>In advance of the UN negotiations next week in Cancun, the press and blogs today have included numerous elaborations on the UK Met Office press release Scientific evidence is Met Office focus at Cancun. The Australian article “Global temperature rises may be underestimated due to errors, Met Office study says” by Ben Webster includes the following statement, “The long-term rate of global warming was about 0.16C a decade in the 1970s, 1980s and 1990s but it slowed in the past 10 years to between 0.05C and 0.13C, depending on which of three major temperature records is used. The Met Office said that changes in the way ocean temperatures were measured had resulted in an under-estimate of about 0.03C in recent years.”
But what the Met Office fails to mention is that the dataset being discussed in the press release, their HADSST2 data, which is the sea surface temperature dataset used in their HADCRUT3 and HADCRUT3v global temperature products, is biased upwards by almost 0.12 deg C after 1998 due to a change in source data in 1998. I’ve illustrated and discussed this bias in two previous posts: Met Office Prediction: “Climate could warm to record levels in 2010” and The Step Change in HADSST Data After the 1997/98 El Nino.
The new source Sea Surface Temperature data was not fully consistent with the source dataset the Hadley Centre used prior to 1998. So when they merged the two datasets, the Hadley Centre failed to account for the inconsistency and created an upward bias in their HADSST2 data. This bias is easily seen when the other Hadley Centre sea surface temperature dataset, HADISST, is subtracted from the HADSST2 data, Figure 1. Note that the HADISST has relied primarily on satellite-based measurements since 1982, but the HADSST2 data is based on buoy and ship readings. The upward step is approximately 0.12 deg C. The bias created by the change in measurement methods over the past decade that was reported on in The Australian would only offset a portion of that shift.
Hopefully, when the Hadley Centre finally releases its updated Sea Surface Temperature dataset (HADSST3) they will eliminate the upward step. And for those interested, here’s a link to a Met Office Scientific Advisory Committee (MOSAC) publication, “Climate monitoring and attribution,” that provides an overview of the upcoming HADSST3 and HADISST2 datasets. Refer to page 3 under the heading of “3. Progress in development of marine datasets.”
The HADSST2 and HADISST data used in this post are available through the KNMI Climate Explorer:
>Hi Bob,So if I was to use the raw UAH and RSS lower atmospheric satellite data for the same 2 time periods you used:1979-1997:http://www.woodfortrees.org/plot/uah/from:1978/to:1997/plot/rss/from:1978/to:19971998-2010:http://www.woodfortrees.org/plot/uah/from:1998/plot/rss/from:1998and I use a similar straight line approach like you did and found a similar temperature step increase, would I be wrong? Just looking at those two graphs, I can actually identify a 0.25C step increase between the 2 satellite data sets between the 2 time periods.Based on that possibility, could the reason be that the step increase identified between those 2 time periods is real and not some biased artifact of the HADSST2 data set like you are suggesting?Perhaps the differences between the 2 data sets is possibly due to some problem with the HADISST data not fully identifying an actual step increase in global SST temperatures and is therefore incompatible with the step increase found in the lower atmospheric satellite data for the same time periods.Dennis H.
>Dennis H wrote, "Just looking at those two graphs, I can actually identify a 0.25C step increase between the 2 satellite data sets between the 2 time periods."You can? Please subtract one from the other and chow me.Also, I'm not sure what your point is, because if you had bothered to click on lthe links to the earlier posts you would have discovered the shift occurs between HADSST2 and other datasets, like ERSST.v2, ERSST.v3b, Reynolds OI.v2.
>And, Dennis, if and when you do take the time to subtract UAH from RSS TLT anomalies to make your point (instead of claiming you believe you see a non-existant shift in 1998), I believe you'll find an offset that's discussed in a few papers by Christy and Spencer. The shift doesn't occur in 1998 by the way.
>Hi Bob,I just got back to read your comments to me.All I did was visually interpret the averages of the monthly UAH and RSS for each time period (1978-1997 and 1998-2010). This is equivalent to your two straight lines drawn through your data points for the 2 time periods.Actually the difference between the averages of these 2 lower atmospheric satellite temperature records are as follows (after plugging the raw data into EXCEL): 1) 1978-1997 => -0.0345C 2) 1998-2010 => 0.2701CSo I actually was underestimating the differences based on visual observation, since the difference between the two averages is actually 0.3046C.So my point is, if your idea that an observed step increase between these two time periods is due to some artifact of different measuring systems, because the similar step increase is being observed with the highly regarded satellite data record and I am not aware of any measurement discrepancy with those two temperature readings and how they are being compiled.Dennis H.
>Dennis H says: "All I did was visually interpret the averages of the monthly UAH and RSS for each time period (1978-1997 and 1998-2010). This is equivalent to your two straight lines drawn through your data points for the 2 time periods."Incorrect. My straight lines were created by EXCEL and they are the calculated averages for the periods illustrated. There's a world of difference between eyeball values and calculated values.Let's get to the bottom line on this. All datasets have an upward shift after the 1997/98 El Nino. And I've presented the reasons for them in a multitude of posts. You get no argument from me about the existance of those shifts. This post was about the ADDITIONAL shift in the HADSST2 dataset that was created by the Hadley Centre's splicing of two incompatible source datasets together. That is why I illustrated the additional bias in the HADSST2 data by subtracting the other Hadley Centre SST dataset (HADISST) from it.
>Bob,Your argument HERE brings up a similar point of argument that I also see with the UAH temperature data (the favorite of the skeptic crowd).Whenever I see a plot of the UAH, RSS, GISS, and HADCRUT temperature data, the UAH data shows higher highs and lower lows than the other data sets: http://www.woodfortrees.org/graph/hadcrut3gl/from:1978/offset:0.39/mean:12/plot/gistemp/from:1978/offset:0.3/mean:12/plot/uah/from:1978/offset:0.54/mean:12/plot/rss/from:1978/offset:0.54/mean:12This pattern of larger extremes seems very similar to the HADSST2 data set when compared to the other available SST data sets:http://i50.tinypic.com/j0y4wo.jpgDoes this mean you are may need to question the validity of the UAH data set as well when it comes down to the amount of step increase being caused by the pattern of extremes? I Think you need to let your fellow skeptics know that there is a possibility of some data quality problems with the UAH data if you are going to continue argue your points here about HADSST2.Dennis H.
>Dennis says: "Does this mean you are may need to question the validity of the UAH data set as well when it comes down to the amount of step increase being caused by the pattern of extremes?" TLT is a different variable than surface temperature. One would expect it to behave differently. Again, this post and the posts linked illustrated the differences between SST datasets.