Climate Change Science Tutorial #1: Overview of Our Understanding of the Climate System and Observed Climate Impacts

Transcription

1 Climate Change Science Tutorial #1: Overview of Our Understanding of the Climate System and Observed Climate Impacts September 2013 ACS Climate Science Project, OMSI Others work, collected by Prof. Julie Fry Reed College

2 Earth s energy balance & radiative forcing F in = F out F out F in 2

3 Earth s energy balance & radiative forcing F in = F out F out F in put an atmosphere on it! 3

4 Earth s energy balance & radiative forcing Atmosphere: transmits visible, absorbs IR T earth, bare : 253 K = -15 C = 5 F solve layer-wise to get an estimate for T ground : 303 K = 30 C = 86 F 4

5 Earth s Energy Balance, now with #s! ~ 30% reflected Radiative fluxes in W m -2 5 Baird & Cann, 2008

6 Earth s Energy Balance, now with #s! RADIATIVE FORCING: changes in the balance! e.g.: 1. Adding greenhouse gases 2. Adding reflective particles 6 Baird & Cann, 2008

7 Earth s Energy Balance, now with #s! Why is CO 2 such an effective greenhouse gas? 7 Baird & Cann, 2008

8 Band saturation: why T increase is not predicted to be linear with pco 2 increase Atmosphere thick with CO 2 8

9 What s doing the greenhouse-ing? IPCC, 2007

10 What s doing the greenhouse-ing? Major warmers: CO 2, CH 4, N 2 O Why are these the major warmers? 10

11 What s doing the greenhouse-ing? Major warmers: CO 2, CH 4, N 2 O Why are these the major warmers? A: They are effective absorbers of IR light with long atmospheric lifetimes 11

12 What s doing the greenhouse-ing? What about decadal changes in cooling agents, e.g. clouds/aerosols? => MUCH greater spatial variability, uncertainty! Trend , AOD yr -1, Hsu et al ACP

13 What s doing the greenhouse-ing? IPCC, 2007

14 The elephant in the atmosphere: CO peak CO 2 at Mauna Loa: 400 ppm Seasonal wiggle of about 2 ppm: biosphere breathing Summer CO 2 drawdown: CO 2 + H 2 O + sunlight O 2 + plant biomass (photosynthesis) Winter CO 2 release: plant decay CO 2 Pre-industrial CO 2 : 280 ppm Animation of latitude dependence:

15 Baird & Cann, 2008 Fate of atmospheric CO 2 Annual anthropogenic CO 2 inputs ~ 7 Gt C per year, of which only ~ 4.7 Gt remains in atmos. Where does the rest go? Annual fluxes in Gt:

16 Baird & Cann, 2008 Fate of atmospheric CO 2 Annual anthropogenic CO 2 inputs ~ 7 Gt C per year, of which only ~ 4.7 Gt remains in atmos. Where does the rest go? Annual fluxes in Gt: Lifetime of CO 2 w.r.t. ocean sink: = Mass/Flux = 800 Gt / 2.2 Gt yr -1 = 400 years!

17 TREE, 2000 Fate of atmospheric CO 2 Annual anthropogenic CO 2 inputs ~ 7 Gt C per year, of which only ~ 4.7 Gt remains in atmos. Where does the rest go? CO 2 sink to forests is poorly quantified! Varies with tree age; lifetime in biomass Annual fluxes in Gt: poorly constrained

18 Rate of Change of CO 2 Mixing Ratio (ppm/yr) Rate of change of [CO 2 ] increasing 3 From Observations Linear Fit to Observations Year

19 CO 2 : biggest driver. How much warming? Climate sensitivity = Expected equilibrium T increase if [CO 2 ] levels off at double pre-industrial (550ppm) Likely to be C Equilibrium climate sensitivity (ECS): Global annual mean surface air temperature change experienced by the climate system after it has attained equilibrium in response to a doubling of atmospheric CO 2. IPCC, 2007

20 What limits accuracy of climate sensitivity estimates using 20th century temperature trends? Uncertainty in aerosols! CO 2 and other GHG warming has been offset by an highly uncertain aerosol forcing in the cooling direction.

