The NASA article Global Climate Change Impact on Crops Expected Within 10 Years, NASA Study Finds by Ellen Gray (11/2/2021) provides an answer:
Climate change may affect the production of maize (corn) and wheat as early as 2030 under a high greenhouse gas emissions scenario, according to a new NASA study published in the journal, Nature Food. Maize crop yields are projected to decline 24%, while wheat could potentially see growth of about 17%.
What is one mechanism for the decline?
Higher temperatures also affect the length of growing seasons and accelerate crop maturity.
“You can think of plants as collecting sunlight over the course of the growing season,” said Ruane. “They’re collecting that energy and then putting it into the plant and the grain. So, if you rush through your growth stages, by the end of the season, you just haven’t collected as much energy.” As a result, the plant produces less total grain than it would with a longer development period. “By growing faster, your yield actually goes down.”
The article includes a nice 2 minute video. For grain harvest data see the World Grain tile on the Statistics Projects page.