The argument for taking global action on climate change now

Current trajectories risk unacceptable climate change:

Ideally determining the global action required to mitigate against climate change would involve three steps:

• The determination of what is acceptable climate change. That is, how much change are
  we prepared to accept before the risks associated with the change become too large?
• Given that we know what an acceptable change is, what atmospheric concentrations of
  greenhouse gases are the limit to ensure stabilisation of the climate system at or below the
  acceptable change?
• What future emissions will ensure that the concentration does not rise above this level?

Achieving acceptable climate change is similar to the objective of the United Nations Framework Convention on Climate Change which sets out to “prevent dangerous anthropogenic interference with the climate system”¹ . But answering the question of what is an acceptable change is extremely difficult. In the first place, perceptions of what is “dangerous” will depend very much on how individual people and nations will be advantaged or disadvantaged with respect to different levels of potential change. Inhabitants of some of the South Pacific island nations have already left their islands as they have become uninhabitable with rising sea levels. To them, the change we have already had is too much. It also depends on the degree of confidence that individual people and nations have that the risks associated with climate change outweigh the value and importance of their dependence on their current energy system. No two people or nations will see acceptable change in the same way.

This having being said, it is important to point out that both scientifically and politically around the world, there is a growing realisation that acceptable change will not be at the upper limit of the IPCC projections for the 21st century. Indeed, throughout much of Europe (see Box 2), a change of about 27deg;C is currently accepted as a guide for strategic planning. From the scientific point of view, there remains some debate concerning what is “dangerous” change. For example, Hansen et al. (2007) have argued that because rapid destabilisation of some components of the climate system may occur as we approach a further 1°C warming this should be regarded as the limit beyond which it will be “dangerous”. Of course, these decisions are never entirely “scientific”. But most of the scientific community recognise that 2°C represents a change of about 40% of that which occurred between the end of the last ice age 15,000 years ago and today. This change made a massive difference to the physical and biological appearance of the Earth, and therefore, in this context, 2°C is seen as being a large change.

If we accept for the moment that 2°C is likely to turn out to be the target for an acceptable change (and there are as many who would argue for a lower target than a higher one), then we know from the climate models that this is equivalent to an increase in carbon dioxide concentration in the atmosphere to approximately 450 ppmv. Table 6 shows several emissions futures with the calculated ranges of expected temperature and sea-level changes (from IPCC 2007d). It shows that only Alternative Future I scenario delivers temperature change in the range of 2°C and that this demands that global emissions peak sometime between 2000 and 2014, reducing to 50-80% below 2000 levels by 2050. The message here is clear: deep cuts in emissions are urgent if we are going to avoid a 2°C warming.

Stabilising concentrations of carbon dioxide in the atmosphere at or below 550 ppmv represents an enormous challenge. This is mainly because, once released into the atmosphere, carbon dioxide stays there for around 80 years. Thus it is not possible to stabilise concentrations at this level, or indeed at similar levels, without very significant reductions in emissions below current levels; that is, to levels comparable to the rate at which carbon can be transported into the deep ocean.

Table 6: Alternative future levels of greenhouse-gas emissions (carbon dioxide and carbon dioxide plus other gases combined) and the consequent changes to global mean surface temperature and sea level. The Table demonstrates that only with early peaking of emissions growth and deeps cuts by 2050, can warming of greater than 2°C be avoided. Source: IPCC (2007d).

We have underestimated the rates and magnitude of change: Since the writing of the main working group report for the IPCC Fourth Assessment Report, a number of published studies have provided evidence that changes might be talking place at a rate faster than previously anticipated. At least, there is a possibility that scientists may be conservative and still tend to underestimate rather than overestimate global warming.

If we use, for example, the amount for warming and the rate of sea-level rise over recent years compared with projections made at the time of the last IPCC Assessment in 2001, we find that observations of both lie at the upper limit of what was projected (See Figure 17).

Figure 17: Future temperature (left panel) and sea-level change (right panel) as projected by the IPCC in 2001, indicated by the grey area and coloured lines. Compared with what has been observed to happen as indicated by the solid red lines. This suggests that actual trends of change are at the upper limit of those projections. Source: Rahmstorf et al. (2007).

The IPCC Fourth Assessment report concluded that the capacity of the oceans and the terrestrial biosphere to absorb increasing amounts of fossil-fuel carbon dioxide into the future would, for several reasons, decrease over time. Some scientists were surprised when earlier in 2007, new observational evidence² suggested that this decreasing capacity had already commenced (Figure 18) meaning that perhaps a greater proportion of emitted carbon dioxide would stay in the atmosphere in the coming years, exacerbating the warming trend.

It is also important to appreciate that the real limitation in terms of what human emissions can be is mainly related to how quickly carbon dioxide can be moved from the surface of the oceans into the deep ocean where they are effectively out of circulation, at least for centuries. Modern science tells us that this transfer rate is around 2 thousand million tonnes of carbon each year. Current rates of emissions are around 8 thousand million tonnes, meaning that atmospheric accumulation is taking place and the climate is warming. It is surprising that some policy developers fail to recognise that this is a limitation of the real physical world; something that no manner of policy development or technology can overcome. We simple have to live within this limitation. Thus when people talk about emissions reductions of around 80%, what they are saying, although often they do not realise this, is that emissions must be reduced from 8 to 2 thousand million tonnes (6/8=75%) if we are going to stabilise global climate.

Finally, observations of what carbon dioxide has been emitted into the atmosphere in recent years3 (and the consequent rate of increase of carbon dioxide in the atmosphere) has shown that despite the international rhetoric devoted to the climate change issue, as a global community, 2006 was the year of greatest emissions into the atmosphere (Figure 19). There has been no sign of a slowing of the rate of emissions, let alone a decrease.

Figure 18: Decreasing fraction of carbon dioxide emissions being absorbed by the oceans. Source: Canadell et al. (2007).

Figure 19: History of the emissions of carbon dioxide into the atmosphere from the world community in total (black lines, 2 estimates) showing that the growth in emissions has continued up until 2006, tracking an IPCC emissions scenario that reflects a major change to global climate into the future (red) rather than one of the emissions futures (blue or green) that would ultimately lead to stabilisation of global temperatures. Source: Raupach et al. (2007).

Thus the climate issue flies in the face of the anticipated demands and delivery of significant growth in energy use through this century, unless very substantial changes are made to the way energy is used (efficiency) and obtained/delivered through improved technology. The climate change issue is an energy-futures issue.

On the one extreme, if all currently anticipated energy demands through this century were to be met through existing carbon-based energy technologies, the emission of carbon dioxide into the atmosphere would grow almost tenfold from its current level (Figure 20). On the other hand, the climate change issue demands about an 80% reduction of emissions through this period.