Crop yields consistently up confounding warming scare stories

By |2018-11-28T21:39:40+00:00November 28th, 2018|Climate|0 Comments

This past week news headlines screamed of catastrophic consequences in the offing from unchecked global warming. The source of this news was the National Climate Assessment, a Congressionally-mandated document, and the fourth of its kind, issued to comply with the Global Change Research Act of 1990.

Coverage of the report in the New York Times was typical: U.S. Climate Report Warns of Damaged Environment and Shrinking Economy. That article went on to assert that agriculture was an area where the impact of climate change would “particularly stand out” and “increasingly disrupt agricultural productivity in the US ….”

The culprit? Increased CO2.

Some deconstruction of this argument is important in putting the press coverage in context, … and it’s somewhat amusing.

CO2, as middle school science textbooks will explain, is necessary for plants to perform photosynthesis.

Indeed, none other than the United Nations Intergovernmental Panel on Climate Change (IPCC) reported in a 2014 report, “elevated CO2 could benefit crops’ yields in the short term by increasing photosynthesis rates.”

Research on corn production at the University of Illinois conducted with the USDA’s Ag Research Service also concluded that “growth at elevated CO2 significantly increased leaf photosynthetic CO2 uptake rate by up to 41 percent.” As the study concluded, corn’s response “to elevated CO2 indicates the potential for greater future crop biomass and harvestable yield across the US Corn Belt.”

The control variables for CO2 under this study were set at 354 parts per million (ppm) and the higher rate (with increased photosynthesis) of 549 ppm. The National Climate Assessment cites current average CO2 levels at about 400 ppm. For a point of reference, in terms of human health, the U.S. Navy sets CO2 monitoring devices on submarines at about 8,000 ppm to warn of dangerous levels.

Consider these snippets from the New York Times’ article,

  • Human activities have caused warming of about 1.8 degrees since about the 1850s, the beginning of large-scale industrial coal burning, the report found.
  • There is always some uncertainty in climate projections but scientists’ estimates about the effects of global warming to date have largely been borne out.

It’s unclear what “largely been borne out” means. The USDA has kept crop records since that agency was created in the 1860’s. Over that period – which coincides with “large-scale industrial coal burning” and other recent human activities alleged to increase warming – national average corn yields have increased more than 7-fold.

Source: USDA

Moreover, crop yield volatility in the past 20 years has been less than it was in the final third of the 1800’s.

Source: USDA

A final note, the media is calling this the Trump Administration’s own report; truth is the report was under way before Trump took office. Moreover, the report was issued with a list of authors for reporters to contact for follow up interviews. There were more than 100 names listed with contact data, but notably, less than 20 had e-mails that ended in .gov More than 80 percent of the authors listed were outside the federal government.