CLIMATE RESPONSES TO PROGRESSIVE MID- LATITUDE AFFORESTATION

Transcription

1 CLIMATE RESPONSES TO PROGRESSIVE MID- LATITUDE AFFORESTATION Marysa Laguë Dept. of Atmospheric Science University of Washington Ecoclimate Lab Advisor: Dr. Abigail Swann

2 1. Global climate impacts of mid-latitude afforestation 2. How climate response scales with area of afforestation M Laguë 2

3 Mid-latitude afforestation drives local and remote shifts in cloud cover and energy transport Energy response scales linearly with the area of afforestation (precipitation doesn t) M Laguë 3

4 How can plants influence the climate? Short Wave Radiation Long Wave Radiation Latent Heat Sensible Heat Carbon Cycling Wind M Laguë 4

5 How can plants influence the climate? Short Wave Radiation Long Wave Radiation Latent Heat Sensible Heat Carbon Cycling Wind Surface Energy Budget M Laguë 5

6 How can plants influence the climate? Short Wave Radiation Long Wave Radiation Latent Heat Sensible Heat Carbon Cycling Wind M Laguë 6

7 How can plants influence the climate? Short Wave Radiation Long Wave Radiation Latent Heat Sensible Heat Carbon Cycling Wind M Laguë 7

8 How can plants influence the climate? Short Wave Radiation Long Wave Radiation Latent Heat Brighter, reflects more energy Sensible Darker, Carbon absorbs more Wind energy Heat Cycling M Laguë 8

9 Climate impacts of vegetation change has been explored at two scales: Regional (anthropogenic) Global/ Continental Scale: tens to hundreds of thousands of km 2 Scale: tens of millions of km M Laguë 9

10 Vegetation change has been explored at two scales: Regional (anthropogenic)? Global/ Continental Scale: tens to hundreds of thousands of km 2 Scale: tens of millions of km M Laguë 10

11 Vegetation change has been explored at two scales: Regional (anthropogenic)? What I m looking at Global/ Continental Scale: tens to hundreds of thousands of km 2 Scale: tens of millions of km M Laguë 11

12 Global land-cover changes don t create gradients Changes in global temperature gradients can drive changes in circulation Not usually considered in regional experiments M Laguë 12

13 Global land-cover changes don t create gradients Changes in global temperature gradients can drive changes in circulation Not usually considered in regional experiments Afforestation of the northern mid-latitudes shifts the intertropical convergence zone (ITCZ) north. Swann M Laguë 13

14 Global land-cover changes don t create gradients Changes in global temperature gradients can drive changes in circulation Not usually considered in regional experiments Afforestation of the northern mid-latitudes shifts the intertropical convergence zone (ITCZ) north. ITCZ Swann M Laguë 14

15 Global land-cover changes don t create gradients Changes in global temperature gradients can drive changes in circulation Not usually considered in regional experiments Afforestation of the northern mid-latitudes shifts the intertropical convergence zone (ITCZ) north. Add trees to northern mid-latitudes ITCZ Swann M Laguë 15

16 Global land-cover changes don t create gradients Changes in global temperature gradients can drive changes in circulation Not usually considered in regional experiments Afforestation of the northern mid-latitudes shifts the intertropical convergence zone (ITCZ) north. Add trees to northern mid-latitudes ITCZ shifts northward ITCZ Swann M Laguë 16

17 Experiments: Incrementally increase the area of trees in the northern mid-latitudes M Laguë 17

18 Experiments: Incrementally increase the area of trees in the northern mid-latitudes Replace present-day grassland and agricultural land with broadleaf deciduous trees M Laguë 18

19 Experiments: Incrementally increase the area of trees in the northern mid-latitudes Replace present-day grassland and agricultural land with broadleaf deciduous trees 8 experiments, each with ~ 2,000,000 km 2 of new trees (about the size of Alaska) M Laguë 19

20 Experiments: Incrementally increase the area of trees in the northern mid-latitudes Replace present-day grassland and agricultural land with broadleaf deciduous trees 8 experiments, each with ~ 2,000,000 km 2 of new trees (about the size of Alaska) Model: CAM 3.0, CLM 3.5, CASA Carbon Cycle, slab ocean, fixed atm CO 2 (350 ppm) Experiments: 50 years Control: 100 years M Laguë 20

