1/31 climate change and energy - mechanical engineeringmammoli/me217_stuff/lectures_f2017/ees... ·...

Climate Change and Energy

David S. Gutzler Earth & Planetary Sciences Dept

gutzler@unm.edu

* 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