John Holdren on Climate Change Challenge 2018 02-15

John P. Holdren
Professor of Environmental Science and Policy
Harvard University
Senior Advisor to the Director
Woods Hole Research Center
Former Assistant to President Obama for Science & Technology
and Director, Office of Science & Technology Policy
Executive Office of the President of the United States
Brown University February 15, 2018
Essence of the energy-climate challenge
• Without energy there is no economy
• Without climate there is no environment
• Without economy and environment there is no
material well-being, no civil society, no personal
or national security
Watson Distinguished Speaker Series
Institute at Brown for Environment and Society
Watson Institute for International and Public Affairs
•

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2
That term implies something…
• uniform across the planet,
• mainly about temperature,
• gradual,
• quite possibly benign.
This seems to have confused people.
What’s actually happening is…
• highly nonuniform,
• not just about temperature,
• rapid compared to capacities for adjustment
• harmful for most places and times
A more descriptive term is “global climate disruption”.
A few basics
Terminology: “global warming” is a misnomer
The changes are not just about temperature.
Climate = weather patterns, meaning averages, extremes, timing,
and spatial distribution of…
• yes, hot & cold, but also…
• cloudy & clear
• humid & dry
• drizzles, downpours, & hail
• snowfall, snowpack, & snowmelt
• breezes, blizzards, tornadoes, & typhoons
Climate change entails disruption of the patterns.
Global average T is just an index of the state of the global climate system
as expressed in these patterns. Small changes in the index correspond to
big changes in the system (much like your body temperature).
A few basics

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When the average of any of these weather variables
changes, the extremes change much more.
A few basics
Original climate Altered climate
Temperature
The principle holds for any “normally distributed” climate variable:
A modest change in the average  big changes at the “tails”.
Climate governs (so altering climate affects)
• availability of water
• productivity of farms, forests, & fisheries
• prevalence of oppressive heat & humidity
• formation & dispersion of air pollutants
• geography of disease
• damages from storms, floods, droughts, wildfires
• property losses from sea-level rise
• expenditures on engineered environments
• distribution & abundance of species
Changes--in averages & extremes--matter because…
A few basics

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Outline of the rest of the presentation
WHAT WE KNOW (beyond a reasonable doubt) ABOUT…
• the pace, character, & causes of climate change
• the ongoing impacts on people & ecosystems
WHAT WE EXPECT
• Scientific best estimates under specified future emissions
• What else could happen (probability/timing uncertain)
WHAT WE CAN DO
• reducing emissions (how much, how fast, by whom)
• adapting to unavoidable change (acting locally)
• the need for (and current lack of) federal leadership
• what states, cities, businesses, NGOs, & citizens can do
What We Know
“Everyone is entitled to his own opinion, but not his own facts.”
Daniel Patrick Moynihan

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Global-average surface air temperature from 1880
2016 was the hottest year on record,
2017 2nd hottest,
2015 3rd hottest,
2014 4th hottest.
Shaded rectangles are decadal averages; from
the 1960s, each has been warmer than the last.
Earth has been warming more or less steadily for the last 100+ years, as the increasing
forcing from the human-caused GHG buildup came to dominate natural variability.
What we know: The pace & character of change
The Arctic, West Antarctic Peninsula, and mid-continents
are warming much faster than the global average
NASA

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Arctic sea-ice extent 1979-2017: it’s shrinking
Inset shows Arctic vs global T rise 1880-2017
Antarctic sea-ice is in trouble, too
2002-2015
Sea-ice loss in Antarctic allows the land ice to flow into the sea.

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Muir Glacier, Alaska, 1941-2004
NSIDC/WDC for Glaciology, Boulder, compiler. 2002, updated 2006. Online glacier
photograph database. Boulder, CO: National Snow and Ice Data Center.
August 1941 August 2004
Glaciers worldwide have been shrinking for decades
The Greenland ice sheet has been losing mass at
rates of 100-500 billion tons per year
Hansen Expert Opinion 2017

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The Antarctic Ice Sheet is likewise losing mass
Hansen Expert Opinion 2017
The pace of sea-level rise is increasing
WMO 2017
Monthly values
3-month running mean
1992-2016 trend = 3.3 mm/yr
2010-2016 trend = 6.0 mm/yr
What We Know: The pace & character of change
Increases result from ice additions,
thermal expansion, and groundwater
depletion.

