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, 2^nd 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]

Current research has shown that climate warming is having a large impact on many types of organisms, including insects, with a distribution shift to their preferred microclimates (Şekercioğlu et al, 2012). Warming of tropical areas will increase pressure on certain insects which are at their maximum temperature capabilities. Ectothermic insects, for example ants, in the tropics have been found to be among the most susceptible to climate warming due to their relatively lower warming tolerance than temperate or high latitude species. This is because tropical species are at their upper temperature limits for survival and so have optimal performance temperatures. Therefore, if the temperature rises, the colony may have to employ a range of strategies to overcome temperature stress, for example by adapting to start foraging at different times of the day to avoid extreme temperatures, or by migrating pole-ward to avoid the rise in temperatures (Andrew et al, 2013).

This dispersal of crop pests involves advances at rates of around 1.7 miles per year. This can have large implications to food security and agriculture, with around 10-16% of global crop production being lost to pests already – enough to feed 8.5% of the global population (The Guardian, 2013). Evidence of increasing food insecurity comes from recent studies of corn and soybean yield trends in the central United States. There was stronger than expected effects of a gradual change in temperature with 25% of corn and 32% of soybean yields being affected by temperature variations over 17 years. This was partly due to indirect factors such as plant pathogens, insects and weeds (Seherm and Coakley, 2003). As well as this the new species can outcompete with the native species already present, for example Switzerland has already observed the arrival of the invasive lady beetle, Harmonia axyridis, which has affected the ecosystem balance. It is predicted that there will be an increase in the number of insect species in Switzerland due to climate warming (Vittoz et al, 2013). The migration of insects due to climate change is therefore having an impact on food insecurity and so is a concern for future crop yields and its effect on future generations.

However it is not just food security that is being threatened by the pole-ward shift in insect populations, but the spread of pathogens. Yet the interaction between climate change, crops and pests are complex, and the extent to which the latitudinal changes in pathogens in response to global warming is largely unknown (Bebber, 2013). Climate influences the range of infectious diseases, while weather affects the timing and intensity of outbreaks. This means a long-term warming trend is encouraging the geographic expansion of several important infections, and since 1975 over 30 diseases have appeared that are new to medicine (for example AIDS, Ebola and Lyme disease). Of equal concern is the resurgence of old diseases, such as malaria and cholera, due to changing ecological and climatic conditions as well as social changes. This is because diseases, such as malaria, are carried by vectors (for example mosquitoes), which can be redistributed by climate change. Evidence of this happening in the past comes from fossils from the end of the last Ice Age, which demonstrate that rapid, pole-ward shifts of insects was accompanied by warming (Epstein, 2001).

As well as this, the spread of weeds may be linked to a changing climate. There are various species of aggressive weeds in tropical and subtropical origins which are currently restricted to Mediterranean environments. The future climatic conditions may lead to expansion of their range into temperate regions, for example Itchgrass, Rottboellia cochinchinensis, is currently found in sugarcane plantations in the southern US but a high-CO₂ world may change the photosynthetic pathway and therefore the prevalence of weeds with different plant species (Fuhrer, 2003). This means increased prevalence of certain weeds which could further reduce crop yields and effect agriculture.

Yet there are some benefits, for example there is some evidence that drier and warmer conditions could reduce several crop diseases, for example late potato blight due to reduced plant susceptibility. But at the same time, milder winters could increase other diseases, such as powdery mildew, brown leaf rust and strip rust (Fuhrer, 2003).

Overall the impacts will depend on the extent of the warming, and Vittoz et al., (2013) predict that the threshold of an average global warming of 2 K should not be exceeded in order to avoid catastrophic feedbacks. However there have been signs that small changes in temperatures have already been affecting a pole-ward migration of insects, for example the corn and soybean yield trends in the United States, leading to increasing risks to crop security and public health. So how do we stop this? Energy Saving Warehouse has various simple ways of reducing your carbon footprint, check it out for ideas!

References

Andrew, N.R, Hart, R.A, Jung, M, Hemmings, Z, Terblanche, J.S, (2013), Can temperate insects take the heat? A case study of the physiological and behavioural responses in a common ant, Iridomyrmex purpureus (Formicidae), with potential climate change, Journal of Insect Physiology, Vol 59 (9), Pp. 870–880

Bebber, D.P, Ramotowski, M.A.T, Gurr, S.J, (2013), Crop pests and pathogens move polewards in a warming world, Nature Climate Change, DOI: 10.1038/NCLIMATE1990

Epstein, P.R, (2001), Climate change and emerging infectious diseases, Microbes and Infection, Vol 3 (9), pp. 747–754

Fuhrer, J, (2003), Agroecosystem responses to combinations of elevated CO₂, ozone, and global climate change, Agriculture, Ecosystems & Environment, Vol 97 (1–3), pp. 1–20

Şekercioğlu, Ç.H, Primack, R.B, Wormworth, J, (2012), The effects of climate change on tropical birds, Biological Conservation, Vol 148 (1), pp. 1–18

Seherm, H, Coakley, S.M, (2003), Plant pathogens in a changing world, Australasian Plant Pathology, Vol32 (2), pp 157-165

The Guardian, (2013), Climate change makes pests move north from the tropics – study, available at: http://www.theguardian.com/environment/2013/sep/02/climate-change-crop-pests?CMP=twt_fd [Date accessed: 03/09/2013]

Vittoz, P, Cherix, D, Gonseth, Y, Lubini, V, Maggini, R, Zbinden, N, Zumbach, S, (2013), Climate change impacts on biodiversity in Switzerland: A review, Journal for Nature Conservation, Vol 21 (3), pp. 154–162