Downplaying Their Own Finding

After years of insisting that urban biases have negligible effect on the the historical temperature record, the IPCC may finally have to accept what skeptics have been saying for years — that:

  1. Most long-lived historical records are from measurement points near cities (no one was measuring temperatures reliably in rural Africa in 1900)
  2. Cities have a heat island over them, up to 8C or more in magnitude, from the heat trapped in concrete, asphalt, and other man made structures.  (My 13-year-old son easily demonstrated this here).
  3. As cities grow, as most have over the last 100 years, temperature measurement points are engulfed by increasingly hotter portions of the heat island.  For example, the GISS shows the most global warming in the US centered around Tucson based on this measurement point, which 100 years ago was rural.

Apparently, Jones et al found recently that a third to a half of the warming reported in the Hadley CRUT3 database in China may be due to urban heat island effects rather than any broader warming trend.  This particularly important since it was a Jones et al letter to Nature years ago that previously gave the IPCC cover to say that there was negligible uncorrected urban warming bias in the major surface temperature records.

Interestingly, Jones et al can really hs to be treated as a hostile witness on this topic.  Their abstract states:

We show that all the land-based data sets for China agree exceptionally well and that their residual warming compared to the SST series since 1951 is relatively small compared to the large-scale warming. Urban-related warming over China is shown to be about 0.1°C decade−1 over the period 1951–2004, with true climatic warming accounting for 0.81°C over this period

By using the words “relatively small” and using a per decade number for the bias but an aggregate number for the underlying warming signal, they are doing everything possible to downplay their own finding (see how your eye catches the numbers 0.1 and 0.81 and compares them, even though they are not on a comparable basis — this is never an accident).  But in fact, the exact same numbers restate this way:  .53C, or 40% of the total measured warming of 1.34C was due to urban biases rather than any actual global warming signal.

Since when is a 40% bias or error “relatively small?”

So why do they fight their own conclusion so hard?  After all, the study still shows a reduced, but existent, historic warming signal.  As do satellites, which are unaffected by this type of bias.  Even skeptics like myself admit such a signal still exists if one weeds out all the biases.

The reason why alarmists, including it seems even the authors themselves, resist this finding is that reduced historic warming makes their catastrophic forecasts of future even more suspect.  Already, their models do not back cast well against history (without some substantial heroic tweaking or plugs), consistently over-estimating past warming.  If the actual past warming was even less, it makes their forecasts going forward look even more absurd.

A few minutes looking at the official US temperature measurement stations here will make one a believer that biases likely exist in historic measurements, particularly since the rest of the world is likely much worse.

  • Eric Anderson

    “By using the words “relatively small” and using a per decade number for the bias but an aggregate number for the underlying warming signal, they are doing everything possible to downplay their own finding (see how your eye catches the numbers 0.1 and 0.81 and compares them, even though they are not on a comparable basis — this is never an accident). But in fact, the exact same numbers restate this way: .53C, or 40% of the total measured warming of 1.34C was due to urban biases rather than any actual global warming signal.”

    This is extremely telling. I’d sure like to believe that their comparison of two different time periods was not intentional, but it is getting harder and harder to give the benefit of the doubt.

  • MikeS

    What’s decade^-1? One-tenth of a decade?

  • NewEnglandDevil

    decade^-1 = per decade
    0.1C decade^-1 = 0.1C/decade


  • joshv

    No measurement that is subject to an uncontrolled and variable bias should be used in science. It’s as simple as that. Either you show that your data is unaffected by UHI effects over the period of time you’d like to use it, or you throw it out.

    Attempts to tease out the UHI portion of warming from the underlying trend are nice exercises in statistical manipulation, but they are not science.

  • Rob

    Does this mean, 0.1C decade^-1 = 0.1C/decade = 0.01C

  • MikeS

    Rob: 1951–2004 times 0.1C/decade = 0.53C

  • Not a surprise to anyone… it’s telling that the best kept surface station data, which is in the US, shows no particular warming trend for around 80 years. As I recall the warmest temperatures were in the 1930’s and this fact has always been downplayed…

    What is also interesting is that hundreds of millions are spent on climate research these days in support of the AGW hypothesis, yet the resulting studies at best lend tenuous support…

  • Paul Power

    That “relatively small” comment is more disingenuous than it seems.

