Transcript mitchellHC

IPCC Climate Change Report
Moving Towards Consensus
Based on real world data
IPCC Consensus process is
Conservative by Nature
IPCC Consensus Evolution
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FAR: 1990: The unequivocal
detection of the enhanced
greenhouse gas effect from
observations is not likely for a
decade or more
SAR: 1995: The balance of evidence
suggestions a discernible human
influence on global climate
Getting Stronger
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TAR: 2001: There is new and stronger
evidence that most of the warming
observed over the last 50 years is
attributable to human activities
AT4: 2007: Most of the observed increase
in globally averaged temperatures since
the mid-20th century is very likely due to
the increase in anthropogenic greenhouse
gas concentrations.
Climate Modeling Evolution
Better Grid Resolution
Basic Approach
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Coefficient of doubling CO2
Leads to CO2 Stabilization
Scenarios
Basic Future Predictions
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A 2°C rise from today's temperatures
produces 30% species extinction
A 3°C warming will lead to widespread
coral deaths
Water availability in the moist tropics and
in the high latitudes will increase, but will
drop in the semi-arid low latitudes
A 1°C warming will decrease agricultural
yields in the low-latitudes; 2°C increases
yields at high latitudes
Preponderance of Evidence
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Want to find indicators of climate change
Requires a) a robust definition and measure of
what constitutes climate and b) an instrumental
precision sufficient to measure change
No one indicator (e.g. smoking gun) exists;
aggregate of all data then forms the
preponderance
Many Hockey Sticks
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This is most people’s view of “Global
Warming”
It is perhaps the worse indicator to use:
Average global temperature has no physical meaning
 How do you measure it?
 Reliability of Measurements in question
 Effects of urbanization difficult to factor in
 What do you use as your baseline?
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Weather is a Seasonal Event
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Yet Hockey stick only plots annual index.
Bothun/Ostrander Monthly Treatment:
La Nina/El Nino
Reinforced with 2D Representation
Winter Signal is Strongest
Amplification of Polar
Warming
Note the significant slop change at 2005: Methane
Feedback signature?
Methane
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Potential role of methane is larger than CO2
GWP = 21
Scales with population growth
Released from permafrost
Released from hydrate deposits
Emissions now rising again due to global
wetlands returning from prolonged drought
Ocean sink capacity no longer
scales with increasing emissions
Record Events depend on wave
form evolution
Global Aerosols – leads to dimming
 Mostly Industrial; African Source is pyrogenic
and biogenic in nature (drought related)
Convolution of positive and negative
forcings are what we observe.
 GHG produces the net positive here
And all is superimposed on El Nino
Cycle
Other indicators
 Sea Ice
 Glacial retreats and glacial mass balance
 Permafrost
 Droughts
 Water vapor feedback
 Cloud cover
 Ocean wave heights
 Sea surface temperature anamolies
Glacial Retreat and Mass Balance
1941 - 2005
Wholesale Change in Mass Balance
Arctic Ice Loss Rapidly Escalating
An Ecosystem Literally Melts Away
Waveform of Concern
Global Sea Level Rise: Greenland Melting
at an unexpectedly higher rate
But 2009 did not continue this
catastrophic trend
 And 2009 point is consistent with long term
trend
Total Ice Sheet Melting
Droughts
Water vapor increases?
Cloud Cover
 Extremely difficult to really measure with any
accuracy
 Extant data are inconclusive and noisy
Wave height data shows something!
Ocean Sea Surface Temperature Response
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Its important to realize that virtually all of the
extra (heat) flux goes into the oceans
Big reservoir of heat
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0.1 degree C increase transferred (instantly)
to the atmosphere produces 100 degree C
increase.
Ocean circulation and redistribution of excess
heat is (fortunately) a slow process
But that is where the “pipeline” warming is
even if CO2 was stablized today!
Sea Level Rising
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Sea Level measured at San Francisco
Known SST oscillations increasing in
amplitude
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North Atlantic Oscillation (notice the post
1995 slope):
Complete Feedback Models too
Difficult to reliably construct
Source of Uncertainties
 Roles of clouds and aerosols in radiative
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transfer models? (e.g. scattering!)
Role of tropical convection and the water vapor
feedback loop?
How well do observations constrain the input
climate parameters?
How to weight the inputs for best fit statistical
model?
Contributions of other greenhouse gases
specifically methane from permafrost release
Uncertain Futures
Manageable
BAD
Humanity Blew It
Global Warming Potential
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TH = Time Horizon (20 or 100 years)
Ax = increased forcing from X (Watts m^2 kg)
x(t) = decay following some hypothetical
instantaneous release of X
Denominator is relevant quantities for CO2
Nominal value for Methane is 21
Do Tipping Points Exist in Climate?
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Does the system have critical phenomena?
Or do the
various and
somewhat
unknown
feedback
mechanisms
serve to
counter this?
The Next Level of Physics in Climate
Science
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More strongly incorporates the role of various
feedbacks particularly water vapor
Identifying critical points (or lack thereof) is
essential in future models
Improved modeling of aerosols and their
scattering properties
Improved modeling of tropical convection to
better understand ocean/atmosphere heat
exchange