Could 4 Billion People Die at 3°C? 0726.rtf -
A long and detailed analysis of why the impacts shown in the matrix below do not happen just at temperatures higher than those shown in the "Climate" column.
The matrix below may best be understood as things that happen with baked-in future temperature change, after we reach the temperatures shown by 2050. This applies to the other columns: GDP Losses, Human Mortality, Nature, and Societal.
The critiquing article begins: "July 27, 2026 – The claim that 4 billion people could die in a 3°C warmer world has become a powerful climate narrative. But what does the science actually support, and where does evidence end and speculation begin?
"Summary
• Mortality depends on exposure, vulnerability and adaptive capacity, making precise death tolls impossible to model.
• The 4 billion deaths at 3°C figure is not a forecast or modeled projection.
• The estimate of 2 billion deaths at 2°C is implausible.
• The timeframe for the 3°C / 4 billion deaths estimate is undefined.
• The 4 billion figure is an educated worst-case estimate, not a robust scientific projection.
• The proposition that 4 billion people or more would be dead if — and more likely, when — global warming reaches 3°C has gained some currency, mainly due to the 4DB (4 billion dead) website and associated activities.
• Now, that is half the current global population, and on current warming trends of 0.3- 0.35°C/decade, the world will hit 3°C around 50 years from now, perhaps earlier, in part because there is little prospect of a rapid decline in fossil fuel emissions [and progress on making CO2 removal cost-effective and widespread] is slow. So that’s a mind-blowing average of 80 million people a year dying due to climate impacts every year from now to 2075? Is that realistic?"
The map projections above show crop yields falling an average of 30% or more across the American Midwest, Southeast Asia, southern China, Australia, Brazil, Argentina, Pakistan, Korea, and Mongolia. Crop yield declines are similar across most of India, the Ukraine, the Middle East, north Africa, and southern Africa, as well as much of the rest of South America. That includes almost 50% in Iowa and Illinois, and more than 50% in Pakistan and northwest India.
Crop yields rise (with +3°C) across Scandinavia; most of Canada; most of Russia, eastern Europe and central Asia; and in north and west China. They rise too in Chile, New Zealand, Kenya, the northern US Rockies, and a few other places.
The IPCC in March 2014 summarrized many such studies below. The key shows % of total number of studies examined.
The bars above show % of the 56 or more studies considered that found various % yield changes (color key at right). The black horizontal bars show the line between yields higher than now and lower ones. Farther into the future, more and more studies project lower yields, especially much lower yields (18% project 50-100% losses after 2090). Assumptions about adaptation, CO2 fertilization, region, and other matters varied from study to study.
The graph below summarizes key parts of the IPCC’s review.
Below is another graph from the March 2014 IPCC Food Impacts summary.
Impacts are worst for wheat and temperate regions. Negative projected soybean impacts were rare.
The two graphs below extrapolate from Hatfield's summary of obersavtions, a bit above.
Note the steep decline in rice production around a tropical city. This is broadly representative of the tropics and subtropics. Yields decline (much) less steeply in currently temperate areas. Soybeans are least vulnerable to heat.
The soybean projections are consistent between the US and IPCC, but the IPCC sees tropics faring better.
This assumes no constraints from nitrogen or water, etc.
Without allowance for increased insect activity and weeds, etc., yields rise 10% for wheat in North Dakota, 18% for soybeans in Kansas, and 5% for rice in Arkansas, but fall 3% for corn in Iowa. The tropics are hit much harder; rice yields fall about 20% in India.
The 2nd graph uses a warming projection more in line with some recent paleoclimate studies. For example, the last time CO2 levels were this high (380-425 ppm (3 and 15 million years ago), which is roughly the square root of 2 (declining marginal return to more CO2) times 1750 CO2 levels of 280 ppm), temperatures were 2-6°C higher (Tripati, Pagani, Csank, etc.)
