How to abuse a climate temperature graph

In recent months I’ve read a number of articles commenting on how climate change has slowed in the last decade, and wondering what this will mean for climate campaigners. Media reports have mentioned a ‘hiatus‘ or a ‘plateau‘ in warming, with many claiming there has been no significant warming for 16 years. The latest was sent to me by Phil, a piece from the Economist that goes to far as to ask if the public “has been systematically deceived”. This is par for the course for climate skeptics, not so much for reputable publications. So what’s going on here?

There are some interesting differences emerging between air temperatures and sea temperatures, and some genuine questions, but for the most part this is a media phenomenon. Despite claims to the contrary, scientists are not surprised or thrown into confusion. That’s because climate change isn’t linear, it has accelerated and slowed in the past, and there are lots of competing factors besides the fairly constant rise in CO2.

One of the most common ways to conclude that the temperature rise has stopped or leveled off is just to choose the starting point of your graph to suit the claim. 1998 is the traditional place to start – here’s the Daily Mail doing it – and then you draw a vaguely straight line to say there hasn’t been any warming. This is a selective use of the data. Let me illustrate by similarly abusing a chart of the gold price.

1. The price of gold is soaring:

runaway-gold

2. No wait, the gold price is actually recovering from a massive collapse and long depression.

recovering

3.The reality is that the gold price depends on a number of factors, including economic cycles and world events. The big spike in 1980 is the result of an oil crisis, events in the Middle East and a rush into gold as the global economy wobbled.

full-gold

By slicing the graph in different places, you can draw very different conclusions about the market for gold. You can do similar things with global temperature graphs. If you start your graph in 1998, it looks like there’s been a drop-off or even a cooling. You only have to back up two years to see how dishonest that is. Nobody would view a graph from 1996 to 2012 and conclude that global warming has stopped.

1996

What a difference two years’ more data makes.

The reality is, of course, that global temperature fluctuates enormously. There are long running cycles, weather patterns, volcanic and solar events. There’s a reason why 1998 was such a hot year. It was an El Nino year, which always results in higher temperatures. You shouldn’t take anomalies as a starting point, and anyone that does has an agenda.

el-ninos

When you stand back and look at the longer time frame, you can see a number of unusually warm years and cold years. You can also see periods where warming trends slowed, through the mid sixties or mid eighties for example. Calling an end to global warming looks a little premature, especially when you realise that a cold year in this decade is considerably warmer than a hot year in the 1980s.

As the Secretary General of the World Meteorological Organisation said this week, “a decade is the minimum possible timeframe for meaningful assessments of climate change.” And when you average things out into decades, there’s no hiatus or plateau at all:

decadal-temperature-trend

One Comment on “How to abuse a climate temperature graph”

  1. kenthinksaloud July 9, 2013 at 7:26 pm #

    An excellent look at how to abuse statistics. Thanks for this!

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