Understanding how carbon dioxide emissions from …

1 Understanding how carbon dioxide emissions from human activity contribute to global climate changeMYLES ALLEN Environmental Change Institute, School of Geography and the Environment & Department of PhysicsUniversity of impact of carbon dioxide emissions on global climate How rising atmospheric CO2causes global warming How industrial emissions are increasing atmospheric CO2 Modeling the impact of increasing CO2concentrations Quantifying human and natural influences on global climate A digression on ice-ages How rising temperatures are affecting global sea level The permanent, cumulative impact of CO2emissions Implications for the impact of delay in emission reductionsThe impact of carbon dioxide emissions on global climate How rising atmospheric CO2causes global warming How industrial emissions are increasing atmospheric CO2 Modeling the impact of increasing CO2concentrations Quantifying human and natural influences on global climate A digression on ice-ages How rising temperatures are affecting global sea level The permanent, cumulative impact of CO2emissions Implications for the impact of delay in emission reductions1824-1860s.

2 Fourier and Tyndall Identified CO2as one of the trace gases responsible for the blanketing effect of the atmosphere, absorbing and emitting infra-red radiation, keeping Earth s surface air molecules interact with electromagnetic radiationSome of the many modes of motion of a CO2moleculeThe fewer modes of motion of an O2or N2molecule+--Some of these modes create asymmetrically-charged dipoles which interact with electromagnetic radiation, particularly in the infra-red part of the first quantitative account of the impact of rising CO2on temperature: SvanteArrhenius Any doubling of the percentage of carbon dioxide in the air would raise the temperature of the earth's surface by 4 C; and if the carbon dioxide were increased fourfold, the temperature would rise by 8 C.

3 Both temperature and density of absorbing CO2molecules decrease with heightView from sideView from aboveRate of energy emitted to space depends on the average temperature of molecules as seen from aboveIncreasing CO2forces energy to escape from higher altitudesView from sideView from aboveRate of energy emitted to space depends on the average temperature of molecules as seen from aboveHigher air is colder, and so radiates less energyView from sideView from aboveRate of energy emitted to space depends on the average temperature of molecules as seen from aboveSo the surface and lower atmosphere have to warm up to restore balanceView from sideView from aboveOriginal state before CO2increase & warmingRate of energy emitted to space depends on the average temperature of molecules as seen from aboveSuccessive CO2doublings have about the same impact on global energy budgetView from sideView from aboveAfter the first CO2doubling and before warmingImpact of rising GHGs on the spectrum of outgoing energy has been directly observed from spaceNimbus 4.

4 1970 Comparison of outgoing spectra, 1997 versus et al (2001)And is tested in the models used for weather forecasting millions of times per daySatellite observed outgoing radiationModelledoutgoing radiationDessleret al, JGR, 2008 Gilbert Plass(1955) and the role of water vapour Noted the CO2theory had been criticized because of strong absorption of infra-red radiation by water vapor. Correctly observed that at the altitudes from which radiation escapes to space, above the humid lower atmosphere, CO2is the dominant greenhouse gas. Emphasized urgency of measuring impact of carbon dioxide emissions on global climate How rising atmospheric CO2causes global warming How industrial emissions are increasing atmospheric CO2 Modeling the impact of increasing CO2concentrations Quantifying human and natural influences on global climate A digression on ice-ages How rising temperatures are affecting global sea level The permanent, cumulative impact of CO2emissions Implications for the impact of delay in emission reductionsRoger Revelle, 1957 Explained how ocean buffer chemistry limits the amount of CO2taken up by the oceans, even in equilibrium.

5 Hence CO2emissions have a permanent impact on climate: we can t rely on the oceans to dilute them David Keeling s observations, 1958-60 Unequivocal evidence that CO2concentrations are rising steadilyCarbon dioxide levels are rising to levels not seen in over 20 million yearsAtmospheric oxygen and carbon isotopes indicate recent CO2increase is created by combustion, not simply released from the oceansWhere is this carbon dioxide coming from?Cumulative CO2emissions added up over timeAnd cumulative sinks: atmospheric accumulation is more than half cumulative fossil fuel emissionsPlants and soils are absorbing some additional CO2but land sink is predicted to weaken as temperatures rise The impact of carbon dioxide emissions on global climate How rising atmospheric CO2causes global warming How industrial emissions are increasing atmospheric CO2 Modeling the impact of increasing CO2concentrations Quantifying human and natural influences on global climate A digression on ice-ages How rising temperatures are affecting global sea level The permanent.

