Climate Change and Energy
David S. Gutzler Earth & Planetary Sciences Dept
* Global warming over the past century
* Attribution of observed climate change à why we blame fossil fuels
* Prediction of 21st century climate change à why you should care
* Some policy considerations à why discuss this topic in ME 217
* EPS/Geog 352 (Global Climate Change)
1/31
Conclusion: Global Warming
5 points, 10 words:
1) It's real
2) It's bad
3) It's us
4) Scientists agree
5) There's hope Leiserowitz (2015)
2/31
1990 1995 2000 2005 2010
US CO2 emissions have leveled off recently
Climate change makes existing environmental stresses worse
Global Surface Temperature 1880-2016 Annual Average
US National Climatic Data Center www.ncdc.noaa.gov
1900 1950 2000
2016
The observational evidence for global warming is unequivocal
3/31
Synthesis of observed changes
Many observed changes consistent with warming temperature. Temperature, and temperature-related variables, represent the principal climate change signal IPCC AR5
4/31
Atmospheric CO2
http://scrippsco2.ucsd.edu/
“Keeling Curve”
5/31
No debate over reality of these curves
IPCC AR4 Fig 2.3
δ13C fluctuations consistent with combustion
The δ13C value of atmospheric CO2 is decreasing, consistent with lab measurements of the 13C/12C isotopic ratio produced by fossil fuel combustion
6/31
How do we know that the observed increase in atmospheric CO2 is anthropogenic?
Annual CO2 emissions (mostly from the Northern Hemisphere) are highly correlated with year-to-year fluctuations in the N/S gradient of observed atmospheric CO2 concentration
Hemispheric CO2 gradient IPCC AR4
(2007) Fig 7.5
7/31
Global Energy Balance
Greenhouse Effect
What different processes could change the energy budget at the surface ...
hence change the surface temperature?
surface
top of atmosphere
S. Arrhenius
8/31
Natural Climate Forcing: Sunspot cycles
11, 22 yr periodicities ... and longer periodicities too? Upward trend in solar max in the 20th Century Sunspots are small and dark, but they represent overall solar brightness Solar constant So ≈ 1365 W/m2 is greatest at solar maximum, when sunspot numbers reach their peak, and roughly 1 W/m2 less at solar minimum
warming?
2000 1900
9/31
Recent solar variability
http://www.swpc.noaa.gov/products/solar-cycle-progression
We passed through an extremely low solar minimum 2008-2010
… which contributed to relatively cool global temperatures during the "hiatus"
… recent record global temperatures have occurred despite declining sunspot numbers
2000 2010 2017
10/31
Volcanic Eruptions and NH Summer Temperature: A 2500 Year Reconstruction
Volcanic Aerosol Forcing
Temperature
Tambora
Sigl et al. (2015)
mayhem
-400 0 400 800 1200 1600 2000
Volcanoes intermittently inject large quantities of aerosols into the stratosphere, temporarily cooling surface … 19th Century cooler, 20th Century warmer, 21st Century ???
11/31
Anthropogenic (human-caused) climate forcing: Particulate air pollution
NASA/Visible Earth
China now burns more coal than the US, Europe and Japan combined
BBC China
12/31
Radiative Forcing Since 1750
WGI AR5 SPM
Long-lived Greenhouse Gases (positive forcing, well understood)
Short-lived pollutants (not well mixed, harder to monitor)
Aerosols (particles) (both + and - forcing, poorly constrained)
Change in land use and the sun (thought to be small on global and century scales)
13/31
Earth's changing energy budget, 1950-2004
Cumulative energy budget for the Earth since 1950. (a) Mostly positive and mostly long-lived forcing agents from 1950 through 2004. (b) The positive forcings have been balanced by stratospheric aerosols, direct and indirect aerosol forcing, increased outgoing radiation from a warming Earth and the amount remaining to heat the Earth. The aerosol direct and indirect effects portion is a residual after computing all other terms.
Murphy et al. (2009) Greenhouse Effect
1700×1021 J in half-century is roughly 2 W/m2 extra energy
Positive forcings
Negative forcings,
energy sinks Particulates
Surface warming
Ocean storage
14/31
Atmospheric General Circulation Models (AGCMs): Dynamics
AGCMs solve conservation equations like these at every model grid box.
conservation of energy
15/31
Are Dynamical Models Any Good?
