An Analysis of the Impact of Climate Change on Seasonal Cycles

8/9/2019 An Analysis of the Impact of Climate Change on Seasonal Cycles

1/16AN ANALYSIS OF THE IMPACT OF CLIMATE CHANGE ON SEASONAL CYCLES

Season CreepHow Global Warming is Already Affecting the World Around Us.


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Acknowledgements

The author would like to thank all those who provided

comments, data or information for this paper, specifically:

Mark D. Schwartz, University of Wisconsin-Milwaukee;

Terry L. Root, Stanford University; Ellen Baum, Clean Air

Task Force; and the staff at Clear the Air and the National

Environmental Trust. In addition, the author would like

to acknowledge the work of the Pew Center on Global

Climate Change and the work that Camille Parmesan,

University of Texas-Austin and Hector Galbraith,

University of Colorado-Boulder did synthesizing the

observable impacts of climate change in the U.S.

This report was made possible with the funding from

The Pew Charitable Trusts. The opinions expressed in

this report are those of the author and do not necessarily

reflect the views of The Pew Charitable Trusts.

Jonathan Banks, Policy Director

Clear the Air

March 2006

Clear the Air is a national public education campaign to

combat global warming and improve air quality.

1200 18th Street, NW

Washington, DC 20036

202-887-1715

www.cleartheair.org

printer to strip union/recycled/soy inks bugs here


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Even though the full

impact of global

warming has yet to be

felt, the world around us

is already feeling the heat. According

to the latest scientific studies

reviewed for this paper, the planet

is warming and higher temperatures

are disrupting our very seasons and

turning their key indicators upside

down. Whats most startling about

the results of this range of studies

is that the researchers themselves

are tying the changes to warming

temperatures in essence, pointing

their fingers at global warming.

While to some, an early arrival

of spring may sound good, an

imbalance in the ecosystem can

wreak havoc. Natural processes

like flowers blooming, birds

nesting, insects emerging, and ice

melting are triggered in large part

by temperature. As temperatures

increase globally, the delicately

balanced system begins to fall into

ecological disarray. We call this

season creep.

In this summary we have analyzed

the most recent scientific evidence

of seasonal changes due to global

warming. Only peer-reviewed studies

published in scientific journals are

included. The results are clear: in the

Season CreepHow Global Warming is AlreadyAffecting the World Around Us

An Analysis of the Impact of

Climate Change on Seasonal Cycles


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United States and across the Northern

Hemisphere, hundreds of species

are changing in response to global

warming. Non-biological seasonal

shifts are occurring as well due to the

warming trend. In short, many of the

familiar signs and signals of spring

are arriving earlier due to global

warming:

Lilacs and honeysuckle are

blooming six days early;

Northern cardinals are singing 22

days early;

Canadian geese, robins and whip-

poor-wills are arriving earlier;

Columbine, forest phlox, butterfly

weed and shooting star are all

blooming earlier;

The breeding season of birds such

as the common murre and Mexican

jays is starting early;

Tree swallows are laying their eggs

nine days early;

Frogs are starting their mating

season 12 days early;

The marine food chain is being

disrupted as plankton bloomsarrive earlier;

Spring snow-melt in the Western

U.S. is happening 4 weeks earlier

than in the mid 20th century;

The growing season in the

upper latitudes of the Northern

Hemisphere is 12 days longer;

Lakes and rivers are freezing six

days later and thawing six days

earlier; and,

Warmer winters are moving the

maple syrup season earlier in the

year.

Canadian geese

are arriving

earlier;

Tree swallows

are laying

their eggs early

SEASON CREEP HOW GLOBAL WARMING IS ALREADY AFFECTING THE WORLD AROUND US

HONEYSUCKLE

TREE SWALLOW

CANADIAN GOOSE


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Why should we care? So what if

the ice melts sooner or the flowers

bloom early? Does it really matter?

It does. In school we were all

taught about the interconnectedness

of the natural world. Changes in

phenology (the relation between

climate and periodic biological

phenomena) in one species can

have dramatic impacts throughout

the ecosystem. For example, when

plants bloom earlier due to warmer

spring temperatures, insects that

rely upon them for food must adjust

their life cycles, as do other species

further up the food chain. If a

species in the chain does not adapt,

the chain is broken, and species begin

disappearing.

