Guest essay by Eric Worrall

Ariel Ortiz-Bobea, an economist at Cornell University, claims all the CO2 and global warming we have added to the atmosphere is harming plant growth and agricultural yields, and we are only keeping up because of better farm practices. But how does Ariel explain the global greening of wilderness regions observed by NASA?

Rapid global heating is hurting farm productivity, study finds

Research shows rising temperatures since 1960s have acted as handbrake to agricultural yield of crops and livestock

Oliver Milman@olliemilman
Fri 2 Apr 2021 02.00 AEDT

The climate crisis is already eating into the output of the world’s agricultural systems, with productivity much lower than it would have been if humans hadn’t rapidly heated the planet, new research has found.

Advances in technology, fertilizer use and global trade have allowed food production to keep pace with a booming global population since the 1960s, albeit with gross inequities that still leave millions of people suffering from malnutrition.

But rising temperatures in this time have acted as a handbrake to farming productivity of crops and livestock, according to the new research, published in Nature Climate Change. Productivity has actually slumped by 21% since 1961, compared to if the world hadn’t been subjected to human-induced heating.

“The impact already is larger than I thought it would be,” said Ariel Ortiz-Bobea, an economist at Cornell University who led the research.

“It was a big surprise to me. The worry I have is that research and development in agriculture takes decades to translate into higher productivity. The projected temperature increase is so fast I don’t know if we are going to keep pace with that.”

The abstract of the study;

Anthropogenic climate change has slowed global agricultural productivity growth

Ariel Ortiz-BobeaToby R. AultCarlos M. CarrilloRobert G. Chambers & David B. Lobell 


Agricultural research has fostered productivity growth, but the historical influence of anthropogenic climate change (ACC) on that growth has not been quantified. We develop a robust econometric model of weather effects on global agricultural total factor productivity (TFP) and combine this model with counterfactual climate scenarios to evaluate impacts of past climate trends on TFP. Our baseline model indicates that ACC has reduced global agricultural TFP by about 21% since 1961, a slowdown that is equivalent to losing the last 7 years of productivity growth. The effect is substantially more severe (a reduction of ~26–34%) in warmer regions such as Africa and Latin America and the Caribbean. We also find that global agriculture has grown more vulnerable to ongoing climate change.

Read more: https://www.nature.com/articles/s41558-021-01000-1

Back in the real world, NASA reports that not only is the world greening thanks to anthropogenic CO2, the extra vegetation is exerting a strong cooling effect on the surface of the planet.

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.

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.Credits: Chi Chen

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.

Read more: https://www.nasa.gov/feature/greening-of-the-earth-mitigates-surface-warming

Ariel seems to suggest that soaring agricultural yields are due to better farm practices overcoming the harm caused by global warming, but this does not explain the massive global greening of wilderness areas observed by NASA. Unfortunately the full study is paywalled, but surely if the underlying trend was increasing climate harm mitigated by better agriculture, only farms would be greener.

Warmer temperatures are no threat to agriculture. Even if Summer temperatures rise beyond the tolerance of some crops, the solution is plant a little earlier. Plenty of temperate climate crops are commercially grown in my district, crops which would never survive the Summer heat. The farmers in my district plant potatoes, carrots, cabbages, celery, and other temperate climate vegetables at the start of Winter, and harvest them in Spring.

via Watts Up With That?


April 2, 2021 at 08:42PM