One thing to think about is a famine that large that crosses major continents would have cultural, societal and regional military impacts as well.
Let's start your hypothetical famine in Africa and spread eastward.
Years -5 to year 0 were rainy years. Crops were bountiful, maybe in some regions, overly abundant.
Years 1-5 Crops are stunted from depletion of nutrients in the ground. Locusts have bloomed across multiple areas. Famines are raging across the continent. The Nile Delta is especially hard hit by the locusts. Approximately 1/3 of the crops are destroyed. Worldwide relief is being shipped in, but it can only feed 1/4 of the calories needed.
Locusts and a rice blight are impacting Indian crops.
Western Stock Exchanges have large drops in their Indexes
Year 6-7 A single year could be withstood. A multiyear famine however cannot not.
People are migrating to regions where the food is. This is putting significant pressure on the local populations. Riots break out in refugee camps. Armed clashes break out between local militaries and police, with camp militias looking for food.
Refugees by the millions are migrating out of Africa through the Middle East and trying to get into Southern Europe. Small scale clashes along the borders of Turkey and Greece are erupting. Turkey suspended from NATO.
Years 8 The blight and locusts have moved into China and North Korea.
Clashes along the border of Turkey and Greece have increased. Greece has called in its military to protect its border. Turkey ramps up their military presence to force open the border. (They cannot handle the influx of refugees either.) Seeing a weakened rival Pakistan ramps up Kashmir attacks and attacks within India.
The major stock markets are at an all time low. Countries like Greece, Italy, Ireland, Iceland, are bankrupt. Germany and France can no longer bear the burden of keeping these countries afloat.
Year 9 Major clashes along the borders of Turkey and Greece. Greece invokes Article 5 of the NATO Treaty. NATO reinforces the borders and calls for calm. Offer some money if Turkey houses the refugees. They refuse.
Widespread famine in North Korea. Fearing the collapse of the government, the DPRK launches small scale provocations to force aid from the west in return of status quo. This includes a ballistic missile attack on ROK forces along DMZ. ROK declares war on NK.
With the West paying attention to NK, and India growing tired of the provocations in Kashmir, launch a ground war into Kashmir to reclaim territory and install a larger buffer with Pakistan.
China refuses to help NK as they are in the middle of the famine as well, NK blatant attack and the fact that they need the West for trade and aid.
Year 10 NK defeated but not before they used a Kamikaze attack with a nuclear warhead on Seoul. 250k dead, nearly 1M injured.
The West can no longer help feed the world. Its stockpiles are depleted. A general anger from the areas impacted the most spread anti-West sentiment.
War now ranging in Kashmir between Pakistan and India. Indian army is far larger, better trained and equipped, pushes deep into what Pakistan determines is their territory. Pakistan issues an ultimatum that unless India withdraws, total war will be declared.
When India refuses, terrorist, later tied back to Pakistan Intelligence Service (the ISI) release nerve agents on police stations and hospitals, bio weapons are dispersed in large crowded areas in Mumbai and other major cities.
India retaliates with several small tactical nuclear weapons aimed at strategic points such as military bases and government installations.
Year 11 - Biological agents usage in India have spread. Over a million are dead from Anthrax, Cholera and Plague.
What started out as a famine now has escalated in a nuclear war in 2 areas. Remember we are just 100 years from when the whole European continent exploded for very similar reasons.