As malnutrition has been identified as a serious health-related problem affecting developed and developing countries around the world alike, the United Nations (UN) has named the time between 2016 and 2025 the Decade of Action on Nutrition . With the aim of reducing global malnutrition as well as diet-related non-communicable diseases by 2025, the World Health Organization (WHO) and the Food and Agriculture Organization of the United Nations (FAO) have set clear targets throughout the Second International Conference on Nutrition. The beginning of the Decade of Action on Nutrition coincides with the implementation of the 17 UN Sustainable Development Goals (SDGs) which were adopted in 2015 and came into force in 2016. Within the framework of the SDGs, the UN aims to end hunger by 2030, achieve food security, improve nutrition, and promote sustainable agriculture (SDG 2). Additionally, the UN aims to ensure healthy lives and promote global well-being for people at all ages (SDG 3) . To achieve these goals, the WHO has implemented a nutrition strategy to ensure access to healthy and sustainably grown diets on a global scale.
These strategies and goals come in pressing times, as malnutrition is affecting people worldwide. It occurs in various forms, the four most relevant including: wasting, which refers to a low weight-for height ratio; stunting, referring to a low height-for-age ratio; underweight, meaning a low weight-for-age ratio; and obesity, which occurs when a person is too heavy for their height . Current estimates indicate that about 8.9 percent of the world population are suffering from hunger, while one in ten people in the world are exposed to severe levels of food insecurity . The highest proportion of undernourished people can be found in Asian countries, directly followed by many African nations. Hunger has increased over the last five years, with 462 million adults being underweight globally (2021) . Children under the age of 5 are at particular risk of long-lasting effects due to early childhood malnutrition. Around 7% of children in this age category suffer from acute under-nutrition , and 45% of deaths among children under 5 years of age are in one way or another linked to under-nutrition . Stunting in young children has decreased globally by 11% compared to 2000; however, an alarming 22% are still affected by it . Little to no progress has been made regarding wasting, which continues to affect around 7% of children around the world .
In terms of number of people affected, obesity, or over-nutrition, seems to be the bigger issue, with numbers almost tripling since 1975. 1.9 billion adults (2016), 340 million adolescents (2016) and roughly 39 million children below the age of 5 years are currently overweight or obese (2021) , with numbers rising slowly but steadily. This means that over-nutrition affects around 6% of children under 5 years of age . Over-nutrition affects developed and developing countries alike and is a reason for concern in many low- and middle-income countries, as they face the double burden of under- and over-nutrition. The main reason for obesity in developing countries is the cheap availability of high-fat, high-sugar but oftentimes nutrient-poor foods combined with low physical activity . Therefore, while under-nutrition affects mostly developing countries, over-nutrition can affect both developed and developing nations.
Where does our food come from now?
The highest share of exported agricultural products, amounting to $118 billion (2021) , comes from the United States of America. Major crops for export include corn, soybean, and wheat. The US is followed by the Netherlands ($79 billion, although mostly in flowers and live plants), Germany ($71 billion through organic products especially) , France ($68 billion through mostly wheat, sugar, wine, and beef)  and Brazil ($55 billion through soybeans, meat, sugar, coffee, corn, and fruit)  (2021). It is projected that international food trade will become even more important in the future. With rising temperatures, the global food system will also continue to become more exposed to the effects of climate change .
Climate change projections on terrestrial food supply
Estimates show that from 1980 to 2011, climate change reduced global maize and wheat production by approximately 5%. If we fail to meet the goals of the Paris Agreement and instead steer towards a 4°C warming by the end of the century, models suggest that there will be a 25% reduction of maize and a 15% reduction of corn by 2100 . The CO2 fertilization effect, possibly beneficial for plant growth, is already included in these calculations.
This decrease of food production goes along with a predicted increasing demand for agricultural products due to a growing world population. Additionally, most of this population growth is projected to happen in regions that already experience high levels of malnutrition or food scarcity, such as many African and Asian countries . Moreover, the stress on food supply will be exacerbated by the impacts of climate change. It must be noted at this point that predictions around climate change impacts have a great spatial variability. This means that some regions, like more northern latitudes, could profit from those changes (through more suitable growing conditions, for example), while the changes are likely to result in a loss of agricultural productivity in other regions.
Especially tropical areas will experience a decline in yields (Figure 2) . Many of those regions, like some African countries, will thus face a three-part challenge: first, present high levels of malnutrition; second, a projected population growth; and third, significant yield losses caused by global warming.
On the bright side, more and more agricultural products are part of the global food trade system, which has the power to balance supply shortages in one country by providing food exports from another country. Nevertheless, climate change can and will also increase pressure on international food trade through increased climate variability and more frequent extreme events .
