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I have created a map of temperature and precipitation changes in the continental US based on monthly NOAA data going back to 1895. The linear trend lines are added wherever they make sense.

Here's the map, and here's a blog post describing it (reproduced below).

If you have any questions or comments, please let me know (especially if the map does not work for you or something is not well explained).



When people talk about climate change is the US, they tend to either concentrate on what is happening with the whole country or large regions, or on very local changes that have a lot of variability. For a more detailed understanding of what exactly has been going on  over the last century we can look at areas called climate divisions.


* What does the map show?

It displays overall changes in temperature and precipitation (rainfall plus snowfall) for each month since 1895. You can also see yearly and seasonal changes.

* What do the colors mean?

Shades of red/purple show an increase in temperature or precipitation. Shades of green indicate a decrease. The exact ranges for each color are displayed in the legend next to the map.

* Why are some areas of the map blank?

If an area is shown, it mean there's a strong trend - in other words, only if there is enough confidence that despite year-to-year variability, the values are climbing up or down.

* What are some examples of large changes?

February temperature since 1895: north and northeast of the country has warmed over 3F.
November precipitation since 1895: east and southeast had over 60% increase.

Yearly temperature since 1970: some parts of Nevada have warmed up by 4-5F.
Yearly precipitation since 1970: several areas in the Dakotas had 30-40% increase.

* How can I see the trends for myself?

Click anywhere on the map. All the data points will be shown in a chart under the map. The trend line will be overlayed on top of the data. Even if an area is blank, you can still click on it and see the chart, but there will be no trend line.

* Where did the data come from?

From NOAA (National Oceanic and Atmospheric Administration).

* Where can I learn more about US weather changes?

In June 2012, Climate Central has published a report about state-by-state temperature changes. The most comprehensive source is the national climate change section of the 2009 report on climate change impacts produced by US Global Change Research Program.

* How did you compute the trend? Did you use linear regression?

Almost. Linear regression would produce approximately the same results, but it assumes certain things about the data that may not always be true. Instead, we used what statisticians call "nonparametric estimation" - in other words, tried to determine if there is a linear trend without assuming anything about the nature of the data. Specifically, we can apply the Mann-Kendall test to see if the data have any trend at all or just change randomly without moving a lot in any direction. If the test says that there is a trend (with p-value <0.05), we can use a method similar to linear regression, the Theil-Sen estimator, to find the most likely straight line that approximates the trend.

* What is p-value?

It's a statistical indicator of how well a linear trend fits, or how well it describes a series of observations. Trend estimation formulas always produce a linear trend (a straight line), but if the data are not really changing more or less together with this straight line, it makes no sense to talk about a trend. This is why trend estimation formulas also produce another number called the p-value. The p-value is always between 0 and 1, but only very small p-values point at good fits. A cutoff value of 0.05 is often used - so if the trend estimation formulas produce a p-value of 0.05 or below, the map shows a trend, otherwise it does not. See the wikipedia articlefor more information.

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Comment Preferences

  •  Odd, They've Got Large Areas In Gray But On (3+ / 0-)
    Recommended by:
    LaughingPlanet, PatriciaVa, Cliss

    my viewer at least no gray on the legend, but the legend does show on mine with 2 different trends both identified with white boxes.

    We are called to speak for the weak, for the voiceless, for victims of our nation and for those it calls enemy.... --ML King "Beyond Vietnam"

    by Gooserock on Mon Jul 09, 2012 at 09:56:10 AM PDT

  •  Useful stuff. nt (2+ / 0-)
    Recommended by:
    LaughingPlanet, Cliss
  •  impressive (1+ / 0-)
    Recommended by:

    I agree with Gooserock above about the gray color; a bit confusing.

    Also, perhaps you can change the map background to remove the green denoting mountain ranges because green is also one of the colors in the legend.

    Thanks for all the hard work!

