Science writer and occasional climate commentator Matt Ridley has published a list of ten questions he feels need to be answered before he is convinced that ‘current climate policy makes sense.’ As the title of his essay is ‘A Lukewarmer’s Ten Tests’ I feel honor bound to at least look at them. It’s easy–Ridley’s a fine writer and his exposition is organized and clear.
The first question he wants answered is: “ I need persuading that the urban heat island effect has been fully purged from the surface temperature record. Satellites are showing less warming than the surface thermometers, and there is evidence that local warming of growing cities, and poor siting of thermometers, is still contaminating the global record.
I also need to be convinced that the adjustments made by those who compile the global temperature records are justified. Since 2008 alone, NASA has added about 0.1C of warming to the trend by unexplained “adjustments” to old records. It is not reassuring that one of the main surface temperature records is produced by an extremist prepared to get himself arrested (James Hansen)”
Much as I am hoping that Mr. Ridley brings some reason and clarity to this debate, as he did with his excellent book The Rational Optimist, I think he starts off poorly here.
What we measure to understand global warming is changes in the temperature not the beginning and end readouts of a thermometer. The Urban Heat Island effect is real. Time of observation for keeping records have changed. The physical location of measurement stations have changed.
All of this (and more) is well-known and well-discussed by scientists. Most recently, Richard Muller and his team tried to revisit this question–and to the best of my knowledge, improved on the understanding of these issues considerably. What they found was clear evidence that nobody is manipulating the figures to pump a little extra global warming in there for political purposes.
Not to say there are no errors. There are. And when scientists find errors in the data, they talk about them and introduce corrections into the data series. Our friends in the skeptic community notice immediately when those corrections push temperatures up–but corrections often adjust them downwards as well.
The central point is that the start and end point of a temperature reading is almost irrelevant to the exercise. If the measurement accurately captures the amount of change, for understanding climate change it doesn’t matter so much whether the change is from 11 to 12 or from 11.5 to 12.5. What matters is that the one degree change is accurately captured.
And we have pretty good evidence that, using correctly sized error bars and admitting the level of uncertainty, we are indeed capturing the change. And that it is not imaginary. And that it is not a political invention.
Steve Mosher (who worked with Muller on his ambitious temperature re-measurement project) and I wrote a book on Climategate a couple of years ago. Two of the central issues there involved temperature measurements. (The second involved tree trunks, not thermometers and is for another day…)
The first problem we found was in a 1990 paper published by Nature and written by Phil Jones (who later advised colleagues to delete emails). The paper was written to minimize the worries about UHI (the Urban Heat Island effect) and used temperature records from different countries to ‘show’ that UHI was vanishingly small.
But some of the stations he used didn’t have the right historical stability for the work he did–his colleague didn’t have the station histories right. This made his conclusions inaccurate. Which is sad, but happens in science.
Sadly, Jones didn’t issue a correction and his paper sat out there for years. It was famous and frequently cited as ‘proof’ that UHI was not a real issue. (This was actually what led to Climategate, through a rather complicated chain of events.)
It was only fifteen years later that Jones published a new paper showing a higher figure for UHI. He never issued a correction for his earlier paper, despite knowing it was wrong for more than a decade.
But even with his ‘mistake’ regarding UHI, it did not affect consideration of climate change overall. Even his new, higher calculations for UHI are not huge. Moreover, most of the earth’s surface is covered by water and UHI doesn’t affect oceans or lakes. And a surprisingly modest percentage of the land on this planet is subject to UHI–we don’t find much of it in either Antarctica or the Sahara.
So, Mr. Ridley–early mistakes caused us to underestimate the effects of the Urban Heat Island effect on temperatures of cities (and smaller population aggregations as well). It had an effect on the temperature record. Some scientists behaved poorly in regards to analysis of this issue.
But it did not mask the changes in temperature over time. And it wasn’t large enough to introduce a spurious signal that was mistaken for global warming.