1.5°C or 2°C: a conduit’s view from the science-policy interface at COP20 in Lima, Peru

Abstract

An average global 2°C warming compared to pre-industrial times is commonly understood as the most important target in climate policy negotiations. It is a temperature target indicative of a fiercely debated threshold between what some consider acceptable warming and warming that implies dangerous anthropogenic interference with the climate system and hence to be avoided. Although this 2°C target has been officially endorsed as scientifically sound and justified in the Copenhagen Report issued by the 15th Conference of the Parties (COP) of the United Nations Framework Convention on Climate Change (UNFCCC) in 2009, the large majority of countries (over two-thirds) that have signed and ratified the UNFCCC strongly object to this target as the core of the long-term goal of keeping temperatures below a certain danger level. Instead, they promote a 1.5°C target as a more adequate limit for dangerous interference. At COP16 in Cancun, parties to the convention recognized the need to consider strengthening the long-term global goal in the so-called 2013-2015 Review, given improved scientific knowledge, including the possible adoption of the 1.5°C target. In this perspective piece, I examine the discussions of a structured expert dialogue (SED) between selected Intergovernmental Panel on Climate Change (IPCC) authors, myself included, and parties to the convention to assess the adequacy of the long-term goal. I pay particular attention to the uneven geographies and power differentials that lay behind the ongoing political debate regarding an adequate target for protecting ecosystems, food security, and sustainable development.

A scientific critique of the two-degree climate change target

“…Those risks are inherently local and sector-specific, and poorly reflected in summary figures such as the "reasons for concern" 25 (Fig. 2e).…”

“…The IPCC has also laid out the normative issues, but is not defending a target because its mandate does not allow it to be policy-prescriptive. Some individual scientists are more outspoken and find even the 2 °C target "utterly inadequate" 25 , or state that "it would seem difficult for the risk averse among us to accept anything much above that [1 °C] as the standard for DAI [dangerous anthropogenic interference]" 41 . Most of the literature, however, stops after a list of ethical dimensions and possible criteria, and leaves open the question of how to balance risk against feasibility and mitigation costs.…”

Understanding and responding to danger from climate change: the role of key risks in the IPCC AR5

“…Such decisions can be supported by risk assessment, here based on WGII AR5 author expert judgment of the available scientific literature, informed by the IPCC expert and government review processes. But such decisions also require value judgments that go beyond science, reflecting a range of legitimate perspectives (Adams-Schoen et al 2015;Adger et al 2009;Dow et al 2013;Knutti and Rogelj 2015;O'Brien and Wolf 2010;Tschakert 2015). In the WGII AR5, the reasons for concern provide a global perspective on climate change risk to inform such judgments, while the many key risks emphasize the complement: climate change will affect most people in most places, but in differing ways with uncertainties through time, diversely reverberating through the human experience.…”

“…Uncertainties will persist around the occurrence of specific impacts and the effectiveness of responses. And the relative importance of consequences will remain contested (Knutti and Rogelj 2015;Tschakert 2015). Climate change responses therefore involve making decisions under uncertainty in a changing world, with judgments informed by both science and broader values and goals.…”

Turn down the heat: regional climate change impacts on development

“…Critical reflection is thus required as to which scale and metric is most appropriate for assessing the risks that climate change poses for development. Global aggregates, for example, often mask important regional differences in vulnerability and consequently the degree of impact (Tschakert 2015) and yield no insights into the distributive effects of climate impacts. Further, what counts as valuable might often be a matter of perspective (Morrissey and Oliver-Smith 2013).…”