climate change in california - choosing our future

8/3/2019 Climate Change in California - Choosing Our Future

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Climate Chang

in California:ChoosingOur Future


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The climate that

our children and

grandchildren will

experience depends

on the emissionschoices we make

today.

Executive Summary

In the coming decades, Californias environment andeconomy will likely be affected by climate changeresulting from global emissions of heat-trapping gases.The latest climate projections for the state suggest thattemperatures will increase considerably during this

century, and the rate of increase depends on the amountand timing of heat-trapping emissions. Building on previousstudies, these projections use two state-of-the-art climatemodels and two contrasting scenarios of future heat-rapping emissions.

By the end of the century, statewide average annualemperatures are projected to increase about four to six

degrees Fahrenheit under the lower-emissions scenario and astriking 7 to 10.5F under thehigher-emissions scenario. Sum-mer temperatures are projectedo increase more dramaticallyhan previously expected, and heat

waves and extreme temperatures

are expected to become morecommon and severe in major cities.Projections of winter precipitationrange from a decrease of about30 percent to a slight increase,

which contrasts with some previous projections of large in-creases. Because Earths climate changes over the course ofdecades, heat-trapping emissions during the early decadesof this century may irreversibly set the conditions forwarming later in the century.

The consequences of climate change are projected to besubstantial in a number of Californias temperature-sensitivesectors under both emissions scenarios, with the most severe

occurring under the higher-emissions scenario. For example,more persistent summer heat could greatly increase the riskof heat-related deaths in both inland and coastal cities unlesspreventive measures are taken. Warmer winter and springemperatures will likely reduce snowpack in the Sierra Nevada,

with serious implications for winter recreation and summerwater supplies.

Higher temperatures could also affect Californias leadingagricultural products, reducing dairy production and dimin-ishing the quality of wine grapes in all but the coolest grape-rowing regions. A warmer and longer growing season and

changes in moisture will likely alter the distribution of Califor-nias natural vegetation, including a severe reduction in theextent of alpine and subalpine vegetation and the widespreaddisplacement of woodlands and shrublands by grasslands.While the effects of rising temperatures are not uniformlynegative, these projections suggest that climate change willhave serious consequences for Californians in the comingdecades.

While Californians cannot stabilize Earths climate byhemselves, they can take individual and collective steps to

slow climate change and reduce its impact. The most impor-ant is lowering emissions of heat-trapping gases (which

Californias large population and economy generate in sub-stantial amounts). Efforts by Californians to reduce emissionscould not only produce globally signicant results, but alsoset new precedents for others to follow.

The impact of climate change can also be reduced by

minimizing other pressures that would exacerbate its effects.For example, the risk of heat-related deaths can be reducedby ensuring that people whose health conditions make themmore vulnerable to extreme heat have access to quality healthcare. And nally, Californians should prepare for those conse-quences of climate change that cannot be avoided, throughcareful planning and investments in adaptation measures.Water managers, for instance, can prepare for less reliablesummer water supplies by implementing effectiveconservation strategies.

Whats at Risk in a Changing Climate

From snow-capped peaks to temperate coastal regions and

dry inland deserts, Californias environment is highly varied.

These diverse climate zones, inuenced by the proximity of

the Pacic Ocean and extensive mountain ranges that trave

the state, create highly distinctive terrestrial and marine eco

systems. In the north, giant redwoods thrive under more tha

100 inches of rainfall per year. In contrast, the unique vegeta

tion of the southeastern deserts survives on less than ve

inches of rainfall each year. Wine grapes ourish in inland

valleys cooled by coastal fog, and valuable agricultural

products including fruit, vegetables, and nuts are cultivated

in the heavily irrigated Central Valley.

