observations and projections of climate change
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AP3A90/APMA90 Climate Change and Food Systems. Observations and projections of climate change. Dan Hodson [email protected]. Observations and projections of climate change. By the end of this lecture you should be able to engage in a discussion about: - PowerPoint PPT PresentationTRANSCRIPT
Observations and projections of climate change
Dan Hodson
AP3A90/APMA90 Climate Change and Food Systems
27/1/2011 1Observations and projections of Climate Change
Observations and projections of climate change
By the end of this lecture you should be able to engage in a discussion about: The Observations of a changing Climate. Climate modelling and Projections of future Climate
Change Uncertainty in Climate modelling and projection.
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What is Climate?
“Climate is what you expect, Weather is what you get”.
Climate is the statistics of weather, e.g. the average of weather conditions over some period of time.
Expect :
Maldives to be Warm
Antarctica to be Cold
Atacama Desert Dry
Bergen Wet
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What is the Climate System?
Land
Ocean
Atmosphere
Ice
Vegetation
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Observations of Climate Change
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Climate Change
Climate can be defined as the average of weather. Climate is what we Expect. A Change in Climate means e.g. a change in the
average weather conditions & change in what we expect e.g.:– Warmer summers– Wetter winters
But also can talk about the Climate in terms of other system components e.g.– The height of the sea.– The number of forest fires each summer.
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Observing the Weather
People have always watched and noted the weather, but Objective measurements using scientific instruments began only ‘recently’:– Thermometers around since 1600’s– Early 1700’s Daniel Gabriel Fahrenheit manufactured first
reliable mercury thermometers.
The Central England Temperature record is the Oldest instrumental record of temperature in the world. – Monthly measurements back to 1649.
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CET
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Observing the Weather
Observations continued in this uncoordinated way for many years.– Individual Weather diaries– Marine weather logbooks
Once weather forecasting began, it was realised that coordinated, reliable, regular measurements of the weather were required.
World Meteorological Organisation (1950) set up to coordinate this observation across the World.
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Global Observing Network
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Locations of land, ship and buoy observations across the world at 6am 14 January 2008
Land observations concentrated in inhabited areas and mainly in the Northern Hemisphere
1970
Has the Earth Surface Warmed?
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IPCC AR4
Different estimates
(smoothed)
~ 0.8ºC
Is the rate of warming increasing?
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IPCC AR4
Global Trends
More warming over land than oceans Some regions have cooled.
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IPCC AR4
Temperature trends at each point on the Earth
The ten warmest years on record
1. 19982. 20053. 20034. 20025. 20096. 20047. 20068. 2007 9. 200110.1997
Eight of these are from the last decade
All are from the last 13 years
(Data taken from the Hadley Centre)
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1. 19982. 20103. 20054. 20035. 20026. 20097. 20048. 20069. 2007 10.2001
Nine of these are from the last decade
All are from the last 13 years
Is it unusual?
Global average temperature rose in the 20th Century
Is this unusual? Have temperatures changed like this in
the past? Problem: Very few temperature
measurements before 1900. How can we measure temperatures
before the invention of the thermometer?
Natural Thermometers!27/1/2011 Observations and projections of Climate Change 15
Tree Rings
Trees grow outwards and lay down a new ring of wood every year.
More vigorous growth = thicker ring.
Growth dependent on temperature, rainfall etc.
Can estimate temperature from the width of rings.
~1000 years.
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Estimates of past Northern Hemisphere Temperature
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IPCC AR4
Recent warming unprecedented
Have other things changed?
Arctic Sea Ice Area Glacier Lengths Sea level height
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Have other things changed?
Oceans are Warming:
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Three Estimates of the Amount of heat in the upper ocean.
Greenhouse Gases?
Carbon Dioxide (CO2)
Nitrous Oxide (N2O)
Methane (CH4)
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Ice Cores
Ancient gases trapped in bubbles in Antarctic Ice.
Can recover ice & gases that have been stored for 10 000s of years.
Can measure levels of Greenhouse gases in Ancient atmosphere.
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Unprecedented?
Rate of increase of greenhouse gases unprecedented in last 20 000 years.
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IPCC AR4
Observations of Climate Change: Summary Many 1000s of measurements form estimate of
changing climate. Global average (mean) surface temperature rose by
~0.8ºC during the 20th Century. 9/10 of the last 10 years were the warmest on record
globally. These warm temperature are likely highest in the
past ~1000 years. Also
– Sea level & Upper ocean heat content rose– Arctic sea ice and Glaciers melted
Concentrations of Major Greenhouse gases risen over 20th Century.– Largest seen in last 20 000 years.
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Modelling the Climate
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Climate System Components
Land
Ocean
Atmosphere
Ice
Vegetation
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Why?
Why do we need a model of the Climate System? Most of Experimental Science
– Take some part of the World.– Make some change.– Measure any Effect.