While most springtime events are

controlled by temperature, some

species time their spring events

based on hours of daylight, pushing

them out of sync with the rest of the

ecosystem that is following increased

temperature signals. Researchers in

Europe have begun studying long

distance migratory birds, specifically

the pied flycatcher. While spring

temperatures have increased in

the flycatchers nesting grounds in

Europe, the flycatchers arrival has

remained constant as it is governed

by length of day in its wintering

grounds in North Africa. This means

that the flycatcher is now arriving

too late from its wintering grounds in

Africa to take advantage of the peak

insect hatchings in Europe, which are

now earlier as a result of the warmer

temperatures at its nesting grounds.1

For many long distance migrants,

phenological changes could pose

grave risks and scientists are only

beginning to identify the dominoes

that could fall should climate change

continue unabated. And, as our

teachers taught us, we humans are inthat chain of dominoes.

As industrialized as we are,

there are still many ways that these

dominoes affect us already. Global

warming is proving disruptive to

cultural and economic activities

The Greenhouse Effect

Impacts of a Warming Arctic: Arctic Climate Impact Assessment ACIA, Overview report. Cambridge

University Press, 2004. http://amap.no/acia/

If a species in the

chain does not

adapt, the chain

is broken, and

species begin

disappearing.


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in a number of communities. For

instance, reductions in the length

and thickness of lake ice cover due

to the warming trend has had a clear

impact this winter many ice fishing

tournaments and winter festivals

have been affected or cancelled

due to insufficient ice. As a result,

traditions that have long been part

of a community s character are

suffering, and the economic benefits

of such events are being lost.

Global WarmingIt Is Here

Today. Human activities during the

last century particularly the burning

of fossil fuels have changed the

composition of the atmosphere in

ways that threaten to dramatically

alter the global climate in the years

to come. Global warming is caused

by the greenhouse effect, a natural

phenomenon in which gases in the

Earth s atmosphere, including water

vapor and carbon dioxide, trap

heat from the sun near the planets

surface. Without a natural greenhouse

effect, temperatures on Earth would

be too cold for life to survive.

Throughout the last century,

however, changes to the chemical

makeup of the Earth s atmosphere

have been accelerating. This is

largely as a result of humans

burning fossil fuels, which releases

large amounts of carbon dioxide

and other greenhouse gases

into the atmosphere. Since the

industrial revolution, atmospheric

concentrations of carbon dioxide

(CO2) have increased by 31 percent.2

Concentrations of other greenhouse

gases have increased as well. These

atmospheric changes have intensified

the greenhouse effect, allowing

less of the suns heat to escape the

Earth s atmosphere. Global average

temperatures increased during the

20th century by more than 1 F, with

Temperature and Greenhouse Gases

Impacts of a Warming Arctic: Arctic Climate Impact Assessment ACIA, Overview report. Cambridge

University Press, 2004. http://amap.no/acia/

Changes to

the makeup

of the Earths

atmosphere

have been

accelerating.


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While its true that the

Earths climate is

constantly changing,

the changes currently being felt are

at a pace that is faster than what

many species may be able to handle.

In a study published in February

in the journal Science, researchersconcluded that the warming in the

late 20th century in the northern

hemisphere is the greatest warming

the Earth has seen in 1,200 years.6

Species have always been forced

to adapt to changing climates, but

normally at a much slower pace.

Even when dramatic changes in

temperature have occurred, such as

during the past glacial cycles, species

tended to track the retreat or onset of the

glaciers instead of evolving to tolerate

new temperature regimes.7 During these

past glacial cycles, the environment was

not the one that exists today. Today,many species have nowhere to run.

Habitat destruction and fragmentation

have created ecological islands that

species may not be able to escape.8

Urban areas, highways and farm lands

surround our natural areas and block the

natural paths species would take to shift

their range in the face of climate change.

In addition, our ecosystems are under

stress from pollution, overexploitation,

and invasive exotic species.

