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The Greening Earth. Ranga B. Myneni* & Compton ‘Jim’ Tucker. With contributions from:. Alexeyev, Anderson, Asrar, Bogaert, Bousquet, Buermann, Ceulemans, Cramer, Dickinson, Dong, Friedlingstein, Hashimoto, Hughes, Jolly, Kaufmann, Kauppi, Keeling, Knyazikhin, Lucht,

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The Greening Earth

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The greening earth l.jpg

The Greening Earth

Ranga B. Myneni* & Compton ‘Jim’ Tucker

With contributions from:

Alexeyev, Anderson, Asrar, Bogaert, Bousquet,

Buermann, Ceulemans, Cramer, Dickinson, Dong,

Friedlingstein, Hashimoto, Hughes, Jolly,

Kaufmann, Kauppi, Keeling, Knyazikhin, Lucht,

Liski, Nemani, Piper, Potter, Prentice, Running,

Shabanov, Sitch, Slayback, Song, Smith and Zhou

Gustav Klimt (1862-1918): Der Park (1910)

This research was funded by NASA-ESE.

MOMA-NY

(1 of 37)

*department of geography, boston university, cybele.bu.edu


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publications

(2 of 37)

http://cybele.bu.edu/

Bogaert et al., 2002. Evidence for a persistent and extensive greening trend in Eurasia inferred from satellite vegetation index data. J. Geophys. Res., Vol. 107

(D11), 10.1029/2001JD001075.

Buermann et al., 2002. Circulation anomalies explain interannual covariability in northern hemisphere temperatures and greenness. J. Geophys. Res.

(accepted Dec 2002).

Dong et al., 2003. Remote sensing of boreal and temperate forest woody biomass: Carbon pools, Sources and Sinks, Remote Sens. Environ. 84: 393–410.

Kaufmann et al., 2000. Effect of orbital drift and sensor changes on the time series of AVHRR vegetation index data. IEEE Trans. Geosci. Remote Sens., 38:

2584-2597.

Kaufmann et al., 2002. Reply to Comment on "Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981- 1999"

by J. R. Ahlbeck. J. Geophys. Res., Vol. 107(D11), 10.1029/2001JD001516.

Lucht et al., 2002. Climatic control of the high-latitude vegetation greening trend and Pinatubo effect. Science, 296:1687-1689 (May-31-2002).

Myneni, R. B., et al., 1998. Interannual variations in satellite-sensed vegetation index data from 1981 to 1991. J. Geophys. Res., 103 (D6): 6145-6160.

Myneni, R. B., et al., 1997. Increased plant growth in the northern high latitudes from 1981-1991. Nature, 386:698-701.

Myneni and Dong et al., 2001. A large carbon sink in the woody biomass of northern forests. Proc. Natl. Acad. Sci. USA., 98(26): 14784-14789.

Nemani et al., 2003. Climate driven increases in terrestrial net primary production from 1982 to 1999. Science (in review Apr 2003).

Shabanov et al., 2002. Analysis of interannual changes in northern vegetation activity observed in AVHRR data during 1981 to 1994. IEEE Trans. Geosci.

Remote Sens., 40:115-130.

Tucker et al., 2001. Higher northern latitude NDVI and growing season trends from 1982 to 1999. Int. J. Biometeorol., 45:184-190.

Zhou et al., 2001. Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981 to 1999, J. Geophys. Res., 106 (D17):

20069-20083.

Zhou et al., 2002. Relation between interannual variations in satellite measures of vegetation greenness and climate between 1982 and 1999. J. Geophys.

Res. 108(D1), doi:10.1029/2002JD002510.


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outline

(3 of 37)

Background on NDVI and NDVI data sets

Greening in the north

- the northern latitude greening trend during the 1980s and 1990s

- persistence of greening in Eurasia vs North America

- the temperature connection

- the connection to circulation anomalies

- northern latitude greening and the forest woody biomass carbon sink

The greening earth and increasing terrestrial net primary production


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reflectance spectrum of a green leaf

(4 of 37)

Pigments in green leaves (notably chlorophyll) absorb strongly at red and blue wavelengths. Lack of such absorption at near-infrared wavelengths results in strong scatter from leaves.

upper epidermis

palisade layer

spongy tissue

lower epidermis

image credit: Govaerts et al.


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(5 of 37)

normalized difference vegetation index, ndvi

The contrast between red and near-infrared reflectance of vegetation is captured by the greenness index, NDVI, as [(nir-red)/(nir+red)].

image credit: Huete et al.