An example for the effects of extreme weather on international food trade could be observed back in 2010. In 2010, Russia was struck by an unprecedented heat wave, with July temperatures climbing to the highest values in 130 years. The heat wave was accompanied by numerous wildfires leading to 17% of total Russian crop area being affected by severe heat or fires . With Russia being the 4th largest wheat exporter and accounting for 14% of global wheat trade, the extreme weather thus had severe effects on the international food market. International grain prices increased as soon as news about a reduced grain production in Russia due to the heat wave were released. In order to protect local customers and ensure food security, the Russian government imposed an export ban on wheat, barley, and rye from August 2010 on, which lasted until July 2011 [12, 13]. Consequently, Russia’s wheat exports dropped by almost 40 % from 2009 to 2010 . This export ban had drastic implications on the importing countries. For example, Russia’s fourth biggest wheat customer, Pakistan, saw 16% higher wheat prices and a 1.6% increase in poverty during this period . According to some studies, the Russian export ban on grain products played a decisive role in the Arab spring, which started in December 2010 in Egypt. The country obtains roughly 50% of its grain supply from Russia and the export stop of grain led to riots and violence on the streets, with people protesting against the increasing prices for food which they were struggling to afford at that time [12, 13].
Under the influence of climate change, extreme events like the Russian heat wave in 2010 are likely to happen more often in future decades. A study by Kornhuber et al. (2020) has shown that with increasing global temperatures, atmospheric dynamics will change, which will lead to a stronger meandering of the jet-stream and more persistent Rossby waves. These changes will mainly impact the northern mid-latitudes, which are often considered as breadbasket regions, given that they export a great share of their agricultural produce . With an increasing share of global food production moving away from regions with the highest projected population growth and towards more northern latitudes, increasing frequency and intensity of extreme events threatens the global food system .
Considering the above-mentioned effects that result from rising carbon concentrations in the atmosphere and global warming, agriculture and the whole food production system need to adapt and change. This gets even clearer, when keeping in mind that without major changes, the agricultural sector alone would exceed the total global carbon budget to limit global warming to below 1.5°C by the end of the century .
Direct effects of CO2 on crops
Rising CO2 levels not only affect temperature and our earth’s climate, but also have an influence on crops. One could argue that a higher CO2 level in the atmosphere would simply act as a natural fertilizer by increasing plant growth – and therefore could be considered as something positive for the overall food production and food security. Unfortunately, this is oversimplified and remains a common myth. Clearly, higher concentrations of CO2 are acknowledged for stimulating plant photosynthesis and growth . However, this is only the case as long as nothing else changes. Higher CO2 levels in the atmosphere not only affect the plant available water and available CO2, but also temperature, rainfall patterns, sea levels and more. Therefore, the direct impacts of increased atmospheric CO2 are likely to be extremely complex. Furthermore, the effects are not only complex, but vary greatly from region to region and from one kind of farming to another . Therefore, it is hard for studies to reveal the concrete outcome for the direct effects of CO2 in the atmosphere on agriculture.
For example, in the case of wheat in Europe, higher CO2 levels in the atmosphere and associated higher temperature could extend the growing season. This is especially the case for regions where temperature is the limiting factor. It is estimated that the growing season is lengthened by about 10 days per degree Celsius  if the mean annual temperature increase remains under 3 degrees Celsius. Increases that are higher than 3 degrees Celsius are likely to be problematic and to limit the growing season again, because the increased evapotranspiration rate leads to decreased crop-water availability.
Besides crop growth and quantity, which can be enhanced by higher CO2 levels under certain conditions, crop quality is also an important issue. Crop quality refers to the amounts of nutrients, as well as the composition between carbohydrates, fats, and proteins. A protein and nutrient deficiency can be especially problematic when it comes to food quality.
Studies revealed that important minerals like iron and zinc are decreasing in legumes and C3 crops (e.g., wheat, soybeans, oats, rice) . This is critical, since many people all over the world rely on those crops as their primary source for iron and zinc. Furthermore, studies revealed that also the protein content is decreasing with elevated CO2 levels. These elevated CO2 levels can reduce the nutritional quality of staple crops. Crops with higher carbohydrate conditions and less protein content as well as less mineral content could be part of our future under climate change.
Especially a deficiency in zinc and iron, which some regions already struggle with, will continue to grow into an even bigger problem in the future. Countries that are already affected by nutrient deficiency will be disproportionately more affected in the future . These deficiencies in iron and zinc can lead to human health issues. A deficiency in zinc for example can lead to a weaker immune system, which makes the human body more vulnerable to infections. A good immune system is always important, but in times of a global pandemic it has an even higher priority. Therefore, good quality crops are important for overall human health across the world.
