Matthew Francis / Forbes – 2015-06-09 01:56:01
(June 4, 2015) — Politicians may dither and talking heads bloviate, but the scientific consensus is clear: climate change is real, humans are responsible, and its effects are already being felt around the world. At the same time, some details are in question, including how fast climate change is increasing and which specific effects we see are due to it as opposed to other sources.
That’s the context for a new paper in Science today from researchers at the National Oceanographic and Atmospheric Administration (NOAA, which is somewhat ironically pronounced “Noah”). Thomas Karl and colleagues took a second look at global surface temperatures — the ordinary temperatures we’re used to seeing on weather news or in our phone apps — and found the official numbers on rising temperatures are too low.
To put it another way: the consensus opinion is that we are currently in a global warming “hiatus”, but Karl and coauthors report instead that temperatures are climbing as fast as ever.
As if we didn’t have enough to worry about.
A new look at temperature data from around the world shows that the rate of climate change is still getting larger, contrary to the latest report by the IPCC.
[Credit: NOAA’s National Centers for Environmental Information]
Let’s back up and look at what this new paper says, and why it’s important. The most recent Intergovernmental Panel on Climate Change (IPCC) report is a huge, nearly unreadable document combining climate data from thousands of scientists around the world.
However, there’s a lot of vital information buried in the report-by-committee language, including the analysis of temperature data from the years 1998 through 2012. (The time it takes to analyze the data and put together these reports always means they’re a little behind the times, though three years isn’t a lot in the scheme of things either.)
The IPCC report showed that temperatures rose over that 15-year period, but at a dramatically slower rate than in previous decades. Since the causes of climate change haven’t diminished, this “hiatus” was puzzling to researchers.
Admittedly, 1998 was a weird year, marked by an especially large El Nino effect, which boosted average temperatures well past normal global warming trends. (That fact and the reported hiatus have been used dishonestly by those wishing to deny climate change is real, but they’re wrongity-wrong-wrong.) However, even taking the El Nino year into account, the temperature increases seemed to be between 1/3 to 1/2 the rate of the rest of the 20th century, leaving researchers looking at a number of possible explanations.
The new Science paper proposes a simpler explanation: maybe there are hidden assumptions in some of the temperature data. The technical term for this is “bias”, which is the language used in the paper; to a scientist, “bias” means a systematic skewing of numbers, rather than an unconscious political or social attitude. However, in either usage, bias is something to be examined and — if problematic — corrected.
In particular, researchers have noted a difference in temperature measurements on the ocean between those measured by ship and by buoys, and between old-style ship temperature measurements and newer methods.
New techniques correct for the differences between those measurements, producing more accurate temperature results. Similarly, climate scientists have gradually been improving their estimates of historical temperature data over land, especially for Arctic regions. Karl and colleagues reanalyzed the trends in the IPCC report using these improved estimation methods.
This extra work found no global warming hiatus: worldwide average temperatures are still rising at least as fast now as they were in the second half of the 20th century.
Tellingly, the improved estimates Karl and coauthors used don’t affect the IPCC calculation of climate change for the entire period of interest (1880 through today). In other words, the rate of climate change they show is pretty much identical to the IPCC report; the only thing they did is make the hiatus vanish.
Before anyone says it: this does not invalidate the entire IPCC report, nor does it in any way cast doubt on the general conclusions from scientists about climate change. After all, this Science paper reaffirms global temperature increase and shows it might be larger than the IPCC report says.
Additionally, the IPCC bases its conclusions on conservative estimates and the best consensus it can achieve among scientists who don’t always agree with each other, simply by nature of being a huge international collaboration.
Some of the methods presented in the new paper are reported in scholarly articles published after the IPCC report was assembled in 2013, so it might be some time before they are widely accepted.
In a sense, these new results change nothing: climate change is a big problem for us, whether the hiatus is real or an artifact of the data. However, every study like this that potentially corrects biases in our data brings us closer to a precise understanding of climate change — and how urgently we need to act to save lives.
Matthew Francis is a physicist, science writer, public speaker and educator. His website is BowlerHatScience.org.
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