Transcript 3.4 Observations Most figures are from latest IPCC report (2013) unless otherwise

3.4 Observations
Most figures are from latest IPCC
report (2013) unless otherwise
stated – see:
http://www.ipcc.ch/report/ar5/wg1/
#.Un_txCQp2qA
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3.4 Observations
Need to consider:
• Instrumental climate record of the last century
or so
• Recent changes in greenhouse gases and
other quantities
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Important Questions Concerning the Climate Record
• How much is the world warming?
• Is the recent warming unusual?
• How rapidly is climate changing compared to
earlier changes?
• Have precipitation and atmospheric moisture
changed?
• Are atmospheric/oceanic circulations
changing?
• Has climate variability (e.g., extremes)
changed?
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Observed Climate Variables
• Temperature (global mean, regional, diurnal
range, upper air...)
• Precipitation, humidity, cloud cover
• Snow cover
• Sea-ice thickness and extent
• Natural modes (El Nino, North Atlantic
Oscillation, Atlantic Multidecadal Oscillation)
• Climate extremes
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Use of ‘Anomalies’
• Anomalies are changes relative to some
particular reference period used to
emphasise positive and negative excursions
around a long-term mean
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The Keeling Curve (named after Dr. Charles Keeling, Scripps)
Plants releasing
CO2
Plants
absorbing
CO2
398 ± 3 ppm
316 ± 2 ppm
Has CO2 been this high over the past 800,000 years?
Neither CO2 nor CH4 have been this high in the past 800,000 years
300
Previous CO2 maximum ~300 ppm
Previous CH4 maximum ~780 ppb
Detection of our increasing carbon emissions –
one of the most important scientific
breakthroughs of the past 150 years
Surface Temperature Changes
Given our knowledge of the greenhouse effect
we would expect that any increase in
greenhouse gases would cause a warming of
the earth’s surface.
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Recent Warming
(IPCC 5th Assessment, 2013)
• Observed global mean
combined land and ocean
surface temperature
anomalies, from 1850 to 2012
from three data sets
• Top panel: annual mean
values
• Bottom panel: decadal mean
values including the estimate
of uncertainty for one dataset
(black). Anomalies are relative
to the mean of 1961−1990.
• Each of the last three decades
has been successively warmer
at the Earth’s surface than any
preceding decade since 1850
Trends
http://www.youtube.com/watch?v=e0vj-0imOLw
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Land-Surface Air Temperature (LSAT)
• LSAT temperatures have
increased from .08 to
.27°C/decade since 1880,
depending on how you
determine the fit
• This reanalysis includes four
different data sets, using
different techniques
• Careful study to address
concerns about station sites,
data distribution, have been
taken into account
• In summary, it is certain that
globally averaged LSAT has
risen since the late 19th century,
and that this warming has been
particularly marked since the
1970s.
Global annual average land-surface
air temperature (LSAT) anomalies
relative to 1961-1990 climatology
from four different datasets
Changes in Climate “Normals”
from 1971-2000 to 1981-2010 Averages NOAA Data\
Climate “Normals” are 30-year averages of NOAA climatological data
(http://www.ncdc.noaa.gov/oa/climate/normals/usnormals.html)
Sea Surface Temperatures (SSTs)
• Measurements of sea
surface temperature are
available from buckets,
engine room intake, hull
contact sensors, moored
and drifting buoys, and
satellites
• Careful data analysis
needed (measurement
biases and validation)
• Nonetheless, certain that
global average sea
surface temperatures
(SSTs) have increased
since the 1950s, as well
as since the beginning of
the 20th century
Global average SST relative to 19611990 climatology from gridded
(interpolated) data sets. Interpolated
(solid), non-interpolated (dashed).
