Global warming increases the risk of heat exhaustion in ectothermic animals

It sounds obvious that hotter organisms are severely affected
by global warming.
Their body temperature — and their biochemical processes — is known to depend on ambient temperature and sunlight
.

However, the damage caused by heat doubled for every degree of ambient temperature that exceeded their tolerance level — even for the researchers who completed the new study
.

The researchers, five animal physiologists from Aarhus University, have just published their findings in the prestigious scientific journal Nature and made it on the cover
.
Their findings were published on
the cover of the journal.
The researchers' study is based on data from some previously published studies on ectothermic animals

It is well known that there is a correlation
between the geographical distribution of ectotherms and their tolerance to ambient temperature conditions.
They can only live where the temperature allows them to grow and reproduce, and the extreme temperatures of winter and summer are not too cold or too hot
for a long time.

If the temperature exceeds the threshold they can tolerate, the animal will be injured
.
These injuries accumulate over time and ultimately determine whether a species can survive
the current temperature conditions.

"The higher the temperature, exceeding the tolerance level of the species, the faster they accumulate harm," explains
Bjerregaard Jrgensen, one of the study's co-authors.

The researchers analyzed the temperature sensitivity
of 112 ectothermic plants to heat stress.
The analysis showed that a temperature increase of only 1°C more than doubled the rate of thermal damage accumulation, and since this is an exponential increase, a temperature increase of 2°C will increase the rate of heat damage accumulation by more than 4 times, while a temperature increase of 3°C will increase the rate of damage by more than
8 times.

The researchers then compared
their temperature-sensitivity data with models of expected increases in maximum temperatures associated with global warming.
These data suggest that heat injury rates in ectothermic animals could increase by an average of 700% globally, while in many environments on land, heat injury rates could increase by more than
2,000%.

For aquatic ectotherms, the corresponding figures are 180% and 500%.

A regional analysis suggests that the impacts of climate change are enormous, especially in the northern temperate zone, which covers much of Europe and North America, as well as in the oceans
around the Arctic.

Although the researchers are not aware of the underlying physiological and biochemical responses that lead to heat stress and death, their study shows that these processes are extremely sensitive to
temperature in all ectothermic animal populations.
This may indicate that a similar process determines the degree of
thermal damage.

"We also can't predict how many species and individuals are at risk of dying from rising temperatures, because the thresholds for heat stress vary widely
from species to species.
In addition, many thermal animals on land can reduce the risk of
heat stroke by finding shade to regulate their body temperature.
This is not easy for aquatic animals," said
Professor Johannes Overgard, co-author of the study.

He added:

"The point is that this high sensitivity to heat damage means that we may be underestimating the impact of
future heat waves.
Our findings suggest that future heat waves will have significant consequences – if not all species will be affected
to the same extent.
”