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It’s getting hot in here
RISING TEMPERATURES
8
A1B
A1T
A1FI
A2
B1
B2
IS92a
Scenarios
Bars show the
range in year 2100
produced by
several models
Several models
all SRES envelope
1000
1200
1400
1600
1800
2000
-0.5
0.0
Departures in temperature in °C (from the 1990 value)
1100
1300
1500
1700
1900
2100
-1.0
Observations, Northern Hemisphere, proxy data
Global
instrumental
observations
Projections
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
UnitedNationsEnvironmentProgramme /GRID-Arendal
Variations of the Earths surface temperature:
year 1000 to year 2100
Natural versus man made
There is new and stronger evidence that most of the warm-
ing observed over the last 50 years is attributable to human
activities. It is unlikely that the warming is to be entirely
natural. Reconstructions of climate data from the last 1,000
years also indicate that this 20th century warming was un-
usual and unlikely to be the response to natural forcing
alone. Volcanic eruptions and variation in solar irradiance
do not explain the warming in the latter half of the 20th
century, but they may have contributed to the observed
warming in the first half.
As we can see frommodels of temperature changes caused
by natural forcing, we should have observed a decrease in
the global average temperature lately, but we have not. We
have observed an increase.
Comparison between modeled and
observed temperature since 1860
Natural and man made causes
Model results
Observations
-1.0
-0.5
0.0
0.5
1.0
1850
1900
1950
2000
The model that includes
man made and natural
causes is the best fit.
Temperature anomalies in °C
Natural causes
-1.0
-0.5
0.0
0.5
1.0
1850
1900
1950
2000
-1.0
-0.5
0.0
0.5
1.0
After 1950,
the temperature rise
cannot be explained
by natural causes alone.
Man made causes
1850
1900
1950
2000
-1.0
-0.5
0.0
0.5
1.0
This temperature
increase cannot be
explained by human
activity alone.
United Nations Environment Programme / GRID-Arendal
The global average surface temperature has increased over the 20th century by about 0.6 degrees
Celsius. This increase in temperature is likely to have been the largest for any century in the last
1000 years.
Evidence from tree ring records, used to re-
construct temperatures over this period, sug-
gests that the 1990s was the warmest period
in a millennium.
It is very likely that nearly all land areas will
warm more rapidly than the global average,
particularly those at high northern latitudes in
the cold season. There are very likely to be
more hot days; fewer cold days, cold waves,
and frost days; and a reduced diurnal tem-
perature range.