Because of these stresses, at least 20 percent

of the worlds mammals, 12 percent of its

birds and 31 percent of its amphibians are

considered threatened with extinction.9 When

climate change is added onto these, the future

for many species is bleak. Recent research

has estimated that one-quarter of all species

will be on the road to extinction by 2050.10

Nowhere To RunA Changing Climate in a Fragmented World

the rate of change for the period

since 1976 roughly three times that

for the past 100 years as a whole.3

According to NASA, 2005 was the

hottest year in more than a century,

and the 1990s were the warmest

decade since measurements began

in 1861.4 If current trends continue,

temperatures could rise by an

additional 2.5 F to 10.4 F by 2100.5

Despite all of this, to many of

us global warming is a remote and

distant thing. We read in the papers

that polar ice caps are predicted to

melt in 2050 or 2100, but then we turn

to more immediate news. However,

scientific evidence is piling up daily,

showing that the first impacts of

global warming are already being

felt and that the rate of change is

occurring more rapidly than originally

expected. And yet, the impacts we are

seeing today may pale in comparison

to what we can expect, if global

warming continues unchecked. If

The 1990s werethe warmest

decade since

measurements

began in 1861.


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or more. Now however, phenology is

one of the primary tools for showing

the current impact of global warming

on our world. By analyzing the

careful historical records of scientists

and correlating them to temperature

records, modern day climatologists

are able to see alarming trends in

the natural cycles that govern our

seasons.

Earlier Signs of Spring

Spring indicies first leaf date departures by year across Northern Hemisphere, 1955-2002.

Schwartz 2006

For years

naturalists have

kept detailedrecords of

when the robins

arrived and

hundreds of

other naturalbeginnings.

between climate and periodic

biological and natural phenomena, is

a little known science that for much

of its history, was just a pastime of

nature lovers around the world. For

years naturalists have kept detailed

records of when the first buds on

poplars opened, when the daffodils

bloomed, when the robins arrived,

and hundreds of other natural

beginnings. In some cases the

records go back more than 100 years

all of these changes are happening in

response to just over a 1 F change

in temperatures, what kinds of

disruptions will we see in response to

the several degrees increase we expect

by this centurys end?

Phenologya 19th century

pastime gives us concrete

evidence of global warmings

fingerprint on our seasons.

Phenology, the study of the relation

ROBIN


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In recently published studies

scientists have shown

the definitive impact of a

changing climate on our

natural environment. These studies

add to the mountain of evidence that

global warming is here and the time

to address it is now.

Spring starting earlier due to

global warming: In a recent study

titled Fingerprints of Global

Warming on Wild Animals and

Plants, by Stanford University

scientist Terry Root and others,

researchers examined the springphenology of 130 species in the

Northern Hemisphere and found that

the first signs of spring are appearing

nearly 10 days earlier on average,

compared with 30 years ago. The

researchers overlaid temperature

data that shows the contribution of

human-caused global warming to

changes in plant and animal behavior.

Root says that this rapid global

environmental change is outpacing

species adaptation.11

Lilacs - the harbinger of an early

spring: Using models of the dates

of first leaf and first bloom in

lilacs and honeysuckle (species

which are good representatives of

the response of many temperate trees

and shrubs) driven by temperature

records for the Northern Hemisphere,

Mark D. Schwartz of the University

of Wisconsin-Milwaukee and his

colleagues have found that spring

is arriving between five and six

days earlier during the 1955-2002

period. This finding is consistent

with the warming trend reflected in

the temperature data and past smaller

scale studies. Schwartz found that

spring was warmer earlier, and that

the last freeze across the Northern

Hemisphere was also becoming

earlier at a similar rate.12

Nature changing its habits:

Another recent meta-analysisby Terry Root of 143 previously

published studies reveals a consistent

temperature-related shift, or

fingerprint, in a number of species,

everything from mollusks to mammals

and grasses to trees. More than 80

percent of the 1,400 plant and animal

species studied show a trend toward

earlier seasonal events. On average,

trees bud, frogs mate, and birds nest

more than a week earlier than they

did 50 years ago. One of the biggest

changes was in the breeding of the

Common Murre which has advanced

by 24 days per decade.13

How Climate Change is

Disrupting the Seasons

The dates of

first leaf and

first bloom of

lilacs show that

spring is arriving

5-6 days earlier.

LILACS


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The timing of

the spring maple

syrup tap season

is crucial and the

traditional tap

time has become

disrupted andhard to predict.

