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Land Plants Do Affect the Climate

About 70% of the Earth’s surface is covered by oceans, and marine phytoplankton likely play a significant role in cloud formation via ice nucleation (and, thus, affect the weather and climate). For example, please see Ref. 1 below.

But a paper published in 2015 (see Ref. 2 below) suggested that we have underestimated the impact of pollen from land plants on cloud formation. (A nice summary of this report: Pollen and clouds: April flowers bring May showers?)

So this led me to wondering about the question of whether “macroscopic” land plants significantly affect the weather. (Let’s leave the microscopic phytoplankton for another time….)

Of course, it follows that if 70% of the Earth’s surface is covered by oceans, then the remaining 30% is land. About 1/3 of the land is cold or hot desert (few or no plants). So, roughly speaking, about 20% of the Earth’s surface is covered with vegetation. And about half of this is forests. Thus, it’s not unreasonable to presume that terrestrial plants may affect the Earth’s climate (time frame = decades), and perhaps even the weather (time frame = minutes to months).

It’s generally accepted that terrestrial ecosystems (especially forests) may have significant effects on the climate. (See, for example, forests’ roles in climate.) Terrestrial ecosystems influence climate by affecting how much solar energy is absorbed by the land surface and by exchanging climatically important gases with the atmosphere.

But Do Land Plants Also Affect the Weather?

I’m skeptical,…

However, it is surprising how much plants affect weather. Plants process and release water vapor (necessary for cloud formation) and absorb and emit energy used to drive weather. Plants also produce their own micro-weather by controlling the humidity and temperature immediately surrounding their leaves through transpiration. Most plants and forest soils have a very low albedo, (about .03 to .20) and absorb a large amount of energy. However, plants don’t contribute to overall warming because the excess warmth is offset by evaporative cooling from transpiration.” (From the excellent website Vegetation: Its Role in Weather and Climate provided by North Carolina State University)

I also found a good online resource for explaining the relationships between forests and weather (see Ref. 3 below) In it, the authors state that:
“1. The main mechanisms by which forests modify weather have been identified. They are the surface albedo, transpiration and evaporation of water vapour, aerodynamic effects, and emission of hydrocarbons whose oxidation can form aerosol particles.
2. Different mechanisms are dominant for each class of forest. Boreal forests affect local weather and climate via their low albedos, causing a local warming. Temperate forests modify weather via the albedo and transpiration of moisture, but their exact impacts on climate are the least certain. Tropical forests cool climate via their very high transpiration rates; the moisture transferred to the atmosphere forms large clouds which reflect incoming solar energy and cause a further cooling.”
(from Ref. 3 below)

And, if you consider seaweeds in the intertidal zone land plants, then:

(1) Stressed seaweed contributes to cloudy coastal skies, study suggests and

(2) Iodide accumulation provides kelp with an inorganic antioxidant impacting atmospheric chemistry.

…but now I think it’s safe to say that land plants do indeed affect the weather (at least under certain circumstances).

References

1. Amos, J. (2015) Ocean plants ‘can help freeze clouds’, BBC News Online

2. Steiner, A. L., et al. (2015) “Pollen as atmospheric cloud condensation nuclei.” Geophysical Research Letters, Vol. 42, pp. 3596–3602. doi: 10.1002/2015GL064060 (Abstract)

3. Sanderson, M., M. Santini, R. Valentini and E. Pope (2012) “Relationships between forests and weather.” EC Directorate General of the Environment. Full Text (PDF)

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