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What We Know:
The Causes of Recent Climate Change
“Science is true whether or not you believe in it.”
Neil DeGrasse Tyson
https://fractionalflow.files.wordpress.com/2014/10/fig-1-world-total-energy-consumption-1800-to-2013.png
Growth of world population & prosperity from 1850
to 2015 led to a 22-fold increase in energy use.
Units are million tonnes of oil equivalent per year
In 2015 the world still depended on coal, oil, & natural gas for about
80% of its total energy supply and two-thirds of its electricity.
What we know: Causes of climate change

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IPCC AR5 SYN Fig SPM-1
Civilization’s CO2 emissions tracked the rise of
fossil-fuel use & deforestation
Global anthropogenic CO2 emissions
The H2O stays in the atmosphere only briefly, so the additions do not
accumulate there. But much of the CO2 stays long and accumulates.
Roughly, coal is CH, oil is CH2, natural gas is CH4, and wood is CH2O. In each
case, their combustion produces CO2 and H2O, all going into the atmosphere.
What we know: Causes
So the atmosphere’s CO2 content grew markedly
Updated from IPCC AR4, WG1 SPM, 2007
The record of CO2
content over the
millennia (from ice
cores, large curve)
shows the gradual
rise from the Agri-
cultural Revolution
and the steep one
from the Industrial
Revolution.
The 2016 CO2 concen-
tration was 403 ppmv,
45% higher than 1750.
The “forcing” (scale
on the right) is the
resulting change in
CO2 vs time from ice cores & direct measurement
the energy balance of the atmosphere since 1750.

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11
Humans have added other heat-trapping gases too
USGCRP 2017
Most important are methane (CH4) & nitrous oxide (N2O) from
energy systems & agriculture and (most recently) CFCs & HFCs
from consumer products & industry
The forcing from the non-CO2 gases is smaller
than that from CO2, but not insignificant.
Human well-mixed GHGs
Net human influence
Human particulates + short-lived GHGs
Solar variability + volcanoes
IPCC AR5, WG1 SPM, 2013
T (C)
Within measurement & analytical uncertainties, essentially
all of the recent observed warming was human-caused.
The wafflers’ claim there’s a lot of uncertainty about the human role is wrong.
Human vs natural influences on T 1950-2010

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°C
depar-
ture
from
1960-90
average
Marcott et al. SCIENCE vol 339, 2013
Blue band is one-sigma uncertainty range (68%
confidence interval).
Natural influences—mainly variations in Earth’s
orbit and axis of rotation—were in a long-term
cooling phase that would have continued for 1000s
of years more but for the influence of humans.
Humans are clearly the cause; nature was heading
the other way. Years before present
What We Know:
Ongoing Impacts on People and Ecosystems
“The debate about when climate change becomes dangerous
should be over. It’s already dangerous.”
John Holdren

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Serious harm from climate change is here now
Around the world we’re seeing, variously, increases in
• floods
• drought
• wildfires
• heat waves
• coral bleaching
• coastal erosion & inundation
• power of the strongest storms
• permafrost thawing & subsidence
• expanding impacts of pests & pathogens
• altered distribution/abundance of valued species
All plausibly linked to climate change by theory, models, and observed
“fingerprints”, most worsening faster than projected.
What we know: Ongoing impacts on people and ecosystems
Growing harm: Heavier downpours  more floods
Percentage increase,
between 1958 and
2012, in the amount
of precipitation falling
in the heaviest 1% of
precipitation events
in each region.
By far the biggest
increase was in the
Northeast.
Source: USGCRP,
Assessment of Climate
Change Impacts in the
United States, May 2014
What We Know: Ongoing impacts on people and ecosystems
A warmer atmosphere holds more water, so more can (and does) come down at one time.

