The Discovery of Global Warming…
Plass
Revelle
Arrhenius
Callendar
Suess
What is the current average air temperature?
Climatologists combine short-term weather records into long-term periods (typically
30 years) when they analyze climate, including global averages.
Between 1961 and 1990, the annual average air temperature for the globe was
around 57.2°F (14.0°C), according to the World Meteorological Organization.
In 2013, the global air temperature was about 1.12°F (0.62°C) above the long-term
average (13.9°C or 57.0 °F) for the 20th century, according to NOAA's National
Climatic Data Center.
• The year 2013 tied with 2003 as the
fourth warmest year globally since
records began in 1880 and marks the
37th consecutive year (since 1976) that
the annual temperature was above the
long-term average.
• 9 of the 10 warmest years on record
have occured during the 21st century.
Only one year during the 20th century—
1998—was warmer than 2013.
https://www2.ucar.edu/climate/faq/what-average-global-temperature-now
According to the IPCC AR5: From 1880 to 2012, the average global
air temperature increased by 0.85°C
http://www.ncdc.noaa.gov/cag/time-series/global
What is the current average sea surface temperature?
Sea surface temperature increased over the 20th century and continues to rise. From 1901
through 2013, temperatures rose at an average rate of 0.13°F per decade.
Sea surface temperatures have been higher during the past three decades than at any other
time since reliable observations began in 1880.
Increases in sea surface temperature have largely occurred over two key periods: between
1910 and 1940, and from about 1970 to the present. Sea surface temperatures appear to
have cooled between 1880 and 1910.
Changes in sea surface temperature vary regionally. While most parts of the world’s oceans
have seen temperatures rise, a few areas have actually experienced cooling—for example,
parts of the North Atlantic
What is the current CO2 level in the atmosphere?
May 2014:
May 2013:
401.85 ppm
399.76 ppm
http://www.esrl.noaa.gov/gmd/ccgg/trends/
Changes in atmospheric CO2 levels over the past 1 My
Current atmospheric CO2 are at greater levels than seen over the last 800,000 years.
http://www.esrl.noaa.gov/gmd/ccgg/trends/history.html
Oceanic (dissolved) CO2 and pH levels
http://www.epa.gov/climatechange/pdfs/print_acidity-2014.pdf
Similar to atmospheric CO2 levels, pH levels are already more extreme than those
experienced by the oceans over the past 800 Ky. By the end of the 21st century,
the projected decline in seawater pH is expected to be three times larger than any
change in pH observed as the Earth’s climate has oscillated between glacial and
interglacial periods.
IPCC AR5: ”The pH of seawater has decreased by 0.1 since the beginning of the industrial era,
corresponding to a 26% increase in hydrogen ion concentration. … It is virtually certain that the
increased storage of carbon by the ocean will increase acidification in the future, continuing the
observed trends of the past decades. … Estimates of future atmospheric and oceanic carbon
dioxide concentrations indicate that, by the end of this century, the average surface ocean pH
could be lower than it has been for more than 50 million years”.
Glacial–interglacial variability in surface water pH (filled blue symbols, note the reversed
axis), superimposed on atmospheric CO2 concentration during the last 800,000 years
(magenta curve) (Pelejero 2010). http://dx.doi.org/10.1016/j.tree.2010.02.002
Changes in Aragonite Saturation
http://www.epa.gov/climatechange/science/indicators/oceans/acidity.html
How much has GLOBAL sea level gone up since industrialization?
From 1901 to 2010, the global average sea level rose by 19 cm as oceans expanded due
to warming and ice melted. The Arctic’s sea ice extent has shrunk in every successive
decade since 1979, with 1.07 million km² of ice loss every decade (IPCC AR5)
http://www.climatechange2013.org/images/report/WG1AR5_Chapter13_FINAL.pdf
How much has GLOBAL sea level gone up since
last ice age?
http://www.giss.nasa.gov/research/briefs/gornitz_09/
Where’s the water locked up?
http://pubs.usgs.gov/fs/2005/3055/
Should we be warming or cooling at present?
