非表示:
キーワード:
economics; environmental studies
要旨:
The established international 2°C target stipulates that global warming should
be limited to below 2°C compared with pre-industrial periods; this has emerged as the most
prominent interpretation of how to avoid dangerous climate change. The 2°C target was
confirmed and made legally binding in the Paris agreement at the “climate summit” (Conference
of Parties 21, COP21) in December 2015. But despite agreement on the target,
greenhouse-gas emissions are unlikely to fall soon and fast enough to meet the target, raising
the question of whether this target needs to be revised or reinterpreted, and also of why there
is insufficient cooperation toward emissions reduction despite the risk of dangerous climate
change. Previous theoretical and experimental research has suggested that cooperation
towards emissions reduction is undermined by uncertainty about the threshold marking the
transition to dangerous climate change. However, even if the threshold and hence the
location of the target are known precisely, uncertainty ensues because of an unknown risk
that arises from missing the collective target. How humans deal with this risk has not been
investigated experimentally. Here we investigate how individuals behave under different risk
scenarios if a collective target is missed. We perform economics experiments framed as a
collective-risk social dilemma and directly examine the extent to which human subjects trade
pay-out reduction for risk. We show that a reduced assessed risk arising from missing the
collective target leads to reduced contributions towards the target; but that risk reduction
causes the subjects almost to maximize their individual pay-out by balancing the effort to
reach the target against the risk posed by missing it. We provide quantitative support for the
argument that group contributions toward the collective target can be interpreted as proportional
to mitigated warming. We conclude that reinterpretation of the 2°C target as less
strict causes additional warming. However, our subjects deal effectively with a risk of dangerous
climate change that they assess to depend gradually on global warming. Our results
suggest that, if the additional warming is judged to be acceptable, a less strict interpretation
of the 2°C target might support finding a trade-off between the effort put into climate
mitigation and the risk of dangerous climate change.
