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 ! why we blame fossil fuels

* Prediction of 21st century climate change ! why climate change might be important

* Policy considerations

* EPS/Geog 352 "Global Climate Change" EPS 436 "Climate Dynamics"

First, a clicker question

If nothing else changes in the climate system, what is the effect of increasing CO2 concentration in the atmosphere on globally averaged surface temperature?

[a] Surface temperature would increase; there is no reasonable doubt about this.

[b] Surface temperature might increase, but it depends on the details of how, where, and how rapidly CO2 is added to the atmosphere.

[c] There is no definitive evidence that connects changes in atmospheric CO2 concentration to changes in surface temperature.

[d] Don’t know.

Global Surface Temperature 1880-2014 Annual Average

Questions:

(1) Detection of climate change? (2) Attribution of climate change? (3) Prediction of climate change?

(4) Impacts: Is this important? Is it urgent?

(5) What (if anything) has, or should, be done about this? ... adaptation and/or mitigation? ... coordinated international policy?

US National Climatic Data Center www.ncdc.noaa.gov

1900 1950 2000

2014

Anthropogenic climate forcing: Greenhouse gas fluctuations

since the last ice age CO2

Recent increases are unambiguously anthropogenic -- no controversy here

IPCC (2007)

CO2 concentration reached 400 ppm last year

10,000 yr ago

400

340

370

280

1957 2015

310

CH4

N2O

Scripps Inst. Oceanography

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

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

a) Hemispheric CO2 gradient IPCC AR4

(2007) Fig 7.5

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

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

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 over the past decade

… and the recent solar maximum has been very weak (small sunspot numbers)

2000 2010 2018

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 ???

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

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)

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.

1700×1021 J in half-century is roughly 2 W/m2 extra energy

Murphy et al. (2009)

Greenhouse Effect

Positive forcings

Negative forcings,

energy sinks Particulates

Surface warming

Ocean storage

Atmospheric General Circulation Models (AGCMs): Dynamics

AGCMs solve conservation equations like these at every model grid box.

conservation of energy

Are Dynamical Models Any Good?

We rely on basic physics to:

Understand energy transfer into/out of the Earth system

Build computer models of climate based on physical principles (conservation of mass, energy, momentum)

Analyze the results of model simulation, and test hypotheses of climate change against observed data

http://www.srh.noaa.gov/abq/

Today's daily weather forecast

... generated by atmospheric models that are essentially the same as used for climate projections

Daily weather forecasts are:

1) Expressed with uncertainty

2) Very skillful (and improving with time)

http://www.srh.noaa.gov/abq/

http://www.srh.noaa.gov/abq/

CMIP5 climate models can reproduce observed 20th Century warming if, and only if, greenhouse gas forcing is included (conclusion unchanged for 20 yr)

What's new? Attribution studies now reach the same conclusion regarding other climate variables, e.g. ocean heat content and Arctic sea ice changes

Attribution of Change in the Instrumental Record

WGI AR5 SPM

Prescribed Radiative Forcing: New scenarios for CMIP5

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

Projection of future climate change assuming that GHG increases are the dominant forcing

DP Fig 3.14

Use time-varying concentrations as input to global climate models (same models used for attribution assessment)

model uncertainty

emissions / carbon cycle uncertainty

Best estimate High consequence

Risk is dominated by margin in contrast to the best estimate of IPCC

!   Probability Density Function (black) for value of a climate change parameter such as global temperature.

!   Consequences (red) are an increasing function of climate change. !   Estimated cost is the area under the product curve (blue). !   Best estimate of climate change parameter is not the most important value

for impact assessment !   High-consequence “fat tail” is more heavily weighted when a threshold is

crossed so quantitative impact analysis should focus on the tail.

IPCC Workshop Report on Uncertainty and Risk (Manning, et al. 2004). 10 0 1 2 3 4 5 6 7 8 9

probability of catastrophic consequence

Uncertainty (not to scale)

1

0 risk threshold

temp threshold

Mark Boslough, SNL

Risk = Probability × Consequence

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 !

What else could cause century-scale climate change? (or ... how might we be wrong?)

Really big forcing (like an asteroid impact) .... but we didn't observe anything like this in the 20th Century

No forcing at all ("internal" variability) .... this accounts for much of observed year-to-year variability .... is it possible that 20th Century warming is an unforced run of warmth?

Models could be flawed (too sensitive to forcing) .... lots of ongoing research to assess models

Forcings incorrectly estimated .... uncertainties in solar and aerosol forcing

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)

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

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

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