How can the radiation balance of Earth change?
1) by changing the incoming solar radiation (e.g., by changes in Earth’s orbit or in the Sun
itself); Milankovitch/Solar Physics
2) by changing the fraction of solar radiation that is reflected (called ‘albedo’; e.g., by
changes in cloud cover, atmospheric particles or vegetation); and
3) by altering the longwave radiation from Earth back towards space (e.g., by changing
greenhouse gas concentrations).
If not 3, then has to be 1 and/or 2 above!
Milankovitch Summary…
Time scales of tens to hundreds of thousands of years, the "astronomical theory" of climate
change holds that changes in the geometry of the Earth's orbit relative to the Sun bring about
subtle changes in the distribution of solar radiation at the Earth's surface that may drive slow,
but significant, intermediate-term changes in climate.
Climate modeling experiments suggest astronomical factors should lead to a slow cooling
of the climate since about 6,000 YBP (at a rate of cooling of between 0.01 and 0.04 degrees C
per century). These are in remarkable agreement with the observed cooling (about 0.02
degrees C per century) from AD 1000 through the mid 19th century.
This long-term cooling trend undergoes a dramatic reversal over the course of the 20th
century.
The 20th century warming trend appears to be that much more anomalous when viewed in
the context of the natural, long-term climate variability of the last millennium, and is therefore
again unlikely to be due to natural factors alone.
Extended reconstructions (for the past 11.3 Ky) indicate that
the current global temperatures are warmer than during 75% of
the Holocene and that IPCC projections for 2100 will exceed the
early Holocene peak (Marcott et al. 2013, Science).
Volcanism and CO2
Isolated eruptions  brief perturbation to
the climate system
Past eruptions are used to test the
radiative and dynamic aspects of climate
models
Global annual present-day CO2 output of
the Earth’s degassing subaerial and
submarine volcanoes range from 0.13 to
0.44 billion metric tons (gigatons) per year
Anthropogenic CO2 emissions are
projected 35 gigatons of CO2 in 2010
T. Gerlach: AGU/EOS 14 June 2011
The small amount of global warming
caused by eruption-generated greenhouse
gases is offset by the greater amount of
global cooling due to eruption-generated
particles in the stratosphere.
35Gt/0.26 Gt
~ 134
Short term effects are cooling.
Does NOT explain the warming of the
past century!!!!
What about solar forcing?
DT ~ 0.5 C
Monitoring of total solar irradiance now covers the last 30 years. The data show a well
established 11-year cycle in irradiance that varies by 0.08% from solar cycle minima to
maxima, with no significant long-term trend.
The energy output of the Sun is incredibly constant (especially on short-time scales) and
thus any changes are too small to have a significant effect on the climate.
Where are we in the glacial/interglacial cycle?
>We should be
cooling!
>We were cooling
post-Holocene
maximum…
• Interglacial ~ 10-15 Ky
• Temperature spikes and then
slow cool down
• Glacial periods longer!
Previous Interglacial
Present Interglacial
(Eemian)
http://www.ncdc.noaa.gov/paleo/abrupt/data2.html
What proportion of anthropogenic CO2 dissolves
in the ocean?
Current %
http://www.earth-syst-sci-data-discuss.net/5/1107/2012/essdd-5-1107-2012.pdf
Best Analog: Paleocene-Eocene Thermal Maximum (PETM)
• 55-56 million years ago
• Largest and most abrupt perturbation to the carbon cycle over the 65 My
Cenozoic
• There were smaller analogs later in the Eocene, but the size of the carbon
flux that must have been brought into the ocean/atmosphere carbon cycle
during the PETM, is on a par with the entire reserve of conventional fossil
fuels at present.
• Temperature change estimates range from 5-to-9 deg C warming (with
some additional uncertainty due to potential problems with the proxy
data)
• Polar amplification in very warm paleo-climates is much larger than
scientists are able to explain using standard models– smaller in the tropics
than at higher latitudes.
