In this guest blog post, originally published in Carbon Brief, Berkeley Earth Research Scientist Dr. Zeke Hausfather fact checks claims that global warming has ‘paused’ over the last eight years. Dr. Hausfather’s previous rebuttal of similar claims, originally published in 2015, is available here.
A decade ago, many in the climate community were fixated on an apparent “pause” in rising global surface temperatures. So many studies were published on the so-called “hiatus” that scientists joked that the journal Nature Climate Change should be renamed Nature Hiatus.
However, after a decade or so of slower-than-average warming, rapid temperature rise returned in 2015-16 and global temperatures have since remained quite warm. The last eight years are the warmest eight years since records began in the mid-1800s.
While the hiatus debate generated a lot of useful research on short-term temperature variability, it is clear now that it was a small variation on a relentlessly upward trend in temperatures.
But nearly a decade later, talk of a “pause” has re-emerged among climate sceptics, with columnist Melanie Phillips claiming in the Times this week that, “contrary to the dogma which holds that a rise in carbon dioxide inescapably heats up the atmosphere, global temperature has embarrassingly flatlined for more than seven years even as CO2 levels have risen”.
This falsehood appears to be sourced from a blog post by long-time climate sceptic Christopher Monckton, which claims to highlight the lack of a trend in global temperatures over the past eight years.
In a rebuttal letter to the Times, Prof Richard Betts – head of climate impacts research at the Met Office Hadley Centre and University of Exeter – points out that it is “fully expected that there will be peaks of particularly high temperatures followed by a few less hot years before the next new record year”.
In fact, the last eight years have been unusually warm – even warmer than expected given the long-term rate of temperature increases – with global temperatures exceeding 1.2C above pre-industrial levels. The temperature record is replete with short-term periods of slower or more rapid warming than average, driven by natural variability on top of the warming from human emissions of CO2 and other greenhouse gases.
There is no evidence that the past eight years were in any way unusual and the hype around – and obvious end of – the prior “pause” should provide a cautionary tale about overinterpreting year-to-year variability today.
Consistent long-term warming
As with the previous hiatus, drawing the conclusion that warming has “flatlined” relies heavily on looking at data over a short period in isolation.
The figure below shows the annual global surface temperature since 2015 from the Copernicus/ERA5 dataset, along with Carbon Brief’s estimate of likely 2022 temperatures based on data from the first six months of the year (central estimate in red, with an uncertainty range shown by the black bar). The blue dashed line shows the linear trend – the rate of change – over the 2015 to 2022 period, which is effectively flat.
However, looking at these eight years in isolation ignores the larger context and provides a misleading impression that global warming has “stopped”.
Indeed, looking at a slightly different eight-year period – 2011 to 2018 rather than 2015 to 2022 – would offer the opposite conclusion, namely that global warming had massively accelerated to a rate of 5.6C per century, as shown by the red dashed line in the figure below.
In reality, both of these are acts of “cherry-picking” – namely, overemphasising short-term variability. Temperatures were a little cooler than would be predicted by the long-term warming trend prior to the 2015-16 super El Niño event, while much of the eight years since that event have been warmer than the trend.
Click here to continue reading on Carbon Brief…