Why the Met Office’s revised forecast still doesn’t show global warming has stopped
- 09 Jan 2013, 10:00
- Roz Pidcock
There have been claims in the papers today and yesterday that
new figures from the Met Office show global warming is "at a
standstill" - and that this is set to continue for the next few
years. But while the new figures do suggest the recent slower rate
of temperature rise may continue for a few years, this doesn't mean
that global warming has stopped - as a statement released by the
Met Office underlines.
Telegraph's article is based on the Met Office's
latest temperature forecast, issued at the end of last year.
The new forecast says that by the period 2013 to 2017, global
temperatures will have risen to about 0.43 degrees above the long
This is 0.11 degrees lower than the Met Office's last round of predictions
for temperature rise over roughly the same period, released in
It appears the Telegraph story was prompted by a blog post on
climate skeptic campaign group the
Global Warming Policy Foundation (GWPF)'s website, which
"[T]his is a forecast of no increase in global temperatures above
The BBC covered the revised forecast on yesterday's Today
programme. Both the
Times and the
Daily Mail swiftly took up the story, taking a similar line to
the Telegraph piece.
All the attention prompted the Met Office to issue a
statement pointing out that a slowdown in temperature rise does
not mean global warming has stopped - a misconception that we've
written about before.
What does the new forecast say?
The Met Office predicts global temperature between 2013 and 2017
is most likely to be about 0.43 degrees Celsius higher than the
long term average, measured between 1971 and 2000. The prediction
includes some room for variation - temperatures could be as much as
0.59 degrees above average, or as little as 0.28 degrees above the
Global temperature rise above the long term average.
Observations are in black and the revised Met Office forecast is in
Met Office Hadley Centre
Temperature projections are lower in the new forecast than in
the Met Office's
previous forecast, issued in 2007. The old forecast predicted
that by the period 2012 to 2016, global temperature would most
likely reach about 0.54 degrees above the long term average with a
likely range of 0.36 to 0.72 degrees. So the new projection is
about 0.1 degrees Celsius cooler.
To put the new forecast in context with current global
temperatures, the warmest 12-month period in the Met Office Hadley
Centre global temperature record occured in 1998, with a global
temperature of 0.40 degrees above the long term average. This is
0.03 degrees lower than the best estimate for temperature rise by
2017 given in the
So why has the Met Office prediction changed? These projections
are based on computer modelling of the climate, and the revised
forecast is based on the Met Office's new model,
HadGem3, which has been updated.
The main difference, according to the Met Office, is the new
model better represents recent natural fluctuations in the climate
system, such as ocean circulation patterns. Such natural climate
fluctuations can significantly affect global temperatures from one
year to the next, and scientists are working to include them more
completely in computer models. The Met Office said in its
"The Met Office is actively researching potential causes of the
recent slowdown in global warming, including natural variability,
the recent deep solar minimum, the influence of forcing from
short-lived species, such as sulphate aerosol emissions, and the
climate response to these forcings."
Global warming hasn't stopped
The Telegraph piece claims that since the projected temperature
for 2013 to 2017 is only "a little higher" than the warmest year so
far in 1998 this means:
"global warming will have stalled in the
intervening two-decade period".
But as we've written before, the fact that temperatures are
currently rising slowly compared to the rapid warming from the
1970s until the late 1990s doesn't mean
global warming has stopped, or stalled. Rather, natural
fluctuations in the climate system are currently having a combined
cooling effect on atmospheric temperatures that's damping the full
extent of human-caused temperature rise - as the Met Office
explained in a response
to a similar claim by journalist David Rose last year.
The fact that natural variability can affect global temperature
from year to year is why
scientists are reluctant to draw general conclusions from less
than several decades worth of data. The Met Office's previous rebuttal
to David Rose explains further:
"Looking at successive decades over this
period, each decade was warmer than the previous - so the 1990s
were warmer than the 1980s, and the 2000s were warmer than both.
Eight of the top ten warmest years have occurred in the last
Signal or noise?
As Dr Peter Stott, Head of Climate Monitoring and Attribution at
the Met Office, said last year, such periods of slower
warming are not unprecedented in the temperature record, a point
that the Telegraph notes in its piece. As Stott put it:
"This variability in global temperatures
is not unusual, with several periods lasting a decade or more with
little or no warming since the instrumental record began".
Natural variability is noise around the long term trend in
global temperatures - which
are increasing. As the Met Office said yesterday, the new
forecasts "have not changed the overall warming signal of about
0.75 °C since 1900."
Meanwhile, the atmosphere is only one part of the climate. The
global ocean has been warming considerably during the period that
the rise in atmospheric temperatures has slowed, which is causing
level to rise substantially. The fact that ice sheets
are melting in both the Arctic and the Antarctic is another
stark indicator of global warming.
As the Telegraph notes with another quote from Stott, the
current period of slower warming is likely to reverse at some point
soon, which means that "global warming could speed up again at any
time". So suggesting that global warming has stopped further up in
the text is pretty misleading. This all demonstrates why we need to
look at at the full picture when considering the likely course of
climate change, not short lived events predicted over just a few
Updated 9th Jan 12:25pm
A sentence in the Met Office's
revised global temperature forecast reads
"The warmest year in the 160-year Met Office Hadley
Centre global temperature record in 1998, with a temperature of
0.40°C above long-term average". This was quoted by several
We queried this with the Met Office, as according to
separate Met Office statement released in
December last year, the latest HadCrut4 temperature dataset puts
2010 as the warmest year, followed by 2005, then 1998.
The Met Office told us that the 0.40 degrees figure is
"based on a 12-month period which isn't synchronised
with the calendar year - in which case 1998 is the warmest on
record". But they do allow that this isn't particularly clear, and
the reference is apparently going to be updated to be in line with
the HadCRUT4 records.
It's worth noting that the temperature averages in the 2013
Met Office annual forecast and the figures in the revised decadal
forecast are comparisons with different long term averages (1961 to
1990 and 1971 to 2000, respectively) - which adds an extra level of
complication to comparisons.