Global Temperature (Land and Sea)
• All 10 of the warmest
years in the record have
occurred since 1997
• 2010 and 2005 tied for
warmest in all three data
sets
• Global mean trends are
significant for all data sets
• HadCRUT4 – warming
from 1850-1900 (earlyindustrial) to 1986-2005
average is 0.61°C
±0.06°C (90%
confidence)
Decadal global mean surface temperature
(GMST) anomalies
Spatial Pattern of Surface Temperature Changes
Trends in Global Mean Surface Temperature
(GMST) from the three datasets of Figure
2.20 for 1901–2012. White areas indicate
incomplete or missing data. Trends have
been calculated only for those grid boxes
with greater than 70% complete records and
more than 20% data availability in first and
last decile of the period.
Black plus signs (+) indicate grid boxes
where trends are significant (i.e., a trend of
zero lies outside the 90% confidence
interval).
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Spatial Pattern of Surface Temperature Changes
Trends in Global Mean Surface
Temperature (GMST) from NCDC
MLOST for three non-consectutive
shorter periods (1911–1940; 1951–
1980; 1981–2012). White areas
indicate incomplete or missing data.
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Summary of Surface Temperature Changes
•
•
•
•
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It is certain that globally averaged near surface temperatures have
increased since the late 19th century.
Each of the past three decades has been warmer than all the previous
decades in the instrumental record, and the decade of the 2000s has
been the warmest.
The global combined land and ocean temperature data show an
increase of about 0.89°C (0.69°C–1.08°C) over the period 1901–
2012 and about 0.72°C (0.49°C–0.89°C) over the period 1951–
2012 when described by a linear trend.
Despite the robust multidecadal timescale warming, there exists
substantial multi-annual variability in the rate of warming with several
periods exhibiting almost no linear trend (including the warming hiatus
since 1998).
Upper Air Temperatures
• Weather balloons (radiosondes)
– T at discrete levels
– Difficulties with changes in instruments
• Satellite (Microwave Sounding Unit – MSU and stratospheric
Sounding Unit - SSU) since 1979
– T over broad regions
– Problems with orbit drift, calibration, etc. -> spurious T trends
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Upper Air Temperatures
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Upper Air Temperatures - Summary
•
•
•
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In summary, based upon multiple independent analyses of
measurements from radiosondes and satellite sensors it is virtually
certain that globally the troposphere has warmed and the stratosphere
has cooled since the mid-20th century.
Despite unanimous agreement on the sign of the trends, substantial
disagreement exists among available estimates as to the rate of
temperature changes, particularly outside the Northern Hemisphere
extra-tropical troposphere, which has been well sampled by
radiosondes.
Hence there is only medium confidence in the rate of change and its
vertical structure in the Northern Hemisphere extra-tropical troposphere
and low confidence elsewhere.
Changes in the Hydrological Cycle: Precipitation
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Changes in the Hydrological Cycle: Precipitation
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Changes in the Hydrological Cycle: Precipitation
In summary, the land areas of the mid-latitudes of the NH show a
likely overall increase in precipitation (medium confidence since
1901, but high confidence after 1951).
Since 1951, precipitation in the high latitudes of the NH also
shows increases, but confidence is low for the changes in this
region.
There is evidence for increased precipitation in the mid-latitudes
of the SH since 1901 (medium confidence). It is likely there was an
abrupt decline in SH mid-latitude precipitation in the early 2000s
consistent with enhanced drying that has very recently recovered.
Precipitation in the tropical land areas has increased (medium
confidence) over the last decade, reversing the drying trend that
occurred from the mid-1970s to mid-1990s reported in AR4.
Consequently, there is little evidence for longer term changes in
tropical precipitation over land.
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Changes in the Hydrological Cycle: Specific Humidity
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Changes in the Hydrological Cycle: Total Column Water Vapor
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Changes in the Hydrological Cycle: Total Column Water Vapor
In summary, radiosonde, GPS and satellite observations
of tropospheric water vapour indicate very likely
increases at near global scales since the 1970s
occurring at a rate that is generally consistent with the
Clausius-Clapeyron relation (about 7% °C–1) and the
observed increase in atmospheric temperature.