The Climate System is the World. Can’t do real experiments on the
Whole Climate System. Need Climate Models.
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Modelling the Climate System Do experiments to find out how Climate components
(e.g. water) behave. Write down a mathematical description of this
behaviour. Convert this into a numerical form for use in a
computer.
Can then use model Earth climate to perform experiments not possible with the real Earth Climate.
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Physics
Is the model Correct?
If we use our Climate Model to simulate 20th Century climate we can compare to our past measurements of the real 20th Century climate.– Model Validation
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Real World ModelAnnual Rainfall
IPCC AR4
Is the model Correct?
Models simulate some variables better than others.– Temperature is predicted accurately– Rainfall less so
Climate models reproduce many of the features of the real climate– Global Patterns temperature & rainfall– Seasonal retreat of ice caps– North Atlantic Gulf Stream
these are not explicitly built into the model, they emerge from the physics.– More confidence that models are reliable.
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Two Experiments
EXPT1: Use our climate models to simulate 20th Century climate as it was.– Known Increases in Greenhouse gases– Known changes in Natural Forcings
• Volcanoes• The slight variations of light from the Sun.
EXPT2: Use our climate models to simulate 20th Century climate as it might have been– No changes in Greenhouse gases– Known changes in Natural Forcings
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Results
EXPT1: Greenhouse gases + Natural Forcings.– Black line: measured 20th
Century Global average Temperature.
– Red Line: Average of same experiment with many different climate models.
EXPT2: Natural Forcings Only.
Implication: Increases in Global average Temperature due to increases in Greenhouse gas emissions.
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IPCC AR4
Projections of future Climate
Change
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Projected global temperatures
A2/A1B/B1 – different estimates of future GHG emissions.– A2 = High Emissions– B1 = Low Emissions
Large range by end of century.
Some warming even if we stopped emitting all GHG today.
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Projected regional temperature changes 2090-2099
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IPCC AR4
B1 (low)
A2 (high)
Northern latitudes warm more.– Melting sea ice –
feedbacks
Land warms more than oceans.
Projected regional Rainfall Changes 2090-2099
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Northern Winter
Northern Summer
Different regions show different rainfall changes.
Northern high latitudes: increased rainfall in N. Hemisphere winter.– Wetter, more flooding.
Southern Africa & Mediterranean reduced rainfall in N. Hem. Summer– Drier, more droughts.
Grey shading – regions where we are confident.
Extremes
These are projections of the increase in the average temperatures and rainfall.
If the average temperature increases, then the chance of heat waves occurring increases.
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2003 European heatwave– Probably hottest EU summer in last
500 years.– Stott et al (2004) likely to be
considered a cool summer in 2100.
Uncertainty in Climate modelling
and projection.
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Climate Projections: Sources of Uncertainty
In Science it’s important to know what you don’t know.
Three sources of uncertainty in climate projections: Uncertainty in future Greenhouse gas levels
(Scenario Uncertainty) Uncertainty in the formulation of the Climate models
(Model Uncertainty) Intrinsic uncertainty in the climate system.
(Internal Variability)
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Scenario Uncertainty
We don’t know what future Greenhouse gas emissions will be.
Produce ‘Scenarios’ – estimates of future emissions based on estimates of future– Population Projections– Economic Development– Structural and Technological Change
Vary from High growth (A1) to Low
growth (B2).
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Emissions Scenarios IPCC,2000
Model Uncertainty
Climate models are only approximate models of the real world. They have low resolution
– A region of 200km x 200km represented by a single point.
They cannot represent small scale processes directly– Formation of rain represented by statistical rather than physical model.
They cannot include all processes in the Climate System– Ocean biology, Dynamic vegetation, Agriculture, Economics are only
just beginning to be included.
There are many Climate models (17 used in last IPCC report)
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Intrinsic Uncertainty (Internal Variability)
If we start our Climate model and watch how the temperature evolves.
If we start the model again, but from a slightly different point
The temperature evolves differently.
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Butterfly effect. Sensitivity to the initial conditions. Because we do not know the exact state of the Climate
system now, we cannot predict the exact future state of the climate.
Working with uncertainty
Although these sources of uncertainty exist we can assess and quantify the scale of uncertainty.
This allows us to assign a level of confidence to climate projections.
This allows the IPCC AR4 to say:– “Most of the observed increase in global average
temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations”.
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Summary
In this lecture we have discussed:
The Observations of a changing Climate. Climate modelling and Projections of future Climate
Change Uncertainty in Climate modelling and projection
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Next Lecture
The next lecture:
The climate system and the IPCCMarch 3rd
Examine the Climate System in detail Discuss the mechanisms for a changing climate Discuss the IPCC & Kyoto Protocol
Dan Hodson
27/1/2011 44Observations and projections of Climate Change