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avhrr ndvi data sets

The Advanced Very High Resolution Radiometers, AVHRR,

have been flown on NOAA polar orbiting afternoon-viewing platforms

NOAA-07: jul 81 to jan 85

NOAA-09: feb 85 to oct 88

NOAA-11: nov 88 to sep 94

NOAA-14: jan 85 to oct 01.

GIMMS and PAL NDVI Data Sets Have

Calibration

Partial Atmospheric Correction

Corrections for Stratospheric Aerosols

10 or 15-day Maximum Value Composites

Run from July 1981 to about mid-2001

GIMMS: GLOBAL INVENTORY MONITORING AND MODELING SYSTEMS

PAL: PATHFINDER AVHRR LAND


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outline

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Background on NDVI and NDVI data sets

Use with caution - download from http://cybele.bu.edu/

Greening in the north

- the northern latitude greening trend during the 1980s and 1990s

- persistence of greening in Eurasia vs North America

- the temperature connection

- the connection to circulation anomalies

- northern latitude greening and the forest woody biomass carbon sink

The greening earth and increasing terrestrial net primary production


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(8 of 37)

greening trend in the north

delayed fall

earlier spring

Jan

Jul Aug

Dec

Jan

Jul Aug

Dec

In the north, where vegetation growth is seasonal, the cumulative growing season greenness, which is the area under the NDVI curve, can change either due to a longer photosynthetically active growing season or due to increased greenness magnitude, or both.

1) Define vegetated pixels in the study area using a land cover map

2) Use NDVI values greater than zero only to avoid sparsely vegetated areas, pixels with snow and any corrupted data

changes in growing season duration

changes in greenness magnitude

Increase

4) Use NDVI threshold to assess changes in dates of spring green-up and autumn green- down (assess sensitivity to threshold value)

3) Assess changes in peak seasonal greenness from July and August average NDVI


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greening trend in the north (1980s & 90s)

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Analysis of GIMMS (v1) ndvi data for the period 1981 to 1999 indicate that:

A larger increase in growing season NDVI magnitude (12 vs 8%) and a longer active

growing season (18 vs 12 days) brought about by an early spring and delayed

autumn are observed in Eurasia relative to North America

8.4%/18 yrs (p<0.05)

11.9 days/18 yrs (p<0.05)

17.5 days/18 yrs (p<0.05)

12.4%/18 yrs (p<0.05)

  • NDVI averaged over boreal growing season months of May to September increased by about 10%,

  • the timing of spring green-up advanced by about 6 days.

  • NDVI averaged over boreal growing season months of May to September increased by about 10%,

  • the timing of spring green-up advanced by about 6 days.

From Zhou et al., (JGR, 106(D17):20069-20083, 2001)


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outline

(10 of 37)

Background on NDVI and NDVI data sets

Use with caution – download from http://cybele.bu.edu

Greening in the north

- the northern latitude greening trend during the 1980s and 1990s

the northern latitudes (>40N) have greened since the early 1980s

- persistence of greening in Eurasia vs North America

- the temperature connection

- the connection to circulation anomalies

- northern latitude greening and the forest woody biomass carbon sink

The greening earth and increasing terrestrial net primary production


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spatial pattern of greening

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Analyses of pixel-based persistence indices from

GIMMS (v1) NDVI data for the period 1981 to 1999 indicate that:

About 61% of the total vegetated area between

40N-70N in Eurasia shows a persistent increase in growing season NDVI over a broad contiguous swath of land from Central Europe through Siberia to the Aldan plateau, where almost 58% (7.3 million km2) is forests and woodlands.

North America, in comparison, shows a fragmented pattern of change, notable only in the forests of the southeast and grasslands of the upper Midwest.

These results are further substantiated from a study that evaluated patch characteristics using landscape ecology metrics (Bogaert et al., JGR, 107(D11):10.1029/2001jd001075, 2002).

From Zhou et al., (JGR, 106(D17):20069-20083, 2001)


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outline

(12 of 37)

Background on NDVI and NDVI data sets

Use with caution – download from http://cybele.bu.edu

Greening in the north

- the northern latitude greening trend during the 1980s and 1990s

the northern latitudes (>40N) have greened since the early 1980s

- persistence of greening in Eurasia vs North America

the greening in Eurasia is more persistent than in North America

- the temperature connection

- the connection to circulation anomalies

- northern latitude greening and the forest woody biomass carbon sink

The greening earth and increasing terrestrial net primary production


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greenness and surface temperature

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The temporal changes and continental differences in NDVI are consistent with

ground based measurements of temperature, an important determinant of

biological activity in the north

T – GISS temperature; EA – Eurasia;

NA - North America

From Zhou et al., (JGR, 106(D17):20069-20083, 2001)


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modeling the temperature connection

The observed trend toward earlier spring budburst and increased maximum leaf area is produced by the model as a consequence of biogeochemical vegetation responses mainly to changes in temperature.