    And remember: if we fail on climate change, nothing else matters. - WarrenS

    by LaughingPlanet on Mon Jul 09, 2012 at 10:02:23 AM PDT

  •  What would similar data for the last 15K years... (0+ / 0-)

    ...look like?

    And wouldn't that be more representative?

    In the Americas, 10K years ago, many residents living in a land-bridge connecting Yucatan to Cuba were displaced, as the sea rose.  No one lived in Manhattan 10K years ago, as a mile-high glacier dominated the island.

    Learn about Centrist Economics, learn about Robert Rubin's Hamilton Project.

    by PatriciaVa on Mon Jul 09, 2012 at 10:09:30 AM PDT

    •  Unfortunately (3+ / 0-)
      Recommended by:
      LaughingPlanet, MGross, pgm 01

      We don't have detailed data going back that far. This map is based on individual station observations recorded by weather people.

      There are good reasons to think that recently man-made emissions have altered the natural behavior of the climate, so we should be looking at both long-term and short-term pictures.

      •  I don't dispute that man has altered climate, but. (0+ / 0-) one can dispute that man was displaced as the seas rose about 10K years ago.  And it's very possible that man lived in Manhattan prior to a mile-high glacier dominating it.

        If one believes in climate change, as I do, one has to decide on the proper course of action.  Every policy prescription to mitigate it has costs.  And it we must balance costs against benefits of action.

        For example, imagine the costs associated with displacing, for the sake of argument, 15K residents on an island which would soon be flooded.  Now compare those costs with a carbon tax or cap and trade, either of which would negatively impact the working and middle-class FAR MORE than the wealthy.

        To me, it's a no-brainer.

        Learn about Centrist Economics, learn about Robert Rubin's Hamilton Project.

        by PatriciaVa on Mon Jul 09, 2012 at 10:29:44 AM PDT

        [ Parent ]

        •  It's a very long conversation. (0+ / 0-)

          So I don't want to get into this discussion here.

          Take a look at this post (and the Weitzman paper linked from there).

        •  yeah--but what you're proposing is reactive (0+ / 0-)

          rather than proactive.  Responding to imminent threats is one thing--but in many cases it simply isn't manageable.  Look at Katrina---a case that SHOULD have been manageable.

          Ultimately what you want is broad-based movement towards a less consumption/production oriented global lifestyle...although the odds of that ever happening are, unfortunately, really low....

  •  Thanks for this, (2+ / 0-)
    Recommended by:
    LaughingPlanet, llywrch


    A very frightening map.  Notice the dark pink, large areas especially in the SW area.  Also the light pink areas are alarming.  If I were living in those areas, I'd start packing my bags and head for 'greener pastures'.

    One of the things that I've read is that the cloud layers have started to disperse from the equator and moved both north and south.  Meaning: the equatorial areas would become hotter and drier.  The north & south regions would become wetter, inundated with huge rainfalls.  This seems to be true, I just read that Sweden again had an enormous rainfall, flooding has now become typical.  

    I suppose it isn't quite so simplistic.  I've also read that the Gulf Stream is slowing down due to the water temperatures increasing.  Which means that the northern regions such as the coast of Norway and other areas such as England will become colder.  What do you think?

    An absolute mess.  

    •  I'm not really qualified to discuss science (2+ / 0-)
      Recommended by:
      bevenro, Cliss

      I just make maps.

      I think the general effect of climate change on precipitation can be described as "wet areas getting wetter, dry areas getting drier". However, there could be a lot of variation, which is one of the reason I've made this map - to see what exactly happening in different areas. It is true that there have been a lot of extreme rain events worldwide recently, but we can't always say if an individual event is caused by climate change.

      As for cloud layers moving away from the ecuator,  you probably mean the expansion of Hadley cells.

      The Gulf Stream slowdown has been discussed by scientist, but it's not a straightforward issue.

  •  any idea what caused the cooldown in the southwest (1+ / 0-)
    Recommended by:

    during the first half of the century?  Found that interesting.

    I also find it interesting that the main increases are in the southwest and the upper midwest.  

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