21 RESULTS 1. Energy & cloud response to midlatitude afforestation 2. How the response scales with different areas of afforestation

22 Change in solar energy absorbed at the surface Experiment - Control New Trees" 8,000,000 km 2 trees added S" N" M Laguë 22

23 Change in solar energy absorbed at the surface Experiment - Control New Trees" More energy is absorbed where trees were added 8,000,000 km 2 trees added S" N" M Laguë 23

24 Change in solar energy absorbed at the surface Experiment - Control New Trees" Absorbing less energy in the tropics why? More energy is absorbed where trees were added 8,000,000 km 2 trees added S" N" M Laguë 24

25 How different model runs compare: Full-sky surface radiation Clear-sky surface radiation M Laguë 25

26 Tropics don t have a change in energy absorption under cloud-free conditions Experiment - Control New Trees" 8,000,000 km 2 trees added S" N" M Laguë 26

27 Tropics don t have a change in energy absorption under cloud-free conditions Experiment - Control New Trees" No change in energy absorption in tropics 8,000,000 km 2 trees added S" N" M Laguë 27

28 Tropics don t have a change in energy absorption under cloud-free conditions Experiment - Control No change in energy absorption in tropic Gain less energy in mid-latitudes when ignoring clouds New Trees" 8,000,000 km 2 trees added S" N" M Laguë 28

29 Change in low cloud cover matches change in tropical energy absorption Experiment - Control New Trees" 8,000,000 km 2 trees added S N M Laguë 29

30 Change in low cloud cover matches change in tropical energy absorption Experiment - Control New Trees" Increase in tropical clouds: reflects more solar energy 8,000,000 km 2 trees added S N M Laguë 30

31 Change in low cloud cover matches change in tropical energy absorption Experiment - Control New Trees" Increase in tropical clouds: reflects more solar energy 8,000,000 km 2 trees added Decrease in mid-lat cloud cover: enhances albedo effect of trees S N M Laguë 31

32 Overall energy gain in the northern hemisphere due to afforestation Experiment - Control New Trees" Tropics are compensating for ~1/3 of the energy gain in mid-latitudes 8,000,000 km 2 trees added S" N" M Laguë 32

33 Summary #1 Impacts of afforestation on the energy budget Dark trees added to NML increase NH energy absorption M Laguë 33

34 Summary #1 Impacts of afforestation on the energy budget Dark trees added to NML increase NH energy absorption Reduced NML cloud cover further increases energy absorption M Laguë 34

35 Summary #1 Impacts of afforestation on the energy budget Dark trees added to NML increase NH energy absorption Reduced NML cloud cover further increases energy absorption Increased tropical cloud cover compensates for ~1/3 of the energy gain in midlatitudes; dampens the impact of mid-latitude afforestation on global circulation M Laguë 35

36 Net gain of energy in northern hemisphere is ~1/3 smaller because of tropical cloud response. Experiment - Control New Trees" S" N" M Laguë 36

37 Increase in absorbed solar energy scales linearly with area of new trees. Δ Absorbed surface sw radiation (clearsky)" Area of Afforestation (millions of km 2 )" Total USA pasture + agricultural area M Laguë 37

38 Energy imbalance between hemispheres ) Shift in energy transport M Laguë 38

39 Extra energy in northern hemisphere drives shift in cross-equatorial energy flux Area of Afforestation (millions of km 2 )" M Laguë 39

40 Change in cross-equatorial energy flux implies a change in the Hadley circulation Add trees to northern mid-latitudes ITCZ shifts northward ITCZ Swann M Laguë 40

41 Despite the shift in energy transport, we don t see a zonal shift in the ITCZ in weaker experiments PRECIP (yearly avg): Case pct100 Control Change in precipitation, experiment - control PRECIP (yearly avg): Case pct50 Control lat lat ,000,000 km 2 of new trees Δ Precipitation (mm/day) mm/day mm/day M Laguë 41

42 Big increase in precipitation over the Sahara up to 400 mm/year. That s enough to support grass in the Sahara. PRECIP (yearly avg): Case agr100 Control Change in precipitation, experiment - control PRECIP (yearly avg): Case pct50 Control lat lat ,500,000 km 2 of new trees Δ Precipitation (mm/day) mm/day mm/day M Laguë 42