With large urban centers such as Los Angeles, San Diego

and San Francisco, California is home to 34.5 million people

more than 200 per square mile. The state is the nations larg

consumer of residential, commercial, and transportation ener

and is second only to Texas in industrial energy use. Not only

does California have the largest and most diverse economy o

any statewith the highest gross state product in the Unite

Statesit can also claim the fth largest economy in the

world. And though it is perhaps best known for its technolo

and entertainment industries, California is also home to a

$30 billion agricultural economy (again the nations largest)

Cover map: Ray Sterner/Applied Physics Laboratory/Johns Hopkins University. Licensed by North Star Science and Technology, LLC.

Cover photos, top to bottom: (mountain snowpack) 1999 Anthony Dunn; (rafters) Bureau of Land Management (BLM);vineyard) AP Photo/Eric Risberg; (girls in fountain) AP Photo/Nick Ut; (Santa Monica) Q.T. Luong/Terragalleria.com


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Climate Projections

The most recent climate projections for Californiashow that the state will likely become considerablywarmer during this century, and the amount of warm-

ing will depend on the rate at which we release heat-trappingases into the atmosphere. These projections improve upon

earlier research by using two of the latest-generation globalclimate models and lower- and higher-emissions scenariosinstead of a single mid-range scenario. The higher-emissionsscenario assumes continued, intensive reliance on fossil fuels,causing heat-trapping emissions to grow rapidly throughouthe century. The lower-emissions scenario envisions a transi-ion to clean energy technologies, causing emissions to peak

by mid-century and then decline below current levels by 2100.The lower-emissions scenario is not the lowest possible

pathway; actual emissions could be lower if early and aggres-sive steps are taken to limit therelease of heat-trapping gases.Acting soon is important isbecause most heat-trapping

ases remain in the atmosphereor a long time and climatechanges occur over the courseof decades. In other words,he climate our children andrandchildren experience later

in this century depends strongly on our emissions duringhe next few decades.

The projections described here provide the best availableestimate of the direction and relative magnitude of climatechanges that are likely to occur. Because climate models differsomewhat in their projections, two state-of-the-art climatemodels were used to provide a range of plausible outcomes

or a particular scenario. In general, the temperature projec-ions described here are considered more robust than the

precipitation projections.Temperature. Temperatures are projected to increase

substantially under both the lower- and higher-emissionsscenarios, with differences between the scenarios emerging bymid-century. Before the century ends, temperature increasesassociated with the higher-emissions scenario are nearlydouble those of the lower-emissions scenario.

Increases in summer temperatures are greater thanpreviously projected using earlier models and emissions scenarios.By mid-century, average summer temperatures are projectedo rise about two to four degrees Fahrenheit under the lower-

emissions scenario and 2.5 to 5.5F under the higher-emissionsscenario depending on the climate model used. Toward theend of the century, average summer temperatures are projectedo rise about 4 to 8.5F under the lower-emissions scenario

and 7.5 to 15F under the higher-emissions scenario. Average winter temperatures are projected to rise about

2 to 2.5F by mid-century under both emissions scenarios.By the end of the century, average winter temperatures areprojected to rise about 4F under the lower-emissions scenarioand 5.5 to 7F under the higher-emissions scenario.

These values are statewide averages for the 30-year periods

used for most of the impact analyses (20202049 and 20702099). Temperatures toward the end of these periods are ex-pected to be somewhat higher. For example, summer tempera-ture increases projected for the 10-year period (20902099)used in the extreme-heat and heat-related mortality analysesdescribed below range from about 3.5 to 9F under the lower-emissions scenario and 8.5 to 18F under the higher-emissionsscenario. The rate of increase also varies across the state, with

inland areas generally experiencing greater warming than thestatewide average and coastal areas experiencing less warming. Precipitation. Winter precipitation, which accounts formost of Californias annual total, decreases 15 to 30 percentbefore the end of the century in three out of four model runs.However, in one model run, winter precipitation increasesapproximately ve percent. These results differ from someprojections developed using earlier models, which suggestedthat precipitation could double or even triple by the end ofthe century. The precipitation projections described heredo not differ between emissions scenarios.

