The Science Of Climate Change

The changing climate

The natural greenhouse effect keeps the planet 33°C warmer than it would otherwise be, allowing the earth to sustain life. Over the last 200 years human activities have resulted in emissions of greenhouse gases, (primarily carbon dioxide from the burning of fossil fuels), which have altered the composition of the atmosphere and caused an ‘enhanced’ greenhouse effect. As a result the earth’s temperature is rising and this, in turn, is changing the climate.

The Framework Convention on Climate Change

Using computer models, the Intergovernmental Panel on Climate Change (IPCC) has projected that if human interference continues to alter the composition of the atmosphere, average surface temperatures could rise between 2 and 3 °C globally over the next 100 years. This unprecedented rate of climatic change would cause significant damage to ecological systems and economies on a global scale.

In response to these climate projections the United Nations Framework Convention on Climate Change (Climate Convention) was adopted by the Intergovernmental Negotiating Committee and signed by 162 countries at the Rio Earth Summit in 1992.

The Climate Convention is a blueprint for precautionary action against the threat of global climate change. Its ultimate objective is to:

‘achieve stabilisation of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic (human made) interference with the climate system.

Such a level should be achieved within a timeframe sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner.’

To achieve these objectives requires limits to both the total amount of change and the rate at which it happens.

Setting limits

The United Nation’s AGGG – Advisory Group on Greenhouse Gases – worked out ‘targets and indicators’ for climate change in 1990. The ‘indicators’ set limits to the total amounts of temperature rise and sea level rise on the basis of known behaviour of ecosystems. In other words, what level of change nature can tolerate, or ‘ecological limits’.

The AGGG report identified these indicators to ‘protect both ecosystems as well as human systems’.

Sea -level rise
Maximum rate of rise 20 – 50mm per decade
Maximum 0.2 – 0.5 metres above 1990 global mean sea-level

The lower rate of rise – 20mm per decade - would permit the vast majority of vulnerable ecosystems, such as natural wetlands and coral reefs to adapt. Beyond this rate, damage to ecosystems will rise rapidly.

Global mean temperature
Maximum rate of 0.1°C per decade
Maximum temperature increase of 1.0°C

2.0° C was ‘viewed as an upper limit beyond which the risks of grave damage to ecosystems and of non-linear responses are expected to increase rapidly’.

In view of this Greenpeace believes that the 2.0° C limit should be seen as one to be avoided by a significant margin. A long term increase in temperature of 1.0° C above pre-industrial levels, with a rate of change of 0.1° C per decade, is the absolute maximum that policy makers should accept.

Carbon budget

Working from the IPCC emissions scenarios and models it is possible to estimate a ‘budget’ for fossil fuels: how much we can extract and burn while limiting the temperature increase to 1°C. The small amount of oil, coal and gas that we can afford to burn could then be used wisely, in an ordered phase out.

Analysis of carbon cycle models suggests that to avoid dangerous climate change over the next 100 years, the total amount of carbon dioxide from the burning of fossil fuels that can be released is around 225 billion tonnes – or gigatonnes – of carbon (GtC)

If no action is taken on deforestation (which also releases carbon dioxide into the atmosphere), the amount will be lower.

Fossil fuel reserves

Reserves of oil, gas and coal identified as ‘economically recoverable’ currently stand at 1,053 GtC. This would, if burnt, lead to a 5.0°C rise in temperature.

In reality ‘reserves’ are rapidly expanding due to oil, gas and coal exploration. The resource base that could be brought into reserves is 4,000 GtC.

Carbon logic

The 225 GtC ‘carbon budget’ is vastly exceeded by known fossil fuel reserves.
At current rates of fossil fuel energy use, the budget e.g. 225 GtC, will be exceeded in 40 years globally.
At current rates of increase in energy use (about 2% per annum) the budget will be exceeded in 30 years.

The logic of this is that 75% of the known, economically recoverable reserves of conventional fossil fuels (as carbon) can never be used as fuel.

If this is considered in terms of the actual resources of oil, coal and gas and other fossil fuels, 95% must remain in the ground.

So logic dictates that fossil fuels must be phased out. Given the size of the oil, coal and gas industry it is clear that governments have never before had to face such a task and are not giving it serious consideration.