I can recall four major existential crises during my 80-plus years; four periods in which the survival of our whole planet, including all those who inhabit it, has been threatened with extinction.

The first such crisis was World War Two, when humanity faced the threat of total domination by fascist, racist and ruthless states. The cost of winning this six-year battle was huge, but one outcome was the determination of the surviving nations, including Germany and Japan, to find ways of working together to avoid such a situation in future.

The second crisis was the deadly competition in the 1960s and 1970s between two nuclear-armed blocs to build unimaginably dangerous weapons systems with enough power to blast our whole world apart. We faced the constant threat of a holocaust which would have destroyed humanity and most life on the planet. We avoided that fate through the determination of politicians working together to end the strategy then known as MAD – mutually assured destruction.

And now we face the third existential crisis, the remorseless spread of Covid-19, the coronavirus pandemic. It is impossible to know how devastating it may become or how long it will last. It is already deeply rooted across Europe. Government decisions are making heavy demands on social relationships and on economic development. Yet we all know that this is a price we now have to pay to limit massive loss of life.

We should congratulate all who have taken such radical preventive measures, including the political parties which have reluctantly accepted so many restrictions on individual liberty. And we must thank everyone working hard to protect us all; especially the social services and the health workers whose continuing generosity and selflessness are so remarkable.

What should follow when we have come through this testing time? I cannot believe that life will simply revert to what it was before. Political parties will face a special opportunity to change the way we live and work together. This should include forward planning for similar major changes of lifestyle and priorities, agreed across the globe.

For we now confront the fourth great existential threat; the overwhelming reality of climate change. What can we learn from those other crises which may help us cope with this one? Measures are needed which will be even more life-changing than those we currently face. One thing stands out clearly; we have to work with others. It is only by agreed international measures that we will save our planet. Narrow nationalism is about as likely to help as shouting into the wind. Just as with coronavirus, we are all in this together.