Wednesday, February 28, 2024

Global Climate Change and a Greening Earth

While the climate change "woe is me" crowd promotes the "earth is boiling" narrative, a study from 2016 by Ziachun Zhu and 32 authors from 24 institutions in eight nations et al looks at an aspect of global environmental change that receives very little attention from the aforementioned crowd.


As background, green leaves use photosynthesis to convert light energy (sunlight) to chemical energy (sugars).  The light energy constructs the sugar molecules, mainly glucose, from water and carbon dioxide, releasing oxygen as a byproduct of the process.  The glucose molecules serve as fuel/energy for the cells of the leaf.  The inorganic carbon from the carbon dioxide used during photosynthesis is incorporated into organic molecules in a process termed carbon fixation resulting in fixed carbon which can be used to build the organic molecules needed by plant cells.


Here is a diagram showing the process by which vegetation turns light and carbon dioxide into sugars and oxygen:


The process of photosynthesis removes large volumes of carbon dioxide from the atmosphere and releases large volumes of oxygen gas as a byproduct which is necessary for most non-plant life.  Furthermore, studies show that increased levels of carbon dioxide in the atmosphere lead to higher levels of photosynthesis which spurs increased plant growth.


On April 25, 2016, Nature Climate Change published Zhu's article entitled "Greening of the Earth and its drivers".  In this research, Zhu et al used three long-term satellite leaf area index (LAI) records and ten global ecosystem models to better understand the four key drivers of LAI trends over the period from 1982 to 2009.  The authors used trends of leaf area index using three remotely sensed data sets sourced from satellite data from NASA's Moderate Resolution Spectrometer and the National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer instruments.  These data sets provided the authors with the amount of leaf cover over earth's vegetated regions.


Trends from the long-term satellite LAI data sets show positive increases over a large portion of the global vegetated area since 1982 with the largest greening trends being located in southeast North America, the northern Amazon Basin, Europe, Central Africa and Southeast Asia.  The authors note that there are several factors that may account for increased plant growth including nitrogen, land cover change and climate change (i.e. temperature, precipitation and sunlight changes).  That said, their simulations suggest that carbon dioxide fertilization contributes 70 percent of the greening effect followed by nitrogen deposition at 8.8 percent and climate change at 8.1 percent, noting that climate change effects actually negatively impact the greening trend in some areas.


Here is a graphic showing the change in leaf area between 1982 and 2015 from the article on the study which appeared on NASA's website:


The increase in greening represents an increase in leaves on plants and trees equivalent in area to two times the area of the continental United States.


Here is a summary of their findings:


"Understanding the mechanisms behind LAI trends is a first, yet critical, step towards better understanding the influence of human actions on terrestrial vegetation, and towards improving future projections of vegetation dynamics. By making use of three LAI data sets, an ensemble of ten ecosystem models, and a fingerprinting technique, we assessed the consistency of observed greening and browning patterns with the effects of key environmental drivers. The use of a ten-model ensemble increases confidence in the attribution, although model simulations diverge in some aspects, particularly for the impacts of climate change and LCC, which suggests an area for future model improvements. Overall, the described LAI trends represent a significant alteration of the productive capacity of terrestrial vegetation through anthropogenic influences."

If there is anything that the past four years have taught us it's that science is far from cut and dried.  There are always different perspectives on the same issue, in this case climate change, so it's critical to prevent oneself from taking an unwavering stance on an issue without a thorough understanding of alternate explanations to observations.   Science is always evolving and accepting that evolution is the key to learning.

1 comment:

  1. The key enzyme in the reduction of carbon dioxide, rubisco, also catalyzes the oxidation of reduced carbon. The reaction is sensitive to the ambient carbon dioxide/oxygen ratio, and the current ratio only mildly favors reduction. The minimum CO2 level for photosynthesis at current O2 levels is about 150 ppm.