Observations and projections of climate change Dan Hodson AP3A90/APMA90 Climate Change and Food Systems 27/1/20111Observations 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. 27/1/20112Observations and projections of Climate Change

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 27/1/20113Observations and projections of Climate Change

What is the Climate System? Land Ocean Atmosphere Ice Vegetation 27/1/20114Observations and projections of Climate Change

Observations of Climate Change 27/1/20115Observations and projections of Climate Change

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. 27/1/2011Observations and projections of Climate Change6

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 /1/2011Observations and projections of Climate Change7/46

CET 27/1/2011Observations and projections of Climate Change8

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. 27/1/2011Observations and projections of Climate Change9

Global Observing Network 27/1/201110Observations and projections of Climate Change 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? 27/1/2011Observations and projections of Climate Change11 IPCC AR4 Different estimates (smoothed) ~ 0.8ºC

Is the rate of warming increasing? 27/1/2011Observations and projections of Climate Change12 IPCC AR4

Global Trends  More warming over land than oceans  Some regions have cooled. 27/1/2011Observations and projections of Climate Change13 IPCC AR4 Temperature trends at each point on the Earth

The ten warmest years on record  Eight of these are from the last decade  All are from the last 13 years (Data taken from the Hadley Centre) 27/1/ Observations and projections of Climate Change  Nine of these are from the last decade  All are from the last 13 years

Is it unusual?  Global average temperature rose in the 20 th Century  Is this unusual?  Have temperatures changed like this in the past?  Problem: Very few temperature measurements before  How can we measure temperatures before the invention of the thermometer?  Natural Thermometers! 27/1/2011Observations and projections of Climate Change15

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. 27/1/2011Observations and projections of Climate Change16

Estimates of past Northern Hemisphere Temperature 27/1/2011Observations and projections of Climate Change17 IPCC AR4 Recent warming unprecedented

Have other things changed?  Arctic Sea Ice Area  Glacier Lengths  Sea level height 27/1/2011Observations and projections of Climate Change18

Have other things changed?  Oceans are Warming: 27/1/2011Observations and projections of Climate Change19 Three Estimates of the Amount of heat in the upper ocean.

Greenhouse Gases?  Carbon Dioxide (CO 2 )  Nitrous Oxide (N 2 O)  Methane (CH 4 ) 27/1/2011Observations and projections of Climate Change20

Ice Cores  Ancient gases trapped in bubbles in Antarctic Ice.  Can recover ice & gases that have been stored for s of years.  Can measure levels of Greenhouse gases in Ancient atmosphere. 27/1/2011Observations and projections of Climate Change21

Unprecedented?  Rate of increase of greenhouse gases unprecedented in last years. 27/1/2011Observations and projections of Climate Change22 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 20 th 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 20 th Century. –Largest seen in last years. 27/1/2011Observations and projections of Climate Change23

Modelling the Climate 27/1/201124Observations and projections of Climate Change

Climate System Components Land Ocean Atmosphere Ice Vegetation 27/1/201125Observations and projections of Climate Change

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. 27/1/2011Observations and projections of Climate Change26

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. 27/1/2011Observations and projections of Climate Change27/46 Physics

Is the model Correct?  If we use our Climate Model to simulate 20 th Century climate we can compare to our past measurements of the real 20 th Century climate. –Model Validation 27/1/2011Observations and projections of Climate Change28 Real WorldModel Annual 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. 27/1/2011Observations and projections of Climate Change29

Two Experiments  EXPT1: Use our climate models to simulate 20 th 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 20 th Century climate as it might have been –No changes in Greenhouse gases –Known changes in Natural Forcings 27/1/2011Observations and projections of Climate Change30

Results  EXPT1: Greenhouse gases + Natural Forcings. –Black line: measured 20 th 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. 27/1/2011Observations and projections of Climate Change31 IPCC AR4

Projections of future Climate Change 27/1/201132Observations and projections of Climate Change

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. 27/1/2011Observations and projections of Climate Change33

Projected regional temperature changes /1/2011Observations and projections of Climate Change34 IPCC AR4 B1 (low) A2 (high)  Northern latitudes warm more. –Melting sea ice – feedbacks  Land warms more than oceans.

Projected regional Rainfall Changes /1/2011Observations and projections of Climate Change35 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. 27/1/2011Observations and projections of Climate Change36  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. 27/1/201137Observations and projections of Climate Change

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) 27/1/2011Observations and projections of Climate Change38

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). 27/1/2011Observations and projections of Climate Change39 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) 27/1/2011Observations and projections of Climate Change40

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. 27/1/2011Observations and projections of Climate Change41  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-20 th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations”. 27/1/2011Observations and projections of Climate Change42

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 27/1/201143Observations and projections of Climate Change

Next Lecture The next lecture: The climate system and the IPCC March 3 rd  Examine the Climate System in detail  Discuss the mechanisms for a changing climate  Discuss the IPCC & Kyoto Protocol Dan Hodson 27/1/201144Observations and projections of Climate Change