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The structured expert dialogue on the 2013–2015 review: a brief summary


The outcome of the first periodic review was captured in Decision 10/CP.21 on the 2013–2015 review. In paragraph 4, Parties decided that, in relation to the long-term global goal, and in the light of the ultimate objective of the Convention, the long term global is to hold the increase in the global average temperature to well below 2°C above pre-industrial levels, and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change. This is reflected in the Paris Agreement (Decision 1/CP.21).      

Prior to the Paris Agreement, the internationally agreed upper limit for global warming, or the increase in global average temperature, was below 2 °C above pre-industrial levels. This was agreed in 2010. The subsequent first periodic review was undertaken to review that goal, and served to strengthen it in December 2016.

Below is a short summary of the process that led to this historic decision. For more information, please see the full, final SED report.


What was the first periodic review tasked to achieve?

In 2010, Parties decided to periodically review the adequacy of the long-term global goal and overall progress towards achieving the goal, including a consideration of the means of implementation. In addition, the first such periodic review was tasked with the consideration of the strengthening the long-term global goal, including in relation to a temperature rise of 1.5 °C above pre-industrial levels. The decision taken by the Parties at the end of the first review can be found here.

What institutional modalities did the first periodic review employ?

The first periodic review was carried out with the assistance of the Subsidiary Body for Scientific and Technological Advice (SBSTA) and the Subsidiary Body for Implementation (SBI), through a joint contact group.

A structured expert dialogue (SED) was established to support the work of this joint contact group and ensure the scientific integrity of the review through a focused exchange of views, information and ideas.

The Joint Working Group (JWG) of the SBSTA and the IPCC has met regularly since its establishment at SBSTA 2. During the period of 2013-2015, its meetings also assisted to ensure coordination and the exchange information on the periodic review, among its other activities. The JWG is composed of presiding officers of the Convention and IPCC, and members of the secretariats. Meetings took place during the sessions of the SBs.

What procedural modalities were employed ?

The first periodic review was supported by a face-to-face dialogue (the SED) between over 70 experts and Parties that took place during five meetings held between June 2013 and February 2015. These meetings ensured that there was a science-policy interface. The meetings were open to all Parties and observers. The review was informed by the best available science, with 53 experts making a total of 60 presentations. An additional 20 experts attended the meetings and participated in the discussions. The presentations were delivered by experts from the Intergovernmental Panel on Climate Change, processes and bodies under the Convention, as well as regional and intergovernmental organizations.

How did the IPCC assessments, and other scientific input, inform the 2013–2015 review?

The SED meetings were a platform for dialogue on the latest scientific knowledge, as it became available, from the IPCC and beyond. The information shared at the SED meetings fed directly into the discussions of the joint contact group over the course of three years. Numerous experts from the IPCC presented the latest findings at the SED meetings. The meetings focused on the latest scientific knowledge from the IPCC Fifth Assessment Cycle. Contributions were made by all three of the IPCC Working Groups.

How was the adequacy of the long-term global goal assessed?

It was assessed by examining the level of risk of climate impacts for any given level of global warming. Parties then discussed whether these risks were unacceptably high and they made a political choice as reflected in the outcomes of the first periodic review.

What did we learn about the threat of climate change?

The threat of climate change is unequivocal and unprecedented. The Intergovernmental Panel on Climate Change (IPCC), in its latest Assessment Report, found that “warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and oceans have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.” In recent decades, these physical changes have caused impacts on natural and human systems on all continents and across the oceans. Future climate change is projected to increase the likelihood of severe, pervasive and irreversible impacts.

What was learned about the relationship between global average temperature change, risks from climate change, cumulative anthropogenic carbon dioxide emissions and changes in global annual GHG emissions?

Prior to the Paris Agreement, the internationally agreed upper limit for global warming, or the increase in global average temperature, was "below 2 °C above pre-industrial levels". That goal corresponded to a certain level of reduction in global GHG emissions. This is because this limit for global warming led to an estimation of the budget of total cumulative anthropogenic carbon dioxide (CO2) emissions and of the corresponding range of CO2 equivalent (CO2 eq) concentration levels in the atmosphere. This in turn made an estimation of the necessary reduction in global annual GHG emissions by mid-century possible.

