Sunday, June 29, 2014

How to use and misuse climate-change data

Here's a  useful clarifying graph from the website Skeptical Science: Getting skeptical about global warming skepticism. I've discovered that even some very intelligent people I know are taken in by the kinds of confusions, misunderstandings, and sophistries explained in the text that follows the graph.

Has there been a long-term, accelerating trend toward global warming? The overwhelming weight of the evidence, plus the overwhelming consensus judgment of climate scientists, indicate that the answer is yes. There's really not much uncertainty about that, aside from details. I think it's fair to say that, at this point, the only serious debates concern how worried we should be about this trend and what we should do about it. I find the arguments that we should be very worried quite convincing ... and, more to the point, so do the vast majority of climate scientists, who know more about this than I do.

Yours for reality-based & analytically intelligent discourse,
Jeff Weintraub

The Escalator

One of the most common misunderstandings amongst climate change "skeptics" is the difference between short-term noise and long-term signal.  This animation shows how the same temperature data (green) that is used to determine the long-term global surface air warming trend of 0.16°C per decade (red) can be used inappropriately to "cherrypick" short time periods that show a cooling trend simply because the endpoints are carefully chosen and the trend is dominated by short-term noise in the data (blue steps).  Isn't it strange how five periods of cooling can add up to a clear warming trend over the last 4 decades? Several factors can have a large impact on short-term temperatures, such as oceanic cycles like the El Niño Southern Oscillation (ENSO) or the 11-year solar cycle.

These short-term cycles don't have long-term effects on the Earth's temperature, unlike the continuing upward trend caused by global warming from human greenhouse gas emissions.

The data (green) are the average of the NASA GISS, NOAA NCDC, and HadCRUT4 monthly global surface temperature anomaly datasets from January 1970 through November 2012, with linear trends for the short time periods Jan 1970 to Oct 1977, Apr 1977 to Dec 1986, Sep 1987 to Nov 1996, Jun 1997 to Dec 2002, and Nov 2002 to Nov 2012 (blue), and also showing the far more reliable linear trend for the full time period (red).
Note: the concept of the Escalator (as well as the term 'going down the up escalator') was first proposed by Bob Lacatena.

[JW: The rest is here.]