Rising Sea Levels

Sea levels along the California coast will likely continuerising over the next century. Depending on the climatemodel used, sea levels could rise at a rate similar to the

historical rate of about seven inches per century or almostfour times faster. The rate is consistently higher under thehigher-emissions scenario.

an Francisco Bay and the Sacramento-San JoaquinDelta are particularly vulnerable to rising sea levels, whichcan increase the risk of storm damage, erosion, and oodingof leveed islands, valuable real estate, and rich wetland eco-

California is expected to experience dramatic warming duringthis century, and the amount of warming depends on ouremissions of heat-trapping gases. This gure shows projectedincreases in statewide average annual temperatures for three10-year periods. Ranges for each emissions scenario representresults from two climate models.

By the end of the

century, a summer

day in San Franciscocould feel like a

summer day in

Tijuana today.


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systems. These consequences could be especially severe duringEl Nio years, when sea levels and coastal waves along theCalifornia coast are already unusually high and winter storms

can bring torrential rains. Higher sea levels could also allowsaltwater intrusion into aquifers and the rich ecosystemsound at the mouths of rivers.

Extreme Heat

As average temperatures rise, extreme-heat conditionssuch as heat waves and very high temperatures areprojected to become more common and severe. Differ-

ences between emissions scenarios emerge by the 2050s andbecome more pronounced during the second half of the cen-ury, with the most persistent and severe high-temperature

conditions projected for inland locations that are already hot.

However, the impact on human health could be greatest incooler coastal cities where extreme-heat conditions have his-orically been relatively rare. Projections for ve major metro-

politan areas (Los Angeles, Riverside/San Bernardino, SanFrancisco, Sacramento, and Fresno) show that: Heat waves1 will likely occur morerequently and last longer. For example,

heat waves that could be expected to occurabout three times per year historically areprojected to roughly double in frequencyby the 2050s and become two to ve timesmore common by the 2090s. The average

heat wave could increase in length fromabout two to ve days during the 1990s toabout 5 to 12 days by the 2050s and 6 to 19days by the 2090s. Heat waves will likely become moreintense, with higher temperatures sustainedover a longer period of time. In Fresno andRiverside, extreme heat waves2 couldaccount for about 25 to 50 percent of allheat waves by the end of the century underhe lower-emissions scenario and about 60o 80 percent of heat waves under the

higher-emissions scenario. By comparison, extreme heatwaves accounted for less than 15 percent of all heat waves inthese locations during the 1990s. The heat wave season will likely grow considerablylonger, particularly in coastal and more southern locations.In Los Angeles, for example, the heat wave season is projectedto increase from about 14 weeks during the 1990s to about19 to 25 weeks by the 2090s under the lower-emissions

scenario and 31 to 37 weeksa total of nearly eight to ninemonthsunder the higher-emissions scenario. Much of theincrease is due to heat waves occurring earlier in the year,when people are more vulnerable to extreme-heat events. High-temperature extremes3 will likely rise and occurmore often. Under the higher-emissions scenario, for example,high temperatures that occurred on the 18 hottest days of theyear during the 1990s are projected to occur on as many as90 to 130 days each year during the 2090s. Under the lower-emissions scenario, such temperatures are projected to occuron about 40 to 65 days each year. Projected high-temperatureextremes increase most rapidly in Riverside/San Bernardinoand Sacramento, rising about 2.5 to 6F by the 2050s and

about 5.5 to 13.5F by the 2090s.

Climate Changeand Human Health

Climate change is likely to affect human health innumerous ways, including increased heat stress andrelated deaths, changes in the incidence of infectious

disease, and a higher risk of respiratory and other problemscaused by deteriorating air quality. This study focuses on mor-tality associated with increased heat, which can cause deaththrough dehydration, heat stroke/exhaustion, heart attack,

stroke, and respiratory distress. The most vulnerable membersof the population include people who are already ill, children,the elderly, and the poor.

