It is clear from the work presented that the risks of climate change may well be greater than we thought. At the same time it showed there is much that can be done to avoid the worse effects of climate change.

UK Prime Minister Tony Blair, in the forward to the report

Background. The Third Assessment Report (TAR) of the Intergovernmental Panel on Climate Change (IPCC, 2001) reviewed in depth all the scientific, technical and socio-economic aspects of climate change.

It concluded that there was strong evidence that climate change due to human emissions of greenhouse gases was already occurring and that future emissions of greenhouse gases were likely to raise global temperatures by between 1.4 and 5.8º C during this century, with a wide range of impacts on the natural world and human society.

Building on the TAR, the conference on Avoiding Dangerous Climate Change (ADCC) considered three scientific questions relating to stabilizing greenhouse gas concentrations in the atmosphere at levels which would avoid dangerous anthropogenic climate change. These questions were:

1. For different levels of climate change what are the key impacts, for different regions and sectors and for the world as a whole?

2. What would such levels of climate change imply in terms of greenhouse gas stabilization concentrations and what would be the emission pathways required to achieve such levels?

3. What options are there for achieving stabilization of greenhouse gases at different stabilization concentrations in the atmosphere, taking into account costs and uncertainties?

ADCC. The resulting material is organized in seven sections that span all aspects of the problem, starting with climate system analysis and ending with an assessment of the technological portfolio needed for global warming containment.

The specific sections are:

1. Key Vulnerabilities of the Climate System and Critical Thresholds. The eight papers in this section illustrate why the term “global warming” is inadequate to describe the changes we can expect in the Earth System.

   We should focus not only on temperature, but also on anticipated shifts (perhaps rapid) in the full range of climate variables, their variability and their extremes; and also on the direct oceanic consequences of atmospheric CO₂ concentration increases. Further, we need to quantify uncertainties arising from uncertainties in future emissions and in climate models, as far as possible, in probabilistic terms.

   [...]Addressing climate change will involve balancing uncertainties in both future change and the consequences of policy actions, and understanding the dangers associated with delayed action.

2. General Perspectives on Dangerous Impacts. This section considers the entire range and diversity of potential climate change impacts on natural and human systems instead of focusing on one or two geophysical watershed events (such as the collapse of the West Antarctic Ice Sheet).

   First, the scientific assessment of climate change risks needs to take into account both gradual and discontinuous processes, the interactions between them, and the synergistic effects of climate change and other human-induced stresses.

   Second, as the planet warms, societies will also be changing. New technologies will emerge, ground-breaking discoveries will be made and population structures and distributions will alter. These dynamics will, in turn, transform the adaptive capacities of communities at all scales and, thereby, the character of dangers faced.

   Third, the notion of resilience is a key element of the analysis. For instance, climate change will expose more people to infection by malaria, but the increment is probably small in relation to the total number at risk. A resilient society, with excellent public health measures containing malaria, will be able to cope.

3. Key Vulnerabilities for Ecosystems and Biodiversity. The papers in this section consider impacts of recent climate change on the carbon cycle and ecosystems.

4. Socio-Economic Effects: Key Vulnerabilities for Water Resources, Agriculture, Food and Settlements. This section focuses on focus on the science behind the determination of key magnitudes, rates and aspects of timing related to the estimated effects of climate change.

5. Regional Perspectives: Polar Regions, Mid-Latitudes, Tropics and Sub-Tropics. The six papers in this section investigate climate impacts in five disparate regions: the Arctic, Australia, California, Africa and Asia.

   The group of papers in this section spans a wide range of regions, climates, impacts and adaptive capacities. The contrast between potential climate impacts and the abilities to cope with these impacts in the developed counties compared with the lesser-developed countries is stark. It highlights the global nature of a problem that respects no geographical boundaries.

6. Emission Pathways. These papers all focus attention on the probabilities of exceeding different concentration or temperature thresholds along alternative pathways.

   They, and others, highlight the consequences of delaying action on climate change....delays are possible, but at the cost of requiring more rapid emissions reduction later.

   [...]a 20-year delay of action could result in required rates of emission reduction 3–9 times greater than that required for a more immediate response to meet the same temperature target.

   [Other authors] offer a word of caution by demonstrating the possibility of a dangerous climate policy mitigation that would slow economic growth to such an extent that vulnerability to climate change might actually be higher (particularly in developing countries).

7. Technological Options. This section includes seven papers that consider the role of technology in climate change from multiple perspectives.

   Both technology and climate change are very slow to change, due to the inherent inertia of their underlying systems. Both are inherently cumulative in nature, meaning that their consequences are large and emerging changes in systems they affect are fundamental.

   Technology is highly malleable in the long run. Mitigation of climate change is also a long-term challenge as it cannot be resolved in the near future. This means that in the long run, technology needs to be central element of response strategies to climate change.

   One robust finding of all seven contributions to this chapter is that fundamental technological and associated institutional changes are needed to stabilize atmospheric concentrations of greenhouse gases, despite the deep uncertainties that surround the science and politics of climate change.

Implications. Of the many different considerations and conclusions highlighted in the report, once especially jumps out to the fore. Based on earlier assessments, the EU had sought to cap the increase in average global temperature to 2º C. The report, however, says that the EU’s target of avoiding climate change of more than 2º C might be too high, with 2º C now being thought possibly sufficient to melt the Greenland ice sheet.

Furthermore, based on current behavior, it looks like the world will easily blow past the 2º C mark into more dangerous territory.

The atmosphere currently contains about 380 parts per million (ppm) of carbon dioxide compared to levels before the industrial revolution of about 270 ppm. To have a good chance of achieving the EU’s target of a 2ºC increase in average global temperature, levels should be stabilized at 450 ppm or below, the report concludes.

However, Sir David King, the UL government’s chief scientific adviser, thinks stabilization at 450 ppm is unlikely.

We are going to be at 400 ppm in 10 years’ time. I predict that without any delight in saying it.

But no country is going to turn off a power station which is providing much-desired energy for its population to tackle this problem—we have to accept that. To aim for 450 ppm would, I am afraid, seem unfeasible.

—Sir David King

The UK, which saw its CO₂ emissions increase by 0.5% in 2004, is itself tracking for a 10% decrease in CO₂ emissions by 2010 instead of the 20% promised.

We know from geological history that there is such a thing as a tipping point.. what [the report] does highlight, is just how important it is soon to change our behavior and do everything we can...and when I say we, I mean the people on the planet...to try and address some of these problems. It’s a big risk we’re taking.

What is concerning about the Exeter report is that it suggests that what has been a long-term policy framework...may be going to cause more major difficulties than people imagined...

—UK Environment Secretary Margaret Beckett on BBC 4

Resources:

• Avoiding Dangerous Climate Change; Cambridge University Press