Climate Change

When it comes to climate change, I'm sure none of my readers are strangers to the fact that global warming is happening, and human populations, as well as the rest of Earth's biodiversity, are threatened by these changes. But what is the real cause of our rising global temperature? Is it just part of the natural pattern of historic climatic fluctuations, or are these rapidly changing conditions predominantly based on human interactions with the environment?

'Climate: causes and effects of climate change' by Dana Desonie, 2007, highlights the variety of impacts that can cause climate change, both human and natural. More recently, David I. Stern and Robert K. Kaufmann's report 'Anthropogenic and Natural Causes of Climate Change' was published in Climatic Change, 2014, which aims to test for causality in the relationship between anthropogenic activity and climate change.

The Intergovernmental Panel on Climate Change published the 'Climate Change Synthesis Report' in 2014, chaired by Rajendra K. Pachauri. This report found that between 1983 and 2012 average temperatures rose 0.85 degrees. Climate change refers to the average changing temperature over time. This change in temperature is predicted to continue to rise.

Human

Economic and population growth fuels greenhouse gas emissions of carbon dioxide, methane and nitrous oxide. Greenhouse gas emissions have been rising from 1970 to 2010, and are arguably the most significant human influence over climate change. The IPCC also found that between 1970 and 2010, the release of C02 from burning fossil fuels accounted for 78% of total greenhouse gas emissions. Methane is produced by rice production and animal farming, and it is believed 60% of emissions come from these anthropogenic activities. The report concludes that it is 'extremely likely' human greenhouse gas emissions are responsible for half of the increase in global temperatures since the 50s. Emissions aren't the only way humans are altering the climate, land use changes impact the Albedo effect and evapo-transpiration rates of the landscape. Furthermore, air pollution can filter incoming solar radiation, a process known as global dimming. This has a cooling affect, however global warming is the dominating process at present.

Climate

On the other hand, throughout Earth's history climate has continuously fluctuated, which could explain the rising temperatures apparent today. 

One reason for this is solar variation, the discontinuous output of the sun. The solar output has been gradually increasing which would be mirrored by rising temperatures on Earth. However, early in Earth's history higher levels of CO2 and consequential greenhouse warming meant temperatures were similar to today. 

Milankovitch cycles, referring to the position of the Earth respective to the sun, are another natural driver of climate change. Solar radiation reaching Earth can vary by up to 25% depending on Earth's position. Ice ages are a function of these cycles.

Since the 1950s the energy output of the sun has not varied in a way to produce the increase in global temperatures recorded from this time, furthermore, as explained at climate.nasa.gov, climatic changes are demonstrated by warming at the Earth's surface and cooling in the upper atmosphere, which does not represent an increase of solar output. It is therefore reasonable to conclude that humans are having a direct effect on Earth's climate.

Mass extinctions

To follow up last weeks post, I've found a video that runs through the big 5 mass extinctions and considers whether we are entering a 6th mass extinction. Watch it here for more information: 

Is this a mass extinction?

Extinction is the last evolutionary process any species undergoes. Extinction is so common it has been estimated that about 99% of species to ever have evolved on our planet have been lost. This level of extinction is generally balanced by the origination of new species. However, during Earth's history there have been 5 events classified as mass extinctions; a relatively short period of time during which 75% of species are lost. It is argued that the number and rate of species losses we are experiencing currently could be so high that we are entering a 6th global mass extinction. Recently, Anthony D. Barnosky explored whether current biodiversity is trending towards a 6th global mass extinction in 'Has the Earth's 6th mass extinction already arrived?' published in Nature in 2011.

Position in time of the big 5 mass extinctions

To understand whether we are undergoing a mass extinction event already, or if we are on track towards one in the near future, it is important to first examine the definition of a mass extinction. By defining a mass extinction, we can make comparisons between past mass extinctions and our rate of extinctions today.

Jack Sepkoski defined a mass extinction as 'any substantial increase in the amount of extinction (i.e. lineage termination) suffered by more than one geographically wide-spread higher taxon during a relatively short interval of geologic time, resulting in an at least temporary decline in their standing diversity' in 'A Phanerozoic overview of mass extinctions', 1986. In more general terms, a mass extinction event involves a magnitude and a rate, and most palaeontologists classify a mass extinction as the loss of 3/4 of Earth's species in a short geological time.

