatures

Filed under: — gavin @ 21 January 2016

To no-one’s great surprise, 2015 was clearly a record year in all the surface temperature analyses (GISTEMP, NOAA, HadCRUT4, Cowtan&Way, JMA + Berkeley Earth). There is a lot of discussion of this in the press, and on the relevant websites, so not much to add here. A few figures didn’t make it into the official announcement (audio) though…

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Marvel et al (2015) Part 2: Media responses

Filed under: — gavin @ 4 January 2016

This is a second post related to the new Marvel et al (2015) paper. The first post dealing with the substantive content is here.

What with #AGU15 going on, and a little bit of overlap in content with Shindell (2014), NASA wasn’t particularly keen to put out a press release for the paper, but we did get a ‘web special‘ put out on Friday Dec 18th, the last day of AGU and a few days after the paper appeared online. I’ve been involved with many similar releases for papers and it is always a struggle to concisely say why a paper is interesting while not overselling it or being too technical (which is why only a small fraction of papers get press releases at all).

As we’ve previously remarked about other people’s press releases (eg. Stainforth et al or Willerslev et al), properly calibrating the aspect of a release that will get picked up by the media can be tricky, and so it proved in this case.

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References

  1. K. Marvel, G.A. Schmidt, R.L. Miller, and L.S. Nazarenko, "Implications for climate sensitivity from the response to individual forcings", Nature Climate Change, vol. 6, pp. 386-389, 2015. http://dx.doi.org/10.1038/nclimate2888

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