Warmest Ever, or Getting Cooler?

You might hear climate change "deniers" saying recent temperatures show global cooling. But then you hear climate "scientists" say that the last ten years are the warmest on record.  Who's right?

They both are.

...That is, if you accept, say, the NASA/GISS Global Annual Mean Surface Air Temperature Change (land-ocean mix) as the "true" global temperature.

(By the way, I do not accept that the NASA/GISS data represent truth. The data NASA provides are not raw temperature readings, or even simple averages of temperature readings. They are adjusted, quality-controlled, homogenized, and fudge-factored in ways we don't know and they're not telling. But for the purposes of the question at hand, let's accept NASA's adjusted and homogenized data.)

The chart below shows recent annual temperatures. The 2009 data point is biased on the high side, since it is the average through October only, thus missing November's and December's cooler readings. (The temperature is the "anomaly," or the difference from the 1951-80 average.)

NASA's data go back to 1880. You can copy the data from NASA's site, paste it to a spreadsheet and make calculations. Or take my word for it. If you take my word for it, the average of the decade ending with 2009 is the highest ten-year average since 1880. If 2009 is excluded (since it's not over yet), the ten years ending with 2007 were the hottest. The climate scientists are right, or were up through 2007, anyway.

But look at the graph.  It looks like temperatures might have peaked recently, maybe in 2005. In fact, the linear regression trend line of these data points is down since 2002. (If 2009 is excluded, the trend line is down since 2001.) The globe has been getting cooler for the last eight years. The climate deniers are right.

If you are on a long walk and have just gone over the highest point in elevation on your trek, your most recent steps will be at the highest elevation of your walk.  But once you've crested that peak, it is downhill from there. That's the idea. You could be at or near the highest point but still be going downhill.

The question is whether the recent down-trend in temperatures will last. The alarmists say it's a temporary cyclical thing (which was not included in their models), but the long-term trend is still upward due to man-caused emissions of greenhouse gases. The "deniers" say that whatever warming there was could very well be over since temperatures vary in natural cycles.

These data alone cannot tell us which hypothesis is correct.

A few things to remember:

  • The data have been adjusted in unknown ways. We have to take it on faith (a faith shaken by the released CRU e-mails) that the annual temperatures as presented in the graph above and in NASA's graphs represent reality.
  • Even if the data proved warming beyond a shadow of a doubt, such warming in itself does not prove anything man-caused.
  • Unexpected variations in temperatures have already caused climate scientists to discover natural influences (e.g., the Atlantic Multidecadal Oscillation) not really understood and not included in the models cited by the U.N.'s IPCC.
  • The temperature trend (linear regression trend) from 1880 through 2009, using NASA's data, is 0.57oC per century. And from 2002 through 2009, it is minus 0.50oC per century.

As I've said before, be wary of "glass half empty" reporting. Yes, recent years are the warmest on record, if you accept NASA's manipulated data. But recent years also indicate the warming has stopped, and there might even cooling, at least temporarily, based on that same data.

And even proving there is a warming trend does not prove it is man-caused.
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