43 Summary Impacts of afforestation on the energy budget Dark trees added to NML increase NH energy absorption Reduced NML cloud cover further increases energy absorption Increased tropical cloud cover compensates for ~1/3 of the energy gain in midlatitudes; dampens the impact of mid-latitude afforestation on global circulation. Circulation response to incrementally larger areas of afforestation M Laguë 43

44 Summary: Impacts of afforestation on the energy budget Dark trees added to NML increase NH energy absorption Reduced NML cloud cover further increases energy absorption Increased tropical cloud cover compensates for part of the energy gain in midlatitudes. This likely dampens the impact of midlatitude afforestation on global circulation. Circulation response to incrementally larger areas of afforestation Energy gain in the northern hemisphere scales linearly with the area of trees added M Laguë 44

45 Summary: Impacts of afforestation on the energy budget Dark trees added to NML increase NH energy absorption Reduced NML cloud cover further increases energy absorption Increased tropical cloud cover compensates for part of the energy gain in midlatitudes. This likely dampens the impact of midlatitude afforestation on global circulation. Circulation response to incrementally larger areas of afforestation Energy gain in the northern hemisphere scales linearly with the area of trees added Changes in energy transport are linear M Laguë 45

46 Summary: Impacts of afforestation on the energy budget Dark trees added to NML increase NH energy absorption Reduced NML cloud cover further increases energy absorption Increased tropical cloud cover compensates for part of the energy gain in midlatitudes. This likely dampens the impact of midlatitude afforestation on global circulation. Circulation response to incrementally larger areas of afforestation Energy gain in the northern hemisphere scales linearly with the area of trees added Changes in energy transport are linear Precipitation response is not linear; changes in rain over the Sahara are large enough to support vegetation M Laguë 46

47 Questions? M Laguë 47

48 Carbon Effects Most forced run: ~18,000,000 km 2 trees Net land uptake of ~228 PgC (this is big: total land carbon sink is on order of 2000 PgC) 228 PgC = 107 ppm CO 2 BUT ocean buffering will release CO 2 in response, so the net effect on atmospheric [CO 2 ] is ~50 ppm (~6 ppm per experiment not that dramatic compared to anthropogenic emissions) M Laguë 48

49 Anthropogenic land use comparison: ~ 1,940,000 km 2 of agriculture in USA ~ 2,480,000 km 2 grazing Source: EPA ( M Laguë 49

50 Climate impacts of global changes in vegetation Deforestation cools global temperatures (on global scales) Afforestation warms global temperatures Albedo effect dominates carbon-cycle effect Global deforestation leads to cooling even though it releases a lot of carbon. CO 2 Bala et al., 2007; Bathiany et al M Laguë 50

51 How much do the clouds compensate? Δ Total energy absorbed: 100% grass case - control" Red line: surface energy absorbed in cloud-free model Green line: surface energy absorbed in full model Blue line: energy absorbed due to clouds only M Laguë 51

52 How much do the clouds compensate? Δ Total energy absorbed: 100% grass case - control" Energy absorbed due to new trees Energy reflected due to new clouds Energy absorbed due to loss of clouds M Laguë 52

53 Increase in absorbed solar energy scales linearly with area of new trees. NH solar energy gain M Laguë 53

54 Increased energy in northern hemisphere scales linearly with area of added trees Northern hemisphere energy gain Total shortwave radiation absorbed by NH Total longwave radiation lost by NH M Laguë 54

55 New clouds reflect ~1/3 of the energy new trees add Total shortwave energy: Absorbed in full model Absorbed in cloud-free model Reflected by clouds Energy absorbed due to cloud loss Energy absorbed by new trees Net NH energy gain due to new trees Energy reflected by new clouds Area of Afforestation (km 2 ) M Laguë 55

56 Precipitation é over the Sahara in all cases; ITCZ slower to respond Δ PRECIP, case - ctrl + 4 million km million km million km million km M Laguë 56

57 Low Cloud Fraction M Laguë 57

58 Northward energy flux broken into atmos+ocn components. Atmos energy equator is north of the equator, as we would expect from the ITCZ M Laguë 58

59 Δ Northward Energy Transport Cross-equatorial energy flux (southward) M Laguë 59

60 Changes in precip are on order of 1mm/day max, or about 30 cm/year. This is enough to produce a change along the southern edge of the Sahara PMIP, Joussaume et al. (1999) M Laguë 60