[Vision2020] RealClimate.org, 10/6/2009: Climate Change Slowing or Stopping?: 371 Responses!

[Paul Rumelhart]

A couple of points about this.  First, it's not just the "blogosphere" 
that is full of this meme, some respected news sites are running with it 
as well.  For example, BBC: 
http://news.bbc.co.uk/2/hi/science/nature/8299079.stm

Second, I have seen no claims that the climate models predicted this 
cooling trend.  I have posted before about the hubris of assuming that 
we have all the myriad variables and interactions dialed in sufficiently 
for the models to be truly predictive.  For example, the Sun has been in 
a very low minimum that has defied previous predictions by astronomers 
as to it's length, and there is some question about whether sunspots 
might disappear entirely in the next few years: 
http://science.nasa.gov/headlines/y2009/03sep_sunspots.htm.  There are 
two major conflicting predictions concerning this topic, one predicts 
sunspots vanishing by 2015, the other predicts them returning "in 
earnest" within the next year.  How many other inputs to these models 
have conflicting predictions, I wonder?

And finally, if our main datasets do not agree sufficiently enough with 
each other as to be able to determine if we are in a cooling trend, then 
how can we trust the predictions of temperature increases that have been 
made, of a few degrees centigrade increases over decades, usually with a 
tenth of a degree centigrade precision?

Paul

Ted Moffett wrote:
> http://www.realclimate.org/index.php/archives/2009/10/a-warming-pause/#more-1265
>
>
>       A warming pause?
>
> Filed under:
>
>     * Climate Science
>       <http://www.realclimate.org/index.php/archives/category/climate-science/>
>
>     * Communicating Climate
>       <http://www.realclimate.org/index.php/archives/category/communicating-climate/>
>
>     * Instrumental Record
>       <http://www.realclimate.org/index.php/archives/category/climate-science/instrumental-record/>
>
>     * skeptics
>       <http://www.realclimate.org/index.php/archives/category/communicating-climate/skeptics/>
>
> — stefan @ 6 October 2009
>  
> Stefan Rahmstorf's bio:
>  
> http://www.realclimate.org/index.php/archives/2004/12/stefan-rahmstorf/
>  
> The blogosphere (and not only that) has been full of the “global 
> warming is taking a break” meme lately. Although we have discussed 
> <http://www.realclimate.org/index.php/archives/2008/12/2008-temperature-summaries-and-spin/> 
> this 
> <http://www.realclimate.org/index.php/archives/2008/11/mind-the-gap/> 
> topic 
> <http://www.realclimate.org/index.php/archives/2008/04/model-data-comparison-lesson-2/> 
> repeatedly 
> <http://www.realclimate.org/index.php/archives/2008/01/uncertainty-noise-and-the-art-of-model-data-comparison/>, 
> it is perhaps worthwhile reiterating two key points about the alleged 
> pause here.
>
> (1) This discussion focuses on just a short time period – starting 
> 1998 or later – covering at most 11 years. Even under conditions of 
> anthropogenic global warming (which would contribute a temperature 
> rise of about 0.2 ºC over this period) a flat period or even cooling 
> trend over such a short time span is nothing special and has happened 
> repeatedly before (see 1987-1996). That simply is due to the fact that 
> short-term natural variability has a similar magnitude (i.e. ~0.2 ºC) 
> and can thus compensate for the anthropogenic effects. Of course, the 
> warming trend keeps going up whilst natural variability just 
> oscillates irregularly up and down, so over longer periods the warming 
> trend wins and natural variability cancels out.
>
> (2) It is highly questionable whether this “pause” is even real. It 
> does show up to some extent (no cooling, but reduced 10-year warming 
> trend) in the Hadley Center data, but it does not show in the GISS 
> data, see Figure 1. There, the past ten 10-year trends (i.e. 
> 1990-1999, 1991-2000 and so on) have all been between 0.17 and 0.34 ºC 
> per decade, close to or above the expected anthropogenic trend, with 
> the most recent one (1999-2008) equal to 0.19 ºC per decade – just as 
> predicted by IPCC as response to anthropogenic forcing.
>
> GISS temperature trends 
> <http://www.realclimate.org/wp-content/uploads/GISStrends.jpg>
>
> /*Figure 1. *Global temperature according to NASA GISS data since 
> 1980. The red line shows annual data, the larger red square a 
> preliminary value for 2009, based on January-August. The green line 
> shows the 25-year linear trend (0.19 ºC per decade). The blue lines 
> show the two most recent ten-year trends (0.18 ºC per decade for 
> 1998-2007, 0.19 ºC per decade for 1999-2008) and illustrate that these 
> recent decadal trends are entirely consistent with the long-term trend 
> and IPCC predictions. Even the highly “cherry-picked” 11-year period 
> starting with the warm 1998 and ending with the cold 2008 still shows 
> a warming trend of 0.11 ºC per decade (which may surprise some lay 
> people who tend to connect the end points, rather than include all ten 
> data points into a proper trend calculation)./
>
> Why do these two surface temperature data sets differ over recent 
> years? We analysed this 
> <http://www.realclimate.org/index.php/archives/2008/11/mind-the-gap/> 
> a while ago here, and the reason is the “hole in the Arctic” in the 
> Hadley data, just where recent warming has been greatest.
>
> Mean temperature difference between the periods 2004-2008 and 
> 1999-2003 <http://www.realclimate.org/wp-content/uploads/ncepawrming.gif>
> /*Figure 2.* The animated graph shows the temperature difference 
> between the two 5-year periods 1999-2003 and 2004-2008. The largest 
> warming has occurred over the Arctic in the past decade and is missing 
> in the Hadley data./
>
> If we want to relate global temperature to global forcings like 
> greenhouse gases, we’d better not have a “hole” in our data set. 
> That’s because global temperature follows a simple planetary heat 
> budget, determined by the balance of what comes in and what goes out. 
> But if data coverage is not really global, the heat budget is not 
> closed. One would have to account for the heat flow across the 
> boundary of the “hole”, i.e. in and out of the Arctic, and the whole 
> thing becomes ill-determined (because we don’t know how much that is). 
> Hence the GISS data are clearly more useful in this respect, and the 
> supposed pause in warming turns out to be just an artifact of the 
> “Arctic hole” in the Hadley data – we don’t even need to refer to 
> natural variability to explain it.
>
> Imagine you want to check whether the balance in your accounts is 
> consistent with your income and spendings – and you find your bank 
> accounts contain less money than you expected, so there is a puzzling 
> shortfall. But then you realise you forgot one of your bank accounts 
> when doing the sums – and voila, that is where the missing money is, 
> so there is no shortfall after all. That missing bank account in the 
> Hadley data is the Arctic – and we’ve shown 
> <http://www.realclimate.org/index.php/archives/2008/11/mind-the-gap/> 
> that this is where the “missing warming” actually is, which is why 
> there is no shortfall in the GISS data, and it is pointless to look 
> for explanations for a warming pause.
>
> It is noteworthy in this context that despite the record low 
> <http://www.pmodwrc.ch/pmod.php?topic=tsi/composite/SolarConstant> in 
> the brightness of the sun over the past three years (it’s been at its 
> faintest since beginning of satellite measurements in the 1970s), a 
> number of warming records <http://www.ncdc.noaa.gov/sotc/> have been 
> broken during this time. March 2008 saw the warmest global land 
> temperature of any March ever recorded in the past 130 years. June and 
> August 2009 saw the warmest land and ocean temperatures in the 
> Southern Hemisphere ever recorded for those months. The global ocean 
> surface temperatures in 2009 broke all previous records for three 
> consecutive months: June, July and August. The years 2007, 2008 and 
> 2009 had the lowest summer Arctic sea ice cover ever recorded, and in 
> 2008 for the first time in living memory the Northwest Passage and the 
> Northeast Passage were simultaneously ice-free. This feat was repeated 
> in 2009. Every single year of this century (2001-2008) has been warmer 
> than all years of the 20th Century except 1998 (which sticks out well 
> above the trend line due to a strong El Niño event).
>
> The bottom line is: the observed warming over the last decade is 100% 
> consistent with the expected anthropogenic warming trend 
> <http://www.pik-potsdam.de/%7Estefan/update_science2007.html> of 0.2 
> ºC per decade, superimposed with short-term natural variability. It is 
> no different in this respect from the two decades before. And with an 
> El Niño developing <http://www.elnino.noaa.gov/> in the Pacific right 
> now, we wouldn’t be surprised if more temperature records were to be 
> broken over the coming year or so.
>
> *Update:* We were told there is a new paper 
> <http://www.agu.org/journals/pip/jd/2009JD012442-pip.pdf> by Simmons 
> et al. in press with JGR that supports our analysis about the Hadley 
> vs GISS trends (sorry, access to subscribers only).
>
> ------------------------------------------
>
> Vision2020 Post: Ted Moffett
>
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