Download Climate change - cause and consequences

Climate change
causes and consequences
Professor Nigel Arnell
Walker Institute for Climate System Research
Commonwealth War Graves Commission
Climate change conference
London, February 11 2008
Recent “unusual” weather…
Summer 2007
Summer 2003
Met Office
Global average temperature
Global average temperature
Temperature anomaly from 1961-1990 average (oC)
1
All of the 10
warmest years
since 1850 have
occurred since
1995
0.8
0.6
0.4
0.2
0
1840
1860
1880
1900
1920
1940
1960
1980
2000
-0.2
-0.4
-0.6
-0.8
Crutem3gl, Climatic Research Unit, University of East Anglia
2020
Outline
• What is driving this change in climate?
• What could happen in the future?
• How will weather change?
• What can we say about the next 20 years?
• What will be the effects of climate policy?
What is driving the change in climate?
Possible explanations:
- natural variability
- variation in solar output
- increasing concentration of greenhouse gases
“Greenhouse” gases alter the radiative balance of
the surface of the earth by trapping outgoing longwave radiation
Carbon dioxide (CO2)
Methane
Nitrous oxides
Water vapour
Changing concentrations
CO2
Methane
Nitrous oxide
IPCC AR4 WG1 2007
Changing emissions
IPCC AR4 WG3 2007
Forcing the climate
IPCC AR4 WG1 2007
Attributing change
IPCC AR4 WG1 2007
Attributing change
IPCC AR4 WG1 2007
What could happen in the future?
Future climate changes will depend on:
(i) rate of future emissions of greenhouse gases
(ii) rate at which these are absorbed by land and
oceans
(iii) how the climate responds to the changing
atmospheric composition
Use climate models to simulate response
Future global temperature change
Different
emissions
Different
climate models
IPCC AR4 WG1 2007
Variations over space
Change in average annual temperature by the
end of the 21st century
A1b
IPCC AR4 WG1 2007
Variations over space
December-February
June-August
IPCC AR4 WG1 2007
Changes in Europe
2-5oC by the end of the century
1-2.5oC by the 2020s
IPCC AR4 WG1 2007
Changes in Europe
IPCC AR4 WG1 2007
Changes in Asia
2-4oC by the end of the century
0.75-2oC by the 2020s
IPCC AR4 WG1 2007
Change in Asia
IPCC AR4 WG1 2007
How will weather change?
A change in “climate” will impact via a change in
local weather
Change in the weather
Widespread:
Increase in the frequency of hot extremes
Decrease in the frequency of cold extremes
In many areas
Increase in the frequency of high-intensity rainfall
Increase in the frequency of “drought” events
Change in key weather patterns
Monsoons:
- monsoon rainfall will probably increase, but this is
uncertain
El Nino:
- uncertainty over how this will change
Tropical cyclones
- will probably increase in intensity, but not necessarily in
frequency
Significant uncertainty over changes in extremes:
we know that they will change, but not how they
will change
High resolution weather simulation
What will happen over the next 20
years?
• Climate change is superimposed on natural
variability; in the medium term this
variability is relatively large
– year to year variability
– multi-year rhythms
Our models don’t necessarily
simulate this very well yet…
The next 20 years
• Model predictions depend on where the
model starts from…
Smith et al. (2007) Science
What effects would climate policy
have?
Article 2:
…stabilization of greenhouse gas
concentrations in the atmosphere at a
level that would prevent dangerous
anthropogenic interference with the
climate system…
• Kyoto target:
- Annex 1 countries reduce emissions by 5% by
2008-12, compared to 1990 levels
• EU target
- Reduce emissions by 20% by 2020
Effects of policy on climate
No climate policy
commitment
With policy targets
Van Vuuren (2007)
Adaptation
We need to adapt to a changing climate
Coping with uncertainty
Develop risk-based
methods with multiple
scenarios
Develop flexible adaptation
measures which do not
rely on precise forecasts
Some conclusions
• Climate change is happening, and is due to
human activity
• By the end of the century, temperatures will be
1.8-4oC higher – and possibly more
• Effects on weather vary locally
• General tendency towards an increasing
frequency of extremes
• Climate policy will not stop impacts over the next
couple of decades
Thank you
www.walker-institute.ac.uk