    You have to compare the .53C to the .81C (not to (.53C + .81C)) which is surely what they meant by “large scale warming”

  • An Inquirer

    In the eyes of people that truly study the issue, Global Warming Pessimists often hurt their own cause by self-serving actions. Regarding UHI, they typically embrace dubious studies such as Parker’s that claim UHI is largely non-existent; they attack studies that show UHI to be significant; and they carelessly dismiss the possibility that UHI has increased in many cities over the last 100 years. Nevertheless, I understand the position of mainstream Global Warming Pessimists is that UHI is real and is large in local cities, but DOES NOT MATTER for GMT trends because cities constitute such a small portion of the globe. The challenge for Skeptics is to show that UHI affects GMT. (As a side, I would caution that GMT has weaknesses as a reliable indicator of global climate change.) If satellites truly pick up near-surface temperatures, then are RSS and UAH results contaminated by UHI? Given that 70% of the world’s surface is water, how can UHI substantially affect GMT trends? With GISS relying on satellite readings for ocean temperature trends, would be surprising that UAH, RSS, and GISS have roughly followed each other for much of the past three decades? I believe that three Skeptical thoughts are worth considering. (1) Perhaps micro siting issues may be a reason GISS has had more divergence (less cooling) lately (since 2000) than UAH and RSS. (2) The similarity between various GMT measures since incorporation of satellite data is not surprising, but the severity of temperatures 70 years ago might be understated. GISS has adjusted those temperatures downward, and adverse impacts of climate trends were much more evident in the 1930s than now. (3) Worldwide, glaciers started retreating over 200 years ago. Whatever caused the Little Ice Age to end is likely to be more “natural” than CO2-induced. (And glaciers typically have not yet retreated to the point that they were during the MWP.) So mainstream Skeptics accept that temperatures have risen since the LIA, but why did the LIA end?

  • Yelling it “DOES NOT MATTER” doesn’t make it true. Obviously it does matter. The issue has been discussed many times in the past now. It does matter because what were ‘rural’ stations 80 or 50 years ago, are often no longer rural.

    The satellite data is valuable but we only have around 30 years of that data. It can’t be used to determine the actual warming that occurred in the whole of the last century.

  • hunter

    Yes, and it’s a little known fact that urban heat islands melt mountain glaciers, heat the oceans, and are strongest in Siberia and the Arctic.

  • Regrettably we don’t have data on mountain glacier melt, ocean heat content or very many temperature records from Siberia and the Arctic going back 100 years, so your comment is obviously foolish.

  • An Inquirer

    Will Nitschke:
    Actually the lack of data may not be as severe as you may think. For glaciers, check out
    There are other resources as well, but a google search on melting glaciers will give you mostly short-sighted research on the issue.
    For ocean temperatures, British sailors have been taking measurements for over 100 years. Unfortunately, methods have evolved (from buckets to more sophisticated techniques), and these inconsistencies hinder the reliability of trends. (HadCru braves to estimate long term SST, but apparently its estimates are overly reliant on Northern Hemisphere data points.) It is of course interesting that the previous poster referred to the Arctic and Siberia — leaving off Antarctica. Also, I understand from that Greenland has lower temperatures now than in the 1940s. Also, one should wonder about the impact of “China’s smog” on Siberia and other northern areas. The issues involve both soot deposits which melt snow/ice and increased nighttime clouds. Finally, there are those nagging reports that Siberian sites decades ago underreported temperatures to get more fuel allocations from Moscow. There was a tremendous drop off in the number of Siberian stations correlated with a suspicious rise in temperatures. So, okay, Will, perphaps I will grant your claim about Siberian temperature records.

  • Words matter

  • Stevo

    “Cities have a heat island over them”

    You think somehow this is a grand revelation that shakes all of climate science to its very foundations? What a prize idiot you are!