Monday, January 9, 2012

Cherrypicker's guide to station trends


  1. Is the US using GHCN only, or have you got USHCN in there too? They really should be used together, I think.

  2. CE,
    I'm using GHCN only - I think all the GHCN stations are also USHCN. About ten years ago GHCN greatly reduced the number of US stations in its database. Before that station density in the US was high vs ROW.

    I could do USHCN separately - I agree with GHCN (saying, I think) that there isn't much point in analysing the world at markedly different station densities.

  3. I agree with all that; I just don't remember NOAA's rationale for choosing which US stations would continue to be updated in GHCN, and which would only be updated in USHCN. Maybe they're the stations that were originally highlighted as good candidates for GHCN, I don't know. I forget; I haven't looked at this stuff in ages.

    Either which way, if GHCN-only-US is a reasonable sample, such that using the full density of USHCN just ends up being irrelevant for this analysis, well then, carry on.

  4. upon reflection - higher density couldn't be irrelevant, because you're offering a cherry-picker's guide. with more stations available, more cherries could be found.

    but I think the above is perfectly sufficient; don't extend the work on my account.

  5. CE,
    The US certainly looks the most densely covered. That's partly because it shows, for some reason, less spatial uniformity.

    The formula I used does not cut the US stations totally in accord with the recent reductions. That's because I require 80% of months reported within the period. So over sixty years, a station would quality even if it stopped in 2000, provided it had very good coverage in the earlier years.

  6. In the next to last sentence is 'losotive' a misspelling of 'positive' - or just a term I'm unfamiliar with?

  7. kevin O,
    Yes, indeed. In most of my typos I can at least see how it happened. Not here.
    Thanks, fixed.

  8. Nick:
    Can you do a longer time series on this? Being in 1880 or such?

    Thank you.

  9. Camburn,
    There's a problem that the number of stations with long trends is small, so the map is more patchy. For example, in the just 60 stations post, I looked for rural stations with 90 years of data, and there were just 61. You can look at the map there to see its sparsity. Allowing urban might have doubled the stations.

    But yes, I could do 90 years, say.

  10. Nick:
    I feel like I am a kid in a candy store on your site.

    The reason I asked for a longer term temp trend was to zero in on the region where I live and compare what you would find on a world wide metric verses what the regional anamoly would be.

    The region I live in has not warmed since the 1930's. We have had cool periods, slight warming, then cool and now we are close to the 1930's temps presently.

    Upper mid west USA.

  11. The map seems warm-biased. Wouldn't it be better to show temperatures on a scale relative to the median. The map does not reveal zones that normally trend warmer or cooler. The U.S. for instance is probably an over-contributor to warming, as would be Australia's Simpson Desert. Most of Earth's population exists between 40 degrees south and north latitude; these are the latitudes most affected by El Nino - La Nina; the Pacific Decadal oscillation and so on; it is also (roughly) the zones where the longest thermometer records and the most thermometers are located. On the global map there are also many grids where there are no permanent, nor historical measurements. I'm unconvinced that warming is not related to climate phases and population concentrations.