Tuesday 7th April 12:53 pm
Global warming ‘pause’ cherry picks the facts
Tuesday 23rd September 2014 2:32 pm
I’m back, with the controversial topic of the so-called ‘pause’ in global warming. Some parts of the news media incorrectly claim that the climate is no longer warming, but is actually cooling. They get to this conclusion by everything from cherry-picking the data, all the way up to telling big fat fibs.
By way of complete contrast, early in 2014, the two most august scientific institutions in the United Kingdom and the USA issued a joint report entitled Climate Change: Evidence And Causes.
These two bodies, the Royal Society and the US National Academy of Sciences, warned that “climate change is more certain than ever.”
Their accurate data shows that the climate, as measured by surface temperature of air and water, is still getting hotter.
But this average global temperature is not the only measure of climate change. There are other indicators that inform us about the state of the global climate.
They include the volume of the Arctic sea ice (which has been shrinking), snow in the Northern Hemisphere (also shrinking) and glaciers (more shrinking).
In the oceans we measure the sea level (which has been rising as an accelerating rate), the amount of heat stored in the ocean (which has been increasing), the sea surface temperature (the last decade is the warmest), and the air temperature over the ocean (also going up).
In the atmosphere, we measure specific humidity (which has been climbing along with the rising temperatures) and temperatures in the lower troposphere, which is the bottom 17 to 20 kilometres of the atmosphere (also rising).
Finally we have air temperature immediately over the land. It turns out that the first decade of the 21st century is the hottest decade since we began thermometer-based records in the 1850s, and yes, each of the last four decades has been hotter than the previous one. This astonishing trend of air temperature heating despite the fact that only a few per cent of all of the heat from global warming goes into heating the air — 93 per cent of the heat goes into the ocean.
There are very many other lines of evidence of global warming. Ice loss in Greenland and the Antarctic is accelerating. Both high altitude jet streams and the tropical weather bands are creeping from the equator to the poles at about five kilometers a year — about 500 kilometres per century.
Worldwide, on average, the seasons are shifting their timing, and the growing periods are changing. Plants are moving to higher and cooler altitudes, and they’re now blooming earlier than at any time in the last 240 years.
These changes are all directly due to the huge amount of global warming energy being dumped into the environment (roughly the energy output of 400,000 Hiroshima-size bombs, every day).
With more energy in the climate system, the ‘pendulum’ of temperature now swings more vigorously. So another result of global warming is that temperature extremes are more frequent. The climate models agree with the observations — there are twice as many record hot days as there are record cold days.
So with all this evidence of continued heating, what exactly is this supposed ‘pause’?
Just have a look at the global climate temperature record from 1970 onwards. It’s climbing upwards, even though it’s bumpy — which is reasonable, considering how many factors can influence the global temperature in the shorter time.
There’s an upward bump in 1998 from the biggest El Niño for a century, and a downward bump half-a-decade earlier from the Mount Pinatubo volcanic eruption. But overall, on average, the temperature trend is upward at a fairly constant rate until around 2005. From then on, the temperature keeps rising, but at a lesser rate.
So the ‘pause’ is a slowing in the rate of increase of heating. The temperature is still clearly rising after 2005 — after all, 2010 stands as the hottest year on record. But the temperature is rising at a slower rate.
How do the climate scientists interpret this?
First, this nine-year window of time (2005 till the present) is a very short time. The ‘noise’ in the global mean temperature is so large that you really need at least a 17-year window to clearly see a trend. This background ‘noise’ includes effects such as El Niño, La Niña, volcanoes, solar variability and so on.
Under normal circumstances, the climate scientists would simply say that nine years is too short a time, because it’s not the statistically significant 17 years.
Second, it turns out that the surface temperature record excludes the Arctic — but this is the fastest warming region on the planet. This has biased the data.
And third, there is a whole bunch of other factors, which I’ll discuss, next time …
This blog first appeared on Dr Karl's Great Moments in Science
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