MAPLE SYRUP TAPPING

Leopold wouldnt recognize this

place: Aldo Leopold, the father

of wildlife ecology, helps provide

one of the longer term analyses of

species changes due to changing

temperatures. In the 1930s and 40s,

Leopold made detailed observations

of the timing of spring events on

his farm in Wisconsin. Recently,

researchers compared his data on

birds and native flowers to their

own surveys taken in the 1980s and1990s to see how species might

have changed during the 61-year

period in the face of a 5 F increase

in March temperatures. Researchers

found that Canadian geese arrive 29

days earlier, robins arrive 10 days

earlier, whip-poor-wills arrive 12

days earlier, northern cardinals sing

22 days earlier, columbine blooms 13

days earlier, forest phlox blooms 15

days earlier, butterfly weed blooms

18 days earlier and shooting star

blooms 10 days earlier. Of the 55

species studied, 35 percent showed

advancement of spring events. On

average, this study found that spring

events are occuring more than seven

days earlier now than they did during

Leopolds time.14

Maple syrup and a warmer

climateits not so sweet: A delicate

balance of sun, rain, snowfall, and

freezing temperatures is what helps

the maple tree turn its starch into the

sugar we in turn make into maple


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PhotoofMexicanjaybyBrianSmall.

The breeding

season of the

Mexican jay

advanced by an

average of 10

days. Egg laying

was also found tobe closely related

to spring monthly

temperatures.

MEXICAN JAY

syrup. A good maple syrup season

depends on nighttime temperatures

below freezing and warm daytime

temperatures greater than 40 F.

If there are a series of nights in

which temperatures dont fall below

freezing, the sap stops flowing. In

general, syrup tappers find that the

first sap flow of the season provides

the highest quality syrup, which

translates into the highest value

syrup.

The timing of the spring tap is

crucial and the traditional tap time

has become disrupted and hard to

predict. In Vermont, trees were

historically tapped between the

middle of March and the middle

of April. With warmer late winter

and early spring temperatures, this

has shifted towards the middle ofFebruary. The U.S. maple syrup

industry has significantly declined

since the early 1900s due to many

factors, including climate related

events such as severe weather and

insect outbreaks. Research is also

showing that actual sap production

may be decreased by warmer

winter and spring temperatures.

Furthermore, as climate modeling

efforts have shown, climate change

could, during the course of several

hundred years, remove the sugar

maple from the New England region

altogether. 15

Early breeding season:

Researchers studying Mexican jays

in the Chiricuahua Mountains of

southern Arizona found that between

1971 and 1998, the breeding season

of the birds advanced by an average

of 10 days. Egg laying was also

found to be closely related to spring

monthly temperatures, which have

increased during the duration of the

study by about 4.5 F.16 In a much

larger study of springtime bird habits,

researchers found that tree swallows

throughout their North American

range are laying their eggs nine days

early. The study looked more than

3,400 nest records that spanned the

years 1959-1991.17


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The study of phenology

provides us with a useful

tool for understanding the

current impacts of global warming on

our environment. However, to date,

phenological work is often limited in its

geographic coverage or it is restricted

to just a few species. Development of a

national network to provide coast to coast

phenological observations, long a dream of

scientists working on these issues, is finally

materializing. At an August 2005 meeting

in Arizona, scientists began the process

of implementing the first U.S.A. National

Phenology Network. The network, once

fully realized, will be instrumental in revealing

large-scale species response patterns to

climate change. The scientists have set

the goals for the network as (1) facilitating

thorough understanding of phenological

phenomena, including their causes and roles

in the biosphere; (2) providing empirical data

for ground-truthing, making the most of the

large public investment in satellite platforms

and remote sensing; (3) allowing the

detection and prediction of environmental

change for myriad applications, including

but not limited to assessing impacts of land

use and climate variability/change; and (4)

engaging thousands of citizen scientists

to contribute to data collection. The result

of these efforts will provide scientists with

a wealth of information to more accurately

characterize the phenological changes

occurring in the U.S. and compare them to

similar work being conducted throughout

the world. The network and materials from

the 2005 workshop can be accessed at:

www.npn.uwm.edu.

The National Phenology Network

Researchersdiscovered that

the food chain in

the North Atlantic

Ocean has been

radically altered.

