The first famine has been declared in the world's newest nation, South Sudan. To understand just how dire the situation is, you need to understand the United Nations' reluctance to use the word: famine.

Famine has a very specific definition.

It must meet three criteria before it can be declared: four out of every 10,000 children die each day, one in five families do not have enough food to meet basic human nutrition requirements, and one in three people are acutely malnourished to the point that they are too weak to go to school or work.

To put this into context, if famine were declared in the state of Victoria, 400 children would die daily from starvation. And if famine were declared in Australia, 1700 children would die every day.

Famine can be hard to comprehend unless you've seen it firsthand. It is ghastly.

As it stands, 1 million men, women and children are on the brink of starvation in South Sudan. And 4.9 million people -- more than 40 percent of South Sudan's population -- are in need of urgent food, agriculture and nutrition assistance. This figure is likely to rise to 5.5 million at the height of the lean season in July if nothing is done to curb the severity and spread of the food crisis.

As is the case with so many emergencies in the developing world, it is girls who suffer most. Plan South Sudan estimates 100,000 girls are currently at immediate risk of harm.

Famine can be hard to comprehend unless you've seen it firsthand. It is ghastly. I was on the ground during the response to the last two famines, first in 1991 in Somalia and then during the 2011 East African drought.

You see children with skeletal arms and legs, desperately clinging to life. And when they are rescued, they have to be put on drips because they are too weak to feed through their mouths. The doctors are trying to bring them back from the edge of death.

I've seen children lose the fight simply because their bodies are so weak. Sometimes, they die from pneumonia because of their compromised immune systems, or they die from diarrhoea because their bodies are too frail to fight the loss of liquid. They are so very vulnerable. It is heartbreaking.

As an aid worker living this reality, you wonder why governments did not release enough money or raise enough resources to help in time. You wonder: how did we get in this situation? You feel guilty and the only thing you can do is your best to try and change it. This is why we need people to listen early and respond early.

If you go back to Ethiopia in 1984 -- which was the biggest famine in a generation -- there was a very harsh drought compounded by the fact that normal food transfers and trade within the country was blocked by war. That created a perfect storm for people to become isolated from food supplies and end up completely destitute. It was largely invisible to the world until BBC reporters were able to get into the country and expose what was happening.

Right now, we are seeing almost exactly the same conditions in South Sudan as we did in the lead up to Ethiopia in '84 and again in Somalia in '91.

It's only when we start to see images of emaciated children hooked up to drips in white tents being attended by emergency doctors that people can fathom the sheer horror of famine.

Here we have the same terrible culmination of conflict and drought, but with the added challenge of climate change. Extreme weather events have spurred along an already tense situation into a deadly one, with ongoing conflict stranding communities in isolated social pockets, restricting their access to aid.

Sadly, when a famine is first declared it is hard to garner support because people simply can't picture what's happening. It's only later on when things are completely broken that we start to pay attention. It's only when we start to see images of emaciated children hooked up to drips in white tents being attended by emergency doctors that people can fathom the sheer horror of famine.

We need everyone to understand this important fact:

now is the time when we can help to protect the most vulnerable in South Sudan from the terrible consequences of disaster. Now is the time when all of us can step in to save South Sudan's children from a horrific death from starvation.

**This article was written by I. Wishart