Estimates for the total number of species on Earth demonstrate a wide range, from 3 million to 100 million. One of the most widely accepted estimates to fall within this range is 8.7 million species, which was proposed by Camilo Mora, et al. in 'How many species are there on Earth and in the Ocean?', 2011. This total number is falling. Stuart L. Pimm predicted a current extinction rate of 20-200 E/MSY (extinctions per million species year), which is 100-1000 times greater than the rate apparent in the fossil record (The Future of Biodiversity, 1995)

As already demonstrated in older blog posts, modern day losses of biodiversity are being worsened by humans; by hunting, clearing habitats and moving species geographically. If these losses are pushing us into a mass extinction event, this could be one of the largest effects of Man on Earth's geology, and a true signature of the Anthropocene.

When trying to compare modern and historical biodiversity, very few groups have adequate records. The fossil record for example is very inconsistent and only few groups of modern animals have been sufficiently assessed, such as mammals, amphibians and birds. Therefore theoretical predictions relating losses of habitat area to losses of species are used. We also have to take into account not only species that have recently gone extinct, but those that are threatened. Barnosky found, using models assuming that all of our threatened species inevitably die out, we could reach big 5 mass extinction levels within 3 centuries. This comes as a warning cry for conservation needs.

Megafauna extinction: Man or climate?

Next up in the fight between Man and Earth: overhunting and climate change battle it out to see who was responsible for the extinction of Pleistocene Megafauna.

Size comparison of mega fauna

Megafauna are giant animals, typically weighing more than 44kg, that were successful across Eurasia, America and Australia during the Pleistocene (which lasted from 2.6 - 0.1 million years ago). The Quaternary extinction event saw the loss of many of these large beasts, at the same time as the last ice age. The extinctions of animals such as giant kangeroos, woolly mammoths, bear sized wombats and huge armadillos spanned from 40,000 years ago to as recently as 10,000 years ago. 

Woolly Mammoth

The last American glacial maximums were between 30,000 - 14,000 years ago in North America and 12,500 - 11,800 years ago in South America, as discussed in 'American megafaunal extinctions'. The latest ice age in Australia reached a maximum around 21,000 years ago. Climate is therefore a strong contender for the changing conditions and subsequent loss of life during the Megafauna extinction event. 

It is however no coincidence that humans were radiating out of Africa at this time, from around 70,000 years ago, spreading through Asia, Australia and finally America where tribes set up in megafauna territories. Africa has retained many species of megafauna, unlike in other continents, which could be because the species here had longer to learn and adapt to homo sapiens, whereas other encounters between man and megafauna across the globe happened more rapidly, giving species less time to adapt. The human hunting of these large targets is a likely cause of their extinction.

Migration pattern of homo sapiens out of Africa

Humans are thought to have contributed to extinctions due to factors other than hunting; human lit fires, which in Australia are believed to have been used to clear pathways through the bush, are another way humans could have impacted the climate and habitat of the areas they first colonised. This was discussed by Cheryl Jones in 'Early humans wiped out Australia's giants', 2010.

Controversially, Research led by the University of New South Wales last year suggests that megafauna extinctions in Australia were caused by climate change alone, rather than human influences. They state there is a lack of evidence of that humans hunted megafauna, and that by the time Aboriginal tribes arrived in Australia there were less than 20 megafauna species left. 

This is where the timing of extinctions and arrival of homosapiens becomes important; if the majority of megafaunal extinctions happened before humans emerged from Africa then climate change must have been the cause of extinction. Although if the emergence of homo sapiens matches the time these giant species went extinct then humans could be responsible. 

It may be that the onset of a colder climate had already altered vegetation and reduced the number of viable habitats, threatening larger species, but hunting by humans was the final blow. The two factors go hand in hand as climate change may have been the driving force of human migrations out of Africa.