• The PETM represents a 'tipping point' and a potential analogue for future
climate change. Little is currently known about the source, quantity or rate
of carbon release, nor of the impact of major reorganisation in ocean
circulations that took place at this time.
• Earth's ecosystems were able to adapt to the PETM because the warming
was gradual; however, the warming we're causing today is about 10 times
as fast
The PETM
•During the PETM the globe warmed around 0.025°C/100 yrs.
•Today, earth is warming at least ten times as fast, somewhere
between 1-4°C /100 years.
•How fast carbon enters the atmosphere translates to the
how fast temperature increases.
When was the last time the aggregate/key parameters
were similar to present day climate?
Temperature: at least 8000 years ago (Holocene maximum)
(note that Medieval Warm Period was not a global phenomenon)
CO2: 800,000 years
Sea Level: The highest global sea level of the past 110,000 years
likely occurred during the Medieval Warm Period of 1100 - 1200
A.D., when warm conditions similar to today's climate caused the
sea level to rise 5 - 8" (12 - 21 cm) higher than present.
http://www.kwaad.net/SeaLevel-MiddleAges-LittleIceAge.html
Aggregate/key parameters Cont’d
pH: The global oceans are the largest natural reservoir for much
of the excess anthropogenic CO2, absorbing approximately 2530% [Sabine et al., 2004]. As a result, dissolved CO2 in the surface
ocean will likely double over its pre-industrial value by the middle
of this century, representing perhaps the most dramatic change in
ocean chemistry in over 20 million years [Feely et al., 2004].
http://coralreefwatch.noaa.gov/satellite/oa/description/oaps_intro_oa.php
SSTs: Global SSTs are higher now than they have been in the last 150 years. Paleoclimate
proxies have limited spatial coverage. (see next graphic for tropical west Pacific warm pool)
https://www.e-education.psu.edu/earth103/node/502
SSTs: Woods Hole study (Fig. below) indicates surface water
temperatures during a part of the Medieval Warm Period that are
similar to today’s
http://www.whoi.edu/main/news-releases/2009?tid=3622&cid=59106
Where have we been? Obs vs. Projections
Observed global CO2 emissions from fossil fuel
burning and cement production compared with
IPCC emissions scenarios. The coloured area
covers all scenarios used to project climate
change by the IPCC (Copenhagen Diagnosis).
IPCC FAR BAU global warming projections
(blue) vs. observed average global surface
temperature change from GISTEMP fiveyear running average (red)
Representative Concentration Pathways
RCP architecture: emissions trajectories and concentrations, energy use, population,
air pollutants and land use, and the consequent radiative forcing and temperature
anomalies specified by each of the four RCP pathways.
RCP 8.5 This RCP is characterized by increasing greenhouse gas emissions over time,
representative of scenarios in the literature that lead to high greenhouse gas concentration
levels (Riahi et al. 2007).
RCP6 A stabilization scenario in which total radiative forcing is stabilized shortly after
2100, without overshoot, by the application of a range of technologies and strategies for
reducing greenhouse gas emissions (Fujino et al. 2006; Hijioka et al. 2008).
RCP 4.5 Also a stabilization scenario in which total radiative forcing is stabilized shortly after
2100, without overshooting the long-run radiative forcing target level (Clarke et al. 2007;
Smith and Wigley 2006; Wise et al. 2009).
RCP2.6 The emission pathway is representative of scenarios in the literature that lead
to very low greenhouse gas concentration levels. It is a “peak-and-decline” scenario; its
radiative forcing level first reaches a value of around 3.1 W/m2 by mid-century, and returns to
2.6 W/m2 by 2100. In order to reach such radiative forcing levels, greenhouse gas emissions
(and indirectly emissions of air pollutants) are reduced substantially, over time (Van Vuuren et
al. 2007a).