This implies 4-12°C warming with CO2 twice 1750 levels. The “equilibrium" climate sensitivities implied are much higher than “transient” (geologically short-term) climate sensitivities derived from many studies by the IPCC. Debate rages from 1° to 5°C for “transient” climate sensitivity for doubled CO2.
Again, this assumes no nitrogen or water constraints.
Without allowance for increased insect activity and weeds, etc., yields fall 7% for wheat in North Dakota, 15% for corn in Iowa, and 13% for rice in Arkansas, but rise 11% for soybeans in Kansas.
The tropics are hit even harder; rice yields fall about 47% in India. Moves to winter wheat in north India no longer work, as even winters are too hot.
A table with a simplistic projection of crop yields around various cities amid the world's major growing regions, for combinations of higher temperatures and double pre-industrial CO2.
In general, corn, rice, and wheat are adversely impacted, but not soybeans. Winter wheat is chosen in Pakistant and India.
Hunger at the 2°C Dinner Table 0826.rtf
Vulnerability to High Temperature Shapes Global Warming Impacts on Rice Yield 0726.rtfPesticides Aren’t Just Making Us Sick, They’re Cooking the Planet 0726.rtf
Appeal for $ to Avert Upcoming Global Hunger Crisis as El Niños Worsen 0626.rtfEurope Faces Biggest Food Price Shock in G7 From Hotter World 0526.rtfHow a Super El Niño Could Trigger Global Famine 0526.rtfClimate Change, Rising Seas Threaten Southern Iran’s Food Security 0126.rtfHow Climate Change Is Pushing Even Rich-Nation Agriculture to the Brink 0526.rtf - Extreme heat harms crops and livestock, while it reduces the number of hours farmers can work.World Food Systems ‘Pushed to the Brink’ by Extreme Heat 0426.rtf - Our crops are productive when the temperature is within a certain range. With extreme heat, this range is often breached. With high heat, crops wither, so many of them don't even get close to being harvested. Moreover, livestock suffer from the heat, as do crops and humans, compounded by less food as crops wither.A Hotter World Will Be Pricier 0426.rtf - Extreme heat in 2022 [+5.7°C in some places] raised European food prices by an estimated 0.7% that year, nudging overall inflation up by about 0.3%.Oceans Are Absorbing Earth’s Excess Energy, in Bad News for Food Systems 0326.rtf - Corals and fisheries are badly affected by hotter ocean temperatures. One study suggests that elevated temperatures alone could hike consumer prices globally by as much as 1.2% each year by 2035. It estimates an increase of up to 0.76% a year in Europe.Climate Change Agricultural Impacts to Heighten Inequality 1221.rtf - Production to fall for maize but rise for wheat.
Projected changes in yields of several crops worldwide as a function of global warming (relative to pre-industrial temperatures) in the absence of adaptation. Best estimates and likely uncertainty ranges are shown.
2 graphs drawn from Obama Science Advisor John Holdren's slides
Local ∆ (+°C) for Low Latitudes
Mid-High Latitudes
from Climate Stabilization Targets by US National Academy of Sciences, late 2011 (on Overviews web page)
Heat in the Heartland - Climate Change and Economic Risk in the Midwest - Risky Business / Grayson 0115.pdf of Farming chapter. Full study is on the Overviews and Heat pages.
Agriculture will be harmed in a major way. Crop losses of 40-64% by 2100 are likely for corn in the Corn Belt and 8-38% by 2100 for soybeans in the same states (IA, IL, IN, OH, MO). The Corn Belt will have moved into Canada, North Dakota, and NW Minnesota. See maps and table below. In most of Missouri and Illinois, plus about half of Iowa and Indiana, crops losses are 25-50%, and worse in a few places. Wheat is much less affected, as it is often grown in the colder months and harvested by June.
Costs of Damages from & Adaptation to Climate Change in East Asia - Asian Develop Bank 2013.pdf - 216 pp
Projections by Asian Development Bank, 2013. PRC = China
Section Map: Food Impacts