Transcript Climate change: an update

Climate change: an update
Recent developments in global warming
Philip Allan Publishers © 2015
Carbon dioxide levels rise
• In 2015 carbon dioxide concentrations
passed the 400 parts per million level.
• Atmospheric carbon dioxide levels are 43%
higher than the pre-industrial level of
280ppm.
• Notice on the graph that the rate of rise is
increasing.
• Many scientists consider 450 ppm to be
‘dangerous’ in terms of future global
warming.
• On current trends, this level is likely to be
reached in the year 2039.
Carbon dioxide levels have been
directly and continuously recorded on
Hawaii since 1958
Philip Allan Publishers © 2015
IPCC Assessment
Report 5
• Latest IPCC report published 2013/14
IPCC assessment report
projections
AR1
1990
+3C by 2100
AR2
1995
+2C by 2100
AR3
2001
+1.4 to 5.8°C by
2100
• The range of projections has narrowed (as
scientific understanding improves and models
get better)
AR4
2007
+1.1 to 6.4°C by
2100
• Sea-level rise projections by 2100 are higher
in AR5 than in AR4:
AR5
2013
+0.5 to 4.9°C by
2100
• ‘Incontrovertible evidence’ and ‘virtually
certain’ human activity is the main driver of
climate change
• 99% sure vs 90% sure in Assessment Report
4 (AR4)
• The most likely rise by 2100 is 2–3C
• 18–59 cm in AR4
• 29–82 cm in AR5 in 2013
A ‘pause’ in warming?
• There has been a widely reported ‘pause’ in global warming.
• Since about 2000 there has been very little warming on land (graph) or in the oceans as a
whole
• In the upper levels of the ocean there has been warming, but much slower than 1990–
2000
• This has been seized upon by climate sceptics as evidence that global warming is not
happening.
• The graph, from NOAA in the USA, shows the ‘pause’ in
a little more detail.
• A strong warming trend, especially from 1990, ended in
about 2000.
• As the blue trend line shows, there have been ‘pauses’
in the past.
• The most recent one is longer.
• All of the 10 warmest recorded years have occurred
since 1998:
Year
Global (anomaly C from 1900 to 2000)
2014
0.69
2010
0.66
2005
0.65
1998
0.63
2003
0.62
2013
0.62
2002
0.61
2006
0.60
2009
0.60
2007
0.59
The cause of the pause?
• Lots of potential explanations
• All involve either a decrease in
incoming solar radiation or a
redistribution of ‘heat’ away from the
surface
• The Met Office has estimated that
sun-spot cycle changes could account
for up to a third of the ‘pause’.
• They cannot account for all of it.
• The most likely candidate is cyclical
changes in ocean currents which are
removing some heat from the
atmosphere into the ocean depths.
• These include El Niño/La Niña in the
Pacific, but also the AMO (Atlantic
Multi-decadal Oscillation) in the North
Atlantic and the Pacific Decadal
Oscillation (PDO).
• These long-term changes to ocean
circulation are poorly understood.
Cause
Evidence
Increase in volcanic
activity since 2000?
No evidence of this
since 2000
Increase in sulphur
dioxide/soot
pollution?
Some evidence, but
also that this peaked
around 2005 so the
effect is likely small
Reduction in solar
output?
Strong evidence of a
‘weaker’ than normal
sun i.e. weaker sun
spot cycles since 2000
Although the process is difficult to
understand, ocean currents do affect global
temperatures.
1998, the third warmest year on record, was
a powerful El Niño year, as was 2010.
2008 and 2011, both quite ‘cool’, were La
Niña years.
Arctic sea ice
• The Arctic sea-ice minimum occurs in
September each year.
• 2014 was the 6th lowest extent recorded.
• On average Arctic sea extent is
2–3 million km2 less than in the late
1970s.
• Only land-based ice melt affects sea
level.
• Ice extent on land and sea affects surface
albedo – which in turns leads to feedback
warming.
• Some evidence of a pattern, i.e. a major
melt year, followed by a partial recovery,
then another downward step
Greenland ice sheet
• The Greenland ice sheet
continues to melt in the summer
months above long-term average
rates.
• The map shows that in 2014,
some areas experienced surface
melting of 100+ days.
• On some days in 2014, close to
40% of the Greenland ice surface
was melting (graph)
• Significant melting is happening
early, and lasting later in the year
compared to the 1980–2010
average.
2015: a critical year
• Passing 400 ppm of carbon dioxide in the
atmosphere in 2015 will be a significant
milestone
• In Nov–Dec 2015 the latest United Nations
Climate Change Conference will take place
in Paris.
• The conference aims to reduce emissions
to limit the global temperature increase to
2°C above pre-industrial levels.
• The conference objective is to achieve a
legally binding and universal agreement on
climate, from all the nations of the world.
• This agreement would go beyond the 1997
Kyoto Protocol and involve all countries, not
only developed ones.
Philip Allan Publishers © 2015
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