COD

Marine environments are also

showing phenological changes:

Most of the research on phenological

changes has been conducted on

land, but researchers recently have

discovered that the food chain in

the North Atlantic Ocean has been

radically altered. Using records

of 66 different types of plankton,

the key to the marine food chain,

researchers tracked changes in peak

plankton bloom throughout a 44

year period. They discovered that

the timing of many plankton bloomshas been moving progressively

forward while others have stayed

stable. Researchers have found that

for the stable forms, length of day

is the likely driver for the timing of

their bloom. The study found that

due to the differences in how fast

each type of plankton is moving its

bloom date forward, a mismatch in

the food chain is occurring. This

is exacerbating the decline of such

commercial fish as cod. During the

study period, North Atlantic spring

sea surface temperatures increased by

almost 1.8 F. 18

Early amphibian breeding: In

one of the longest scientific records,

researchers studying frogs in Ithaca,

New York were able to compare

recent data from the 1990s to turn

of the century data. Researchers

found that temperatures in the area

have increased during the matingseason by 1.8-4 F and that male

frogs in almost 70 percent of the

species present at the studied lakes

were beginning their mating calls

approximately 12 days earlier than

they were in the early 1900s.19

Satellites show longer growing

season: Using satellite imagery

researchers have been able to


13/1611

Spring snowmelt

in the Western

U.S. is occurring

up to four weeks

earlier.

demonstrate that the growing

season in the higher latitudes of the

Northern Hemisphere (north of an

imaginary line between Portland,

ME and Portland, OR), has expanded

by approximately 12 days. The

lower latitudes have also shown an

increase in growing season, but not

as pronounced.20

Melting ice and snow: Spring

snow melt and lake ice-out (the

thawing of ice on the surface of a

body of water) dates are other spring

phenomena that are trending earlier

in the year. Researchers at the

Scripps Institution of Oceanography

have found that spring snow melt

in the Western U.S. is occurring up

to four weeks earlier than it was in

1948. While some of the changes are

attributed to other decadal weather

events, the researchers clearly state

that global warming is increasing

the trend toward earlier melt. The

implications for the water starved

West are huge: early melt means less

water when it is most needed in the

late summer.21

In the Northeast, researchers withthe U.S. Geological Survey (USGS)

have found that lakes are thawing

nine to 16 days earlier than they

were in 1850. This correlates with

a temperature increase during the

same time period in the region of

2.7 F.22 In addition, the USGS team

found that river ice thickness was

decreasing as well, by as much as 23

cm.23

Researchers at the University

of Wisconsin compiled data from

lakes and rivers across the Northern

Hemisphere to analyze the trend

in freeze and thaw dates. They

found that on average, that lakes

and rivers were freezing almost six

days later and thawing more than six

days early during the 1846 to 1995

period. Again, temperature recordsshowing a 2 F increase for the study

area show the fingerprint of global

warming.24

Changing the oddsa national

solution to global warming.

The impacts of global warming are

already being felt. If we are to avoid

the most catastrophic impacts, the

U.S. must take immediate action to

dramatically reduce its greenhouse

gas emissions. There is no silver

bullet, but we must implement

policies that:

Prevent irreversible harm to our

climate and our world.

Guarantee that global warming

pollution will go down and not up.

Assure enforceable deadlines for

making reductions.

The U.S. can produce substantial,

near-term reductions in domestic

greenhouse-gas emissions by using

market mechanisms to provide

companies with the incentives and

flexibility necessary for them to

take steps to reduce their pollution.

These mechanisms have been used

in the context of acid rain here in the

U.S. and are now being employed in

other parts of the world to address

climate change.


14/1612


Endnotes

1. Both, C. and Visser, M., May 17, 2001.

Adjustment to climate change is constrained

by arrival date in long-distance migrant bird.

Nature, Vol 411.

2. Intergovernmental Panel on Climate Change,

2001. IPCC Third Assessment Report Climate

Change 2001: Summary for Policy Makers.


January 2005.IPCC Third Assessment Report

Climate Change 2001: Summary for Policy

Makers, 2001; and World MeteorologicalOrganization, United Nations, WMO Statement

on the Status of the Global Climate in 2004:

Global Temperature in 2004 Fourth Warmest

(press release).

4. J. Hansen, R. Ruedy, M. Sato, and K. Lo,

NASA Goddard Institute for Space Studies and

Columbia University Earth Institute, December

2005. GISS Surface Temperature Analysis,

Global Temperature Trends: 2005 Summation.


2001. IPCC Third Assessment Report Climate

Change 2001: Summary for Policy Makers.

