Geological and biological climate factors

Plate Tectonics

Plate tectonic processes influence climate in various ways. Tectonic activity can change the distribution of continents and influence ocean currents. It is often connected with volcanic activity or mountain building. As mountain-building processes take millions of years, their global climatic effects show on the long timescale. However, mountains also alter local climates on a short timescale. Just think of the rain-shadow effect of the Andes or the Rocky Mountains. One and the same natural climate change factor can work on different timescales!

Volcanic activity

Volcanic eruptions release various gases, aerosols, and solid particles (e.g. ash) into the atmosphere. While eruptions often last days or weeks, their effects can last much longer.

Ash particles and sulfur aerosols reflect incoming solar radiation, causing global cooling. For example, the Tambora eruption in 1815 caused intense volcanic cooling. 1816 was known as the “year without summer”. However, volcanic cooling normally lasts for a few years only. Ash particles fall back to the ground within a few hours to weeks. Aerosols can stay in the atmosphere for up to three or four years. Once these particles no longer block the sunlight, global temperature rises back to pre-eruptional levels.

Volcanic eruptions also release greenhouse gases, such as CO₂ and methane. These gasses have a warming effect and can remain in the atmosphere for thousands of years. However, the amount of greenhouse gases released by single volcanic eruptions is negligible compared to anthropogenic sources. Periods of high volcanic activity during Earth’s history are a different topic. It is theorized that large-scale volcanic activity such as ocean-floor spreading could have released lots of CO₂. Over millions of years, this could have caused global warming including the melting of ice sheets and sea-level rise.

Ocean currents

Plate tectonic constellations (the relative positions of continents and straits) have a great influence on global ocean currents, changing the paths of major ocean currents. Ocean currents are driven by differences in water temperature and salinity, closely coupled with e.g. sea levels and the atmospheric circulation system. The ocean is Earth’s largest carbon store and regulates atmospheric CO₂ concentration. Oceans also store and transport heat, this can have a big influence on local climates. The gulf stream warming up Northern Europe is one example. The system of ocean circulation works on a medium timescale (several decades to ten thousand years), so it is much slower than the atmospheric circulation system.

Asteroid impacts

Asteroid impacts cause climatic effects similar to volcanic eruptions. However, these effects might be more intense and short-lived. Dust and aerosols are ejected into the atmosphere, where they reflect sunlight and cause global cooling. Scientists assume that an asteroid impact was responsible for the extinction of the dinosaurs. Intense cooling after the impact might have lasted for several months to decades.

It is theorized that this cooling period was followed by a long and stable global warm period. Chemical reactions between the asteroid and rocks on Earth might have released greenhouse gases and caused global warming.

Changes in land cover

Components of the biosphere (all living organisms) have a measurable impact on Earth’s climate, both on a local and global scale. Plants consume CO₂ through photosynthesis. Over long timescales, an increase in vegetation land cover can reduce global atmospheric CO₂ levels.

On a short timescale, scientists observe a curious pattern: Since more landmasses are located north of the equator than south of it, vegetation measurably changes global CO₂ levels. During the Northern Hemisphere spring and summer, photosynthesis of decreases global CO₂ levels by about 3%. This annual pattern of CO₂ content in our atmosphere is due to seasonal vegetation cycles.

Figure 1: Timescales of geological and biological climate change factors range from a few years to several million years. Changes in land cover, asteroid impacts, volcanic activity, plate tectonics, and ocean circulation all have global and local climatic effects.