During World War II, James Lovelock and Owen Liddell did experiments that were among the first to ask the question, what is the hottest temperature animal life can survive? In his 2020 book Novacene, Lovelock describes how they found any idea of animal experimentation abhorrent so instead decided to do the exceedingly painful tests on themselves by burning their skin with a 1-centimetre-diameter copper rod. They found that:

• At temperatures below 50ºC (122ºF) there was no burning in five minutes;
• At 50ºC (122ºF) it would cause a first degree burn in one minute; and
• at 60ºC (140ºF) it took only one second.

‘Mainstream’ life as Lovelock puts it, is under enormous threat once temperatures exceed about 50ºC and NASA reports that human life (and therefore most animal life similar to us) is adapted to thrive at temperatures around 4 – 35ºC (39 – 95ºF), which is a very narrow threshold for existence.

In the US, summer 2020 was ranked as one of the hottest on record. This month (June 2021), a heatwave across the US has shattered records again, with maximum temperatures mostly falling just shy of the 50ºC (122ºF) danger threshold. The forecast high temperature in Death Valley on Wednesday was in fact 124ºF. The highest ever recorded there was 134ºF in 1913 but there are always fluctuations in climate. The concern at present, is that these life-threatening temperatures are almost an annual occurrence now.

These are the global land and ocean temperatures from 1880 to 2015 according to the US National Climate Data Center. Red indicates years of above-average and blue years of below-average conditions.

Of course animals can survive by sweating, burrowing underground or standing in shade. But when the ambient air temperature exceeds the 50ºC (122ºF) threshold, it becomes increasingly likely that everything living, will die – that includes all animals and humans. We suffer particularly badly when humidity is high, because the moisture in the air stops us being able to sweat and reduce our core temperature. In conditions of 50% humidity and 50ºC, we wouldn’t last more than about a day.

Australian Health Insurer NIB asked what is the hottest temperature life can survive and produced this article looking at risk of death according to heat and humidity (naturally health insurance companies are looking very closely at these profiles). Information Source: NASA | Live Science

Most humans or similar animals will die after a few minutes in high humidity temperatures of 60ºC (140ºF). At temperatures below that and above 50ºC (122ºF) it becomes extremely difficult to live.

At this point it’s worth remembering how much similarity we share with animals and that we are dependent on many of the same life support systems because Earth’s ecosystems were built by animals, so they provide perfect conditions for survival.

Our interdependency on animals is why we share a combined fate. There is only one thing keeping our planet cool – ecosystems. Or else, Earth would have descended into a Venus-like hothouse state long ago. Ecosystems can only be kept cool if they are stable and stability can only be achieved with diverse and abundant animal-life.

While extreme climate change is caused largely by our over-consumption of fossil fuels, we must also remember that the loss of any other animal life from heat is affecting systems that we also rely on for a habitable Earth.