While warmer winter temperatures are expected to reducecold-related deaths in some regions, the increasing health risksassociated with summer heat are expected to far outweigh

any positive effects of warmer wintersin California. Estimates of future heat-related mortality for the ve metro-politan areas studied show that:

The risk of heat-related mortalityincreases rapidly with continued warm-ing. The annual number of heat-related

deaths is projected to increase an averageof about 60 to 180 percent by the 2050sand 130 to more than 500 percent byhe end of the century in four of the ve

cities analyzed. In the fth city (Fresno),he number of heat-related deaths changes

only slightly, despite more frequentdangerous-heat conditions. This maybe because Fresno already has effectivemeans of coping with heat.

The risk grows with increasingemissions of heat-trapping gases. On

As temperatures rise, a summer day inSacramento in the 2090s could feel like

a summer day in Las Vegas today.

Rising sea levels increasethe risk of ooding in theSacramento-San JoaquinDelta, where rich farm-land, small communities,highways, and utilitiesare protected by severalthousand miles of levees.

RobertA.Eplett,CAGo

vernorsOfceofEmergencyServices

APPhoto/CharlesRexArbogast


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average, mortality estimates for the higher-emissions scenarioare on the order of 10 to 100 percent higher than estimatesor the lower-emissions scenario during the 2050s and about

100 to 150 percent higher during the 2090s. These ndingssuggest that, for the ve cities combined, we could preventsomewhere between 500 and 5,000 heat-related deathsduring the 2050s and more than 8,000 deaths during the2090s by following a lower-emissions pathway.

Of the ve cities, San Francisco appears mostsusceptible to increasing heat, as the populationaccustomedo relatively cool conditionshas limited ability to adjust to

heat. Fresno, which already experiences frequent extremeheat, appears to be the least susceptible to increasing heat.

Water Resources in California

Already scarce throughout the western United States,water is essential to maintaining Californias agricul-

ural economy, expanding population, and uniqueecosystems. Meeting the states growing water demand isparticularly challenging because its geography and climate

keep water supply and demand out of balance.Most of the states precipitation falls in the north during

he winter, while much of the demand for water occurs in thesouth during the spring and summer. As a result, a vast networkof reservoirs and aqueducts is needed to capture, store, anddistribute water from the Colorado River and NorthernCalifornia waterways. Climate change will likely further reducewater supplies during the spring and summer, requiring costly

new infrastructure and changes in the institutions thatgovern Californias water resources.

Reduced Snowpack and Stream Flow

Rising temperatures, possibly exacerbated by reducedwinter precipitation, will severely reduce snowpack inhe Sierra Nevada. This, in turn, will affect stream ow,

water supplies, and winter recreation. The Sierra Nevadasnowpackroughly equal to half the storage capacity inCalifornias human-made reservoirsis a critical source

People living in urban areas, especially children, the elderly,and the poor, are most vulnerable to rising heat.

20202049

California

60%remaining

California

20702099

California

Decreasing Sierra Nevada Snowpack

100 80 60 40 20 0

Remaining Snowpack (%)

Lower Emissions Higher Emissions Higher Emissions

11%remaining

California

By the end of the century, Sierra Nevada snowpack could be reduced to less than a third of current levels, even under a lower-emissionsscenario. This gure shows projections of spring snowpack in the Sacramento-San Joaquin watershed, which provides water to about 28

million agricultural and urban users in California. (Based on climate projections from the HadCM3 climate model.)

PPhoto/FranckPrevel


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of water during the late spring and summer. Spring snowpackis expected to decline as warmer winter storms more frequently

bring rain to the mountains instead of snow, and warmeremperatures cause the snowpack to melt prematurely.