The global scientific gathering met earlier this year to discuss this topic at the Oxford megafauna conference. They concluded that hunting by humans was a 'decisive factor' in the megafauna extinctions.

Want to see what some of these giant beasts would have looked like? Check out the megafauna video.

Golden Spike of the Anthropocene

William Ruddiman, a palaeoclimatologist and big name in the Anthropocene debate, identifies the beginning of the Anthropocene as 8000 years ago, in his paper 'The Anthropogenic era began thousands of years ago', 2003. Conversely, Paul Crutzen places the beginning of this new geological epoch much more recently, at the start of the Industrial revolution in the 18th century. At some point in the history of humans, our activity on Earth became significant enough to consider ourselves in a human-caused geological time. So when is this golden spike for the Anthropocene?

The earliest proposed start to the Anthropocene is 50,000 years ago, coinciding with megafauna extinctions, and global human colonisation. The megafauna extinction event saw the loss of many large mammals, as described by the Australian Museum. Robin McKie, science editor for The Guardian, argued in 'What killed off the giant beasts - climate change or man?', 2014, that these extinctions resulted from contributing factors of climate and human activity, at the end of the last ice age. Human hunting of these giant mammals is therefore one of the first anthropogenic impacts on biodiversity on Earth leading to changes in our geology.

Erle Ellis argues that the Anthropocene starts later than this. By 8,000 years ago, with only 'a population of just 10 million or so' the use of agriculture and fire to clear forests had 'altered as much as a fifth of Earth's ice-free land' (Forget Mother Nature: this is a world of our making, 2011). Early farmers without means to plough their land had to move on frequently to more fertile fields, leaving previously cultivated areas in various stages of recovery. This activity created the first 'anthromes' or anthropogenic biomes. By the industrial revolution 'more than half of the terrestrial biosphere had been converted into anthromes', so our impact had already been made on the atmosphere and soil sediments. Today around 38% of terrestrial land is used for farming (Age of man). Similarly, in William Ruddimans' opinion, the early use of agriculture released enough Co2 to prevent another ice age, meaning humans have been the greatest geological force on Earth since the start of the Holocene. Both Ellis and Ruddiman would place the golden spike of the Anthropocene at the dawn of agriculture, potentially replacing the Holocene altogether.

On the other Hand, Paul Crutzen argues in his work The Anthropocene, 2006, that the European industrial revolution marks the significant turning point in human impacts on Earth, 'coinciding with James Watt's design of the steam engine in 1784'. Since the industrial revolution, the burning of fossil fuels and release of Co2 have been represented in ice cores as an 'uninterrupted rise' of carbon dioxide levels. Based on atmospheric composition, the 18th century could mark the greatest change in geology and be seen as the start of the Anthropocene.

The International Union of Geological Sciences will have the final say, who will aim to decide by 2016 whether the Anthropocene will replace the Holocene.

Action costs heavily, inaction costs more

This week I attended a talk by the Renewable Energy Foundation on 'Thermo-economics' - meaning how energy links to economic debate. The presentation focused on why government renewable energy subsidies are unsustainable. However, this week's Climate Change 2014 synthesis report by the Intergovernmental Panel on Climate Change sums up my feelings on the matter entirely. Making headlines such as 'rapid carbon emission cuts vital to stop severe impact of climate change' and 'fossil fuels should be phased out by 2100' the point of the report couldn't be more clear. 

Intergovernmental Panel on Climate Change

Our use of fossil fuels and emissions of carbon have to be seriously cut to prevent irreversible climate change on Earth. Although government subsidies may be raising the future price of household energy bills, I would personally rather pay more for energy than run out entirely. We need to prioritise our planet over our pockets. BBC news states: 'The UN said inaction would cost ''much more'' than taking the necessary action'. Cost doesn't only refer to economics. 

'Severe, widespread and irreversible impacts' is the tagline to remember from the report. The need to move away from fossil fuels and towards renewables is real and urgent. Does this outweigh the need for emerging economies to develop without restrictions, such as England during its industrial revolution? I believe so.

Although a bit off topic, the report makes an interesting read and covers a matter I think should be at the forefront of all economic and environmental debate.