It’s Always a Hot Day Somewhere on Earth, 24 Hours a Day, Every Day of The Year.

Grasslands typically dry out within 10 to 20 days without rain.
Trees, or forests, can sustain evaporation for 30 to 60 days.
If they have healthy access to groundwater, they can easily survive a year of drought.

This means that during a dry period, there is at least a 40 - day difference in evaporation capacity and, as mentioned, much more if trees can reach groundwater.

Let’s take those 40 days as an example.
After that time, the grassland is dry no more evaporation.
The forest, however, continues to evaporate, even during a heatwave of 36°C.

On a clear, hot day, the sun delivers around 6 kWh of energy per square meter to the Earth’s surface, heating the ground.
In southern regions it’s more, in northern regions less.

A tree, through its cooling ability evaporation converts roughly one-third of that incoming solar energy into latent energy, or cooling energy, through the process of water turning into vapor.

This comparison is not scientifically exact, but it illustrates the principle:

Think of an electric heater:

• The oven is Hot (sensible heat)
• The power cable is Cold (latent energy energy stored in phase change)

With 6 kWh per day of solar input, this means 2 kWh per square meter per day are converted into cooling energy that is effectively removed from the local heat balance and radiated out of the climate system in to space.

Across one square kilometer of healthy forest with a closed canopy, that adds up to an incredible 2 gigawatt-hours of cooling energy per day.

That equals the average daily energy consumption of 250,000 households, including heating and cooling throughout the year, per square kilometer of forest.

Those 250,000 households represent a densely built urban area of about 60 km² roughly 7.7 by 7.7 kilometers, for example, the inner ring of Munich.

This means that during a 40-day heat period, every square kilometer of grassland adds as much heat to the climate system as 250,000 households would consume heat that no longer becomes latent energy but stays in the atmosphere, accumulating, and ultimately ending up in the oceans. In other words, the planet’s natural air conditioner is turned off exactly when it’s needed most. This excess energy can only leave the climate system again when it is re-converted into water vapor elsewhere.

This explains why the city of Medellin, Colombia, managed to lower its average temperature by 2°C in less than 10 years simply by planting a few green corridors where there used to be only grass.

Now imagine transforming Germany’s (349,000 km²) permanent grassland area, about 47,000 km² (13.5% of the country’s surface) into agroforestry systems with closed tree canopies. Those 40 days alone would be enough to offset the thermal energy equivalent to Germany’s entire annual energy consumption, including the energy required for transportation and the share of international traffic such as ships and aircraft.

In just 40 days the difference between grassland and forest!

Heat can be removed from the Earth’s climate system only through evaporation. All other forms of energy accumulation remain trapped in the system and continue to warm it.

Only trees are efficient enough to be considered The Earth’s Climate Devices. When necessary, they can evaporate more than four times as much water as a lake precisely when that cooling is most needed.