6 Cumulative impact of CO2emissions Implications for the impact of delay in emission reductionsModeling the impact of rising CO2concentrations: the global energy budget Increased CO2and other forms of pollution are already reducing outgoing radiation by about W/m2 Equals million TWhper year World primary energy consumption is ~175,000 TWhper year The planet as a whole has to warm up to restore the balance between incoming and outgoing the global energy additional W/m2 INdue to increased additional W/m2 OUTdue to 1 C observed W/m2increasing heat content of the climate systemMost of that energy imbalance is being trapped in the oceans 135 ZJ/decade First documented by Sydney Levituset al (2000)The global energy budget, now and in equilibriumDFexternal=l+m()

7 DT+DQoceanDF2xCO2=lDT2xCO2 Net energy imbalance due to external drivers = c. W/m2 Additional energy emitted to space per degree of warming due to disequilibriumWarming relative to pre-industrial = c. 1 CRate of energy accumulation in climate system = c. W/m2 Equilibrium warming due to doubling CO2( Climate Sensitivity )Additional energy emitted to space per degree of warming in equilibriumEnergy imbalance due to doubling CO2= W/m2 Now:Equilibrium: Bottom-up estimates of warming due to doubling of CO2 Manabeand Wetherald, 1967: single-column radiativeconvective model, C Manabeand Wetherald, 1975: three-dimensional general circulation model, CThe 1979 National Academy of Sciences Report Gave a range of C for equilibrium warming on doubling CO2, emphasizing.

8 Oceans could delay the estimated warming for several decades We may not be given a warning until the CO2loading is such that an appreciable climate change is inevitable. Evidence that a detectable signal was not needed to make predictions19001920194019601980200020202 040206020800123456 Warming relative to pre-industrial (oC)Observed global average temperaturesPre-1977 Post-19771900192019401960198020002020204 0206020800123456 Warming relative to pre-industrial (oC)Observed global average temperaturesPre-1977 Post-1977 Figure 1 from William D. Nordhaus, Strategies for Control of carbon dioxide , Cowles Discussion Paper 477, January 6, 1977 The impact of carbon dioxide emissions on global climate How rising atmospheric CO2causes global warming How industrial emissions are increasing atmospheric CO2 Modeling the impact of increasing CO2concentrations Quantifying human and natural influences on global climate A digression on ice-ages How rising temperatures are affecting global sea level The permanent, cumulative impact of CO2emissions Implications for the impact of delay in emission reductionsWarming itself is relative to 1861-1880 (oC)

9 Observed monthly global average temperaturesObserved changes are a consequence of human and natural influences: Wallace Broeker, 1974 The impact of carbon dioxide emissions on global climate How rising atmospheric CO2causes global warming How industrial emissions are increasing atmospheric CO2 Modeling the impact of increasing CO2concentrations Quantifying human and natural influences on global climate A digression on ice-ages How rising temperatures are affecting global sea level The permanent, cumulative impact of CO2emissions Implications for the impact of delay in emission reductionsThe origins of the Little Ice Age, 1400-1900 Gradual C cooling over the millennium.

10 Onset can be explained as a response to higher volcanic activity and low solar numberN. Hemisphere temperatureVolcanicactivityMilutinMilank ovitchand the origins of the ice agesMilankovitchcycles and ice-core records over the past 800,000 yearsPermanent ice observed (even in Antarctica) only appeared after CO2dropped below 400ppmAge (Millions of years before present)More recent drivers of change in global temperature1900192019401960198020002020- 4-2024 Top-of-atmosphere imbalance (W/m2)Drivers of change in the global energy balance:Human activityLong- and short-term solar variabilityVolcanic activityThe shape of the responses to these drivers is determined by simple energy relative to 1861-1880 (oC)Expected responses to external drivers:Human activityLong- and short-term solar variabilityVolcanic activityWe use these fingerprints to test the null-hypothesis that CO2has no warming relative to 1861-1880 (oC) warming in 2016 (oC)Total human-induced warming for this level of CO2-induced warmingBest-fit contribution from solar and volcanic activityCombinationBest fit to observed warming allowing any amplification of respo