Download An Overview of Canada`s Changing Climate Contents of the 2014

An Overview of Canada’s
Changing Climate
Bush, E.J., J.W. Loder, T.S. James, L.D.
Mortsch and S.J. Cohen.
In Canada in a Changing Climate:
Sector Perspectives on Impacts and Adaptation.
2014
Contents of the 2014 update report
FULL REPORT
Synthesis
1. Introduction
2. An Overview of Canada’s Changing
Climate
(EC, DFO, NRCan)
3. Natural Resources
4. Food Production
5. Industry
6. Biodiversity and Protected Areas
7. Human Health
8. Water and Transportation
Infrastructure
9. Adaptation: Linking Research and
Practice
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Contents of Chapter Two
1. Introduction
2. Changes in Air Temperature and
Precipitation
3. Changes to the Cryosphere
•
Permafrost
•
Snow cover
•
Glaciers
•
Freshwater Ice and Sea Ice
4. Changes to Freshwater Resources
5. Changes in Ocean Climate
•
Temperature
•
Salinity and density stratification
•
Hypoxia and acidity
•
Sea level change
6. Summary
Chapter discusses both observed and projected changes for each component
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Chapter objectives
•
Bring climate information of broad interest to Canadians together in one
place
– Large suite of indicators for changes in temperature, precipitation,
freshwater, snow, ice and permafrost, ocean climate and sea level
– Focus is on changes at the national scale; regional variability discussed
•
Update results from the 2008 report
– Focus on literature from the past few years
– Provide updated climate change projections from 2008 report
•
Increase awareness about the scope and magnitude of changes that are
occurring already across Canada and those that are expected to occur over
the coming century and beyond
The chapter draws heavily on long-term monitoring programs of Environment
Canada, Fisheries and Oceans Canada and Natural Resources Canada.
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Chapter scope: the climate system
IPCC, 2007
5
Assessing climate change and human influence
becomes more challenging at regional scales
Detection and attribution of change from analyses of long
observational records, understanding of causes and use of models
Sparse Observations + Large Natural Variability (e.g. Decadal-Scale)
Challenges in Separating Anthropogenic and Natural Change
Projections of future change, from recent changes, coupled
climate model simulations, and knowledge of Earth’s climate system
Uncertainty in climate system response + Model limitations
Need ensemble projections from many models
Challenges in Downscaling to regional scale projections
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3
Global warming is unequivocal and greenhouse
gases are the dominant cause
•
Global temperature
has increased about
0.85°C since 1880
•
Each of the last three
decades has been
warmer than all
preceding decades
since 1850
•
Observed warming has
been primarily due to
human emissions of
greenhouse gases
1oC
2000s
1990s
1980s
(IPCC, 2013)
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Warming in Canada has been about twice the
global average
Annual mean temperature anomalies
(°C) relative to 1961-1990
Trend in annual mean surface temperature, between 1950-2010 of 1.5°C
EnvCan, 2011
• Nighttime min temperatures rising faster than daytime max temperatures
• Increasing number of warm summer days and decreasing number of cold
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winter nights
4
Warming has been widespread across Canada
Trends in seasonal mean temperature, 1950-2010
Winter
Warming
observed in
all seasons
Summer
Most
pronounced
in winter and
spring, and
weakest in
the fall.
Fall
Spring
Largest in
west (winter
and spring)
and north
(fall)
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Vincent et al., 2012
Precipitation has been increasing across Canada as
a whole; less snowfall in winter in southern Canada
1950-2010
• Increase in total annual
precipitation of ~16%
• Increasing annual rainfall
• Variability across Canada
• Snowfall shifting to rainfall in
southern Canada in winter
EnvCan, 2011
Rainfall
Snowfall
Annual rainfall and snowfall
trends, 1950-2009 (mm/yr)
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Mekis and Vincent, 2011
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There have been significant changes in heavy
rainfalls in some areas
•
•
•
No consistent pattern of
change for Canada
Trends in extreme precipitation,
1950-2010
Observed changes are
consistent with those for
North America and
Northern Hemisphere
land areas
Global analyses indicate
trends towards more
severe drought in
southern and western
Canada since 1950
Vincent and Mekis, 2006, updated
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This century, Canada could look quite different than
the Canada we are currently adapted to
Low emissions scenario
WINTER
SUMMER
Air Temperature
SUMMER
High emissions scenario
WINTER
Projected seasonal changes in surface air temperature (°C), 2080s
Precipitation
Low emissions scenario
SUMMER
WINTER
High emissions scenario
SUMMER
WINTER
Projected seasonal changes in precipitation (%), 2080s
Canadian Climate Change Scenarios Network: www.cccsn.ec.gc.ca/
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Some types of extreme weather will increase as the
climate continues to warm; others will decrease
Projected changes in temperature extremes
Extremes in daily
temperature
•
•
Increases in the frequency and magnitude of unusually warm days and
