EXPLAINER: Is climate change boosting hunger around the world?

As a warming planet brings higher sea levels and wilder weather - from droughts to floods - the challenge of growing food is getting tougher with less reliable harvests.

Temperature and rainfall shifts are altering the range of crop pests, bringing damaging infestations - from fall armyworm to locusts - to new locations or in old ones more often. 

Coastal areas are seeing farmland eroded or tainted with plant-killing seawater as melting glaciers swell rivers and the ocean, and storms drive salt-water further inland.

And scientists say hotter temperatures are reducing the levels of key nutrients in major crops, threatening more malnutrition even if people can get enough food to eat. 

A November study by the U.S. National Aeronautics and Space Administration (NASA) predicted global maize harvests could fall nearly a quarter by century-end if climate-heating emissions continue to rise. 

Declines in production would start becoming apparent by 2030, NASA researchers said - a serious problem as the global population and demand for food continue to grow.

Grain production could fall 10% by 2100 around the world if farmers fail to find effective ways to adapt to climate shifts, warned a June study by researchers from Boston University and other institutions, which looked at maize, rice, soy and wheat. 

"Globally, farmers' capacity to adapt to climate change impacts, even over longer periods, might be limited," said lead author and Boston University climate change economist Ian Sue Wing.

Shrinking or more uncertain harvests, alongside rising demand for food, could fuel riots over shortages and high prices, growing hunger and migration, security analysts warn. 

Here's what scientists, aid experts and researchers are saying about the impacts of climate change on food security:

How does a heating planet affect food production?

Besides crop losses from droughts, floods and storms, hotter temperature extremes can make it harder for farmers, especially in the tropics, to work outside, cutting their productivity.

Higher heat can also cause harvested food to spoil faster before it reaches markets, leading to more waste, while heavy rainfall can make roads impassable, preventing farmers from getting their produce to buyers.

On the other hand, rising levels of carbon dioxide in the atmosphere, largely from burning fossil fuels, can help some crops grow, as they take in carbon dioxide and water.

But those gains will be short-lived, scientists warn, as hotter temperatures make it harder for many key grain crops - from wheat to maize - to mature and also reduce their nutritional content. 

Are today's hunger crises mainly caused by climate change?

Not necessarily. While climate-linked weather extremes and pest outbreaks are causing more failed harvests, the coronavirus pandemic also is fuelling hunger, as families lose jobs, income, trade opportunities and breadwinners to the virus.

A November U.N. report found that hunger rose 30% in Latin America and the Caribbean in 2020 compared to the previous year, in part because of growing poverty linked to COVID-19 impacts.

In 2020, four in 10 people in the region faced moderate or severe hunger at some point in the year, the highest levels in two decades, the report said. 

But while the pandemic has exacerbated the situation, hunger has been rising since 2014, said Rossana Polastri, regional director for the International Fund for Agricultural Development.

"We must fix deep vulnerabilities in our food systems," she said.

In Madagascar, the worst drought in decades has led some international aid agencies to describe surging hunger there as the world's first climate change-induced famine.

But a team of scientists who specialise in working out how much an extreme event can be attributed to global warming said the African island nation's drought was largely within normal weather variability and not predominantly climate change-driven.

In a country with widespread poverty and deforestation, large numbers of people already living precariously close to hunger, little irrigation and COVID-19 restrictions on movement, climate change is not the main driver of hunger, they said in a new study.

What can farmers and the rest of us do to keep food supplies steady as climate pressures grow?

Innovations such as "submarine rice" - capable of surviving floods - or drought-tolerant maize varieties can help farmers get a decent harvest even in challenging conditions.

Farmers can also protect their own incomes and families by growing a wider range of crops, to avoid everything being wiped out by unexpected pests or extreme weather, as well as investing in storage, including solar-powered refrigeration. 

Crop insurance programmes and wider use of irrigation, to help farmers cope with worsening drought, can also help protect agricultural incomes and help farmers recover after losses.

But making those changes requires cash - and today only about 5% of all global climate finance goes to efforts to adapt to more extreme weather and rising seas, handicapping that work. 

Smarter decisions by those buying food can also protect global supplies.

Plant-based diets, containing little or no meat, create far fewer climate-changing emissions, require less land and water, and mean more food goes to people than livestock, analysts say.

Cutting food waste - a huge global problem in homes, markets and restaurants - is another way to help ensure there is enough to go around without the need to keep expanding farmland, which often destroys carbon-storing forests.

If rising hunger is left unchecked, what could happen?

In Afghanistan, worsening hunger as a result of lingering drought and political turmoil is contributing to a surge in child marriages, as desperate families seek dowries. 

Rising migration from Central America to the United States, meanwhile, is also linked to growing crop failures and poverty - partly a result of climate change pressures. 

Humanitarian agencies are warning climate change is likely to hike demand for food aid and other assistance that they will be unable to meet, while security experts fear worsening hunger could spark civil unrest and push more people to migrate.