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East Baton Rouge, LA, August 2016: Up to 20 inches of rain in 3 days
Downpours  Floods (continued)
“Hundred-year” floods now occur once a decade or more in many places.
Three “five-hundred-year” floods occurred in Houston in three years.
Hurricane Harvey brought >50 inches of rain over 5 days to parts of Texas in August 2017.
Credit: Ken James / Bloomberg
California’s Folsom Lake at 17% capacity, 02-02-14
Growing harm: In a wetter world overall, many
drought-prone regions are getting more so!

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Growing harm: drought (continued)
• Higher temperatures = bigger losses
to evaporation.
• More of the rain falling in extreme
events = more loss to flood runoff,
less moisture soaking into soil.
• Mountains get more rain, less snow,
yielding more runoff in winter and
leaving less for summer.
• Earlier spring snowmelt also leaves
less runoff for summer.
• Altered atmospheric circulation patterns can also play a role.
Growing harm: Drought in the Amazon
WMO 2017
Precipitation index
for Brazil, 1/15 – 12/16
The Woods Hole Research
Center is a leader in work
on drying & burning in the
Amazon.

2/15/2018
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0
2
4
6
8
10
12
1983 19841985 1986 1987198819891990 1991 19921993 1994 19951996 19971998 19992000 2001 20022003 2004 2005200620072008 20092010 2011 2012 20132014 2015
Data from National Interagency Fire Center
Growing harm: Wildfires
Millions of acres burned annually in U.S. wildfires
6
4
2
0
1981 - 2015
10
8
Contributing factors are heat,
drought, more dead trees
killed by pests, and more
lightning in a warming world.
Update: 2016 was 5.5 M acres, 2017
was 10.0 M acres
Wildfires (continued)
• The fire season in the USA is
about 3 months longer than
it was 40 years ago.
• The average fire is much
bigger & hotter than before.
Small wildfires burn at 1300-
1400F; big ones can burn at
2000F or more, spreading
faster, with far greater risks
for firefighters.
• In Alaska, even the tundra
has experienced wildfires in
recent years.
• The smoke from today’s big
wildfires can carry health-
harming fine particulates
thousands of miles.
What we know: Ongoing harm

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17
Wildfires (continued): Smoke spreads nation-wide
What we know: Ongoing impacts on people & ecosystems
Fine particulate matter (PM-2.5) from wildfires is a serious health hazard.
Growing harm: huge increase in heat waves
34
Probability distribution for Jun-Jul-Aug temperature anomaly on land in the
Northern Hemisphere. Baseline normal distribution is for 1951-80.
Standard Deviations
Hansen at al., PNAS, 2012
Portion of Northern Hemisphere land experiencing > 3σ summer heat in a given year
increased from 0.1-0.2% in 1951-80 to 10% in 2001-2011—a 50- to 100-fold increase.

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Growing harm: More N hemisphere winter extremes
Scientific American blog, January 2014
Rapid Arctic warming
weakens/slows polar
vortex. Resulting
wavy jet stream
alternating, slow-
moving southward
incursions of cold air
and northward
incursions of warm
air. In U.S. Northeast,
collision of cold
Arctic air with
moisture-laden air
over warmed
Atlantic can cause
extreme snowfall.
Growing harm: Coral bleaching
“As of February 2017, the ongoing global coral bleaching event
continues to be the longest and most widespread ever recorded.”
https://coralreefwatch.noaa.gov/satellite/analyses_guidance/global_coral_bleaching_2014-17_status.php
Jarvis Reef, South Pacific (courtesy WHOI)

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Growing harm: Ocean acidification
The link is that dissolved CO2 forms weak
carbonic acid (H2O + CO2  H2CO3),
lowering the pH.
About 1/3 of CO2 added to atmosphere is quickly taken up by the
surface layer of the oceans (roughly, the top 80 meters).
World Bank / Potsdam Institute Nov 2012
Growing harm: Death of coral reefs in Florida Keys
NASA Aqua satellite
imagery. Washington
Post, 26 June 2017
Florida’s coral reefs are
being devastated by
multiple stresses, of
which warming water
and acidification are
the most important.
Less than 10% of the
reef system is now
covered by living coral.
(Red circles show
percentage declines
since 1996.)