nights
Decreases in unusually cold days and nights
Long duration events
•
Increase in the length, frequency and intensity of warm spells, heat
waves over most land areas, including Canada
Rare hot extremes
•
One-in-twenty year extreme hot day projected to become about a onein-five year event over most of Canada by mid-century
Projected changes in precipitation extremes
Heavy precipitation
•
More frequent heavy precipitation events are projected with an
associated increased risk of flooding
Rare precipitation events
•
Rare events projected to become about twice as frequent by midcentury over most of Canada
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Snow cover is declining especially in Spring
Observed - Earlier spring snow melt is
driving the declining # days with snow cover
in the second half of the snow season
Projected - Widespread
decreases in the duration of
snow cover throughout the
year
2080s vs 1980s
1950-2007
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7
Summer sea ice cover is declining and getting
thinner in Canadian waters
Canadian Ice Service Digital Archive data,
decadal changes over 1968-2010
• All ice trends include first year and multiyear ice
• Rapid declines in summer ice cover are
evident in Canadian sea ice regions
• Largest declines of 17% per decade
• Consistent with Arctic Ocean results, ice
cover is getting thinner in some areas (less
multi-year ice)
• Canadian archipelago receives in-flow of
multi-year ice from the Arctic Ocean
• Ice conditions could remain difficult
there into the future
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% change per decade
Derksen et al. 2012
Permafrost temperatures have increased in
recent decades
• Ground
temperatures have
increased in both
warm discontinuous permafrost
zones and colder
areas
Norman Wells
Alert
• Warming and
thawing of
permafrost will
continue but
thawing of cold
permafrost could
take many
decades to
centuries
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Credit: Sharon Smith, NRCAN
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Glaciers in both western Canada and the high
Arctic are receding
Changes in net mass balance indicate whether the glacier is gaining or
losing ice
Observed:
• Significant
declines in
glacier mass are
evident over the
past several
decades
• Western glaciers
are reaching
record low
extents
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Credit: NRCAN, GSC
Observed Changes to Freshwater Resources
Trends in 1-day maximum (left) and minimum (right) river
flow, 1970-2005.
Ecosystem Status and Trends Report, 2010
• Watersheds strongly influenced by spring snowmelt (most of Canada
except for the Pacific coast) can be expected to experience an earlier
peak in maximum runoff in the spring
• Depending on the amount of warming, this peak could occur several
weeks earlier than present timing in a warmer climate
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Projected changes in annual runoff
Global models
Regional
studies
(IPCC WGII, 2014)
Fig. 23, Ch. 2
• Projected changes for the 2050s, from 44
•
global model runs, based on ~2°C warming
Pronounced increase in run-off in northern
Canada, but smaller changes in southern
Canada (with uncertainty in sign)
•
•
Projected changes for the 2050s,
from regional studies
-/+ indicates both decreases and
increases in southern Canada, and
overall uncertainty
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Ocean climate change around Canada
Canada is bounded by three
oceans with a complex coastline
and many coastal seas.
Arctic
NW
Atlantic
NE
Pacific
DFO Long-term
Monitoring Sites
Ocean variability is heavily
influenced by the atmosphere, but
the oceans also have internal
variability and large influences on
the atmosphere on both global and
regional scales.
Long-term observational records
are more limited than for the
atmosphere, so detection of
climate change is more difficult
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10
Observed Changes in Global Ocean Climate
(IPCC AR4, 2007)
In mid-high latitudes
Surface warming and freshening
reduced surface water density
increased stratification
reduced oxygen and nutrient supply
Increased CO2 uptake
decreased pH / increased acidity
shallower CaCO3 saturation depths
impacts on shell formation
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Observed Changes in Global Ocean Climate
(IPCC AR4, 2007)
In mid-high latitudes
Surface warming and freshening
reduced surface water density
increased stratification
reduced oxygen and nutrient supply
Increased CO2 uptake
decreased pH / increased acidity
shallower CaCO3 saturation depths
impacts on shell formation
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Temperature, salinity and subsurface oxygen
are changing off Canada’s Pacific coast
Ocean Temperature
Long-term warming trends
of ~0.1oC per decade in
near-surface waters
2oC
Weak freshening trends at
some locations
Dissolved Oxygen
Strong natural decadalscale variability (e.g. El
Niño)
(DFO Monitoring Programs)
100
μmole/kg
Decreasing subsurface
oxygen in NE Pacific and
along BC shelf
=> Ocean hypoxia a
serious issue for some
marine organisms
Hypoxic
1920
2010
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Temperature, salinity and subsurface oxygen are
also changing off Canada’s Atlantic coast
Long-term warming trends of
~0.1-0.2oC per decade in the
Gulf of St. Lawrence and Bay
of Fundy
Ocean Temperature
Long-term surface freshening
in the Bay of Fundy.
