Climate Change: Observations and Projections Dan Hodson AP3A90/APMA90 Climate Change and Food Systems

Climate Change: Observations and Projections In this lecture:  What is Climate?  Observations of a changing Climate.  Climate modelling and Projections of future Climate Change  Uncertainty in Climate modelling and projection. 08/02/20132Climate Change: Observations and Projections.

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 08/02/20133Climate Change: Observations and Projections.

The Climate System Land Ocean Atmosphere Ice Vegetation 08/02/20134Climate Change: Observations and Projections.

The Atmosphere 08/02/20135Climate Change: Observations and Projections.

Atmospheric Composition Dry air contains: –Nitrogen 78% by volume –Oxygen 21% by volume –Argon 0.9% –The remaining 0.1% Carbon Dioxide (CO 2 ) Methane (CH 4 ) Nitrous Oxide (N 2 O) + other trace gases PLUS Water vapour (variable amounts ~1%) 08/02/20136Climate Change: Observations and Projections. Greenhouse Gases

The Greenhouse Effect 08/02/20137Climate Change: Observations and Projections.

Electromagnetic Radiation  All objects emit Electromagnetic Radiation (Light).  Very hot objects emit visible light (Shortwave).  Cooler objects emit infrared light (Longwave).  This radiation carries Energy away from an object which can then be absorbed by another object. Fir0002/Flagstaffotos 08/02/20138Climate Change: Observations and Projections.

08/02/2013 Main Greenhouse Gases  Although small fraction of Atmosphere, large impact.  Greenhouses gases are almost transparent to Shortwave radiation from the Sun, but almost opaque to Longwave radiation from the Earth.  Hence Greenhouse gases trap some outgoing Longwave radiation -> Disequilibrium -> Warming.  With no Greenhouse gases, average temperature of the Earth’s surface would be -19ºC rather than 14ºC. Greenhouse Gases The remaining 0.1% Carbon Dioxide (CO 2 ) Methane (CH 4 ) Nitrous Oxide (N 2 O) Water vapour 9Climate Change: Observations and Projections.

The Greenhouse Effect 08/02/201310Climate Change: Observations and Projections.

Observations of Climate Change 08/02/201311Climate Change: Observations and Projections.

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. 08/02/2013Climate Change: Observations and Projections.12

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 /02/2013Climate Change: Observations and Projections.13/46

CET 08/02/2013Climate Change: Observations and Projections.14

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. 08/02/2013Climate Change: Observations and Projections.15

Global Observing Network 08/02/201316Climate Change: Observations and Projections. 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? 08/02/2013Climate Change: Observations and Projections.17 IPCC AR4 Different estimates (smoothed) ~ 0.8ºC

Is the rate of warming increasing? 08/02/2013Climate Change: Observations and Projections.18 IPCC AR4

Global Trends  More warming over land than oceans  Some regions have cooled. 08/02/2013Climate Change: Observations and Projections.19 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) 08/02/ Climate Change: Observations and Projections  Nine of these are from the last decade  All are from the last 15 years 2012

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! 08/02/2013Climate Change: Observations and Projections.21

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. 08/02/2013Climate Change: Observations and Projections.22

Estimates of past Northern Hemisphere Temperature 08/02/2013Climate Change: Observations and Projections.23 IPCC AR4 Recent warming unprecedented

Have other things changed?  Arctic Sea Ice Area  Glacier Lengths  Sea level height 08/02/2013Climate Change: Observations and Projections.24

Have other things changed?  Oceans are Warming: 08/02/2013Climate Change: Observations and Projections.25 Three Estimates of the Amount of heat in the upper ocean.

Greenhouse Gases  Carbon Dioxide –Burning of Fossil Fuel –Manufacture of Cement (~5% global) –Deforestation  Methane –Agriculture –Natural Gas –Landfill decomposition  Nitrous Oxide –Artificial fertilizers –Burning of Fossil Fuel  Are these changes unusual? 08/02/201326Climate Change: Observations and Projections.

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. 08/02/2013Climate Change: Observations and Projections.27

Unprecedented?  Rate of increase of greenhouse gases unprecedented in last years. 08/02/2013Climate Change: Observations and Projections.28 IPCC AR4 End of Last Ice Age

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. 08/02/2013Climate Change: Observations and Projections.29

Modelling the Climate 08/02/201330Climate Change: Observations and Projections.

Climate System Components Land Ocean Atmosphere Ice Vegetation 08/02/201331Climate Change: Observations and Projections.

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. 08/02/2013Climate Change: Observations and Projections.32

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. 08/02/2013Climate Change: Observations and Projections.33/46 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 08/02/2013Climate Change: Observations and Projections.34 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. 08/02/2013Climate Change: Observations and Projections.35

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 08/02/2013Climate Change: Observations and Projections.36

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. 08/02/2013Climate Change: Observations and Projections.37 IPCC AR4

Projections of future Climate Change 08/02/201338Climate Change: Observations and Projections.

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. 08/02/2013Climate Change: Observations and Projections.39

Projected regional temperature changes /02/2013Climate Change: Observations and Projections.40 IPCC AR4 B1 (low) A2 (high)  Northern latitudes warm more. –Melting sea ice – feedbacks  Land warms more than oceans.

Projected regional Rainfall Changes /02/2013Climate Change: Observations and Projections.41 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. 08/02/2013Climate Change: Observations and Projections.42  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. 08/02/201343Climate Change: Observations and Projections.

Climate Projections: Sources of Uncertainty In Science it’s important to understand 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) 08/02/2013Climate Change: Observations and Projections.44

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). 08/02/2013Climate Change: Observations and Projections.45 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) 08/02/2013Climate Change: Observations and Projections.46

Intrinsic Uncertainty (Internal Variability)  If we start our Climate model and watch how the temperature evolves.  If we start the model again, but with e.g. slightly cooler initial temperatures.  The temperature evolves differently. 08/02/2013Climate Change: Observations and Projections.47  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”. 08/02/2013Climate Change: Observations and Projections.48

Summary In this lecture we have discussed:  What Climate is.  Observations of a Changing Climate.  Climate Modelling and Projections of future Climate Change  Uncertainty in Climate Modelling and Projection. 08/02/201349Climate Change: Observations and Projections.

Next Lecture The next lecture: Climate Change and Livestock Les Crompton Jan 15 th Dan Hodson 08/02/201350Climate Change: Observations and Projections.