Climate Feedback Mechanisms
This was for uni, but I’ve made it a little bit more accessible and put it here just incase you wanna scare the shit out of yourself.
Climate feedback mechanisms (FM) play a large and dynamic role in altering the radiative forcing (RF) (Temperature) of the atmosphere. A good understanding of how they work and how much they can change RF is important for predicting possible future climate scenarios. A FM is defined as a systematic response to perturbation (change of state), which can either enhance the change (positive feedback mechanism (PFM)), or decrease the change (negative feedback mechanism (NFM)) (IPCC 2014). FM can be driven by physical, chemical or biological processes, can take place within hours, years or millennia and cause different degrees of perturbation. Within the earth’s climate system there are both PFM and NFM, while PFM cause increases in the temperature of the atmosphere, NFM decrease warming (IPCC 2014). The most significant NFM is black-body radiation feedback, were increasingly long wave radiation is emitted back into space as the earth heats up, however, the effect is small compared to many of the PFM (IPCC 2014; Soden & Held 2008; Sejas and Cai 2016).
The most significant of the PFM are caused by cycles that control carbon, global albedo and water vapour, three facets that allow us to maintain the stable world we evolved in. Indeed, there are a range of PFM ’s that are causing huge changes in the carbon cycle on both a short and long term scale, these are predicted to have both rapid and a slow effect on temperatures. One of the most important and potently rapid feedback mechanisms is the release of methane from huge stores in the permafrost, thaw lakes and from clathrates under the ocean (Methane = CH4, which has 23 x the ability of CO2 to warm the planet (hence et is bad bad bad)) (IPCC 2014; Walter et al. 2006; Archer 2005). Methane is released through permafrost melt via the thawing of frozen soils simultaneously exposing and water logging decomposed carbon, this induces anaerobic respiration and releases even more methane, increasing temperatures via the greenhouse effect (IPCC 2014; Abbott 2015). According to some studies, with sustained warming (just like is predicted) the Arctic alone could release 350 Gt of carbon, double the amount in the atmosphere today (This pretty much means a runaway greenhouse effect/warming >10 c, take a look at the figure below which shows at 120 PgCo2 released we may have more then 7 C warming ) (IPCC 2014). Indeed, modelling shows by 2100, 250 Pg CO2 and 5 pG methane maybe emitted (IPCC 2014). Further, methane emissions from thaw lakes are known to be released by ebullition and thermokaest erosion (Walter et al. 2006). It is estimates there is 500 Gt ( 1 Gt/Giga tonne = 1 Pg/Petra gram) of carbon stores that could greatly intensify the PFM (Walter et al. 2006). Another PFM that maybe triggered by warming is the release of CH4 from the sea floor, due to a warming ocean, driving microbial activity that rapidly oxidizes clathrate hydrates (Elliott et al, 2010). There is approximately 5000–10,00 Gt C stored as CH4 in the clathrate hydrates and the release of 100 Pg CH4 is predicted by 2100 (Archer 3005; Harvey and Huang 1995). The release of such large methane stores are likely to cause irreversible changes to the RF on multi-millennial time scale, and could be one of the most significant PFL in the future (IPCC 2014).
a quick back of the envelope calculate says our predictions are saying we will release…
(from the Arctic ) 250 Pg CO2 + 125 Pg CO2-e (5 Pg CH4 x 25 = CO2-e (because 1 CH4 equals 25 CO2) + 2500 Pg CO2-e (from the Ocean floor) = 2875 Pg CO2-e .
But wait! there is more..
Additionally, PFM are seen in changes to the terrestrial carbon stores (IPCC 2014; Heimann 2008). Biological processes of photosynthesis and respiration respond to climate variations on a global scale due to changes in CO2, water availability and temperatures (Heinmann 2008). Although, there is a slight NFM whereby higher net primary productivity (NPP) is observed due to CO2 fertilization and warmer temperatures, it has been concluded that this only reduced atmospheric carbon until water , nitrogen availability and temperatures are too extreme (Heinmann 2008). This is observed in forest dieback in areas such as the Western Amazon and Southeast Asia (Hainmann, 2008; IPCC 2014). A comparison of different models shows that there was high CO2 sequestration in the nineteenth and twentieth century but it is expected there will be a substantial decrease as the world warms, making a stronger PFM (Heinmann 2008).
The ability of the planet to reflect both short and long waver radiation back into space is known as the albedo effect and is curial in reducing RF (IPCC 2014; Curry and Schramm 1995). Snow and Ice play a large role in the earths albedo, but as heating creases they melting and increasing RF of the atmosphere (IPCC 2014; Curry and Schramm 1995). Indeed, as sea ice in the Arctic melts there is greater adsorption of heat into the Southern Ocean, causing further melting of sea ice and radiation adsorption (IPCC 2014; Riihela et al. 2013). This enhances polar amplification; whereby polar regions have a higher then average temperature (IPCC 2014).
As well as changes in albedo, climate change is creating overall changes in water vapour and cloud formation which can act as PFM. Increases in water vapour acts as a strong greenhouse gas and ultimately increases RF (IPCC 2014).
Evidently there are many types of FM within the global climate system, but PFM that change the carbon cycle, the earth albedo and water vapour are understood to be of the most important. Alone some of the projections under increased in GHG emissions from changes in the carbon cycle lead to catastrophic warming, while combined with warming due to changes in albedo and water vapour are less quantifiable their increases can only faster and more extreme warming.
Abbott, B. and Jones, J.2015. Permafrost collapse alters soil carbon stocks, respiration, CH4, and N2O in upland tundra. Global Change Biology 21(12) .pp. 4570–4587.
Archer, D. 2005, Fate of fossil fuel CO2 in geologic time. Journal of Geography Research: Oceans 110(9).
Curry, J. and Schramm, J. 1995, Sea Ice-Albedo Climate Feedback mechanism. Ameraical Meterological Society, 8, pp. 240–247.
Elliott, S., Reagan, M., Moridis, G. and Smith, P. 2010. Geochemistry of clathrate-derived methane in Arctic ocean waters. Geophysical Research Letters 37(12).
Harvey, L. and Huang, Z.1995. Evaluation of the potential impact of methane clathrate detsabilization on future global warming. Journal of Geophyical Research: Atmosphere. 100(D2). pp.2905–2926.
Heinmann, M. and Reichetein, M. 2008. Terrestrial ecosystem carbon dynamics and climate feedbacks. Nature 45. pp. 289–292.
IPCC. 2014. Climate Change 2014: Sythesis Report, Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. IPCC, Geneva, Switzerland.
Soden, B. and Held, I. 2006.An Assessment of Climate Feedbacks in Coupled Ocean-Atmosphere Models. American meteorological Society 19. Pp. 3354–3360.
Sejas, S. and Cai, M. 2015. Isolating the temperature Freedback Loop and Its Effects on Surface Temperature. American Meteorological Society 10.
Riihela, A., Manninen, T. and Lain, V. 2013. Observed changes in the albedo of the Arctic sea-ice zone for the period 1982–2009. Nature Climate Change 3, pp. 895–898.
Walter, K., Zimov, S., Chanton, J., Verbyla, D. and Chapin F. 2006. Methane bubbling from Siberia thaw lakes as a positive feedback to climate warming. Nature 443. Pp. 71–75.