2oC
Ocean Salinity
(DFO Monitoring Programs)
1
1910
2010
Increasing salinity at depth in
the Gulf of St. Lawrence due
to competing influences from
surface freshening and
ocean circulation changes
No net long-term changes in
temperature and salinity off
Newfoundland and Labrador
due to strong natural multidecadal variability
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Changes in Ocean Acidity
Increasing CO2 in the atmosphere leads to increasing CO2 in the ocean
•
lowers pH leading to “ocean acidification”
•
pH has decreased by ~0.1 since the beginning of the industrial era
Observational data off Canada, although sparse, indicate that
acidification is generally occurring at rates near the global average but
larger in some areas
•
e.g. at depth in the St. Lawrence Estuary
Ocean acidification effects are more pronounced in the cold fresh
waters of the Arctic where carbonate saturation depths are already
shallow
Ocean acidification has numerous adverse implications for marine
ecosystems, including increased
difficulty for some organisms to
build calcareous shells.
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Global mean sea level rose through the 20th
century, and has risen faster in the past 2 decades
300 mm
Global mean sea
level increased by 21
cm from 1880 to
2012.
Global sea-level rose
at 1.7 ± 0.5 mm/yr in
20th century.
For 1993-2003,
global sea-level has
risen at 3.1 ± 0.7
mm/yr and this trend
continues to the
present.
0
1870
2020
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Relative sea level (RSL) rise along Canadian coastlines is
strongly influenced by vertical land motion due to
rebound from past glaciation
Model simulation of vertical land motion due to Glacial Isostatic Adjustment
(also known as “postglacial rebound”)
Land rising in central
parts of continent and
sinking around edges
Beaufort
This contributes to RSL
fall in some areas (e.g.
Hudson Bay, north shore
of Gulf of St. Lawrence)
and to RSL rise in others
(e.g. Beaufort, Maritimes)
Maritimes
(ICE-5G,
Peltier 2004)
Vertical land motion due
to tectonics contributes to
RSL along BC coast (not
shown here).
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Most Projections Indicate a Continuing Acceleration
of Global Sea-level Rise through the 21st Century
Shading: IPCC TAR.
Vertical bars:
IPCC 4th AR.
Global sea level
may rise by more
than 1 metre by
2100. A rise of
ten’s of centimetres
is all but assured.
Future relative sealevel change will
continue to be
influenced by
vertical land
motion.
Global seal level will continue to rise beyond 2100, perhaps by many metres.
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Extreme high water levels are expected to increase in
frequency where mean sea-level is projected to rise
• Rise in relative sea level will contribute to increased
extreme (high) water levels, flooding, and coastal
erosion in parts of Canada.
• Reduced sea-ice cover is expected to contribute to
extreme water levels and coastal erosion in some
regions of Arctic and Atlantic Canada.
• Increased storminess is also expected to contribute
to increased extreme water levels and coastal
erosion, but projections are equivocal about
magnitude and location.
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Future Changes in Ocean Climate
Expect over 50-100 years:
• Widespread warming, especially in surface waters
• Decreasing extent and volume of sea ice
• Surface freshening in most areas
• Coastal sea level rise and increasing occurrence of coastal erosion and
flooding in many areas
• Increases in wave activity in areas with reduced sea ice
• Widespread increasing ocean acidity and decreasing subsurface oxygen
Important:
- Seasonal and spatial variability
- Natural decadal-scale variability may predominate for some variables in
some areas over the next few decades
- Limitations of models for quantitative projections with robust confidence
for most variables
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Assessment Synthesis key conclusion #1:
Canada’s climate is changing, with observed changes in
air temperature, precipitation, snow and ice cover and
other indicators. Further changes are inevitable.
OBSERVED TRENDS:
Atmosphere / land surface
•
•
Surface temperature in Canada has increased by 1.5°C since 1950, about twice global average.
Cold extremes have decreased, hot extremes have increased, precipitation has increased overall
and winter snowfall is shifting to rainfall in southern Canada; widespread reductions in the
amount and duration of snow and ice cover.
Oceans:
•
•
Upper-ocean warming and reductions in subsurface oxygen off most of Pacific and Atlantic
Canada, and increasing ocean acidity off all three Canadian coasts.
Sea level is rising more quickly than the global average along Canadian coastal areas where the
land is subsiding due to glacial rebound, while sea level has fallen in some other areas where
glacial rebound or tectonics is causing the land to rise.
FUTURE CHANGES:
•
•
Continuation and exacerbation of many of the observed trends - warming, increased
precipitation, reduced ice and snow cover, increasing ocean acidity and rising sea level.
Regional and short term variability will persist, particularly for indicators such as surface
freshwater availability.
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