climate change: observations and projections

Download Climate Change: Observations and Projections

Post on 23-Feb-2016




0 download

Embed Size (px)


AP3A90/APMA90 Climate Change and Food Systems. Climate Change: Observations and Projections. Dan Hodson Climate Change: Observations and Projections. In this lecture: What is Climate? Observations of a changing Climate. - PowerPoint PPT Presentation


The climate and climate change

Climate Change: Observations and ProjectionsDan Climate Change and Food Systems Climate Change: Observations and ProjectionsIn this lecture:What is Climate?Observations of a changing Climate.Climate modelling and Projections of future Climate ChangeUncertainty in Climate modelling and projection.08/02/20132

Climate 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 Wet08/02/20133Climate Change: Observations and Projections.Climate is also understood to include the higher moments of the statistics of weather for example the variance or variability of a quantity. We might expect the average temperature in the Maldives 30 C, but the day to day temperature may vary +/- 5C around this mean (the variance).

The Climate SystemLandOceanAtmosphereIceVegetation08/02/20134Climate Change: Observations and Projections.We will discuss these components in detail in the lecture: The Climate System and the IPCC Atmosphere08/02/20135Climate Change: Observations and Projections.Atmospheric Composition Dry air contains:Nitrogen 78% by volumeOxygen 21% by volumeArgon 0.9%The remaining 0.1%Carbon Dioxide (CO2)Methane (CH4)Nitrous Oxide (N2O)+ other trace gasesPLUS Water vapour (variable amounts ~1%)08/02/20136Climate Change: Observations and Projections.Greenhouse Gases

The Greenhouse Effect08/02/20137Climate Change: Observations and Projections.Electromagnetic RadiationAll 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.


08/02/20138Climate Change: Observations and Projections. Greenhouse GasesAlthough 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 Earths surface would be -19C rather than 14C.

Greenhouse GasesThe remaining 0.1%Carbon Dioxide (CO2)Methane (CH4)Nitrous Oxide (N2O)Water vapour9Climate Change: Observations and Projections.The Greenhouse Effect

08/02/201310Climate Change: Observations and Projections. of Climate Change08/02/201311Climate Change: Observations and Projections.Climate ChangeClimate 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 summersWetter wintersBut 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.12Observing the WeatherPeople have always watched and noted the weather, but Objective measurements using scientific instruments began only recently:Thermometers around since 1600s Early 1700s 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 1649.08/02/2013Climate Change: Observations and Projections.13/46CET08/02/2013Climate Change: Observations and Projections.14 the WeatherObservations continued in this uncoordinated way for many years.Individual Weather diariesMarine weather logbooksOnce 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.15Global Observing Network

08/02/201316Climate Change: Observations and Projections.Locations of land, ship and buoy observations across the world at 6am 14 January 2008Land observations concentrated in inhabited areas and mainly in the Northern Hemisphere

1970Locations of land, ship and buoy observations across the world at 6am 14 January 2008Distribution of measurements not uniform - Land observations concentrated in inhabited areas and mainly in the Northern HemisphereIn addition to dedicated weather stations, amateurs and commercial ships and airplanes contributeMany locations release weather balloons which measure most of the troposphereSatellites have been used since the 70s and provide a global viewFor climate monitoring purposes a long record of observations are neededOnly short satellite recordGood coverage of all oceans only happened in the last 5 yearsHas the Earth Surface Warmed?08/02/2013Climate Change: Observations and Projections.17

IPCC AR4 Different estimates (smoothed)~ 0.8CAverage across all months in the year, all measurements across the globe sea and land.Corrected for non-uniform distribution of measurements across the globeColoured curves are four different estimates (from different research groups) of the global average temperature change they have been smoothed to remove some of the year-to-year (noisy) variations.

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

IPCC AR4 No real increase in global average (mean) temperatures before 1900.Rate of warming appears to be increasing.Global TrendsMore warming over land than oceansSome 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 record19982005200320022009200420062007 20011997

Eight of these are from the last decadeAll are from the last 13 years(Data taken from the Hadley Centre)08/02/201320Climate Change: Observations and Projections.199820102005200320022009200420062007 2001

Nine of these are from the last decadeAll are from the last 15 years2012Is it unusual?Global average temperature rose in the 20th CenturyIs 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!08/02/2013Climate Change: Observations and Projections.21

Tree RingsTrees 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 Temperature08/02/2013Climate Change: Observations and Projections.23

IPCC AR4 Recent warming unprecedentedHave other things changed?Arctic Sea Ice AreaGlacier LengthsSea 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 GasesCarbon DioxideBurning of Fossil FuelManufacture of Cement (~5% global)DeforestationMethaneAgricultureNatural GasLandfill decompositionNitrous OxideArtificial fertilizersBurning of Fossil FuelAre these changes unusual?

08/02/201326Climate Change: Observations and Projections.Ice CoresAncient 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.08/02/2013Climate Change: Observations and Projections.27

Unprecedented?Rate of increase of greenhouse gases unprecedented in last 20 000 years.08/02/2013Climate Change: Observations and Projections.28

IPCC AR4 End of Last Ice AgeObservations of Climate Change: SummaryMany 1000s of measurements form estimate of changing climate. Global average (mean) surface temperature rose by ~0.8C 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. AlsoSea level & Upper ocean heat content roseArctic sea ice and Glaciers meltedConcentrations of Major Greenhouse gases risen over 20th Century.Largest seen in last 20 000 years.08/02/2013Climate Change: Observations and Projections.29Modelling the Climate08/02/201330Climate Change: Observations and Projections.

Climate System ComponentsLandOceanAtmosphereIceVegetation08/02/201331Climate Change: Observations and Projections.

Why?Why do we need a model of the Climate System?Most of Experimental ScienceTake some part of the World.Make some change.Measure any Effect.The Climate System is the World.Cant do real experiments on theWhole Climate System.Need Climate Models.08/02/2013Climat


View more >