Did global warming stop 15 years ago?

15th Oct 2012

Anyone hoping for (or perhaps dreading) more indian summers in the future may have been startled to read this weekend that global warming stopped happening 15 years ago.

Mail on Sunday: "Global warming stopped 16 years ago, reveals Met Office report quietly released... and here is the chart to prove it"


Star: "Global warming 'ended 15 years ago'"

The chart that proves the theory, according to the Mail on Sunday, is this:

The Met Office was cited as the source of the figures by all the reports, however the weather service were quick to point out yesterday that the conclusions being drawn didn't come from them. In fact, the Met Office claimed the Mail on Sunday were reporting "misleading information".

The Met Office clear up a small misunderstanding straight away:

"the Met Office has not issued a report on this issue. We can only assume the article is referring to the completion of work to update the HadCRUT4 global temperature dataset compiled by ourselves and the University of East Anglia's Climate Research Unit."

The actual figures recorded by HadCRUT4 seem to roughly match those used in the Mail on Sunday's graph. At this point it's worth looking at the figures in a broader context:

So does the Mail on Sunday have a point? There is certainly a noticeable flatlining looking just at the most recent decade, but the Met Office's key argument is that it simply isn't possible to look at such a narrow window:

"As we've stressed before, choosing a starting or end point on short-term scales can be very misleading. Climate change can only be detected from multi-decadal timescales due to the inherent variability in the climate system. If you use a longer period from HadCRUT4 the trend looks very different."

As is apparent in the graph, periods of steady or reduced warming aren't uncommon:

"Over the last 140 years global surface temperatures have risen by about 0.8ºC. However, within this record there have been several periods lasting a decade or more during which temperatures have risen very slowly or cooled. The current period of reduced warming is not unprecedented and 15 year long periods are not unusual."

The Mail on Sunday goes on to report that future projections of global temperature rises (such as the Intergovernmental panel on climate change's projected rise of 0.2 degrees celsius per decade) could be flawed given the findings for the last decade. 

While Full Fact can't vouch for the veracity of a method of measuring global warming, it's clearly not possible to say for certain whether this is a blip or the start of a prolonged period of flatlining or even falling temperatures.

What is even more clear is that the reports haven't heeded the warning from the Met Office that these figures need to be understood in a wider context than just one decade, given the large variations in the annual measurements.

This data in isolation isn't anywhere near sufficient evidence to prove that global warming stopped 15 years ago. In other words, you can't look through a window and expect to see the whole landscape.