Future Climate Change
How do you know whether to trust a prediction
about the future?
All predictions are based on “global circulation models”
(GCMs, AOGCMs)
- model accuracy is verified by its ability to predict
observed changes
trustworthy
untrustworthy
1
IPCC/UN asked modelers worldwide to use six
emissions scenarios in their simulations
The six “SRES scenarios” differ in 3 important ways:
2100
Population
(billions)
Energy Use
(EJ/yr)
% Carbonfree Energy
CO2 (ppm)
Scenario
1990 A1FI A1B A1T A2
5.3
7.1
7.1
7.0
15.1
B1
B2
7.0
10.4
351 2,100 2,200 2,000 1,700 500 1,350
18
31
65
85
28
52
49
950
700
550
850
550
600
The future depends on choices we’re making now
CO2 is predicted to reach 550-950 ppm by 2100
A1FI
A2
A1B
B1
Could be higher, if positive feedbacks are strong
- Earth’s climate has several “tipping points”
Other GHGs will also increase
2
As a consequence, Earth’s average temperature is
predicted to rise by 2.0-4.6o C by 2100
History A1B
3.0o
A1FI
A1T
A2
B1
B2
4.6o
2.6o
4.0o
2.0o
2.7o
Earth will warm even if we stop emitting today
A1FI
A2
A1B
B1
0.6o
Zero emissions
3
Temperature rise is likely to persist for ≥ 1,000 years
after we stop emitting greenhouse gasses
Warming will be most severe in the arctic
B1: Arctic warming of ~ 4o
(global mean of 2o)
A1B: Arctic warming of ~ 6o
(global mean of 3o)
A2: Arctic warming of ~7-8o
(global mean of 4o)
- Arctic is site of strongest
positive feedbacks
4
Continued melting of the cryosphere
- Arctic summer sea ice may disappear before 2100
What’s happened over the last 21,000 years?
www.youtube.com/watch?v=C3Jwnp-Z3yE&hd=1
The future projection is based on the assumption of
complete cessation of carbon dioxide emissions in 2100
(~IPCC A2). Because future world population is
uncertain, it was frozen at 7 billion people.
5
Many glaciers are likely to disappear by 2100,
including all intertropical glaciers by 2030
- more than a billion people rely on glaciers and seasonal
snowpacks for water supply
- including 750,000,000 people in China and India
Continued loss of seasonal snowcover
- largest decreases over western U.S. and eastern Europe
6
Continued loss of ice sheets
- full melting of Greenland ice sheet → 7 m sea level rise
- full melting of Antarctic ice sheet → 57 m sea level rise
Permafrost will continue to thaw
- top 25 m estimated to contain ~750-950 Gt of carbon
- 750 Gt currently in atmosphere
7
Tundra permafrost contains more carbon than the
aboveground vegetation of several major biomes
Soil
Total
600
400
200
Tu
nd
ra
W
et
la
nd
s
C
ro
pl
an
ds
0
Tr
op
ic
al
Te
fo
m
re
pe
st
s
ra
te
fo
re
B
st
or
s
ea
lf
Tr
or
op
es
ic
ts
Te
al
sa
m
pe
va
ra
nn
te
as
gr
as
sl
an
ds
D
es
er
ts
Gigatons of Carbon
Vegetation
- globally, >4 times more carbon in soils than in vegetation
8
Sea level rise of 1-2 meters by 2100 (?)
- up to 300 million people could be flooded each year
with 1 meter rise
- at least 10 million/yr
Southeast Asia and islands would be most affected
9
Much of U.S. would be affected by 1 meter rise
Much of Florida would also be under water
10
So would much of the east coast
Long-term sea level rise due to melting of ice sheets
even if climate is stabilized
11
Continued later freezing and earlier break-up of lake
and river ice
- 3 week increase in summer lake stratification period
Altered precipitation patterns
- small increase (5%) in global precipitation
- but much geographic and seasonal variation
Winter
Summer
- increases in high latitudes in both seasons
- but decreases in mid-latitude summer precipitation
12
Big increase in severe precipitation events
- especially over NH land
- flooding, erosion, disease
Severe storms have increased in US since 1948
13
Increased droughts also
Land area in extreme drought predicted to increase
from 1% → 30% by 2100 in the A2 scenario
in at least severe drought:
5% → 40%
in at least moderate drought: 20% → 50%
14
Latitudinal gradient in winter precipitation in U.S.
Summer rainfall is predicted to decrease throughout U.S.
15
US breadbasket could become largely unsuitable
for agriculture
Increased heat waves
16
The number of days >90o will increase in Michigan
The number of days >90o will increase in Michigan
17
The number of days >90o will increase in Michigan
Large increases in “extremely hot” winters, summers,
and years in US during 2071-2100
Extremely Hot Winters
Number hotter than a “1 in 20 year event” during 1961-1990
18
Large increases in “extremely hot” winters, summers,
and years in US during 2071-2100
Extremely Hot
Hot Summers
Winters
Extremely
Number hotter than a “1 in 20 year event” during 1961-1990
Large increases in “extremely hot” winters, summers,
and years in US during 2071-2100
Extremely Hot
Hot Years
Winters
Extremely
Summers
Number hotter than a “1 in 20 year event” during 1961-1990
19
By 2100 in Europe, every other summer
could be like 2003
>40,000 Europeans died from heat stress
Future summers are very likely to be hotter than any
experienced thus far
20
Future summers are very likely to be hotter than any
experienced thus far
Drought and famine especially in Africa
21
Fire frequency is predicted to increase in many areas
Cessation of the Great Ocean Conveyor Belt?
- if so, temporary cooling of North Atlantic
Positive global feedback
22
Hmmm….. not likely
Increased frequency of stronger hurricanes
- 80% increase in Categories 4-5 over last 35 years,
most likely due to warmer oceans
23
Most models predict increase in Category 5 hurricanes
Storm surge would be much more damaging
24
What might Earth look like in the year 10,000?
https://content.wuala.com/contents/karlr/Dokumente/Bluemarble10000.mp4?key=GC7WpnktmsVI&dl=1
Bottom line:
Current trends are expected to continue, but at an
accelerating rate
What is today an extreme event is likely to become
commonplace
If “tipping points” are reached, change may be
more rapid, and less reversible, than predicted thus
far
25