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Growing harm: Thawing/subsiding permafrost
Norwegian Polar Institute, 2009
Russia Fairbanks, AK
EPA 2016
Growing harm: Rising sea  coastal inundation

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Growing harm: rising sea  coastal erosion
Cape Cod Times
Cape Cod loses 33 acres per year to inundation and coastal erosion.
Growing harm: Stronger tropical storms
• 10/12: Sandy, largest ever in Atlantic
• 11/13: Haiyan, strongest in N Pacific
• 10/15: Patricia, strongest worldwide
• 10/15: Chapala, strongest to strike Yemen
• 02/16: Winston, strongest in S Pacific
• 04/16: Fantala, strongest in Indian Ocean
• 10/17: Ophelia, strongest in E Atlantic
Sandy
Winston

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22
Growing harm: Pest outbreaks
USGCRP 2009
Pine bark beetles, with a longer breeding season courtesy of warming, devastate
trees weakened by heat & drought in California, Colorado, Alaska…
Growing harm: Increased vector-borne disease
What We Know: The ongoing impacts on people and ecosystems
Climate Nexus

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23
Growing harm: Impacts on valued species
Shifting patterns in Pacific climate, West
Coast salmon survival rates, and increased
volatility in ecosystem services
Valued species: Walruses impacted by shrinking sea ice
Courtesy Fran
Ulmer
Along with whales, seals, polar bears
Gary Braasch

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24
What’s Coming:
The future of climate change and its impacts
“Prediction is difficult…especially about the future.”
attributed to Yogi Berra and Neils Bohr
What’s coming depends on future emissions
IPCC 2013
Target of ∆T ≤ 2ºC
IPCC Scenarios
Last time T was
2ºC above 1900
level was 130,000
yr BP, with sea
level 4-6 m higher
than today.
Last time T was
3ºC above 1900
level was ~30
million yr BP, with
sea level 20-30 m
higher than today.
Note: Shaded
bands denote 1
standard deviation
from mean in
ensembles of
model runs
Scientific best estimates under specified future emissions
Global average T
continues to
increase under
all plausible
scenarios.
Momentum in
the climate sys-
tem means T
continues to go
up even after at
mospheric con-
ditions stabilize.
And sea level
continues to go
up even after T
stabilizes.

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25
Under high emissions: heat extremes multiply
38.
Under high emissions: SW Europe roasts
observations
HadCM3 Medium-High (SRES A2)
2003
2040s
2060s
Temperatureanomaly(wrt1961-90)°C
July-August T in southwestern Europe
The 2003 heatwave killed
35,000-70,000 people in
France, Spain, & Italy.
Summers as hot as 2003 will
likely be the norm by the
2040s and will be considered
unusually cool by the 2060s.

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Under high emissions: much of USA roasts, too
National Academies, Stabilization Targets, 2010
These declines
are without
taking into
account any
increase in
major droughts.

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27
Frequency of 4-6 month duration droughts (events per 30 years)
Under high emissions: Drought frequency soars
2070-2099, IPCC A2 scenario
1961-1990
Results shown are the mean of 8
global climate models.
Drought defined as soil moisture
below historical 10th percentile value
for that calendar month.
Source: Sheffield and Wood 2008 Climate
Dynamics (2008) 31:79–105
DOI 10.1007/s00382-007-0340-z
events per 30 years
Percentages shown are
increases in median annual
area burned, referenced to
1950-2003 averages, for a 1°C
rise in global average
temperature.
National Academies,
Stabilization Targets,
2010
Even a 2C increase
(low emissions)
portends a large
worsening of
wildfires

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28
Increased storminess in all scenarios
Bhatia and Vechhi, Princeton U, 5 April 2017
Princeton hurricane model projects increase in land-
falling Cat 3-5 hurricanes in the Northeast
These findings are for the IPCC’s
RCP4.5 emissions scenario—a
mid-range case, not the worst!

