What does 2013 being the 4th hottest year on record tell us about climate change?
- 23 Jan 2014, 14:00
- Roz Pidcock
On Tuesday, scientists released the latest
analysis of global temperatures - which shows 2013 tied
with 2003 for the fourth warmest year since 1880. But what can one
year's temperature data tell us about climate change? We asked
some climate scientists for their thoughts.
2013 in context
Each year, the United States National Oceanic and
Atmospheric Administration (NOAA) releases its analysis of global
temperature over the past year - and the official figures for 2013
are in. On Tuesday, a press
release accompanying the figures reported:
"The year 2013 ties with 2003
as the fourth warmest year globally since records began in 1880.
The annual global combined land and ocean surface temperature was
0.62 degrees Celsius above the 20th century average
Using a slightly different method, the US space
ranked 2013 as the seventh warmest on record, tied with
2009 and 2006.
The question of what a single year's temperature can
tell us about climate change pops up each year when the official
figures are released.
This time last year, we asked
Dr Gavin Schmidt, climate scientist at NASA GISS, for his
thoughts on 2012 being ranked the ninth warmest on record. Schmidt
"That 2012 is fifth, ninth, or
twenty-seventh is not really the point. Instead, it is the fact
that the long term trends and the decade-on-decade differences are
all up (as has been predicted for decades)."
And the same goes for this year. Rather than whether
one year was hotter than the last, scientists look at changes over
several decades to see how the climate is changing.
Long term warming
As NASA points out, the data for 2013 continues a long
term warming trend. The press release reads:
"With the exception of 1998,
the 10 warmest years in the 134-year record all have occurred since
2000, with 2010 and 2005 ranking as the warmest years on
2013 was the 4th warmest year on record since
1880, according to official NOAA data released on Tuesday. Source:
The important point, as
Professor Phil Jones from the Climatic Research Unit at the
University of East Anglia explained to us this time last year, is
that the world is warmer than it was a few decades ago.
"What matters is that
the 2000s were warmer than the 1990s and they were in turn warmer
than the 1980s etc back to the 1960s."
Or to put it a different way, 2013
was the 37th consecutive year that the
annual global temperature has been above the 20th century
average, according to
NOAA's new analysis.
Natural highs and lows
But why do we see differences in global
temperature from one year to the next? It's mainly down to natural
oscillations in ocean temperature, as Jones explained:
"Much of the
year-to-year variability of global temperature averages is caused
by whether we have an El Nino or La Nina or neither type (neutral)
occurring...1998 was exceptionally warm...because of the 1997/1998
El Nino event."
While 2013 was not the hottest year on record,
it fits into what scientists know about natural
variability. As the NASA press release
"[W]eather patterns always
will cause fluctuations in average temperatures from year to year
... Each successive year will not necessarily be warmer than the
year before, but with the current level of greenhouse gas
emissions, scientists expect each successive decade to be warmer
than the previous."
This is the reason measurements over long periods of
time are so important, adds Schmidt:
"While one year or one season
can be affected by random weather events, this analysis shows the
necessity for continued, long-term monitoring."
While scientists are cautious about interpreting
one year's worth of temperature data, together with highs in recent
years it fits in with scientists' understanding of climate change.
Ken Caldeira from the Carnegie Institution of
Washington, told us recently:
"Each hot year is
another piece of accumulating evidence. This accumulating mountain
of evidence has confirmed the science of climate change so that now
we have as much confidence in the basic climate science as we have
in the fundamental science of plate tectonics or biological