Significant trends in tropospheric relative humidity at
large spatial scales have not been observed, with the
exception of near-surface air over land where relative
humidity has decreased in recent years.
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Changes in the Cryosphere
• Snow cover
• Sea-ice extent
• Mountain glaciers
- Average Arctic temperatures have increased
at almost twice the global average rate in
past 100 years.
WMO International Polar Year 2007-2008
www.ipy.org
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Observed Northern Hemisphere Snow Cover
TOP
• Annual snow-cover
extent decreased by
10% since 1966
• Mostly accounted for
by spring/summer
since 1980s
BOTTOM
• Annual snow cover
anomalies correlate
with T (dashed line)
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Observed Northern Hemisphere Sea-Ice Extent
http://www.nasa.gov/content/goddard/arctic
-sea-ice-minimum-in-2013-is-sixth-loweston-record/#.UoA_0iQp2qB
Observed Northern Hemisphere Sea-Ice Extent
Summer minimum Arctic sea ice extent
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If trend continues Arctic will be ice-free by ~2050
Observed Northern Hemisphere Sea-Ice Extent
NASA Goddard Space Flight Center (orange line shows average minimum
ice extent (for 1979-2010 period). 2012 has lowest sea ice extent in more
than 30 years.
Observations of glacier retreat
Glacier Espejo, Pico Bolivar (5002 m)
Venezuela
< 2 km2 of ice left
in Venezuela
1910
1988
2008
Jahn [1931]; Schubert [1992, 1999]
Observed Mountain Glacier Length
• 169 glacier length records
• Glacier retreat is worldwide
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Update from latest IPCC report (2013)
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Summary of Observed Cryospheric Changes
• Consistency of cryospheric changes and
temperature changes
• NH snow cover correlates well with spring
temperature changes
• Reduced sea-ice extent consistent with
increases in spring temperatures
• Small changes in Arctic winter ice, despite
large changes in winter T
• Major retreat of glaciers consistent with 20thcentury T changes
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How much has sea level gone up in the 20th century?
Red: reconstructed
(+ 90% confidence
intervals)
Blue: coastal tide
gauge measurements
Black: satellite
altimetry
Current global sea level rise: 3.5 mm/yr
IPCC, AR4, WG1, 2007;
BAMS, Aug. 2009
Sea-level Rise
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What places will be most affected by
sea-level rise by 2050 ?
Extreme:> 1 million people displaced
High: > 50,000 people displaced
Medium > 5,000 people displaced
IPCC, AR4, WG2, 2007
Atmospheric/Oceanic Circulations (El Nino)
• Occurrence of
strong El Ninos
may be higher
since 1980s
• But significance
is low due to
strong contribtion
of natural
variability
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Atmospheric/Oceanic Circulations (NAO)
• North Atlantic
Oscillation (NAO) is a
measure of circulation
patterns in the NH
• Positive index implies
warmer Europe
• Greater occurrence of
positive indices since
1980s
• NAO trending towards
negative values
recently.
• Difficult to separate
natural variability and
long-term change
http://www.cgd.ucar.edu/cas/jhurrell/indices.html
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Climate Extremes (extreme temperatures)
10th percentile
Trends in days/decade 19512003 (relative to 1961-1990).
90th percentile
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Climate Extremes (heatwaves)
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Climate Extremes (precipitation)
Contribution from ‘very wet’ days
(95th precentile) to total decadal
precipitation.
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Precipitation
• Increases in amounts of very heavy precipitation (1958-2007)
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The map shows percent increases in the amount falling in very heavy
precipitation events (defined as the heaviest 1 percent of all daily events)
from 1958 to 2007 for each region. There are clear trends toward more very
heavy precipitation for the nation as a whole, and particularly
in the Northeast and Midwest (updated from Groissman et al,2004)
Next Section
• Next lecture will be concerned with modeling
results
• Key for interpreting the causes of climate
change
• Key for making projections
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