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29
Sea level likely to rise another 0.5-2 m by 2100
NOAA OAR CPO-1, December 2012
Sea-level rise continues for many centuries after
2100 in all scenarios, ultimately reaching 2 meters
or more per degree of global avg warming.
Sea level: Flooded area with 1 meter rise

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30
Acidification: Continued
drop in ocean pH in all
scenarios, with significant
impacts on marine life
Steffen et al., 2004
Increased acidity lowers the
availability of CaCO3 to
organisms that use it for forming
their shells & skeletons,
including corals.
Adverse effects are already
being observed.
Coral reefs could be dead or in
peril over most of their range by
mid to late 21st century.
1870, 280 ppm
2003, 375 ppm
2065, 515 ppm
Scientific best estimates under
specified future emissions
Some of the worst possibilities
• Rapid CH4 and CO2 release from thawing permafrost &
warming Arctic sediments, accelerating all climate-related
impacts (WHRC focus)
• Massive drying & fires in the (formerly) moist tropics, with
huge damage to local peoples & biodiversity (WHRC focus)
• Greatly accelerated sea-level rise from rapid disintegration
of Greenland and Antarctic ice sheets
• Ocean fisheries crash caused by combination of warming,
acidification, oxygen depletion, toxics, overfishing…
• Collapse of the Atlantic Meridional Overturning Circu-
lation, shutting down the Gulf Stream
All of these become more likely as T rises above 1.5C.
What else could happen (probability/timing/magnitude not well quantified)

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31
What We Should Do
“If you don’t change direction, you’ll end up where you’re heading.”
Lao Tzu
There’s a big difference in expected harm
depending on the action society takes
IPCC WGII, 2014
The high-emissions scenario, with global avg T increase
of 5C or more, would entail catastrophic impacts.
What We Can Do

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32
What We Should Do
So hiding our heads in the sand is not smart
Society’s options
There are only three:
• Mitigation, meaning measures to reduce the pace &
magnitude of the changes in global climate being
caused by human activities.
• Adaptation, meaning measures to reduce the
adverse impacts on human well-being resulting from
the changes in climate that do occur.
• Suffering the adverse impacts and societal
disruption that are not avoided by either mitigation or
adaptation.
What We Should Do

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33
Concerning the three options…
• We’re already doing some of each.
• What’s up for grabs is the future mix.
• Minimizing the amount of suffering in that mix can
only be achieved by doing a lot of mitigation and a
lot of adaptation.
– Mitigation alone won’t work because climate change is
already occurring & can’t be stopped quickly.
– Adaptation alone won’t work because adaptation gets
costlier & less effective as climate change grows.
– We need enough mitigation to avoid the unmanage-
able, enough adaptation to manage the unavoidable.
What We Should Do
Mitigation possibilities include…
(CERTAINLY)
• Reduce emissions of greenhouse gases & soot from
the energy sector
• Reduce deforestation; increase reforestation &
afforestation
• Modify agricultural practices to reduce emissions of
greenhouse gases & build up soil carbon
(CONCEIVABLY)
• “Scrub” greenhouse gases from the atmosphere
technologically
• “Geo-engineering” to create cooling effects offsetting
greenhouse heating
What We Should Do

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34
How much mitigation, how soon?
• Limiting ∆Tavg to ≤2ºC is now considered by many the
most prudent target that still may be attainable.
– EU embraced this target in 2002, G-8 & G-20 in 2009
– Paris added 1.5C as “aspirational goal” in 2015
• To have a >50% chance of staying below 2ºC:
– atmospheric concentration of heat-trapping substances
must stabilize at around 450 ppm CO2 equivalent (CO2e);
– to get there, developed-country emissions needed to peak
around 2015 and decline rapidly thereafter, and
– developing-country emissions must peak no later than 2025
and decline rapidly thereafter.
What We Should Do
Adequate mitigation will require addressing most heat-trapping
substances across most emitting sectors in most countries.
Mitigation: Everybody must get on board
Distribution of CO2
emissions among
nations
CO2 and non-CO2 GHG
Sectoral sources of global GHG emissions
What We Should Do

