Climate as the cause?
Historic mass extinctions, the Late Permian (251mya), and End Triassic (205mya), for instance, demonstrate that climate change is certainly capable of initiating large-scale species loss. This recent paper agrees that climatically driven habitat shifts could conceivably have resulted in the loss of many species of megafauna, but it also highlights the uncertainty of this topic. We cannot pinpoint a single cause of extinctions, rather, it seems that a number of factors had a part to play.
In a modern context, our understanding of the complex dynamics of nature is still limited. We don’t fully comprehend short term versus long-term environmental stochasticity, or population processes in relation to community dynamics and stability. Thus it is hard to reach conclusions about the potential behaviour of communities and ecosystems from studies of individuals and populations.
There are consistent large-scale environmental responses to low average rates of climate change, suggesting that the modern landscape is inflexible to ecosystem change in response to climate alterations, hence the widespread loss and fragmentation of habitats. With further warming may come dire ecological and socio-economic consequences (Walther et al. 2002).
Source: http://www.skepticalscience.com/empirical-evidence-for-global-warming.htm
Humans as agents of change?
While the reasons behind historic events remain unclear, evidence points fairly convincingly towards humans as the cause for the current mass extinction. Anthropogenic pollution of the atmosphere which results in untimely feedbacks and planetary warming, and destructive, insensitive expansion of man-made environments, must surely lead to changes of such magnitude that habitats are unable to support the species that evolved to live there. Estimations (Novacek and Cleland 2001, Rockstrom et al. 2009) of future extinction rates based on comparison with background rates suggest that 30% of species currently present on Earth could vanish by the middle of the 21st century. Even our closest genetic relatives, Chimpanzees, are threatened because of human activity. A combination of habitat loss, disease, hunting, and human population increase means that the most endangered Chimpanzee species, Pan troglodytes vellerosus, could go extinct in just 20 years.
Rainforest destruction, intensive agriculture, and degradation and overexploitation of marine ecosystems present similarly large threats to species diversity. Alteration of global biogeochemical cycles, and changes to feedbacks between the hydrosphere, atmosphere and lithosphere could well accelerate rate of species loss. In spite of Rachel Carson’s emphatic 1960s discourse warning of the deleterious impact of DDT and other chemicals, human use of pesticides has tripled in the past 40 years to a current level of 2.5 m tones/year, and human activity has doubled the amount of Nitrogen in global cycles.
Novacek andCleland (2001) state that shifting land use is the most intensive driver of terrestrial environmental change. By the year 2030, there may be 8.2bn people to feed, which will require the grain harvest to be increased by 2%/year. If rates of topsoil removal seen in the past 20 years continue, there may be no suitable platform on which to do this.
Lessons from the past?
Fossil data doesn’t provide an effective illustration of the exact cause of previous mass extinction events, but gives us a powerful indication of the reality of extinction nonetheless.
The difference now, though, is that while previous mass extinction events took place over long timescales, and the situation for recovery was similar, we do not have the luxury of time to allow ecosystems to rebound (Novacek and Cleland 2001).
What to do?
· The current trend could reverse itself, but this would take long time, and according to Malthusian theory, would require fewer humans to exist on Earth.
· Recovery could occur if a considerable protection policy were to be implemented. This would include large-scale ecosystem management and mitigation of current disruption of biogeochemical cycles (Novacek and Cleland 2001).
All is not lost?
Primatologist Jane Goodall argues that in spite of everything, there are reasons to be optimistic about the future. The powerful human brain is capable of complex problem solving, and companies have begun to become more attentive to greening operations. In addition, we should have faith in the resilience of nature. If species can re-colonise areas destroyed by atomic activity, then resistance to change should be possible elsewhere.
Finally, some snippets from performances in ‘Saving Species. Sustaining Life’ by A.L. Kennedy and Miles Chambers respectively, remind us of our place within nature, and our responsibility to care for, and protect it, lest it vanish forever.
‘Do we remember we are animals as well as people, and tend ourselves with mercy? Do we remember we are people as well as animals, allow ourselves joys within moderation, a place within nature, a place in the balance of the world that can be beautiful, but has no mercy? If we kill it, it will kill us back’.
‘This place is all we’ve got. This is our home, and our children’s, children’s, children’s home. Don’t tell me you forgot’.
References
Lorenzen E.D., Nogues-Bravo D., Orlando L, Weinstock J., Binladen J. Marske K.A., Ugan A., Boregaard M.K., Gilbert M.T.P., Nielsen R., Ho S.Y.W., Goebel T, Graf K.E., Byers D., Stenderup J.T., Rasmussen M., Campos P.F., Leonart J.A., Koepfli K.-P., Froese D., Zazula G., Stafford T.W., Aaris-Sorensen K., Batra P., and Haywood A.M., Singarayer J.S., Valdes P.J., Boeskorov G., Burns J.A., Davydov S.P., Haile J., Jenkins D.L., Kosintev P., Kuznetsova T., Lai X., Martin L.D., McDonald H.G., Mol D., Meldgaard M., Munch K., Stephan E., Sablin M., Sommer R.S., Sipko T., Scott E., Suchard M.A., Tikhonov A., Willerslev R., Wayne R.K., Cooper A., Hofreiter M., Sher A., Shapiro B., Rahbek C. and Willerslev E. (2011) ‘Species-specific responses of Late Quaternary megafauna to climate and humans’, Nature, 479, 359-364.
Novacek M.J. and Cleland E.E. (2001) ‘The current biodiversity extinction event: Scenarios for mitigation and recovery’, Proceedings of the National Academy of Sciences of the United States of America, 98, 10, 5466-5470.
Rokstrom J., Steffen W., Noone K., Persson A., Chapin F.S., Lambin E.F., Lenton T.M., Scheffer M., Folke C., Schellnhuber H.J., Nykvist B., de Wit C.A., Hughes T., van der Leeuw S., Rodhe H., Sorlin S., Snyder P.K., Constanza R., Svedin U., Falkenmark M., Karlberg M., Karlberg L., Corell R.W., Fabry V., Hansen J., Walker B., Liverman D., Richardson K., Crutsen P. and Foley J.A. (2001) ‘A safe operating space for humanity’, Nature, 461, 472-475.
Walther G.-R., Post E., Convey P., Menzel A., Parmesan C., Beebee T.J.C., Fromentin J.-M., Hoegh-Guldberg O., and Bairlein F. (2002) ‘Ecological responses to recent climate change’, Nature, 416, 389-395.
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