By mid-century, spring snowpack in the Sierra Nevadais projected to decline about 25 to 40 percent. Toward theend of the century, losses could reach 30 to 70 percentor 3.5 to 9 million acre-feet of storage) under the lower-

emissions scenario or a stunning 70 to 90 percent (or 9 to11 million acre-feet) under the higher-emissions scenario. A combination of delayed snow accumulation andearlier snowmelt could shorten the Sierra Nevada ski seasonby three to six weeks by 2050. Toward the end of the century,climate change could delay the start of the ski season three to

six weeks under the lower-emissions scenario, possibly affect-ing holiday prots, and shorten the ski season by 7 to 15weeks. Under the higher-emissions scenario, the minimumsnow conditions required for current ski resort operationsmight never occur. In most cases, total annual stream ow into majorierra Nevada reservoirs4 is projected to drop about 10 to

20 percent before mid-century and 25 to 30 percent beforehe end of the century, with the greatest decrease occurring

under the higher-emissions scenario. In one model run,however, a modest increase in winter precipitation leadso a slight increase in stream ow.

As the timing of runoff shifts earlier, spring and

summer stream ow is projected to decline about 10 to20 percent before mid-century under the lower-emissionsscenario and 20 to 25 percent under the higher-emissionsscenario. Before the end of the century, spring and summerstream ow could be reduced as much as 40 percent underhe lower-emissions scenario and 45 to 55 percent underhe higher-emissions scenario.

Managing Water Resources in a Changing Climate

Changes in snowpack and stream ow have importantimplications for water managers, who must balance theneeds of water users against ood protection and habitat

requirements. Since the demand for water is greatest whenand where it is in short supply, meeting Californias growingdemand in the face of less reliable supplies will likely requirechanges in how the states reservoirs and water distributionsystems are managed. Such decisions are complicated by acumbersome water rights system that generally gives prece-dence to the earliest diverters of water and farmers adjacentto existing streams and rivers on a rst in time, rst in

right basis. As a greater proportion of annual runoff occurs duringthe winter and droughts become more common, managerswill have an increasingly difcult time balancing the need tocapture runoff for future use and the need to maintain spacefor winter ood protection. Additional aboveground storagecould be built, but economic and environmental costs makesuch projects problematic. Surface water could be transferredto groundwater aquifers for storage, but such projects are bothcostly and vulnerable to unauthorized extraction and waterquality problems. Water shortages will likely become more commonas summer stream ow becomes less reliable. Toward the

end of the century, the number of years with dry or criticallylow stream ow conditions is projected to increase from32 percent during the years 19061999 to between 50 and65 percent unless precipitation increases. As stream ow be-comes less reliable, the value of rights to mid- and late-seasonnatural stream ow is likely to decline, disrupting the currentwater rights system.

Coping with the worst consequences of climate changecould require major changes in the way water is allocated inCalifornia. Agricultural users sometimes sell their water rightsto municipal water districts, suggesting that such adjustmentscan be made. However, the process is likely to be slow andexpensive.

Rising Temperatures andCalifornia Agriculture

Climate change could affect California agriculture byincreasing water demand in the face of less reliablesupplies, altering the abundance and distribution of

pests and pathogens, and causing variations in crop qualityand yield. In addition, rising levels of carbon dioxide in theatmosphere can also affect agriculture directly, by stimulatingproduction and increasing the efciency with which cropplants use water. This report focuses on the direct effects of

high temperatures on dairy products and wine grapes (Califor-nias leading agricultural products) and does not considerchanges in water availability or the effects of rising carbondioxide levels.

Wine Grapes

California is known throughout the world for its wines.Along with the famous Napa and Sonoma Valleys, winegrapes are grown throughout the Central Valley and alongthe northern and central coasts, adding up to a $3.2 billionindustry. High-quality grapes are key to producing high-quality wine, and grape quality is sensitive to heat and

Rain from warmer winter storms and earlier snowmelt in themountains could prematurely ll reservoirs, forcing managers torelease and thus lose water that would otherwise be availablefor summer use.