A biogeochemical model of vegetation using observed climate data predicted the high northern latitude greening trend over the past two decades observed by satellites and a marked setback in this trend after the Mount Pinatubo volcano eruption in 1991.

From Lucht et al., (Science, 296:1687-1689, 2002)


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outline

(15 of 37)

Background on NDVI and NDVI data sets

Use with caution – download from http://cybele.bu.edu

Greening in the north

- the northern latitude greening trend during the 1980s and 1990s

the northern latitudes (>40N) have greened since the early 1980s

- persistence of greening in Eurasia vs North America

the greening in Eurasia is more persistent than in North America

- the temperature connection

it is temperature, not co2, that is the related to greening

- the connection to circulation anomalies

- northern latitude greening and the forest woody biomass carbon sink

The greening earth and increasing terrestrial net primary production


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(16 of 37)

cca analysis

what is causing these correlations?

are these relations valid at finer (pixel) scales?

Zhou et al., (2001)

Data

NDVI data: FASIR GIMMS v1 (1982-98) (Courtesy of Los et al.)

Surface temperature from GISS (Hansen et al., 1999)

NINO3 index (Reynolds and Smith, 1994)

AO index (first EOF of NH SLP 20N-90N; Thompson and Wallace, 1998)

Method

Canonical Correlation Analysis (CCA) to isolate coupled spatial patterns between

temperature and NDVI and assess their possible relationship to large-scale circulation anomalies

From Buermann and Anderson et al. (JGR, in press)


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the enso mode

Geographic Plot of the Grid-point Correlations for the 1st CF

TEMPERATURE

Spring (MAM) Temp and Spring NDVI, 10N-90N

First canonical factor: the ENSO signal

Temperature (r=0.78)

NDVI (r=0.76)

NINO3 SON (81-97)

NDVI

Principal Component

These figures indicate that the first factor captures the NH spring ENSO tele-

connection signal in the surface temperature and NDVI fields.

During warm ENSO events, warmer and greener conditions prevail in spring over North America, far east Asia and to some extent over Europe. The ENSO related patterns explain 10.8% (13.5%) of the total spring surface temperature (NDVI) variability.


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the ao mode

Geographic Plot of the Grid-point Correlations for the 2nd CF

TEMPERATURE

Spring (MAM) Temp and Spring NDVI, 10N-90N

Second canonical factor: the AO signal

Temperature (r=0.85)

NDVI (r=0.83)

Principal Component

NDVI

AO (DJB), 82-98

NAO (DJF), 82-98

These figures indicate that the first factor captures the NH spring AO teleconnection signal in the surface temperature and NDVI fields.

The fact that there is quantitative agreement between the temporal and spatial features isolated via the CCA algorithm and those associated with ENSO and AO indices suggests that surface temperature signatures associated with these two predominant modes of global climate variability are also important drivers for variability in northern hemisphere greenness.


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outline

(19 of 37)

Background on NDVI and NDVI data sets

Use with caution – download from http://cybele.bu.edu

Greening in the north

- the northern latitude greening trend during the 1980s and 1990s

the northern latitudes (>40N) have greened since the early 1980s

- persistence of greening in Eurasia vs North America

the greening in Eurasia is more persistent than in North America

- the temperature connection

it is temperature, not co2, that is the related to greening

- the connection to circulation anomalies

ENSO and AO are partly responsible for the correlation between

temperature and NDVI

- northern latitude greening and the forest woody biomass carbon sink

The greening earth and increasing terrestrial net primary production


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(20 of 37)

biomass carbon stocks, sources and sinks

Motivation

About 1 to 2 giga (10^9) tons of carbon (Gt C) a year are suggested to be sequestered in pools on northern land.

Debate is currently underway regarding which of the forest biomass sinks can be

used by the industrialized nations to meet their commitments under the Kyoto

protocol.

This study is limited to analysis of the carbon pool in the woody biomass of northern temperate and boreal forests, which cover an area of about 1.4 to 1.5 billion hectares.

