Our World In Data (OWID) ran a series of articles by Hannah Ritchie which explores the impact of climate change on crop production. On balance the stories get the facts straight, pointing out that yields of key staple crops have increased dramatically, in large part due to the CO2 fertilization effect and modestly warmer temperatures; however, parts of the stories stray into speculation that some crops have increased less than they would have and that they will decline in the future because of climate change. The latter claims are mistaken, based on disputed computer model outputs and unjustified beliefs about crop responses to modest temperature increases, not experience or data, which is what OWID should stick to.
Ritchie’s series of articles, “Crop yields have increased dramatically in recent decades, but crops like maize would have improved more without climate change,” “How will climate change affect crop yields in the future?,” and “Climate change will affect food production, but here are the things we can do to adapt,” are by and large well written, data driven pieces describing the current beneficial impact of climate change on crop production, and the tremendous potential of wider penetration of modern agricultural technologies into developing countries to increase production further. The only flaws in the articles are where she cites unverified studies depending upon flawed climate model projections to speculate concerning what might have happened to some crops absent warmer temperatures, and what might happen in the future.
Ritchie’s series starts off on solid ground noting the tremendous growth in cereal crops and regionally important staple crops. Ritchie writes:
When considering the net impacts of climate on food production, we need to consider three key factors: higher concentrations of CO2, warmer temperatures, and changes in rainfall (which can cause too much, or not enough, water).
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Carbon dioxide helps plants grow in two ways.
First, it increases the rate of photosynthesis. Plants use sunlight to create sugars out of CO2 and water. When there’s more CO2 in the atmosphere, this process can go faster.
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Second, it means plants can use water more efficiently
Ritchie then goes on to detail how higher CO2 concentrations have boosted crop yields. This is a fact that Climate Realism has pointed out in across more than 200 articles previously, here, here, and here to point to a few examples. Data from the U.N. Food and Agriculture Organization (FAO) show that wheat, rice, corn and other top cereal crops have repeatedly set new records for yield and production during the recent period of modest warming.
- Cereal yields have increased nearly 52 percent, with the most recent record for yield set in 2022; and
- Cereal production grew by approximately 57 percent. (see the chart, below)
There are three cereal crops Ritche expresses concern about, maize, millet, and sorghum, claiming that they would have increased more absent climate change, but that is based on a counterfactual analysis based on computer model projections, not data. She cites studies which suggest that many of the areas these crops are grown in have surpassed or are soon to surpass their optimal growing temperatures, with every increase above the maximum optimum range resulting in declining yields. Yet in the face of a 1.3℃ to 1.5℃ rise over the past century, all three of those crops have experienced substantial yield increases across recent decades, both globally and in the tropical developing Asian and African countries she worries might not be fully benefitting from CO2 fertilization.
Concerning maize, FAO data show that between 1991 and 2022, global maize yields increased by approximately 55 percent and about 49 percent in Africa.
The data from the FAO for millet and sorghum are similar, with each crop experiencing substantial yield gains, globally, and across Africa and Asia over the past three decades of modest warming. (see the graph below).
As has been discussed in more than 200 articles on Climate Realism, what is true of global cereal production, is true for most crops, like fruits, legumes, tubers, and vegetables, in most countries around the world. Yields have set records repeatedly during the recent period of climate change, food security has increased, and hunger and malnutrition have fallen.
Ritchie cites a few studies which suggest that the yields of maize, millet, and sorghum would have been even higher absent warming, which resulted in much of their growing regions experiencing temperatures outside of their optimal range — a problem which will only grow in the future if CO2 emissions aren’t restrained — but such claims suffer from a number of flaws. First, most of the regions of concern for the growth of maize, millet, and sorghum, sit astride or are near the equator. Yet the climate change theory says equatorial regions are least likely to experience much temperature rise – rather temperatures are expected to increase dramatically nearest the poles. Little or no temperature rise for the regions of concern means exceeding what some scientists speculate are optimum temperatures should not be a problem.
Second, Ritchie is right that changes in precipitation can reduce crop production, but once again, that should not be a concern. Many of the areas Ritchie highlights in Africa and Asia experience periodic or even seasonal drought. Since, as Ritchie notes, CO2 fertilization results in crops using water more efficiently, losing less water due to transpiration, crops should benefit. On the other hand, many countries in Africa and Asia depend on rainfall for crop production, with limited access to modern irrigation infrastructure. Here, climate change helps because most research suggests, and the IPCC projects, that climate change will result in increased precipitation, which means more water for crops, and if the water is seasonal as it is in many countries, more water that can be stored for use when rain or snowfall is lacking.
Third, the claim that climate change harms crops is contradictory in theory. Climate alarmists claim higher CO2 is driving rising temperatures – if so, the higher temperatures are a by-product of rising CO2, meaning without the CO2, temperatures might not rise. Yet, CO2 is the key factor driving growing crop yields, so absent increasing CO2, crops yields would have increased and continue to grow more slowly than they did, if at all. On this theory, if you want benefits CO2 fertilization, you have to accept the modest temperature increase. Cutting CO2 concentrations to avoid a minimal temperature rise would be to kill the golden goose for crop yields, resulting in a larger decline in or slower growth of yields than any modest decrease in yields that might result from the associated supposed small temperature rise.
What are we left with. Crop yields have increased due to rising CO2 concentrations, reducing hunger in the process. In addition, there is no reason to believe CO2 fertilization won’t continue to produce yield increased for the foreseeable future, unless climate policies result in lower CO2 concentrations.
On the other hand, as Ritchie points, out any foreseeable negative climate change impacts on crops, most especially in developing countries, would be far outweighed if they gain broader access to modern agricultural technologies, such as fertilizers, pesticides, modern farm equipment, and infrastructure. As Ritchie writes:
[T]here are other things we can do to mitigate this risk and counteract some of these pressures.
There are still huge yield gaps across the world today. “Yield gaps” are the difference between the yields that farmers currently get and could get if they had access to the best seeds, fertilizers, pesticides, irrigation, and practices that already exist today.
Let’s take the example of Kenya and maize. Farmers currently grow around 1.4 tonnes per hectare. However, researchers estimate that farmers could get 4.2 tonnes if they had access to the best technologies and practices available today. That means the yield gap is 2.8 tonnes. …
In some of the worst climate scenarios, Kenya could see a 20% to 25% decline in maize yields. If nothing else changed, that would cut its current yield of 1.4 tonnes to around 1.1 tonnes: a drop of 0.3 tonnes.
However, the current yield gap of 2.8 tonnes is much larger than the 0.3 tonnes drop that might be expected with climate change.
Yet, modern agriculture depends heavily on fossil fuel use: from the chemicals used to enhance crop growth; to the chemicals used protect crops from pests; to the machinery used to plant, water, harvest, store, and transport crops. So, for agriculture, any possible negative climate change impact on agriculture from using fossil fuels, is far outweighed by the tremendous benefits their use directly delivers to food producers and consumers.
You can’t have high yields without CO2 and modern, fossil fuel intensive, agricultural infrastructure. That’s the overall lesson readers should take away from Ritchie’s Our World In Data series of articles.