MichaelNevins(USArmyCorpsofEngineers)


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moisture stress during ripening. Rising temperatures duringhe growing season could cause grapes to ripen prematurely,

and reduce grape quality. Temperature projections for the toprape-producing counties suggest growing conditions will

likely deteriorate over the coming decades, except in thecoolest locations.

Warmer temperatures throughout the growing seasonare projected to cause wine grapes to ripen as much as one to

wo months earlier before the end of the century, and highertemperatures during thenal month of ripeningwould likely reduce grapequality. During the earlydecades of the century,grape-growing conditionsare projected to change littlein many regions, includingNapa, Sonoma, and Men-docino Counties, but deteri-orate in the warmer Central

Valley. However, towardthe end of the century,warmer temperatures areprojected to degrade grape-growing conditions in allbut the coolest coastallocations (Mendocinoand Monterey Counties).

Dairy

Heat stress in dairy cowscan lead to poor feed-ing, weight loss, and reducedmilk production, whichbegins to decline at temper-

atures as low as 77F, and can drop substantially as tempera-ures climb above 90F. Californias $3 billion dairy industry

is currently concentrated in the southern Central Valley,where temperatures are projected to rise rapidly during thecoming decades.

Toward the end of the century, high temperatures couldreduce milk production by as much as 5 to 10 percent underhe lower-emissions scenario and 10 to 20 percent under the

higher-emissions scenario. Measures for relieving heat stress,such as providing shade and sprinklers, can be effective under

some conditions but become less so with increasing tempera-ure and humidity.

Changes in VegetationDistribution

Californias size, varied terrain, and diverse climatezones combine to create a wide range of naturalecosystems that support thousands of plant and

animal species, including many that are found only in thestate. Projected increases in temperature and re frequencywill likely cause rapid changes in vegetation distribution,

which has serious implications for ecosystem health andspecies diversity.

Alpine and subalpine vegetation will likely be displacedas mixed evergreen conifer forest extends its range upwardin elevation. With limited opportunity for migration, lossesof alpine and subalpine vegetation cover could reach 40 to50 percent before 2050 and 60 to 80 percent by 2100,with consistently greater losses under the higher-emissions

scenario.Throughout much of the northern portion of thestate, warmer temperatures are projected to cause a change inforest composition from evergreen conifer forest (dominatedby Douglas r and white r) to mixed evergreen forest(dominated by tan oak, madrone, and live oak).

Warmer temperatures and drier conditions in mostinland areas are expected to increase re frequency, leading tothe likely displacement of shrublands and woodlands by grasses(which regrow quickly after res). In contrast, projected in-creases in humidity along the southern coast would discour-age re, allowing coastal forests to expand their range. Theprominent role re plays in these projections suggests that

further work should be done to assess changes in re risk andthe associated impact on property, air quality, and ecosystems.

In the southern Central Valley, the hotter and drierconditions projected in most model runs would reduce thegrowth of grasses as well as trees and shrubs, leading to anexpansion of desert. In one model run, however, less warmingand slightly wetter conditions are projected to increase refrequency, allowing grasslands to displace shrublands as inother parts of the state.

Meeting the Challenges ofClimate Change in California

Californias population of 34 millionalready thelargest in the nationis expected to grow to 59 mil-lion by the year 2040 and could reach 92 million by

2100. Growing demand for vital resources and the expansion

ising temperatures will likely reducerape quality in all but the coolest

wine-growing regions in California.

With no place to move in the face ofrising temperatures, many of Californiasubalpine and alpine forests andmeadows will likely be lost.

APPhoto/EricRisberg


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of urban centers will compound the effects of climate changeon water resources, human health, and natural ecosystems.

