The United Nations AGGG - Advisory Group on Greenhouse Gases - worked out "targets and indicators" for climate change in 1990. These were summarised in the document "Responding to Climate Change: Tools For Policy Development", edited by Jill Jager and published by the Stockholm Environment Institute.

The "indicators" set limits to rates and 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 Framework Convention on Climate Change signed at Rio in 1992 makes staying within ecological limits a central objective. It states that the objective is: "stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic [human made] interference with the climate system" and it adds "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".

So it requires limits to both the total amount of change and the rate.

The UNEP AGGG report (pp 19 - 20) 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

Global mean temperature:

* maximum rate of 0.1.C per decade
* maximum increase of 1.0.C

It said that above 1.0C there may be "rapid, unpredictable and non-linear responses that could lead to extensive ecosystem damage". A total 2.0C increase 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". [The report also identified the CO2 [equivalent] concentrations corresponding to these as 330 - 400ppm for 1.0C and 400 - 560ppm for 2.0C].

Greenpeace bases its ecological limits on these findings and the subsequent assessments of knowledge by the IPCC [Intergovernmental Panel on Climate Change].

Notably:

• global mean temperature has already risen 0.3 - 0.6.C above pre-industrial levels (IPCC)
• current rates of increase are at or above the 0.1.C per decade rate and due to existing and forecast emissions are expected to be 0.2 - 0.3.C per decade in the next few decades
• the IPCC Second Assessment Report suggests that observations of actual change in temperature suggest the "sensitivity" of the climate is close to 3.5C, i.e. this is the amount that the global mean temperature is expected to go up for a doubling of CO2 (equivalent), and this is expected to occur before 2050 (probably by 2030).
• even using a lower sensitivity assumption of 2.5.C the IPCC forecasts a 1.5.C rise above pre-industrial levels by 2050 Greenpeace believes that policy should therefore be to meet the following limits:
• limit the long term committed increase of temperature to less than 1.C
• bring the rate of change to below 0.1.C per decade as fast as possible - i.e. within a few decades at most
• limit long term sea level rise to less than 20cm
• limit rate of sea level rise to 20mm/decade maximum

What actually happens can only be significantly affected by changes (i.e. major reductions) in emissions of greenhouse gases, both in total (for example taking "long term" as being up to 2100) and in terms of the "pathway" or trajectory that emissions take, e.g. how much is emitted sooner, or later.

[In effect, limiting the "long term" temperature rise may mean getting back to 1.0C above pre-industrial levels as it may not be possible to avoid a rise of 1.0C above pre-industrial levels. Because of the lag in effect between temperature rise in the air and the expansion of the sea, it may be possible to avoid breaking the limit for sea level rise if fast enough action is taken.]

In order to meet both the total and per decade target limits identified above, a "carbon budget" can be estimated as follows (GtC - gigatonnes = billions of tonnes of carbon in CO2):

• with no action to stop current trends of deforestation (as forests act as a "sink" for some carbon, and release it when destroyed) - 145GtC
• with action to halt deforestation, stabilising the role of forests at current levels - 225GtC
• with action to halt deforestation and afforestation to sequester (take up) an extra 40GtC - 260GtC

Each year the world releases 5-6GtC from fossil fuels and has released 150GtC since industrialisation began around 1860. As the AGGG recognized, it may be too late to stop a rise of 1.0C (some of the "committed" temperature rise from existing atmospheric pollution will not be fully apparent until well into the next century).

These "carbon budgets" are vastly exceeded by known fossil fuel reserves, and are even exceeded by known oil reserves.

A phase out of fossil fuels therefore logically follows.

An urgent start is required for several reasons:

• To meet ecological limits for rates of sea level and temperature rise
• Because at current rates of fossil fuel energy use the budget e.g. 225GtC will be exceeded in 40 years globally
• Because at current rates of increase in energy use (about 2%) an e.g. 225GtC budget would be exceeded in 30 years
• Because energy planning and infrastructure is long term and major change is required (switch to renewables)
• Because industrialised countries will be required to give a lead to other countries and begin a phase out sooner (Denmark already effectively has a phase out plan), and, under the Climate Convention these "Annexe 1" countries are obliged to "take precautionary measures to anticipate, prevent or minimise the causes of climate change and mitigate its adverse effects"

In addition, climate change may proceed faster as a result of "surprise" positive feedbacks not included in models.

Even if more optimistic scenarios are used, the logic of an immediate start to negotiating a fossil fuel phase out remains.

For example a 1.0C limit with a 225GtC budget under a 3.5.C climate sensitivity would still be 300GtC if sensitivity was 2.5.C: still far less than fossil fuel reserves. Similarly, the EU has a target of a 2.0C limit to temperature rise and this would imply a carbon budget of 410GtC at 3.5.C sensitivity and 585GtC at 2.5C sensitivity.

Reserves of oil, gas and coal identified as "economically recoverable" are 1053GtC, 820GtC excluding "unconventional" sources such as oil shales. This would, if burnt, lead to a 5.0C rise. In reality, "reserves" are rapidly expanding due to oil, coal and gas exploration. The "resource base" that could be brought into reserves is 4,000GtC.

The IPCC business as usual scenario implies burning 1420GtC: and a consequent 2.4.C rise by 2100 (2.5.C sensitivity) and ultimately over 4.0C (5.6C with 3.5C sensitivity).

This is the carbon logic. The inescapable conclusion, and Greenpeace's immediate call for action, is:

• Fossil fuels must be phased out - reserves and resources can never all be burned
• Political action is required to initiate a global phase out regime, which should be led by industrialised nations
• Further exploration and development of fossil fuel resources by industrial nations should be halted immediately, as it makes the problem worse and more difficult to solve

Greenpeace believes that in order to meet ecological limits safeguarding natural and human systems, a limit in the range 145 - 260GtC should be set, which for 225GtC (also implying drastic action on deforestation) would, on current trends of usage, mean a complete global phase out of fossil fuels within 30 - 40 years.

Achieving a fossil fuel phase out on such a timescale will involve very dramatic reductions in emissions of carbon dioxide. As a first step Greenpeace advocates that at the Third Conference of the parties of the Framework Convention on Climate Change in Kyoto in December 1997, all industrialised nations be required to reduce CO2 emissions 20% on 1990 levels by 2005.