US National Hurricane Center http://www.nhc.noaa.gov/
This plot shows:
Mean and spread of forecasted center of the storm, for next 5 d
Intensity (M – H – S etc) Landfall warnings
16/31
Track Forecast for Hurricane Irma: Thurs 9/07
Attribution of 20th Century Climate Change
Climate models reproduce observed 20th Century global warming ….
if, and only if, human-caused forcings (Greenhouse gases and particulate air pollution) are included
IPCC AR5
17/31
Prescribed Radiative Forcing
Representative Concentration Pathways (RCPs) are designed to illustrate a range of options for mitigating anthropogenic climate change
Emissions Scenarios
Meinshausen et al. (2011)
1800 1900 2000 2100
History RCPs ECPs
Fossil CO2
CH4
N2O
O3 depleters
2000 2050 2100
Aggregate
18/31
Projection of future climate change assuming that GHG increases are the dominant forcing
Use time-varying concentrations as input to global climate models (same models used for attribution assessment)
model uncertainty
emissions / carbon cycle uncertainty
19/31
Projected 21st Century Changes
Continental and polar enhancement of projected warming
Low Emissions RCP2.6
High Emissions RCP8.5
"Wet gets wetter Dry gets drier" Enhanced seasonal cycle of precipitation
No obvious threshold effects
TEMPERATURE
PRECIPITATION
…. subject to large quantitative uncertainty IPCC AR5
20/31
Projected huge decrease in North American snowpack
Diminished snowpack melts earlier in the year
! earlier timing of snowmelt runoff peaks in seasonal hydrographs
Brown and Mote (2009)
US NCA3 (2014), adapted from Cayan et al (2013)
21/31
Projected Sea Level Change
WGI AR5 SPM
Sea Level will continue to rise, very likely at an accelerated pace. Thermal expansion remains the largest contributor to projected Sea Level rise throughout the 21st Century in CMIP5 models .... so these projections may underestimate future change
2100 2000
0.5m à
22/31
Climate Science, Bottom Line
Warming of the climate system is unequivocal, and since the 1950s many of the observed changes are unprecedented over decades to millennia. The atmosphere and oceans have warmed, the amounts of snow and ice have diminished, sea level has risen and the concentrations of greenhouse gases have increased.
It is extremely likely* that human activities caused more than half of the observed increase in global mean surface temperature from 1951–2010. [*extremely likely = 95-100% certainty] Projected 21st Century changes and impacts are potentially profound, but difficult to quantify.
WGI, WGII AR5 (2013)
23/31
What Should We Do? Risk assessment of impacts:
Consideration of extremes
IPCC SREX (2012)
24/31
All projections of future trends contain large quantitative uncertainties
Extreme events (the tails of a probability distribution) may be more significant than changes in average climate
RISK = PROBABILITY × CONSEQUENCE
Irma forecasts Thurs 9/07
The 1992 Rio Summit (UNCED) adopts "UN Framework Convention on Climate Change"
(UNFCCC ... enters into force in 1994)
which includes: • statement of the need to limit atmospheric greenhouse gas concentrations • provisional stabilization target for CO2 emissions (1990 level)
but does not include enforcement provisions
UNFCCC defines "Climate Change" thusly: "attributed directly or indirectly to human activities ... and which is in addition to natural climate variability observed over comparable time periods"
25/31
Overall goals: Stabilize global-average anthropogenic temperature change to ≤ 2°C
Emissions Reduction commitments: Parties commit to determine non-binding Nationally Determined
Contributions ("NDCs"or sometimes "INDCs") No formalized exception to NDCs for developing countries "Stock-taking" to be carried out regularly; first one in 2018 Clean Development Mechanism: A replacement for the Kyoto Protocol's CDM will be determined in future
The Paris COP21 Agreement ���in support of UNFCCC Objectives (text adopted 12/15)
26/31
Observed Greenhouse Gas Emissions
WG3 AR5 SPM
More than 20% increase in total emissions between 2000 and 2010 Currently 65% of total GHG emissions are fossil fuel CO2
1970 1980 1990 2000 2010
27 Gt 33 Gt
38 Gt 40 Gt
49 Gt
CO2 Fossil
N2O
CH4
CO2 Land
Kyoto
27/31
Stabilization Wedges
Pacala & Socolow (2004)
GOAL: "Solve the carbon problem in the next 50 years"
* Divide the overall emissions challenge up into identifiable, feasible "wedges" of reduction
* Set technology & policy goals for each wedge to bring emissions down from BAU (A2 scenario) to emissions stabilization (not stabilized CO2 concentration) by 2054
28/31
15 Potential Wedges
Pacala & Socolow (2004)
Each wedge based on existing technology
... but some require development to implement on a global scale
Each wedge represents a strategy to reduce C emissions in 2054 by 1 Gt/yr:
2004 emission: 7 Gt/yr 2054 A2 proj: 14 Gt/yr
4 wedges Conservation
9 wedges New Energy
2 wedges Forests/soils
29/31
Enough Wedges?
Davis et al (2013)
Pacala & Socolow (2004) Emissions growth since 2004: add 2
Support continued economic growth: add 12
Stabilize concentration, not emissions: add 10
Maybe we need 31, not 7 30/31
Conclusion: Global Warming
5 points, 10 words:
1) It's real
2) It's bad
3) It's us
4) Scientists agree
5) There's hope Leiserowitz (2015)
31/31
1990 1995 2000 2005 2010
US CO2 emissions have leveled off recently
See you next semester in my Global Climate Change course
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