Transcript Climate change - is it really happening

Climate Change – is it really happening?
Kathy Maskell
Walker Institute for Climate System Research,
University of Reading
Overview
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Where we are with the science
What’s new in IPCC (2007) – focus on WG1
Skeptics – countering their agruments
Current challenges for climate science
Global mean temperatures are rising
faster with time
Period
Rate
50 0.1280.026
100 0.0740.018
Years /decade
IPCC (2007)
Evidence of warming…. across the globe,
atmosphere, land and ocean
since 1979
Surface
Atmosphere
Evidence of warming….
• Land and ocean surface
• Ocean to depths of at least 3000 m
• Warmer oceans > thermal expansion and sea level rise
IPCC (2007)
‘Warming of the climate system is
unequivocal’ – IPCC 2007
• The land, oceans and the air are all warming, sea ice
and glaciers are melting
Mountain
2004
1941
glaciers
are melting
Sub-Saharan Africa and
Mediterranean are getting drier
Northern Europe
is getting wetter
Recent warming is unusual
The northern hemisphere is probably the warmest it’s been
for at least 1300 years
Temperature can be
inferred from tree ring
width
Mann et al., Science 1999 (Northern Hemisphere only)
People are changing the atmosphere in drastic
ways
Carbon dioxide levels are higher than at any time in last
650,000 years! (IPCC 2007)
Greenhouse gases – sources and sinks
Carbon dioxide - sources
~2/3 from fossil fuels
~1/3 from deforestation
Carbon dioxide – sinks
30% into ocean, 25% uptake by terrestrial
biosphere
45% remained in atmosphere – removed slowly
Methane – from cows, paddy fields ..
Natural sources – e.g., wetlands
Nitrous oxide – from agriculture and land-use change
Natural sources
Other human effects on climate?
Aerosols - small particles
– From SO2, biomass burning, industrial dust
– Typically reflect sunlight back to space
– IPCC (2007) better quantified, but still quite
uncertain
Typically
produce a
cooling
DIRECT EFFECT
scatter sunlight
back to space
INDIRECT EFFECT
make clouds brighter
and last longer
Natural factors …. can they explain the
warming?
Variation’s in the Sun’s output
Volcanoes
11-year sun-spot cycle
Effects short-lived 1-2 years
BASIC SCIENCE: Effect of human activities
since 1750 - positive radiative forcing
Radiative Forcing (RF)
IPCC (2007)
The Climate System
Climate models must contain the atmosphere, the
oceans, ice and the land surface and consider all the
possible influences on climate
The physics within climate models
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Climate models are our laboratory.
We use them to understand past changes and to
predict the future.
The earth is represented by a
grid of squares, typically of
length 250 km, and by a stack
of layers.
This gives us a 3-D picture of
the circulation of the
atmosphere and oceans
Human influence seen on every continent
New in IPCC (2007) human influence “very likely” (90%)
IPCC (2007)
How do we forecast climate?
Future greenhouse
gas/aerosol emissions depend on population, energy
use, new technologies, etc
Climate forcing
Climate system
response and feedbacks
- clouds, ice, oceans etc
Emissions of CO2 through the 21st century
Climate change will get worse in the 21st
Century
By 2100: world could be 2 to 4oC warmer – on top of the
0.7oC we’ve already seen.
IPCC (2007)
IPCC (2001)
Regional temperature changes
Warming greatest over land
and at most high
northern latitudes
and least over the
Southern Ocean
and parts of the
North Atlantic
Ocean
2020s
2080s
low
med
high
IPCC (2007)
IPCC (2007): Projections of likely shifts in rainfall
patterns
 % change in rainfall by end of 21st
century, where more than 2/3 of
the models agree on the sign of
the change.
 White areas denote regions
where no consistent signal is
predicted e.g. Africa.
IPCC (2007)
Other projected changes
• Sea level rise
– Mainly due to thermal expansion of sea water
– 0.2 to 0.6m rise by 2100
– Not the same everywhere – regional pattern not well
known (could be 2 or 3 times global mean)
• Ice sheets
• Recent dramatic melting around
Antarctic and Greenland
• These dynamical effects not included
in numbers above
IPCC (2007)
By: Roger Braithwaite and Jay Zwally.
Key areas of uncertainty and challenges for
climate research
• There’s still a big range in temperature
projections – due to differences in model
feedbacks (clouds especially)
• Carbon cycle feedbacks …
• Regional patterns and extremes – especially
rainfall
• Interactions between climate variability and
climate change
Modelling climate at higher resolution
Improves: El Niño and its effects, hurricanes and
other tropical weather, mid-latitude storms
CLIMATE
CHANGE
IS HAPPENING…….
Climate
change
is happening.
Climate change is serious.
Time for action ….
Find out more …….
www.walker-institute.ac.uk
www.ipcc.ch
ipcc-wg1.ucar.edu
…..AND
ITS EFFECTS ARE LIKELY TO BE VERY PROFOUND
Solar irradiance does not correlate
with recent warming
Surface Temperature
Solar Irradiance
Solar forcing over 20th century –
positive, but much smaller than
greenhouse gases
Figure courtesy of Gareth Jones
How unusual is the current warmth?
Impacts of climate change (IPCC 2007 – WG2)
• Human influence evident in observed impacts
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(earlier spring, rivers and lakes, heat related deaths,
agriculture)
1/3rd of species at increased risk of extinction
Millions at risk from coastal flooding
Human health – heat, drought, diseases
Food
– yields likely to increase at higher latitudes (up to 3ºC warming)
– yields decrease in developing world
• Water
– more rainfall at high latitudes
– decrease in areas already water stressed
– Less water stored in snow and ice – less spring, summer meltwater