An article by Page (2011), presented the idea that there may be a ‘tipping point’ or threshold where there is an abrupt change, a possible result could be a shift from one state to another, and for example freezing point is the threshold between ice and water (Hassol, 2004). There is previous evidence of tipping points related to climate being passed, for example the collapsing of the West Antarctic ice sheet, which raised sea levels by 3 meters (Page, 2011), or the 5ºC drop in temperature over Greenland during the period of warming after the last ice age (Hassol, 2004). It is thought that this drop in temperature was due to crossing the threshold of the thermohaline system, resulting in a reduction of currents to Europe and the Arctic as well as impacting temperature on the entire globe (Hassol, 2004). This is very similar, although on a much larger scale, to the Great Salinity Anomaly event in the late 1960s which was thought to have been caused by a change in salinity levels due to a large input of freshwater from the ice in the Arctic Ocean (Schmitt, 1996). Worryingly there is still controversy as to how this event was even was caused, as well as the exact effects of it. This means that if it were to happen again, we will be unprepared.
But will a large scale event like the collapsing of the West Antarctic ice sheet or the Great Salinity Anomaly happen now?
There is increasing worry that something will, and an event like this could cause catastrophic damage. The threat of global warming lies with the increasing temperatures brought about mainly due to human influence, but also natural fluctuations, for example the 2 ºC increase in temperature which followed the last ice age (Jackson and Jackson, 2000). We are already experiencing changes such as the melting of the polar ice caps, with NASA and NOAA data showing roughly a million square miles of sea ice has already disappeared in the last three decades from the Arctic alone (NRDC, 2007). This in turn will have its own direct effects, such as an increase in sea level with an estimated half a metre rise during this century (Holden, 2008; Hassol, 2004), as well as an increase in the albedo effect (The ice reflects around 85-90% of the sun’s rays back out of the atmosphere, keeping the planet cool, however if the ice melts the ocean which only reflects 10%, causing the absorption of the rays which heats the earth (Hassol, 2004)).
By looking into the past we can predict the future consequences of a warming climate, however there are still areas we do not understand and it is these that we will be unprepared for if they occur. The major historical events are linked together with the passing of a tipping point, be it temperature or salinity for example, and so if the threshold is not known we cannot predict if or perhaps when it will happen in the future.
References
Hassol, S.J, (2004), Impacts of a warming Arctic, Arctic Climate Impact Assessment (ACIA), Cambridge University Press, Canada
Holden, J, (2008), ‘Quaternary environmental change’ in Holden, J, (ed) ‘An introduction to physical geography and the environment’, Second edition, Pearsons, Essex, p572
Jackson, A.R.W, Jackson, J.M (2000), Environmental Science: The Natural Environment and Human Impact, 2nd edition, Essex, p349
Natural Resources Defence Council (NRDC), (2007), Climate Facts: Polar Bears on Thin Ice, http://www.nrdc.org/globalwarming/thinice.pdf [01/11/2011]
Page, M.L, (2011), Climate change: What we do know – and what we don’t, New Scientist, 212, 2835, p36 – 43
Schmitt, R.W, (1996), If Rain Falls on the Ocean – Does it Make a Sound? Fresh Water’s Effect on Ocean Phenomena, Woods Hole Oceanographic Institution, http://www.whoi.edu/oceanus/viewArticle.do?id=2344 [01/11/2011]