Where are we heading? CO2 Projections
Historical emissions continue to near the top of any set of emissions
scenarios
Where are we heading? Temperature Projections
If we do nothing about
climate
change,
we’re
choosing a path that will
look most like RCP8.5. Recall
that this is the one where
emissions keep rising just as
they have done throughout
the 20th century. On the
other hand, if we get serious
about curbing emissions,
we’ll end up in a future
that’s probably somewhere
between RCP2.6 and RCP4.5
(the two blue lines).
Given current concentrations and on-going emissions of greenhouse gases, it is likely
that by the end of this century, the increase in global temperature will exceed 1.5°C
compared to 1850 to 1900 for all but one scenario (IPCC AR5).
Global Temperature Hiatus?
The IPCC attributes the hiatus in roughly equal measure to
• A cooling trend from natural variability (e.g., oceanic factors)
• Changes in Earth’s radiative balance since 2000 (series of weak volcanic eruptions +
solar activity/downturn of sunspots).
• Most of the hiatus has been in the subtropics and midlatitudes. The Arctic has warmed
dramatically over the last 15 years, with record depletions of summer sea ice and record
amounts of melt over the Greenland ice sheet.
• The pattern of observations shown closely resembles the signature of the Pacific
Decadal Oscillation (PDO)
• The amount of ocean heat stored at deeper levels (below 700 meters, or 2300 feet) has
increased markedly during the atmospheric hiatus (Trenberth
http://www2.ucar.edu/atmosnews/opinion/10883/inside-warming-hiatus
Global Temperature Hiatus?
Where are we heading? Sea Level Projections
Sea levels are rising faster now than in the previous two millennia, and the rise
will continue to accelerate – regardless of the emissions scenario, even with
strong climate mitigation.
One of the biggest changes, over the 4th IPCC report, is more rapid sea-level rise
– projected (28-98 cm by 2100). This is more than 50% higher than the old
projections (18-59 cm) using the same emission scenarios/time periods.
From A geological perspective on potential future sea-level rise. Rohling et al. 2013.
Where are we heading? Global Ocean pH
CMIP5 multi-model simulated time series from 1950 to 2100 for
global mean ocean surface pH.
Numbers…
How do we know when there are numerous examples from
history of science of consensus, overturned…
• Geocentric Universe
• Fixity of species
• Absolute nature of time and space, pervaded
by luminiferous aether
• Deterministic character of atomic interactions
• Fixity of continents
Five main candidates for scientific methods and standards
1. Methodological: induction, deduction, falsification
2. Evidential: replication, peer review, consistency, consilience of
evidence (proxy and instrument)
3. Performance: test of time, prediction verifies
4. Best Explanation
5. Community Standards
Evasion by speculative hypothesis
• Proposed speculative hypotheses (about natural variation)
without providing evidence of their actual/physical roles.
•
Speculative reassurances about human capacity for adaptation.
• Alarmist claims about collapse of US economy, largely without
evidence
Scientific Concensus
928 Peer-Reviewed Articles 1993-2003
Science 2004
6 Categories: 1) endorsement, 2) impact evaluation,
3) mitigation, 4) methods, 5) paleoclimate analysis,
and 6) concensus rejection:
75% in categories 1-3 with either explicit or implicit
endorsement
25% in categories 4 & 5 with no position
0% rejection of concensus
Science is precisely about consensus, because consensus is the result of the application of
‘community’ standards. There is a broad consensus – and has been since 1993.
A Few Other Climate-Related Sites…
RealClimate
Dog Walk
Skeptical Science
IPCC AR5 Home
Arctic Sea Ice Blog
NASA Glacier Monitor
National Snow/Ice Data Center
POLAR Science Center
National Climate Data Center
NOAA CO2 Trends
Climate Education Videos/Aplets/Etc.
Earth: The Operators’ Manual
“It’s Us”
“CO2 and the Atmosphere”
“Humans and Energy”
NASA Radiation Balance Model
How to talk to an Ostrich
Arctic Sea Ice 2012
Cosmos Climate Episode Clip