I was 22 years old when I had to leave my homeland, South Africa. I had no choice. I was living underground for a year by then, to avoid being arrested. This was 1987, in the midst of one of the most bloody and violent periods in the history of Apartheid South Africa. The green peaceful streets of Oxford, where I was lucky enough to end up, seemed like a cartoon to me. They seemed unreal, while the violence I left behind felt very real and near. I stayed awake at night thinking of friends and relatives left behind.

I remember these feelings now every time I look at the heartbreaking images of people fleeing devastation – whether floods in Bangladesh or war in Syria. The images of desperate parents holding on to their children, trying to get them through barbed wired fences, or off small inflatable boats. I see them and I think about my own daughter. How would I feel if I was one of these parents? When I fled, I had only myself to care for.

‘No one leaves home’ writes Kenyan born Somali poet Warsan Shire, ‘unless home is the mouth of a shark’. ‘No one puts their children in a boat unless the water is safer than the land’.

21st September marks the International Day of Peace. And this year, again, there is not much peace around to celebrate.

In Syria alone – according to some estimates one of two Syrians has died or fled home since the war began. According to the UN 7.6 million are internally displaced. 4.1 million refugees are abroad. Most of them in countries surrounding Syria. Some are turning to Europe as a safe haven.

There are times when drawing borders between countries, people, between politics and the environment must stop. There comes a time when all that matters is humanity and solidarity. This is such a time. The acts of courage and compassion shown by so many individuals and communities across Europe I find deeply inspiring.

Many of my colleagues in Greenpeace are also trying to reach out and support refugees. In Hungary and Croatia, volunteers have joined the humanitarian effort, including practical things like setting up a solar charging station in hot spots so that people can recharge their phones and access WiFi. In Greece, our office is in close contact with international relief NGOs ​to support their efforts ​and is working with local groups to collect and send relief packages to the Islands where many refugees are stranded.

I want to personally thank all who are reaching out to help. In this moving ocean of solidarity, every drop matters. We must all join together and say loud and clear: #Refugeeswelcome!

Tomorrow I travel to New York to attend the UN Summit on Sustainable Development Goals. My trip will be an easy one, but I will remember those times when my journeys, too, were journeys of fear. I will think of those facing days, months and years of relentless, life threatening journeys, with no guaranteed safety at the end of the road.

As fellow human beings we owe it to them to raise our voices, to stand in solidarity and to address the root causes of global insecurity. We need to insist on finding real solutions – including getting off fossil fuels. Conflicts are always complex. But looking at current conflicts from Iraq, Ukraine, Sudan, the South China Sea to Nigeria it is clear that the access, the transport and thus the dependence on fossil fuels do play a role.

“Resource wars” are not new. But today we can overcome them. In New York, I will argue for a world powered by 100% renewables for all by 2050. This world is in our grasp, our latest Energy Revolution scenario shows that without doubt. It is also the world we must choose if we want peace. Wind turbines, photovoltaic systems, insulation materials or double glazed windows are the “weapons” we must deploy to help create a safer world.

I was lucky enough to see Apartheid ended by people power and international solidarity a few years after I was forced to leave South Africa. Apartheid was abolished, and I am now free to return. Will those displaced now ever have that privilege? I do not know. But we must work for the peaceful, safe world for all, that would make this possible.