Since the Industrial Revolution humans have been adding significantly to the greenhouse gas blanket that surrounds the Earth. Established physical principles suggest that this should raise the Earth’s temperature. In the century that has passed since this warming was first predicted, the average surface of the globe has warmed by about 0.8°C. A multitude of different lines of evidence have confirmed that emissions of human origin are the primary cause of this warming. These include measurements of incoming and outgoing radiation, the lack of any plausible alternative explanation and distinctive “fingerprints” that identify the warming as caused by an enhanced greenhouse effect (Intergovernmental Panel on Climate Change [IPCC], 2007).

Future warming has been estimated based on a sound scientific understanding of physical systems and feedbacks as well as the study of past temperature changes. Using these methods, the IPCC (2007) estimates a warming of between 1.1 and 6.4°C over pre-industrial temperatures for the coming century, depending on how much we emit, exactly how sensitive the climate is to greenhouse gases and how the natural carbon cycle responds to the increasing CO₂ and temperatures. This warming is expected to have profoundly negative impacts on many people and ecosystems, particularly those that are already vulnerable.

More than 100 countries have adopted a target limit of 2°C of warming relative to pre-industrial temperatures. To exceed this would have very dangerous consequences for many people. A study by Meinshausen et al. (2009) suggests that to have a 70% chance of staying below 2°C it will be necessary for global greenhouse gas emissions to peak before 2020, be cut by 50% by 2050 and approach zero before 2100. To provide an 84% chance, a 72% global cut by 2050 would be required. Other studies have suggested broadly similar figures (Allen et al., 2009; Weaver et al., 2007). If the world was to converge on equal per capita emissions by 2050, global cuts of this magnitude would require a per capita cut in the UK of 92% or 86% from 1990 levels by 2050.

As the required global cut is severe, such a scenario would require poor countries to also make cuts by 2050. The long industrialised countries hold the historical responsibility for climate change and possess far greater resources to invest in low carbon technologies. The UK should therefore take on a greater share of the burden and cut emissions faster in order to allow the majority world a longer time period to decarbonise. Furthermore, because imported goods account for about a third of our emissions (Helm et al., 2007) deeper domestic cuts are required in order to compensate for foreign emissions produced on our behalf.

In conclusion it is recommended that in the UK we should aim to reduce our greenhouse gas emissions to zero as fast as possible. In this report we adopt 2030 as our target year. Because warming is ultimately caused by cumulative emissions over time, we should also keep the quantity of greenhouse gases emitted during the transition phase as low as possible.

References:

Allen, M. et al. (2009) “Warming caused by cumulative carbon emissions towards the trillionth tonne”, Nature, 458(7242), pp.1163-1166.

Helm, D., R. Smale & J. Phillips (2007) “Too Good To Be True? The UK’s Climate Change Record”, Dieter Helm CBE [online]. Available at: http://www.dieterhelm.co.uk/sites/default/files/Carbon_record_2007.pdf [Live: March 2010].

Intergovernmental Panel on Climate Change (IPCC) (2007) Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007, Cambridge: Cambridge University Press.

Meinshausen, M. et al. (2009) “Greenhouse-gas emission targets for limiting global warming to 2°C”, Nature, 458(7242), pp. 1158-1162.

Weaver, A.J. et al. (2007) “Long term climate implications of 2050 emission reduction targets”, Geophysical Research Letters, 34, L19703.