The Covid-19 pandemic is the biggest test the world has faced since World War II. There is a natural tendency in the face of crisis to take care of one’s own first. But true leadership understands that there are times to think big and more generously. Such thinking was behind the Marshall Plan and the formation of the United Nations after World War II. This is also such a moment. We must work together as societies and as an international community to save lives, ease suffering and lessen the shattering economic and social consequences of Covid-19.

The impact of the coronavirus is immediate and dreadful. We must act now and we must act together. Just as we must act together to address another urgent global emergency that we must not lose sight of — climate change. Last week, the World Meteorological Organization released data showing that temperatures have already increased 1.1 degrees centigrade above preindustrial levels. The world is on track for devastating climate disruption from which no one can self-isolate.

Now, on every continent and in every sea, climate disruption is becoming the new normal. Human conduct is also leading to severe biodiversity loss, changing animal-human interaction and distorting ecosystem processes that regulate our planetary health and control many services that humans depend on. Science is screaming to us that we are close to running out of time — approaching a point of no return for human health, which depends on planetary health.

Addressing climate change and Covid-19 simultaneously and at enough scale requires a response stronger than any seen before to safeguard lives and livelihoods. A recovery from the coronavirus crisis must not take us just back to where we were last summer. It is an opportunity to build more sustainable and inclusive economies and societies — a more resilient and prosperous world. Recently the International Renewable Energy Agency released data showing that transforming energy systems could boost global G.D.P. by $98 trillion by 2050, delivering 2.4 percent more G.D.P. growth than current plans. Boosting investments in renewable energy alone would add 42 million jobs globally, create health care savings eight times the cost of the investment, and prevent a future crisis.