This is a partial repost because I don’t think that people saw it downstairs.

I just read this paper. It is from PNAS; September, this year.

This is a very readable paper. It is vital that people understand that when scientists say that starvation on a massive scale is coming if we do not change our ways, that people realize we are talking here, in America and not just world wide.

This is real folks. There is no hyperbole. The lowest end estimates made by this paper, taking the lowest end of current projections is only a 30% reduction in our crops - by the end of the century. The high end is 82%.

Nonlinear temperature effects indicate severe
damages to U.S. crop yields under climate change

Wolfram Schlenkera,1 and Michael J. Robertsb

Abstract:

The United States produces 41% of the world’s corn and 38% of the
world’s soybeans. These crops comprise two of the four largest
sources of caloric energy produced and are thus critical for world
food supply. We pair a panel of county-level yields for these two
crops, plus cotton (a warmer-weather crop), with a new fine-scale
weather dataset that incorporates the whole distribution of temperatures
within each day and across all days in the growing
season. We find that yields increase with temperature up to 29 C
for corn, 30 C for soybeans, and 32 C for cotton but that temperatures
above these thresholds are very harmful. The slope of
the decline above the optimum is significantly steeper than the
incline below it. The same nonlinear and asymmetric relationship
is found when we isolate either time-series or cross-sectional
variations in temperatures and yields. This suggests limited historical
adaptation of seed varieties or management practices to
warmer temperatures because the cross-section includes farmers’
adaptations to warmer climates and the time-series does not.
Holding current growing regions fixed, area-weighted average
yields are predicted to decrease by 30–46% before the end of the
century under the slowest (B1) warming scenario and decrease by
63–82% under the most rapid warming scenario (A1FI) under the
Hadley III model.