We define forests as the following remote

sensing land covers: broad leaf forests,

needle leaf forests, mixed forests and woody

savannas.

From Myneni and Dong et al. (PNAS, 98(26):14784-14789, 2001)


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inventory data and greenness

Year-to-year changes in biomass are quite small, about two orders of magnitude smaller than

the biomass pool. At decadal and longer time scales, the biomass changes can be considerable

due to accrual of the differences between gains and losses.

Potentially, these can be observed as low frequency variations in decadal scale greenness, in

much the same way as century scale greenness changes are suggestive of successional changes.

Forest inventory data from 171 provinces in six countries that represent

a wide variety of inventory practices,

provincial forest area, ecosystem types, age structures and time periods.

We use 5-yr averages of growing

season NDVI total (GIMMS v1), the

area under seasonal NDVI curve and

above a threshold, which captures

both the average seasonal level of

greenness and growing season duration, and therefore is an ideal measure of seasonal greenness.


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uncertainty analysis

The relation between woody biomass and seasonal greenness is estimated as,

1/biomass = a + [(1/ndvi)/latitude^2] + g latitude

where, biomass: inventory estimate (tons/ha), ndvi: cumulative growing season ndvi averaged

over five years of the inventory, latitude: average of latitudes over forest pixels in each province

and, ,  and : regression coefficients

The relative difference between remote sensing and inventory estimates is 27% for above-stump biomass (10.4 tons C/ha), 33% for total biomass (16.1 tons C/ha), 50% for changes in pool size (0.33 tons C/ha/yr)


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spatial picture of the biomass sink

Pool changes were then evaluated as the difference between the late 1990s and early 1980s pool estimates, pixel-by-pixel, and quoted on a per year basis.

The carbon pool in the woody biomass of northern forests (1.5 billion ha) is estimated to be 61  20 Gt C during the late 1990s.

Our sink estimate for the woody biomass during the 1980s and 1990s is 0.680.34 Gt C/yr.


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country analysis

The estimates of the three large countries, Canada, Russia and the USA, are crucial because they account for 78% of the pool, 73% of the sink and 77% of the forest area.

For Canada, we estimate a sink of about 73 Mt C/yr which is comparable to an

inventory estimate by the Canadian forest service about 85 Mt C/yr.


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(25 of 37)

country analysis

Our pool, sink and forest area estimates for the USA are are comparable to TBFRA-2000 estimates. Our sink estimate for the USA (142 Mt C/yr) is comparable to most estimates for the 1980s (110 to 150 Mt C/yr).


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country analysis

Estimates for Russia differ principally because of differences in the definition of forest area. When expressed on a per unit forest area basis, the various estimates are comparable.


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reasons

The spatial patterns, however, offer some clues:

a) longer growing seasons from warming in the northern latitudes possibly explain some

of the changes, and

c) fire suppression and

forest re-growth in the

USA

d) declining harvests in

Russia

b) increased incidences of fires

and infestations in Canada

f) forest expansion and re-growth

in China

e) improved silviculture in

Nordic and European countries


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outline

Background on NDVI and NDVI data sets

Use with caution – download from http://cybele.bu.edu

Greening in the north

- the northern latitude greening trend during the 1980s and 1990s

the northern latitudes (>40N) have greened since the early 1980s

- persistence of greening in Eurasia vs North America

the greening in Eurasia is more persistent than in North America

- the temperature connection

it is temperature, not co2, that is the related to greening

- the connection to circulation anomalies

ENSO and AO are partly responsible for the correlation between

temperature and NDVI

- northern latitude greening and the forest woody biomass carbon sink

biomass carbon sinks represent 10% of the annual fossil fuel emissions

The greening earth and increasing terrestrial net primary production


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(29 of 37)

motivation

Global environmental changes between 1980 and 2000 have been

significant:

- Two of the warmest decades in the instrumental record

- Three intense El Nino events (1982-83; 1987-88; 1997-98)

- Changes in tropical cloudiness and monsoon dynamics

- A 9.3% increase in atmospheric co2 concentration

- A 36% increase in global population (4.45 billion in 1980 to 6.08

billion in 2000)

Image credit: IPCC

A substantial incentive to understand trends and variability in

terrestrial Net Primary Production because NPP:

- is the foundation of food, fiber and fuel for human consumption

- determines seasonal and interannual variations in atmospheric co2

- integrates climatic, ecological, geochemical and human influences

on the biosphere

Image credit: FAO

How have global environmental changes affected (eased or strengthened) climatic

constraints to plant growth and NPP?