6. J. Osborn and K. Briffa, February 10, 2006.

The Spatial Extent of 20th Century Warming in

the Context of the past 1,200 years. Science.

7. Davis, M. and C. Zabinski, 1991. Changes in

geographical range resulting from greenhouse

warming: Effects on biodiversity in forests.

Yale University Press , New Haven, CT, 1992

and Huntley, B.How plants respond to climate

change: Migration rates, individualism and the

consequences for plant communities. Journal of

Botany 67:15-22.

8. Pyke, C., 2004. Habitat loss confounds climate

change impacts. Frontiers in Ecology and the

Environment: Vol. 2, No. 4, pp. 178182.

9. The IUCN Red List of Threatened Species,

2004. International Union for Conservation of

Nature and Natural Resources. http://www.

iucnredlist.org/info/tables/table1

10. Thomas, C. et. al, January 2004.Extinction

Risks from Climate Change. Nature 427, 145-148.

11. Root, T et. al., May 24, 2005.Human-

modified temperatures induce species changes:

Joint attribution. Proceedings of the NationalAcademy of Sciences, vol. 102, no. 21.

12. Schwartz, M., Ahas, R. and Aasa, A., 2006.

Onset of spring starting earlier across the

Northern Hemisphere. Global Change Biology,

12, 343-351.

13. Root, T. et. al., January 2, 2003. Fingerprints

of global warming on wild animals and plants.

Nature 421, 57-60.

14. Bradley, N. et. al., August 17, 1999.

Phenological changes reflect climate change

in Wisconsin. Proceedings of the National

Academy of Sciences, Vol. 96, Issue 17, 9701-9704.

15. Rock, B. and Spencer, S. 2001. Case study

2: the maple sugar industry. Chapter 5, New

England Regional Assessment. Available at

http://www.necci.sr.unh.edu/2001-NERA-

Foundation-Doc.html

16. Brown, J., et. al., 1999.Long-term trend

toward earlier breeding in an American bird: A

response to global warming? Proceedings of the

National Academy of Sciences, 96:5565-5569.

17. Dunn, P. and Winkler, D., 1999. Climate

change has affected the breeding date of

tree swallows throughout North America.

Proceedings of the Royal Society of London, B

266:2487-2490.

18. Edwards, M. and Richardson, A., August

2004. Impact of climate change on marine

pelagic phenology and trophic mismatch. Nature

430, 881-884.

19. Gibbs, J. and Breisch, A., 2001. Climate

warming and calling phenology of frogs near

Ithaca, New York, 1900-1999. Conservation

Biology 15:1175-1178.

20. Zhou, L. et. al., 2001. Variations in northern

vegetation activity inferred from satellite data of

vegetation index during 1981 to 1999. Journal o

Geophysical Research, Volume 106, Issue D17

21. Stewart, I. et. al., January 2004. Changes

towards earlier streamflow timing across

Western North America. Climatic Change, Vol.

62.

22. Hodgkins, G., Huntington, T., and

James II, I., December 16, 2002.Historical

changes in lake ice-out dates as indicators of

climate change in New England, 1850-2000.International Journal of Climatology, 22: 1819-

1827.

23. Hodgkins, G., Huntington, T., and Dudley,

R., 2003.Historical trend in river ice thickness

and coherence in hydroclimatological trends in

Maine. Climatic Change, 61: 217-236.

24. Magnuson, J., et. al., September 8, 2000.

Historical trends in lake and river ice cover in

the Northern Hemisphere. Science, vol. 289.

In 2005, as part of the mark-up

of the Energy Policy Act of 2005,

the Senate passed a bipartisan

resolution acknowledging the

science behind global warming and

calling for legislation to slow, stop

and reverse emissions of global

warming pollution, by mandatory

means. The resolution, offered by

Senators Jeff Bingaman (D-NM)

and Arlen Specter (R-PA), marks the

first time a majority of senators has

recognized the pressing need to take

action to address global warming.

Its time for Congress to make

good on the promise of that

resolution. We have the technology

to begin addressing this problem.

What is needed is political will. As

the evidence continues to mount

that global warming is here now and

is threatening everything from the

birds and the bees to our cities and

towns our leaders should rise to the

occasion and set national pollution

limits to begin dealing with the very

real threat of climate change.


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An Analysis of the Impact of Climate Change on Seasonal Cycles