What did we learned about a global goal framed as a temperature limit?

A temperature-only limit does not capture all changes in the climate system that follow from greenhouse gas (GHG) emissions and may thus lead to other changes being overlooked. This is because large-scale climate system responses, including those related to ocean acidification and sea level rise, may be affected by more than temperature, and are irreversible on at least a multi-century to millennial timescale. Adding other limits to the long-term global goal, however, such as sea level rise or ocean acidification, only reinforces the basic finding emerging from the analysis of the temperature limit, namely that we need to take urgent and strong action to reduce GHG emissions.

What did we learn about the timescale of climate change?

Despite the irreversibility of global warming, cutting CO2 emissions now will affect future warming within a few years. Removing CO2 from the atmosphere results in cooling. The timescale of physical changes depends on the type of changes (e.g. warming will immediately impact precipitation or extreme weather, whereas changes in the Greenland ice sheet melting or sea level rise would take much longer to occur). With respect to overshooting, the timescales for which the carbon budget for the long-term global goal is exceeded are similar to the timescales for which temperature exceeds the goal. If a temperature limit were exceeded (also referred to as “an overshoot”), warming could be returned to that limit in the longer term if the CO2 content of the atmosphere is later actively reduced.

What emissions pathway is required?

Limiting global warming in line with the global goal agreed in 2010 (below 2 °C) implied a large reduction in global GHG emissions in the short to medium term; global carbon dioxide neutrality early in the second half of this century; and negative global GHG emissions towards the end of the twenty-first century. The longer we wait to bend the currently increasing curve of global emissions downward, the steeper we will have to bend it, even with negative emissions. Limiting global warming in line with the goal would necessitate a radical transition (deep decarbonization now and going forward), not merely a fine tuning of current trends.

How likely is a temperature overshoot?

A 430–480 ppm concentration in 2100 corresponds to 2 °C.The atmospheric concentration of CO2 eq in 2011 was already about 430 ppm.  It will therefore be difficult to avoid a temporary concentration overshoot. While uncertainties exist as to the changes in land and ocean sinks for high-emission scenarios, the direction is clear: the higher the emissions, the more the capacity of sinks will be weakened.CO2 removal technologies are needed to compensate for past GHG emissions overshooting the target and, in the second half of the century, for emissions that cannot be reduced to zero (e.g. non-CO2 emissions from agriculture). Although reducing non-CO2 emissions can be an important element of mitigation strategies, the temperature change is mainly determined by the cumulative budget of CO2 emissions, and CO2 emissions drive long-term warming.

How can climate impacts be framed in terms of risk?

Impacts of climate change can be framed in terms of emerging and key risks at the global, regional and sectoral levels. Each risk can be assessed for the present, the near term and for different levels of warming. Risk levels often increase with temperature and are sometimes linked to the rate of warming, as well as to magnitudes of sea level rise and ocean acidification.

How do mitigation and adaptation affect the levels of risk?

The benefits of mitigation are illustrated by the reduction in risk levels related to degrees of warming. The risks posed by climate change can also be reduced at different levels through various levels of adaptation action. In the near-term (2030–2040) risks are similar for all emission scenarios because warming does not vary significantly, with atmospheric GHG concentrations remaining at first similar. Therefore, adaptation provides the main opportunities to control risks for this period. However, mitigation investments made in the immediate future play an essential role in addressing climate change throughout this century. In order to qualify the level of risk and the possibility for adaptation, experts used coordinated expert judgment based on a set of explicit criteria. A key element of local or regional perspectives of risks is the value judgment of when the scale (e.g. frequency and severity) of climate impacts results in a transition from “acceptable” to “unacceptable”. Adaptation can be restricted by a range of factors, such as those related to geography, high-emission pathways or socioeconomic constraints in adaptive capacity. Constraints to “high” adaptation are context-sensitive and reflect the fact that adaptation is in general difficult to assess, particularly for long-term time frames, beyond mid-century.

For more information, please see the full, final SED report.

The full agenda of the meetings and presentations made during the meetings of the SED can be found here: