Warming Stopped in 1998

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.

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Objection:

Global temperatures have been trending down since 1998. Global Warming is over.

Answer:

At the time, 1998 was a record high year in both the CRU and the NASA GISS analysis.  In fact, it was not just a record year, it blew away the previous record by .2oC. (That previous record went all the way back to 1997, by the way!) According to NASA, it was elevated far above the trend line because 1998 was the year of the strongest El Nino of the century. Choosing that year as a starting point is a classic cherry pick and demonstrates why it is necessary to remove the very chaotic year to year variability that exists (aka: weather) by smoothing out the data. Looking at the CRU’s graph below, you can see the result of that smoothing in black.

Clearly 1998 is an anomaly and the trend has not reversed.  (Even the apparent levelling at the end is not the real smoothing.  The smoothed trend in 2005 depends on all of its surrounding years, including a few years still in the future.)  By the way, choosing the CRU analysis is also a cherry pick because NASA has 2005 breaking the 1998 record, though by very little.

Now this is an excusable mistake for average folks who do not need the rigors of statistical analysis in their day jobs, but any scientist in pretty much any field knows that you can not extract any meaningful information about trends in noisy data from single-year end points. This is why it is hard to hear a scientist make this argument and still believe that they are a voice of integrity in this debate, rather it appears more to be an abuse of the trust people would like to place in them as scientists.  Bob Carter is such a voice and was the first to trot out this argument in an article in the Daily Telegraph.  Since then it has echoed far and wide and has been used by Richard Lindzen as well as a host of sceptic websites.  

Interestingly, Bob Carter seems to know what he is doing as he tries to pre-empt objections in his article by basically insinuating that any choice of starting point, (such as 1978), will just be a cherry pick with the opposite motive! But cherry picking is about choosing data for the sole purpose of supporting a pre-conceived conclusion, it is not the simple act of choosing at all, as one must choose some starting point. In the case of his example year, 1978, this is often chosen simply because it is the first year that satellite records of tropospheric temperatures were available.

So what choices are there, what are the reasons for those choices and what are the conclusions we can draw from them?

1. As just mentioned above, one could chose to examine the last 30 years because that is the period of time where both surface and tropospheric readings were available. We have been experiencing warming of approximately .2oC/decade during this time.  It would take a couple of decades trending down before we could say the recent warming did in fact end in 1998.
2. You could choose 1970 in the NASA GISS analysis as this was the start of the late 20th century warming and as such it is a significant feature of the temperature record. The surface temperature over this period shows .6oC warming.
3. You could choose 1965 in the CRU analysis as this is when the recent warming started in their record. This record shows around .5oC warming of the smoothed trend line.
4. You could choose 1880 in the NASA record. This shows .8oC warming.
5. You could choose 1855 in the CRU record. This shows .8oC warming.  Again, with this trend and the above we can not say it is over without many decades more data all indicating cooling.
6. You could choose to look at the last 500 years in the bore hole record analysis because that is its entire length. This puts today about 1oC above the temperatures in the first 3 centuries of that record.  The record of today’s trend in that kind of analysis will be hidden from view for many more decades.
7. You could choose to look at the last one thousand years, because that is as far back as the dendrochronology studies reliably go. Then the conclusion is:
   

   Although each of the temperature reconstructions are different (due to differing calibration methods and data used), they all show some similar patterns of temperature change over the last several centuries. Most striking is the fact that each record reveals that the 20th century is the warmest of the entire record, and that warming was most dramatic after 1920.

8. You could choose to look at the entire period of time since the end of the last ice age, around 10kyrs ago. Then the conclusion is that GHG warming has reversed a very long and stable period with a very slight downward trend and we are now at a global temperature not experienced in the history of human civilisation, the entire Holocene.  Such a long view applied to today will take many centuries to clear up.  The situation is a bit more urgent than that!

I think that about covers any periods of time relevant to today’s society. Clearly, "it has stopped warming" is only supported by taking a single specific year out of context and using a 7 year window to look at multi-decadal trends in climate. That is a classic cherry pick.

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This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.

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“Warming Stopped in 1998” was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.