I have noted before that cherry-picking short-term trends in data – and scrupulously omitting mention of the same data set when the trend reverses – is a favoured tactic of polemicists attempting to argue against scientific evidence. Let’s take a look at a couple of graphs from sources Andrew Bolt was keen on not so long ago.

Exhibit A

Just last month, Andrew loved this graph:

june

He said:

NASA’s Aqua satellite – one of the four main measurements of world temperature – found June had dropped back to just .001 degrees above the average for the past 30 years.

That means we’re back to “normal”, even if “normal” now is slightly warmer than the average for last century, during which the planet came out of the Little Ice Age that ended 150 years ago.

This month?

uah_lt_since_1979

Exhibit B

At the beginning of May, Bolt noted that Arctic sea ice had “risen” and suggested Four Corners would not give that trend the same coverage they gave to declining Arctic sea ice. At the time, he used this graph:

tttt_thumb

And now?

20090804_figure2

Ice extent averaged for July 2009 was the third lowest in the satellite record for the month of July. The long-term trend indicates a decline of 6.1% per decade in July ice extent since 1979, relative to the 1979 to 2000 average, an average of 62,000 square kilometers (24,000 square miles) of ice per year.

Conclusion

What do these updated graphs mean in relation to climate change? Nothing much, really – the temperature rise is likely due to the emerging El Nino phenomenon, and the annual level of Arctic sea ice is affected by weather patterns (although the long-term trend is a worrying sign).

Which is what they meant when Bolt used the earlier ones. If he was to post the current graphs, it would reveal to any sensible reader the foolishness of his reliance on these sorts of data. But instead, he’ll probably drop these data sets out of his repertoire and find some new graphs that help his agenda.

UPDATE: Bolt gives the temperature data a very quick mention – without posting the graph – at the end of this post.

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