21 Different types of Aerosols Beijing Bangladesh Northern India Bay of Bengal Source: SeaWiFS satellite Kuwait Source: Terra/MODIS satellite Source: Terra/MODIS satellite

22 Ship Tracks and Contrails Examples of Aerosol Indirect Effects on Clouds

23 Sulfate Cooling Mid 20th Century Aerosol direct effect thought to explain temporary hiatus in T increase

24 Could cleaning up airborne particulates accelerate warming? Might we want to keep those particles aloft?? Or even add more?

25 Recent news: How to explain the observed hiatus in warming?

26 Explanation paper #1: Cancelling anthropogenic effects Radiative forcing of anthropogenic sulfur emissions (purple line), net anthropogenic forcing (blue line), linear estimate of net anthropogenic forcing (blue dash), total radiative forcing (red line), radiative forcing of solar insolation (orange line), and observed temperature (black). The SOI (divided by 10) is given in green. SOI data are presented as annual mean sea level pressure anomalies at Tahiti and Darwin. Post-1998 period of interest (highlighted gray). Anthropogenic activities that warm and cool the planet largely cancel after 1998, which allows natural variables to play a more significant role. Kaufmann et al, PNAS 2011

27 Explanation 2: Cooling of surface ocean (natural La Niña cycles) Kosaka & Xie, Nature 2013

28 Explanation 2: Cooling of surface ocean (natural La Niña cycles)

29 this will not go away on its own

30 Observations of a changing climate

31 IPCC, 2007 Temperature trends Land warming faster than oceans (recall thermal inertia) Rate of warming doubled in later half of 20 th century

32 Attribution: Temperature trend can only be modeled with anthropogenic contribution

33 IPCC, 2007 Cryosphere trends NH Changes in Snow Cover Hemispheric Changes in Sea Ice Extent

34 Glacier Lengths

35 Tropical Glaciers

36 Snows of Kilimanjaro February 17, 1993 February 21, 2000

37 Larsen Ice Shelf Collapse

38 Shrinking polar ice caps Movie: /a003464/yearly_composite.mp4

39 Global Mean Sea Level Measurements ~ 20 cm = 8 ~ 0.5 ft 1961 to 2003 global mean sea level rise: 1.8 ± 0.5 mm yr 1 Thermal expansion: 0.42 ± 0.12 mm yr 1 Melting of glaciers, ice caps & ice sheets: 0.7 ± 0.5 mm yr 1 IPCC 2007

40 IPCC, 2007 Precipitation trends Over the 20 th century: wetter eastern North America and southern South America, western Australia, northern Europe and northern and central Asia dryer Sahel (Africa), southern Europe, southern Africa and parts of southern Asia Extreme precipitation: Warmer sea surface temperatures in the Atlantic are correlated with increasing intense tropical cyclone activity.

41 Projected future precipitation changes

42 Hurricane Intensity Change

43 Global Mean Sea Level Measurements ~ 20 cm = 8 ~ 0.5 ft IPCC 2007

44 Global Mean Sea Level Measurements ~ 20 cm = 8 ~ 0.5 ft 1961 to 2003 global mean sea level rise: 1.8 ± 0.5 mm yr 1 Spatial pattern: Thermal expansion: 0.42 ± 0.12 mm yr 1 Melting of glaciers, ice caps & ice sheets: 0.7 ± 0.5 mm yr 1 IPCC 2007

45 Sea Level Projections 1.5 ft 0.5 ft IPCC 2007

46 Bangladesh Under 1 Meter Sea Level Rise

47 Mosquito-borne diseases

48 So. is this an option? Estimates: Need 1 5 Tg S/yr to negate Doubled CO 2