From Nemani et al., (Science; in review, 2003)


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step 1: limiting factors

Plant growth is assumed to be principally limited by sub-optimal climatic conditions such as low temperatures, inadequate rainfall and cloudiness (Churkina and Running, 1998). We used 1960-1990 average climate data (Leemans and Cramer, 1991) to develop scaling factors between 0 and 1 that indicate the reduction in growth potential.

Dominant Controls

water availability 40%

temperature 33%

solar radiation 27%

Total vegetated area: 117 M km2


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step 2: trends in climate data

Data: Reanalysis data (6-hourly 2 m height temperatures, 2-m height specific humidity, and

incident solar radiation) from NCEP to represent climate variability from 1982 to 1999.

The observed climatic changes have been mostly in the direction of reducing climatic constraints to plant growth. Therefore, it seems likely that vegetation responded to such changes positively.

Potential Climate Limits for Plant Growth

Interannual trends in daily average temperature 1982-99

Interannual trend in vapor pressure deficit 1982-99

Interannual trend in solar radiation 1982-99


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step 3: npp evaluation

The NPP Algorithm

Step 1

convert absorbed radiation

to optimal gross production

Step 2

downgrade by climate limiting

factors to obtain gpp

Step 3

subtract respiration to obtain npp

Trends in NPP are positive over 55% of the global vegetated area and are statistically more significant than the declining trends observed over 19% of the vegetated area.

Average of interannual trends (1982-99) in growing season NPP estimated with GIMMS and PAL (v3) FPAR


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climate, npp and atmospheric co2 growth rate

Interannual variations in global NPP are correlated with

global atmospheric CO2 growth rates (r = 0.70, p<0.001).

NPP declined during all three El Niño events.

Analyses of variation in the plant photosynthesis-

respiration balance, expressed as NPP/GPP ratio (right

panel), showed observed declines in NPP during El Niño

years to be dominated by increases in respiration due to

warmer temperatures.

Although the atmospheric co2 growth rate depends on the net air-sea and land-atmosphere exchanges, these results highlight the preeminent role of plant growth in global carbon cycle.


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npp trends by latitude

Ecosystems in all tropical regions and those in the high

latitudes of the Northern Hemisphere accounted for 80%

of the increase in global NPP between 1982 and 1999.

El Niño impacts are strong at low latitudes when

compared to mid- and high latitudes.

A strong decline in NPP following the Mt. Pinatubo

eruption (1991) was evident only at the high latitudes of

the Northern Hemisphere. Cooler temperatures resulting

from the eruption decreased the growing season

length at high latitude.

The same cooling may have promoted plant growth in low

latitude ecosystems by reducing the evaporative demand

and respiration losses.


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npp trends in the tropics

The evergreen forests of the Amazon

region showed NPP increases, on

average, of >1.0% / yr, contributing to

over 40% of the global NPP increases

between 1982 and 1999.

An increase in NPP of <0.22% per ppm

increase in CO2, within the range of

experimental evidence, could be

invoked to explain all of the estimated

global NPP increase of 6.17% / 18yr.

NPP increases of >1%/yr as in the case

of Amazonia require a fertilization

effect greater than 0.5% per ppm of

CO2 increase, which appears to be

much greater than those reported by

field experiments.

We suggest increases in solar radiation, as a result of declining cloud cover, in these

predominantly radiation-limited forests as a plausible explanation for the increased NPP.


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outline

Background on NDVI and NDVI data sets

Use with caution – download from http://cybele.bu.edu

Greening in the north

- the northern latitude greening trend during the 1980s and 1990s

the northern latitudes (>40N) have greened since the early 1980s

- persistence of greening in Eurasia vs North America

the greening in Eurasia is more persistent than in North America

- the temperature connection

it is temperature, not co2, that is the related to greening

- the connection to circulation anomalies

ENSO and AO are partly responsible for the correlation between

temperature and NDVI

- northern latitude greening and the forest woody biomass carbon sink

biomass carbon sinks represent 10% of the annual fossil fuel emissions

The greening earth and increasing terrestrial net primary production

Tropical and northern ecosystems drive increases in terrestrial npp as a result

of easing of climatic limits to plant growth


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(37 of 37)

bottomline

Since the early 1980s about,

  • half the vegetated lands greened by about

  • 11%

  • 15% of the vegetated lands browned by

  • about 3%

  • 1/3rd of the vegetated lands showed no

  • changes.

These changes are due to easing of climatic constraints to plant growth.

The End


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