The projected impact of climate change is greater underhe higher-emissions scenario, suggesting we can minimize

risks and adaptation costs by taking steps now to lower emis-sions of heat-trapping gases. California residents, resourcemanagers and users, and policy makers can help reduce thepotential impact of climate change through threecomplementary strategies: Reducing emissions of heat-trapping gasesis themost important step to curbing the rate and extent of climatechange. California can accomplish this and build on its legacy

of environmental leadership by continuing to increase indus-rial and building efciency, switching to renewable energysources such as wind and bioenergy, and introducing cleanervehicles. These strategies not only reduce emissions of heat-

rapping gases but also typically yield signicant economicsavings and other environmental benets. Minimizing pressures on the environmentthat canexacerbate the impact of climate change. For example, limit-ing human encroachment on sensitive ecosystems can helpreduce the risk of habitat fragmentation.

E N D N O T E S

1 Heat waves are dened as three or more consecutive days with tempera-

tures exceeding locally dened thresholds. The temperature thresholds forthe ve cities studied are: Los Angeles, 90F; Sacramento, 99F; Fresno, 102F;Riverside/San Bernardino, 102F; and San Francisco, 79F.

Extreme heat waves are dened based on threshold temperature conditionsthat occurred during the one or two most severe heat waves of eachdecade during the 19611990 reference period.

3 High-temperature extremes are dened based on the average maximumtemperatures for the hottest ve percent (or roughly 18 hottest days) ofthe year during the 19901999 reference period.

4 Results are for inows to seven major dams and reservoirs in theSacramento/San Joaquin water system, including three in the NorthernSierra (Shasta, Oroville, and Folsom) and four in the Southern Sierra(New Melones, New Don Pedro, Lake McClure, and Pine Flat).

M i f ti i il bl t li t h i

2397 Shattuck Ave., Suite 203Berkeley, CA 94704-1567(510) 843-1872

Two Brattle SquareCambridge, MA 02238-9105(617) 547-5552

[email protected]

Change, and Impacts on California, published in The Proceedings of the National Academy of Sciences(101:34, 2004), areport by K. Hayhoe, ATMOS Research and Consulting; D. Cayan, Scripps Institution of Oceanography; C.B. Field, CarnegieInstitution of Washington; P.C. Frumhoff, Union of Concerned Scientists; E.P. Maurer, Santa Clara University; N.L.Miller, Lawrence Berkeley National Laboratory; S.C. Moser, National Center for Atmospheric Research; S.H. Schneider,Stanford University; K.N. Cahill, Stanford University; E.E. Cleland, Stanford University; L.L. Dale, Lawrence Berkeley

ational Laboratory; R. Drapek, USDA Forest Service; W.M. Hanemann, University of California, Berkeley; L.S. Kalkstein,University of Delaware; J. Lenihan, USDA Forest Service; C.K. Lunch, Stanford University; R.P. Neilson, USDA ForestService; S.C. Sheridan, Kent State University; and J.H. Verville, Union of Concerned Scientists. The PNAS nd relatednalyses are described in detail at www.climatechoices.org. Support was provided in part by The Energy Foundation, The

Fred Gellert Family Foundation, The William and Flora Hewlett Foundation, The David and Lucile Packard Foundation,Oak Foundation, V. Kann Rasmussen Foundation, Wallace Global Fund, an anonymous foundation, and the Gunther family.

For more information, please contact: Katharine Hayhoe (ATMOS Research and Consulting, 574-288-1507) orAmy Luers (Union of Concerned Scientists, 510-843-1872).

Preparing for those consequences of climate changethat cannot be avoided, through careful planning and im-plementation of adaptation strategies. The health risks ofrising heat in major urban centers can be lessened, for exam-ple, by implementing heat warning systems and communityintervention programs that provide assistance to the mostvulnerable members of the population during dangerous-heat conditions.

Lowering emissions of heat-trapping gases is the most important step to slow climate change and reduce its impact. Because California isa substantial contributor to global emissions, its efforts to reduce emissions from cars and power plants could produce globally signicantresults and set new precedents for others to follow.

climate change in california - choosing our future

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