2/15/2018
35
Is the needed mitigation affordable?
• Detailed analysis by the McKinsey group indicates that a carbon
tax increasing over time to $70 per ton of CO2e by 2030 (in 2015
dollars) would put the world on a 2C trajectory.
 The total tax bill (reaching $2T per year in 2030) is not the cost,
because the average cost to reduce emissions would be much less
than $70 per ton. Gov’ts could spend most of it in other ways.
 GWP in 2030 at 2.5%/yr growth between now and then would be
$170 trillion, so even the $2 trillion figure would be ~1%.
• World now spends 2% of GWP on defense; USA spends 3.3% of
GDP on defense, 1.7% on env protection. Such costs are not
“losses”, just choices about resource allocation.
• Most economic models find aggressive mitigation reduces GWP
by 2-3% of GWP in 2100, but they underestimate innovation.
Far less affordable would be costs of unmitigated climate change.
What We Should Do
Adaptation possibilities include…
• Developing heat-, drought-, and salt-resistant crop
varieties
• Strengthening public-health & environmental-
engineering defenses against tropical diseases
• Preserving & enhancing “green infrastructure”
(ecosystem features that protect against extremes)
• Preparing hospitals & transportation systems for heat
waves, power outages, and high water.
• Building dikes and storm-surge barriers against sea-level
rise
• Avoiding further development on flood plains & near sea
level
Many are “win-win”: They’d make sense in any case.
What We Should Do

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36
The need for (& current lack of) Federal leadership
THE OBAMA ADMINISTRATION…
• Boosted climate research & monitoring; invested in clean-
energy R&D & incentives; promulgated aggressive efficiency
standards; promoted climate-change adaptation
• Launched the “Climate Action Plan” with further mitigation,
adaptation, & international initiatives; reached agreement
with China leading to Paris accords with 195 countries
THE TRUMP ADMINISTRATION…
• Put climate contrarians in charge at OMB, EPA, DOI, & DOE
while leaving most key science positions unfilled; proposed
deep budget cuts in climate science & clean energy R&D
• Cancelled Obama’s Climate Action Plan & Executive Orders
on adaptation; withdrew from Paris accords
What We Should Do
What states, communities, businesses, scientists,
philanthropists, & opinion leaders should do
• States, communities, & businesses (and universities!) should
devise and implement their own mitigation & adaptation plans (as
many already have been doing).
• Scientists should continue to…
– monitor & analyze climate change and improve projections;
– explain to every available audience what we know, how we
know it, how it affects that audience, how we can fix it.
• Philanthropists should seek to fill gaps in climate research &
education created by Federal government’s cutbacks.
• Opinion leaders should refine their ability to explain climate
change impacts & remedies and rebut contrarian errors.
• All should let Congress & President Trump know that abdicating
U.S. government leadership on climate change is folly.
What We Should Do

2/15/2018
37
What else individuals should do
REDUCE YOUR OWN CARBON FOOTPRINT
• Get an energy audit of your home & shrink its energy waste
• Replace incandescent (and even fluorescent) lights with LEDs
• Put solar cells on your roof
• Walk, bike, or take public transportation rather than driving
• For needed driving, get a hybrid, all-electric, or other high-
fuel-economy car
• Recycle, and, better yet, re-use (shopping bags, utensils,
drink containers…)
• Eat less meat
• Invest in companies that are taking action on climate (and
disinvest in those that aren’t)
• And, for the biggest impact available to young people, have
one fewer kid!
What We Should Do
“Trend is not destiny.”
Rene Dubos
Thank you!

John Holdren on Climate Change Challenge 2018 02-15

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