A new study reports that increased vegetation growth during the recent decades, known as the "Greening Earth", has a strong cooling effect on the land due to increased efficiency of heat and water vapor transfer to the atmosphere
A new study published in the journal Science Advances
titled "Biophysical impacts of Earth greening largely controlled by aerodynamic resistance"
reports that the entire land surface would have been much warmer without the cooling effect of increased green cover during the recent decades. The study used high-quality satellite data from NASA's MODIS sensors and NCAR's state-of-the-art numerical earth system model.
© Chi Chen
Satellite observations show widespread increasing trends of leaf area index (LAI), known as the Earth greening. However, the biophysical impacts of this greening on land surface temperature (LST) remain unclear. Here, we quantify the biophysical impacts of Earth greening on LST from 2000 to 2014 and disentangle the contributions of different factors using a physically based attribution model. We find that 93% of the global vegetated area shows negative sensitivity of LST to LAI increase at the annual scale, especially for semi-arid woody vegetation
. Further considering the LAI trends (P≤0.1), 30% of the global vegetated area is cooled by these trends and 5% is warmed. Aerodynamic resistance is the dominant factor in controlling Earth greening's biophysical impacts: The increase in LAI produces a decrease in aerodynamic resistance, thereby favoring increased turbulent heat transfer between the land and the atmosphere, especially latent heat flux.The greening of the lands during the first fifteen years in the 21st century
represented an additional heat dissipation (2.97×1021 J) from the surface equivalent to five times the total energy produced and used by humans in 2015 (5.71×1020 J). This greening-induced cooling effect was twenty-five times stronger than the warming effect caused by tropical deforestation.
"In the fight against climate change, plants are the lonely-only defenders. Stopping deforestation and ecologically sensible large-scale tree-planting could be one simple, but not sufficient, defense against climate change." said the lead author Dr. Chi Chen a former Ph.D. student at Boston University, now a postdoc researcher at DOE's Lawrence Berkeley National Lab.
Quantifying the vegetation effect on land surface temperature (LST) is challenging. The observed changes in LST are the results of a series of compounding biophysical processes.
"Disentangling the signal from different biophysical processes is essential to solving this question." said the coauthor Prof. Dan Li of the Department of Earth and Environment at Boston University. He added, "We developed an attribution framework that correctly represented the cause-and-effect of these biophysical processes."Vegetation transpires water to cool itself from solar heating."Increased amount of leaves adds roughness which breaks the stillness of the air. More water vapor is thus transpired which leads to a cooler land surface,"
said Prof. Pierre Gentine of Earth and Environmental Engineering at Columbia University.NASA satellites have been observing increased green cover on land, which is thought to be due to intensive agriculture to feed growing populations and ambitious tree-planting programs - for example, the so-called "Green Great Wall" in China."These programs have been quite successful in ameliorating land degradation and enhancing carbon storage,"
said coauthor Prof. Shilong Piao of the College of Urban and Environmental Sciences at Peking University.
The vegetation cooling effect is large from the energy dissipation perspective, but only about 10%-20% compared to the pace of global warming. The cooling effect from greening is less significant in tropical forests with high leaf areas.
"This is a warning sign about climate change. We should be cautious that the rainforests, which are at the forefront of the fight against global warming, are reaching the limits of their capacity to absorb carbon and cool the surface."
commented Dr. Rama Nemani, from NASA's Ames Research Center.
Read the paper at Science Advances.
It is indeed a complex issue and, contrary to the articles claims of 'global warming, there is evidently more to Earth's overall climate than just an increase in vegetation, with one significant driver being solar activity.
In his book Earth Changes and the Human-Cosmic Connection
, Pierre Lescaudron writes:
Climate change propaganda aside, it's clear that by the end of the 20th Century, the
'warming' data that global warming climatologists had been using to advance their
thesis had given way to lower average temperatures, and that this cooling (like the
warming that preceded it) is not of human but cosmic origin.
If, as claimed by proponents of anthropogenic global warming, human carbon dioxide emissions are the main cause of recent warming on Earth, how could that explain why other planets in our solar system
have been warming too? Over the last 50 years or so, Earth's average temperature has, by
some accounts, risen about one degree. During this same time period, global warming has
been observed on Mars, Neptune, and Pluto. Is this just coincidence?
For years now, the mainstream media has fiercely supported the man-made warming
dogma while clear evidence of global cooling has been piling up. Despite 10 years of
denial, independent scientists have persuaded many to acknowledge the global cooling
that began at the turn of the century. The Space and Science Research Center, an
independent US climate research company, forecasts a future climate scenario quite
different from that predicted by the IPCC:
The Space and Science Research Center (SSRC) announces today that the most
recent global temperature data through January 31, 2011 using NASA and NOAA
weather satellites supports the previous forecast from the SSRC that a historic
drop in global temperatures is under way and that the previously predicted
climate change to one of a long and deep global cooling era has begun.
SSRC Director John L. Casey explains, 'Based on the data from the AMSR-E
instrument on board the NASA Aqua satellite, sea surface temperatures just
posted this week showed their steepest decline since the satellite was made
operational in 2002.
This major drop from the warm temperature levels seen in
2010 is also echoed by a dramatic decline in atmospheric temperatures in the
lower troposphere, where we live, with the data coming from NOAA satellites. At
present rates of descent, both ocean and atmospheric temperatures are likely to
soon surpass the temperature lows set in the 2007-2008 period. Even with a small
correction that is usually seen after such a rapid drop, there is no doubt that the
Earth is entering a prolonged global cooling period and will soon set another
record drop in temperatures by the November-December 2012 time frame as
was forecast in the SSRC press release from May 10, 2010.' 401
As demonstrated above the Sun has been unusually quiet for several years. The Sun rises
every morning and, sure enough, every evening it sets. However, solar activity fluctuates
along with the temperature of our planet:
The above only shows a correlation between solar activity (sunspot number) and Earth's
© NOAASunspot number vs. average temperature over a 10,000-year span.
surface temperature. Further down, we will explain how reduced solar activity (and also
increase in atmospheric cometary dust) causes Earth's global cooling. [...]
And so it would appear that following a warming period, as has been the case throughout Earth's history, a significant cooling era has begun. See:
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