How would much smaller heat capacity of water affect the life on Earth?

Question

Water, as is, with its physical and chemical properties, is the base of any living being on Earth.

Water has a rather high specific heat capacity of 4.184 J/gC, which in itself has a great effect on Earth's climate and all sorts of beings heat regulation. What would happen if water had a much lower specific heat capacity, such as, for example, quicksilver 0.14 J/gC.

I can foresee, sweating being incredibly less efficient, and, similar to deserts, oceans would be burning hot during the day and, perhaps, freeze down in the night, possibly killing life at the surface or forcing them to adapt. Maybe trees would explode when water freezes and expands in their capillaries.

This change happens momentarily for an unknown reason in modern time, that is now.

What would be the most drastic consequences for life on Earth of water having low heat capacity and to which state would the life evolve on Earth?

Answer 1

Massive (near)-instantaneous biosphere cataclysm

The oceans are a massive thermal mass which absorb solar radiation during the day and emit it at night. They moderate the climate and have a significant effect on the weather in coastal regions. Solar radiation boiling water from the ocean's surface forms a major, and crucial, part of the water cycle.

Ocean surface temperatures vary on daily and seasonal cycles by as much as 30 degrees in some areas. The magnitude of that temperature variation depends strongly on the specific heat capacity of water. Reducing that constant by a factor of 30 means that the same amount of solar radiation will make the water heat up more. A lot more. Expect summer water temperatures to hit 90°C+ for a wide range of equatorial latitudes, and be 40°C+ across most of the planet. Virtually all aquatic life will find itself environmentally unsuited to such conditions and with no migration path to a cooler location, hence a near total collapse of the marine biosphere within one sidereal year.

The total collapse of the marine biosphere will cause near total collapse of the ecosystem on land, but most higher animals will be dead already. All warm-blooded animals rely on their vascular system to transfer heat from their internal organs to their surface where it can be radiated. Since you haven't changed the enthalpy of vaporisation of water, the energy removed by one molecule of water evaporating as sweat hasn't changed and so sweating is actually still as effective as it was before. However in order for the same volume of blood to carry the same energy from core to surface while flowing at roughly the same rate would mean the blood reaching a temperature 30 times higher than before, which is both impossible (since we don't have that much temperature headroom before hitting the boiling point of water) and instantly fatal in any case. Even if an animal is capable of raising its heartrate tenfold from rest, the temperature differential between blood and ambient would triple, which would be immediately fatal.

Plants and cold-blooded animals would not immediately die from these effects, but cold-blooded animals still need to drink, and for most of the day in most places on earth standing water would be dangerously hot. Some might find a new evolutionary niche though.

However, even though you have not affected the enthalpy of vaporisation, which forms the majority of the energy cost of taking a mole of water from 25°C to steam, the change does reduce that overall cost by about 12%. In the delicately-balanced system that is global temperature management, this is probably catastrophic, resulting in a massive increase in water vapour in the atmosphere. This coupled with the total collapse of the polar ice sheets due to warmer oceans would probably trigger a runaway greenhouse effect that would make the environment very inhospitable to the few remaining lifeforms.