Genetically modified seeds
Periods of dryness, heavy rain, and other extreme events have a direct impact on crop growth and agriculture. Furthermore, new invasive insect species due to climate change or new crop diseases hit the agricultural sector and global food security hard. Therefore, the demand is high to genetically modify seeds in a such a way that they can better tolerate dry conditions and stress. These seeds that are modified in their DNA are called genetically modified seeds. The degree to which the seeds are modified varies, but all modifications have the same goal: make the seeds more adaptable to certain environmental circumstances.
Currently, soy, maize, cotton, and canola are the top four crops which are seeded in genetically modified versions . The most induced traits are herbicide tolerance and insect resistance. There are also other experiments with crops to make them more resistant to drier soils. Having crops that are more resilient when it comes to water stress could be beneficial in the face of climate change. Having genetically modified crops that are more insect resistant could also reduce the amount of pesticides used by farmers.
There is no clear statement on whether the consumption of genetically modified seeds is good or bad for human health. However, there are concerns, not only from an ethical point of view. To control and supervise every impact that a genetically modified seed has on the plant, on the soil, or on the consumer is a complex and hard to achieve task. Many environmental organizations, like the BUND, have strong concerns about growing genetically modified seeds because the overall impacts of the modifications are not clear yet. In summary, genetically modified seeds may help to keep up food production in the face of climate change. But the question of whether this is the only solution to provide a high level of global food security remains.
Climate change and its impacts on oceanic fisheries
Not only the food on our lands is in danger due to climate change but also that in our oceans. Oceans absorb 93% of the heat that accumulates in the earth’s atmosphere and a quarter of the carbon dioxide (CO2) emitted by fossil fuels, making them important players in climate dynamics. Temperature variations, acidification, deoxygenation, and changes in currents are all effects of climate change on marine ecosystems. These impacts can alter the distribution of fish stocks and the food they consume. Furthermore, these stocks face over-fishing and other anthropogenic pressures. To preserve our oceans and maintain fish populations, we must move towards sustainable fishing. To manage fishing sustainably, it is also necessary to adapt to the challenges that climate change presents .
In the last 30 years, marine heatwaves are thought to have increased by more than 50%. Ocean temperatures are expected to rise by 1-4°C globally by 2100 . Marine life is being damaged by these changes. Temperature spikes and acidity can result in the decline or death of marine environments and species. The distribution of fish stocks and the structure of ecosystems are changing because of shifting ocean currents and warming seas. It is predicted that the tropics will see a 40% decrease of oceanic life by 2050; on the other hand, some areas in North Atlantic and North Pacific are witnessing some increases in the range of some fish species .
Many people around the world rely on fish as a significant source of food and livelihood. According to FAO, 3.3 billion people acquire at least 20% of their daily protein intake from fish. Moreover, 39 million people are employed for wild capture of fishing and 37% of people living in coastal communities are directly employed in the fishing industry. Notably, half of the traded sea food comes from developing nations. Asia accounted for 85% of the global population involved in fisheries and aquaculture, followed by Africa (9%) and the Americas (4%) in 2018 . With the increase of anthropogenic influence on oceanic activities, the potential for negative consequences for people, species, and marine habitats increases. The more sustainable our fishing becomes, the more vulnerable populations as well as future generations will benefit from food security and a stable livelihood in a well-functioning ecosystem.
One example of a human-induced disaster with negative consequences for ecology and for the people dependent on it as a source of food supply and livelihood is the Aral Sea case. The situation started in 1960s, as the Soviet Union diverted Amu Darya and Syr Darya, the two major inflows of Aral Sea. The blockage of the water source, combined with high summer temperatures of 60ºC at lake’s location in the Turkestan Desert, led to an increase in the salinity of water from 1% to 10% and a shrinkage of lake area by 10% from its original size. By 2007, the aquatic life could no longer thrive. The two river deltas’ wetlands, as well as their accompanying ecosystems, largely vanished. The shoreline has shrunk to 10km inside the former lake shore, and the surface of the water body is more saline. With the fish gone and ecosystems vastly altered, local communities have no longer been able to rely on the sea as a significant source of livelihood and resources. Additionally, due to the lack of moisture and the loss of most of the lake’s moderating influence, the regional climate is drier, with more severe temperature extremes. An increasing number of dust storms blow salt, pesticides, and herbicides into nearby towns, causing a variety of respiratory illnesses.
As we can see, global food supply is already at risk, but will be subjected to further stress due to anthropogenically induced climate change as it alters atmospheric CO2 balances, causes heavier and more frequent extreme events, and affects temperature and precipitation patterns. This will have detrimental consequences on the achievement of the Sustainable Development Goals 2 and 3, as it will exacerbate hunger and insecurity in developing countries and put the health of populations across the world at risk. Mitigating climate change is of utmost priority and will help save millions of lives.
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