It is to be recalled that we launched a series of articles on major discourses in climate change a couple of weeks back in collaboration with Aschalew Assefa of the Horn of Africa Regional Environment Centre/Network, for whom we would like to extend our gratitude once again. Accordingly, Planet Finite has come up with a second set of articles on climate change controversies. This week features the first part.

Climate Change Controversies

Misleading argument 1: Climate change not down to humans
The Earth’s climate is always changing and this is nothing to do with humans. Even before the industrial revolution, when humans began pumping carbon dioxide into the atmosphere on a large scale, the earth experienced warm periods such as the medieval warm period.
What does the science say?
It is true that the world has experienced warmer or colder periods in the past without any interference from humans. The ice ages are well-known examples of global changes to the climate. There have also been regional changes such as periods known as the ‘Medieval Warm Period’, when grapes were grown extensively in England, and the ‘Little Ice Age’, when the River Thames sometimes froze over. However, in contrast to these climate phases, the increase of three-quarters of a degree centigrade (0.74°C) in average global temperatures that we have seen over the last century is larger than can be accounted for by natural factors alone. 
The Earth’s climate is complex and influenced by many things - particularly changes in the Earth’s orbit in relation to the Sun, which has driven the cycles of ice ages in the past, as well as volcanic eruptions and variations in the energy being emitted from the Sun. But even when we take all these factors into account, we cannot explain the temperature rises that we have seen over the last 100 years both on land and in the oceans - for example, eleven of the last twelve years have been the hottest since records started in 1850.
So what is causing this increase in average global temperature? The natural greenhouse gas effect keeps the Earth around 30°C warmer than it would otherwise be and, without it, the Earth would be extremely cold. It works because greenhouse gases such as carbon dioxide, methane, but mostly water vapour, act like a blanket around the Earth. These gases allow the Sun’s rays to reach the Earth’s surface but hinder the heat they create from escaping back into space. Indeed, the ability of carbon dioxide and other greenhouse gases to trap heat in this way has been understood for nearly 200 years and is regarded as firmly established science.
Any increases in the levels of greenhouse gases in the atmosphere mean that more heat is trapped and global temperatures increase - an effect known as ‘global warming’. We know from looking at gases found trapped in cores of polar ice that the levels of carbon dioxide in the atmosphere are now 35 per cent greater than they have been for at least the last 650,000 years. From the radioactivity and chemical composition of the gas we know that this is mainly due to the burning of fossil fuels, as well as the production of cement and the widespread burning of the world’s forests.  The increase in global temperature is consistent with what science tells us we should expect when the levels of carbon dioxide and other greenhouse gases in the atmosphere increase in the way that they have.
It has been alleged that the increased level of carbon dioxide in the atmosphere is due to emissions from volcanoes, but these account for less than one per cent of the emissions due to human activities.
Misleading argument
2: CO2 not responsible for global warming’
Carbon dioxide only makes up a small part of the atmosphere and so cannot be responsible for global warming.
What does the science say?
Carbon dioxide only makes up a small amount of the atmosphere, but even in tiny concentrations it has a large influence on our climate.
The properties of greenhouse gases such as carbon dioxide mean that they strongly absorb heat a fact that can be easily demonstrated in a simple laboratory experiment. While there are larger concentrations of other gases in the atmosphere, such as nitrogen, because they do not have these heat trapping qualities they have no effect on warming the climate whatsoever.
Water vapour is the most significant greenhouse gas. It occurs naturally, although global warming caused by human activities will indirectly affect how much is in the atmosphere through, for example, increased evaporation from oceans and rivers. This will, in turn, cause either cooling or warming depending on what form such as different types of clouds the water vapour occurs in.Humans have been adding to the effect of water vapour and other naturally occurring greenhouse gases by pumping greenhouse gases such as carbon dioxide into the atmosphere through, for example, the burning of fossil fuels and deforestation. Before industrialization, carbon dioxide made up about 0.03 per cent of the atmosphere or 280ppm (parts per million). Today, due to human influence it is about 380ppm. Even these tiny quantities have resulted in an increase in global temperatures of 0.75ºC (see misleading argument 1). 

(to be continued next week)